Journal articles: 'Sub-Inhibitory concentrations of antibiotics'

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Mojsoska, Biljana, Melanie Ghoul, Gabriel G. Perron, Håvard Jenssen, and Fatima AlZahra’a Alatraktchi. "Changes in toxin production of environmental Pseudomonas aeruginosa isolates exposed to sub-inhibitory concentrations of three common antibiotics." PLOS ONE 16, no. 3 (March 4, 2021): e0248014. http://dx.doi.org/10.1371/journal.pone.0248014.

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Pseudomonas aeruginosa is an environmental pathogen that can cause severe infections in immunocompromised patients. P. aeruginosa infections are typically treated with multiple antibiotics including tobramycin, ciprofloxacin, and meropenem. However, antibiotics do not always entirely clear the bacteria from the infection site, where they may remain virulent. This is because the effective antibiotic concentration and diffusion in vitro may differ from the in vivo environment in patients. Therefore, it is important to understand the effect of non-lethal sub-inhibitory antibiotic concentrations on bacterial phenotype. Here, we investigate if sub-inhibitory antimicrobial concentrations cause alterations in bacterial virulence factor production using pyocyanin as a model toxin. We tested this using the aforementioned antibiotics on 10 environmental P. aeruginosa strains. Using on-the-spot electrochemical screening, we were able to directly quantify changes in production of pyocyanin in a measurement time of 17 seconds. Upon selecting 3 representative strains to further test the effects of sub-minimum inhibitory concentration (MICs), we found that pyocyanin production changed significantly when the bacteria were exposed to 10-fold MIC of the 3 antibiotics tested, and this was strain specific. A series of biologically relevant measured pyocyanin concentrations were also used to assess the effects of increased virulence on a culture of epithelial cells. We found a decreased viability of the epithelial cells when incubated with biologically relevant pyocyanin concentrations. This suggests that the antibiotic-induced virulence also is a value worth being enclosed in regular testing of pathogens.

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Jamal, W., B. I. Duerden, and V. O. Rotimi. "The influence of exposure to various concentrations of five antimicrobial agents on intracellular cytotoxin B production in <i>Clostridioides difficile</i>." African Journal of Clinical and Experimental Microbiology 24, no. 3 (July 19, 2023): 266–73. http://dx.doi.org/10.4314/ajcem.v24i3.6.

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Background: Clostridioides difficile is an important cause of healthcare-associated diarrhea. Several anti- microbial agents are known to promote C. difficile infection (CDI). The impact of various concentrations of ampicillin (AMP), cefotaxime (CTX), clindamycin (CC), metronidazole (MTZ) and vancomycin (VAN) on intra-cellular cytotoxin B production was investigated in this study. Methodology: Six clinical strains of C. difficile were grown at minimum inhibitory concentration (MIC) and sub-MIC concentrations of these antibiotics. Inoculum standardization was performed by Miles and Misra method. Intracellular toxin B production was detected using Vero cell cytotoxicity assay in sonicated cultures on days 1, 2, 3, 4, 5 and 7 days of incubation. Results: There was a heterogeneous relationship between antibiotic exposure and the intra-cellular toxin production by the toxigenic strains. Clinical strains of C. difficile when exposed to MIC and sub-inhibitory concentrations of certain antibiotics produced high cytotoxin levels. All toxigenic isolates produced increased levels of cell-bound cytotoxin after exposure to antibiotics but there was no consistent pattern and the response to different doses varied considerably. Metronidazole was the most potent inducer of cell-bound cytotoxin followed by cefotaxime and clindamycin. Vancomycin induced the least amount of cytotoxin activity. Conclusion: The effects of sub-inhibitory concentration of antibiotic that predispose to C. difficile infection may partially suppress the normal gut flora, allowing colonization and growth of C. difficile, and may affect the level of toxin produced.

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Casciaro, Bruno, Floriana Cappiello, Walter Verrusio, Mauro Cacciafesta, and Maria Luisa Mangoni. "Antimicrobial Peptides and their Multiple Effects at Sub-Inhibitory Concentrations." Current Topics in Medicinal Chemistry 20, no. 14 (June 11, 2020): 1264–73. http://dx.doi.org/10.2174/1568026620666200427090912.

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The frequent occurrence of multidrug-resistant strains to conventional antimicrobials has led to a clear decline in antibiotic therapies. Therefore, new molecules with different mechanisms of action are extremely necessary. Due to their unique properties, antimicrobial peptides (AMPs) represent a valid alternative to conventional antibiotics and many of them have been characterized for their activity and cytotoxicity. However, the effects that these peptides cause at concentrations below the minimum growth inhibitory concentration (MIC) have yet to be fully analyzed along with the underlying molecular mechanism. In this mini-review, the ability of AMPs to synergize with different antibiotic classes or different natural compounds is examined. Furthermore, data on microbial resistance induction are reported to highlight the importance of antibiotic resistance in the fight against infections. Finally, the effects that sub-MIC levels of AMPs can have on the bacterial pathogenicity are summarized while showing how signaling pathways can be valid therapeutic targets for the treatment of infectious diseases. All these aspects support the high potential of AMPs as lead compounds for the development of new drugs with antibacterial and immunomodulatory activities.

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Browne, Katrina, Rajesh Kuppusamy, William R. Walsh, David StC Black, Mark D. P. Willcox, Naresh Kumar, and Renxun Chen. "Antimicrobial Peptidomimetics Prevent the Development of Resistance against Gentamicin and Ciprofloxacin in Staphylococcus and Pseudomonas Bacteria." International Journal of Molecular Sciences 24, no. 19 (October 6, 2023): 14966. http://dx.doi.org/10.3390/ijms241914966.

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Bacteria readily acquire resistance to traditional antibiotics, resulting in pan-resistant strains with no available treatment. Antimicrobial resistance is a global challenge and without the development of effective antimicrobials, the foundation of modern medicine is at risk. Combination therapies such as antibiotic–antibiotic and antibiotic–adjuvant combinations are strategies used to combat antibiotic resistance. Current research focuses on antimicrobial peptidomimetics as adjuvant compounds, due to their promising activity against antibiotic-resistant bacteria. Here, for the first time we demonstrate that antibiotic–peptidomimetic combinations mitigate the development of antibiotic resistance in Staphylococcus aureus and Pseudomonas aeruginosa. When ciprofloxacin and gentamicin were passaged individually at sub-inhibitory concentrations for 10 days, the minimum inhibitory concentrations (MICs) increased up to 32-fold and 128-fold for S. aureus and P. aeruginosa, respectively. In contrast, when antibiotics were passaged in combination with peptidomimetics (Melimine, Mel4, RK758), the MICs of both antibiotics and peptidomimetics remained constant, indicating these combinations were able to mitigate the development of antibiotic-resistance. Furthermore, antibiotic–peptidomimetic combinations demonstrated synergistic activity against both Gram-positive and Gram-negative bacteria, reducing the concentration needed for bactericidal activity. This has significant potential clinical applications—including preventing the spread of antibiotic-resistant strains in hospitals and communities, reviving ineffective antibiotics, and lowering the toxicity of antimicrobial chemotherapy.

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Nanduri, Bindu, Mark L. Lawrence, Divya Swetha Peddinti, and Shane C. Burgess. "Effects of Subminimum Inhibitory Concentrations of Antibiotics on thePasteurella multocidaProteome: A Systems Approach." Comparative and Functional Genomics 2008 (2008): 1–12. http://dx.doi.org/10.1155/2008/254836.

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To identify key regulators of subminimum inhibitory concentration (sub-MIC) antibiotic response in thePasteurella multocidaproteome, we applied systems approaches. Using 2D-LC-ESI-MS2, we achieved 53% proteome coverage. To study the differential protein expression in response to sub-MIC antibiotics in the context of protein interaction networks, we inferredP. multocidaPm70 protein interaction network from orthologous proteins. We then overlaid the differential protein expression data onto theP. multocidaprotein interaction network to study the bacterial response. We identified proteins that could enhance antimicrobial activity. Overall compensatory response to antibiotics was characterized by altered expression of proteins involved in purine metabolism, stress response, and cell envelope permeability.

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Portela, Raquel, Filipe Valcovo, Pedro L. Almeida, Rita G. Sobral, and Catarina R. Leal. "Antibiotic Activity Screened by the Rheology of S. aureus Cultures." Fluids 5, no. 2 (May 18, 2020): 76. http://dx.doi.org/10.3390/fluids5020076.

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Multidrug resistant bacteria are one of the most serious public health threats nowadays. How bacteria, as a population, react to the presence of antibiotics is of major importance to the outcome of the chosen treatment. In this study we addressed the impact of oxacillin, a β-lactam, the most clinically relevant class of antibiotics, in the viscosity profile of the methicillin resistant Staphylococcus aureus (MRSA) strain COL. In the first approach, the antibiotic was added, at concentrations under the minimum inhibitory concentration (sub-MIC), to the culture of S. aureus and steady-state shear flow curves were obtained for discrete time points during the bacterial growth, with and without the presence of the antibiotic, showing distinct viscosity progress over time. The different behaviors obtained led us to test the impact of the sub-inhibitory concentration and a concentration that inhibited growth. In the second approach, the viscosity growth curves were measured at a constant shear rate of 10 s−1, over time. The obtained rheological behaviors revealed distinctive characteristics associated to the presence of each concentration of the tested antibiotic. These results bring new insights to the bacteria response to a well-known bacteriolytic antibiotic.

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Trancassini, M., M. I. Brenciaglia, M. C. Ghezzi, P. Cipriani, and F. Filadoro. "Modification ofPseudomonas aeruginosaVirulence Factors by Sub-Inhibitory Concentrations of Antibiotics." Journal of Chemotherapy 4, no. 2 (April 1992): 78–81. http://dx.doi.org/10.1080/1120009x.1992.11739144.

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Chee, Jessica. "Identifying genes associated with biofilm production in Pseudomonas aeruginosa." Meducator 1, no. 33 (June 19, 2018): 19–22. http://dx.doi.org/10.15173/m.v1i33.1796.

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Pseudomonas aeruginosa is an opportunistic pathogen associated with a variety of life-threatening diseases. Infections caused by P. aeruginosa can be nearly untreatable because of its multidrug-resistance. One of the characteristics of P. aeruginosa that helps it survive in high drug concentrations is its ability to form biofilms–large communities of cells encompassed by extracellular polymeric substances that defend against many antibiotics. In fact, sub-minimum inhibitory concentrations of antibiotics stimulate biofilm production. This project aims to identify genes associated with biofilm induction in P. aeruginosa by screening a transposon mutant library for mutants that fail to show increased biofilm production when exposed to sub-minimum inhibitory concentrations of cefixime, tobramycin, and thiostrepton. So far, we have identified one gene, PA2714, that encodes a predicted molybdopterin oxidoreductase required for biofilm production. Because of the strong association between biofilm production and antibiotic tolerance in P. aeruginosa, the gene identified in this screen may be a useful therapeutic target for novel antimicrobialsthat can disrupt biofilm formation.

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Chow, Louise K. M., Timothy M. Ghaly, and Michael R. Gillings. "A survey of sub-inhibitory concentrations of antibiotics in the environment." Journal of Environmental Sciences 99 (January 2021): 21–27. http://dx.doi.org/10.1016/j.jes.2020.05.030.

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György, Éva, Károly Arnold Unguran, and Éva Laslo. "Biocide Tolerance and Impact of Sanitizer Concentrations on the Antibiotic Resistance of Bacteria Originating from Cheese." Foods 12, no. 21 (October 27, 2023): 3937. http://dx.doi.org/10.3390/foods12213937.

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In this study, we determined and identified the bacterial diversity of different types of artisanal and industrially produced cheese. The antibiotic (erythromycin, chloramphenicol, kanamycin, ampicillin, clindamycin, streptomycin, tetracycline, and gentamicin) and biocide (peracetic acid, sodium hypochlorite, and benzalkonium chloride) resistance of clinically relevant bacteria was determined as follows: Staphylococcus aureus, Macrococcus caseolyticus, Bacillus sp., Kocuria varians, Escherichia coli, Enterococcus faecalis, Citrobacter freundii, Citrobacter pasteurii, Klebsiella oxytoca, Klebsiella michiganensis, Enterobacter sp., Enterobacter cloacae, Enterobacter sichuanensis, Raoultella ornithinolytica, Shigella flexneri, and Salmonella enterica. Also, the effect of the sub-inhibitory concentration of three biocides on antibiotic resistance was determined. The microbiota of evaluated dairy products comprise diverse and heterogeneous groups of bacteria with respect to antibiotic and disinfectant tolerance. The results indicated that resistance was common in the case of ampicillin, chloramphenicol, erythromycin, and streptomycin. Bacillus sp. SCSSZT2/3, Enterococcus faecalis SRGT/1, E. coli SAT/1, Raoultella ornithinolytica MTT/5, and S. aureus SIJ/2 showed resistance to most antibiotics. The tested bacteria showed sensitivity to peracetic acid and a different level of tolerance to benzalkonium chloride and sodium hypochlorite. The inhibition zone diameter of antibiotics against Enterococcus faecalis SZT/2, S. aureus JS11, E. coli CSKO2, and Kocuria varians GRT/10 was affected only by the sub-inhibitory concentration of peracetic acid.

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Molina-Quiroz, Roberto C., Cecilia A. Silva, Cristian F. Molina, Lorenzo E. Leiva, Sebastián Reyes-Cerpa, Inés Contreras, and Carlos A. Santiviago. "Exposure to sub-inhibitory concentrations of cefotaxime enhances the systemic colonization of Salmonella Typhimurium in BALB/c mice." Open Biology 5, no. 10 (October 2015): 150070. http://dx.doi.org/10.1098/rsob.150070.

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It has been proposed that sub-inhibitory concentrations of antibiotics play a role in virulence modulation. In this study, we evaluated the ability of Salmonella enterica serovar Typhimurium (hereafter S . Typhimurium) to colonize systemically BALB/c mice after exposure to a sub-inhibitory concentration of cefotaxime (CTX). In vivo competition assays showed a fivefold increase in systemic colonization of CTX-exposed bacteria when compared to untreated bacteria. To identify the molecular mechanisms involved in this phenomenon, we carried out a high-throughput genetic screen. A transposon library of S . Typhimurium mutants was subjected to negative selection in the presence of a sub-inhibitory concentration of CTX and genes related to anaerobic metabolism, biosynthesis of purines, pyrimidines, amino acids and other metabolites were identified as needed to survive in this condition. In addition, an impaired ability for oxygen consumption was observed when bacteria were cultured in the presence of a sub-inhibitory concentration of CTX. Altogether, our data indicate that exposure to sub-lethal concentrations of CTX increases the systemic colonization of S. Typhimurium in BALB/c mice in part by the establishment of a fitness alteration conducive to anaerobic metabolism.

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Kwiecińska-Piróg, Joanna, Krzysztof Skowron, Tomasz Bogiel, Agata Białucha, Jana Przekwas, and Eugenia Gospodarek-Komkowska. "Vitamin C in the Presence of Sub-Inhibitory Concentration of Aminoglycosides and Fluoroquinolones Alters Proteus mirabilis Biofilm Inhibitory Rate." Antibiotics 8, no. 3 (August 11, 2019): 116. http://dx.doi.org/10.3390/antibiotics8030116.

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Vitamin C has antimicrobial activity and is often used as an oral supplement accompanying antibiotic treatment in urinary tract infections (UTI). Proteus mirabilis is the third common species responsible for UTIs that are mostly treated with fluoroquinolones or aminoglycosides. Treatment of the UTI caused by P. mirabilis is problematic due to the ability to form biofilm on the urinary catheters. The aim of the study was to evaluate the influence of ascorbic acid in combination with antibiotics on P. mirabilis abilities to form biofilm. The susceptibility of P. mirabilis reference strain ATCC® 29906™ and four clinical strains isolated from the urine samples of patients with urinary catheter were evaluated according to EUCAST recommendations. The influence of ascorbic acid (0.4 mg × mL−1) in combination with antibiotics on biofilm formation was evaluated spectrophotometrically. Aminoglycosides at sub-inhibitory concentrations more successfully limited biofilm formation by P. mirabilis strains without ascorbic acid addition. Inhibition rate differences at the lowest concentrations of gentamicin and amikacin were statistically significant (p ≤ 0.05). Ascorbic acid addition to the culture medium limited the inhibitory effect of fluoroquinolones, facilitating biofilm formation by P. mirabilis strains. The addition of ascorbic acid during aminoglycosides therapy may disturb treatment of urinary tract infections related to the presence of P. mirabilis biofilm.

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Dusane, Devendra H., Che O’May, and Nathalie Tufenkji. "Effect of tannic and gallic acids alone or in combination with carbenicillin or tetracycline on Chromobacterium violaceum CV026 growth, motility, and biofilm formation." Canadian Journal of Microbiology 61, no. 7 (July 2015): 487–94. http://dx.doi.org/10.1139/cjm-2015-0101.

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Chromobacterium violaceum is an opportunistic pathogen that causes infections that are difficult to treat. The goal of this research was to evaluate the effect of selected tannins (tannic acid (TA) and gallic acid (GA)) on bacterial growth, motility, antibiotic (carbenicillin, tetracycline) susceptibility, and biofilm formation. Both tannins, particularly TA, impaired bacterial growth levels and swimming motilities at sub-minimum inhibitory concentrations (sub-MICs). In combination with tannins, antibiotics showed increased MICs, suggesting that tannins interfered with antibacterial activity. Sub-MICs of tetracycline or TA alone enhanced biofilm formation of C. violaceum; however, in combination, these compounds inhibited biofilm formation. In contrast, carbenicillin at sub-MICs was effective in inhibiting C. violaceum biofilm formation; however, in combination with lower concentrations of TA or GA, biofilms were enhanced. These results provide insights into the effects of tannins on C. violaceum growth and their varying interaction with antibiotics used to target C. violaceum infections.

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Ilizirov, Yana, Andrei Formanovsky, Irina Mikhura, Yossi Paitan, Faina Nakonechny, and Marina Nisnevitch. "Effect of Photodynamic Antibacterial Chemotherapy Combined with Antibiotics on Gram-Positive and Gram-Negative Bacteria." Molecules 23, no. 12 (November 30, 2018): 3152. http://dx.doi.org/10.3390/molecules23123152.

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The well-known and rapidly growing phenomenon of bacterial resistance to antibiotics is caused by uncontrolled, excessive and inappropriate use of antibiotics. One of alternatives to antibiotics is Photodynamic Antibacterial Chemotherapy (PACT). In the present study, the effect of PACT using a photosensitizer Rose Bengal alone and in combination with antibiotics including methicillin and derivatives of sulfanilamide synthesized by us was tested against antibiotic-sensitive and antibiotic-resistant clinical isolates of Gram-positive S. aureus and Gram-negative P. aeruginosa. Antibiotic-sensitive and resistant strains of P. aeruginosa were eradicated by Rose Bengal under illumination and by sulfanilamide but were not inhibited by new sulfanilamide derivatives. No increase in sensitivity of P. aeruginosa cells to sulfanilamide was observed upon a combination of Rose Bengal and sulfanilamide under illumination. All tested S. aureus strains (MSSA and MRSA) were effectively inhibited by PACT. When treated with sub-MIC concentrations of Rose Bengal under illumination, the minimum inhibitory concentrations (MIC) of methicillin decreased significantly for MSSA and MRSA strains. In some cases, antibiotic sensitivity of resistant strains can be restored by combining antibiotics with PACT.

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Mulvey, George, David J. Rafter, and Glen D. Armstrong. "Potential for using antibiotics combined with a Shiga toxin-absorbing agent for treating 0157:H7 Escherichia coli infections." Canadian Journal of Chemistry 80, no. 8 (August 1, 2002): 871–74. http://dx.doi.org/10.1139/v02-028.

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Antibiotics are not recommended for treating O157:H7 Escherichia coli infections because they may promote Shiga toxin (Stx) release from these bacteria. This could increase the risk of Stx-mediated complications in patients suffering from such infections. Here, we observed increased cell-free Stx in E. coli O157:H7 cultures exposed to sub-inhibitory concentrations of several antibiotics. Synsorb-Pk, an agent with a high affinity for Stx, absorbed Stx activity from the antibiotic-treated cultures. These data suggest certain antibiotics, given in combination with an orally administered Stx-binding agent, may be useful in treating O157:H7 E. coli infections.Key words: Shiga toxin, Synsorb, Escherichia coli, O157:H7, antibiotics, therapy.

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Christena, Lowrence Rene, Vimalanathan Mangalagowri, Prabhakaran Pradheeba, Khan Behlol Ayaz Ahmed, Bastin Infanta Sandhiya Shalini, Mohan Vidyalakshmi, Veerappan Anbazhagan, and Nagarajan Sai subramanian. "Copper nanoparticles as an efflux pump inhibitor to tackle drug resistant bacteria." RSC Advances 5, no. 17 (2015): 12899–909. http://dx.doi.org/10.1039/c4ra15382k.

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Doss, S. A., G. S. Tillotson, and S. G. B. Amyes. "Effect of sub-inhibitory concentrations of antibiotics on the virulence ofStaphylococcus aureus." Journal of Applied Bacteriology 75, no. 2 (August 1993): 123–28. http://dx.doi.org/10.1111/j.1365-2672.1993.tb02756.x.

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Williams, Calistus C., G. A. Ajibade, Victoria Moltong Yilwa, and Nwankwo Cornelius Tochukwu. "Signaling Molecules in Pseudomonas aeruginosa Response to Antibiotics at Sub-Inhibitory Concentrations." Asian Journal of Biotechnology and Bioresource Technology 10, no. 4 (October 14, 2024): 60–71. http://dx.doi.org/10.9734/ajb2t/2024/v10i4219.

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Signaling Molecules are N-acylhomoserine lactones (AHLs) that form the Pseudomonas aeruginosa cell information system which determines gene expressions in a population dependent manner called quorum sensing (QS). Signal molecules, which are chemically varied, control genes expressions to antibiotics resistance, pathogenicity, motility, biofilm development, bioluminescence, secondary metabolite production, and plasmid transfer. This research was aimed to identify the signaling molecules in Pseudomonas aeruginosa response to antibiotics at sub-inhibitory concentrations. One hundred and fifty (150) clinical swab specimens were collected from urinary catheter wound and ear infection of patients and the swabs inoculated using standard microbiology method. The isolates were characterized based on the bacteriological methods such as morphology and biochemical tests. The isolates were further confirmed by species specific PCR by amplification of 16S rRNA and the amplicons were analyzed by gel electrophoresis; and further genomic sequencing was done and blast with NCBI database mining. Disc diffusion method was applied for the antibiotics susceptibility pattern. The isolates cell suspensions were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). The result of the isolation showed 22(59.46%) from wound infections, 12(32.43%) from ear infections and 3(8.11%) from urinary catheter. The isolates were Gram negative, produced β-hemolysis on blood agar and the morphology is small pigmented circular in form. The isolates showed positive result to catalase, oxidase, citrate, nitrate and indole tests. The amplification of 16S rRNA gene region resulted in the band size of 1500bp PCR product and the BLAST analysis gave 99% similarity. The resistant antibiotics susceptibility showed that Pseudomonas aeruginosa is multidrug resistant bacteria. The GC-MS results obtained from urinary catheter isolates showed four (4) signaling molecules such as N-Octanoyl-L-homoserine Lactone, N-Decanoyl-DL-Homoserine Lactone, N-Dodecanoyl-DL-Homoserine Lactone and N-Tetradecanoyl-L-Homoserine Lactone. Three (3) signaling molecules such as N-Octanoyl-L-homoserine Lactone, N-Decanoyl-DL-Homoserine Lactone and N-Tetradecanoyl-L-Homoserine Lactone were obtained from wound isolates. N-Tetradecanoyl-L-Homoserine Lactone was the only signaling molecule obtained from ear isolates. Further research should be done to develop rapid tests that could be possible to detect acyl homoserine specific to Pseudomonsa aeruginosa present to human samples and deliver results in real time. Signaling molecules inhibitors (SMI) are possible potential therapeutics that could produce the subsequent class of antibacterial drugs. The fundamental role of each signal molecule in the production of biofilms and virulent factors should also be investigated, as well as whether Pseudomonas aeruginosa needs one or more signaling molecules to form quorum sensing. Identification of the signals molecules (AHLs) of P. aeruginosa and developing signaling molecules inhibitors (SMI) can have an important prognostic, diagnostic and therapeutic value in human medicine for the treatment of P. aeruginosa infections.

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Sandegren, Linus. "Low sub-minimal inhibitory concentrations of antibiotics generate new types of resistance." Sustainable Chemistry and Pharmacy 11 (March 2019): 46–48. http://dx.doi.org/10.1016/j.scp.2018.12.006.

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Goldoni, P., M. Castellani Pastoris, L. Cattani, L. Sinibaldi, and N. Orsi. "Effect of Sub-Inhibitory Concentrations of Antibiotics on the Hemolytic Activity ofLegionella." Journal of Chemotherapy 5, no. 5 (October 1993): 293–96. http://dx.doi.org/10.1080/1120009x.1993.11739247.

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Williams, C. C., G. A. Ajibade, and V. M. Y. Dan. "Identification of Antibiotics Susceptibility Patterns at Sub-inhibitory Concentrations in Pseudomonas aeruginosa." Asian Journal of Biotechnology and Bioresource Technology 10, no. 2 (March 26, 2024): 11–19. http://dx.doi.org/10.9734/ajb2t/2024/v10i2201.

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Pseudomonas aeruginosa is a Gram negative bacterium that has been recognized as an opportunistic pathogen. It is the most common bacterium associated with nosocomial infections and ventilator-associated pneumonia. It exhibits high innate resistance to various ranges of antibiotics thereby causing high morbidity and mortality rate. This research was aimed to identify the antibiotics susceptibility patterns at sub-inhibitory concentration in Pseudomonas aeruginosa. One hundred and fifty (150) clinical swab specimens were collected from urinary catheters; wound and ear infections of patients and the swabs inoculated using standard microbiology method. The isolates were characterized based on the bacteriological methods such as morphology and biochemical tests. The isolates were further confirmed by species specific by PCR amplification of 16S rRNA and the amplicons were analyzed by gel electrophoresis; and further genomic sequencing was done and blast with NCBI database mining. The antimicrobial susceptibility of the isolates was done by disc diffusion methods. The result of the isolation showed 22(59.46%) from wound infections, 12(32.43%) from ear infections and 3(8.11%) from urinary catheter. The isolates were Gram-negative, produced β-hemolysis on blood agar and the morphology is small pigmented circular. The isolates showed positive results to catalase, oxidase, citrate, nitrate and indole tests. The amplification of the 16S rRNA gene region resulted in the band size of 1500bp PCR product and the BLAST analysis gave 99% similarity. The results of susceptibility analysis showed that the isolates from the urinary catheter, wound and ear infection were 82%, 68% and 47% respectively, resistance to Piperacillin tazobactem, Cefoperazon, Ofloxacin, Tetracycline, Amikacin, Gentamycin, Bacitracin, Clarithromycin, Cefalotin, Levofloxacin and Cefpiroma. Antimicrobial susceptibility tests in P. aeruginosa isolates revealedshowed that they were multi-drug resistant. At sub-inhibitory concentrations of antibiotics within the microbial environment, Pseudomonas aeruginosa becomes more resistant. Perhaps, these antimicrobials could have other signaling activities within the environment. Therefore, there is a need for more research work to develop therapeutics combination to combat the recalcitrant nature of Pseudomonas aeruginosa.

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Liu, Cunwei, Jia Liu, Qinghui Lu, Ping Wang, and Qinghua Zou. "The Mechanism of Tigecycline Resistance in Acinetobacter baumannii under Sub-Minimal Inhibitory Concentrations of Tigecycline." International Journal of Molecular Sciences 25, no. 3 (February 2, 2024): 1819. http://dx.doi.org/10.3390/ijms25031819.

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The presence of sub-minimal inhibitory concentration (sub-MIC) antibiotics in our environment is widespread, and their ability to induce antibiotic resistance is inevitable. Acinetobacter baumannii, a pathogen known for its strong ability to acquire antibiotic resistance, has recently shown clinical resistance to the last-line antibiotic tigecycline. To unravel the complex mechanism of A. baumannii drug resistance, we subjected tigecycline-susceptible, -intermediate, and -mildly-resistant strains to successive increases in sub-MIC tigecycline and ultimately obtained tigecycline-resistant strains. The proteome of both key intermediate and final strains during the selection process was analyzed using nanoLC-MS/MS. Among the more than 2600 proteins detected in all strains, we found that RND efflux pump AdeABC was associated with the adaptability of A. baumannii to tigecycline under sub-MIC pressure. qRT-PCR analysis also revealed higher expression of AdeAB in strains that can quickly acquire tigecycline resistance compared with strains that displayed lower adaptability. To validate our findings, we added an efflux pump inhibitor, carbonyl cyanide m-chlorophenyl hydrazine (CCCP), to the medium and observed its ability to inhibit tigecycline resistance in A. baumannii strains with quick adaptability. This study contributes to a better understanding of the mechanisms underlying tigecycline resistance in A. baumannii under sub-MIC pressure.

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Giovagnoni, Giulia, Benedetta Tugnoli, Andrea Piva, and Ester Grilli. "Dual Antimicrobial Effect of Medium-Chain Fatty Acids against an Italian Multidrug Resistant Brachyspira hyodysenteriae Strain." Microorganisms 10, no. 2 (January 27, 2022): 301. http://dx.doi.org/10.3390/microorganisms10020301.

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The fastidious nature of Brachyspira hyodysenteriae limits an accurate in vitro pre-screening of conventionally used antibiotics and other candidate alternative antimicrobials. This results in a non-judicious use of antibiotics, leading to an exponential increase of the antibiotic resistance issue and a slowdown in the research for new molecules that might stop this serious phenomenon. In this study we tested four antibiotics (tylosin, lincomycin, doxycycline, and tiamulin) and medium-chain fatty acids (MCFA; hexanoic, octanoic, decanoic, and dodecanoic acid) against an Italian field strain of B. hyodysenteriae and the ATCC 27164 strain as reference. We determined the minimal inhibitory concentrations of these substances, underlining the multidrug resistance pattern of the field strain and, on the contrary, a consistent and stable inhibitory effect of the tested MCFA against both strains. Then, sub-inhibitory concentrations of antibiotics and MCFA were examined in modulating a panel of B. hyodysenteriae virulence genes (tlyA, tlyB, bhlp16, bhlp29.7, and bhmp39f). Results of gene expression analysis were variable, with up- and downregulations not properly correlated with particular substances or target genes. Decanoic and dodecanoic acid with their direct and indirect antimicrobial property were the most effective among MCFA, suggesting them as good candidates for subsequent in vivo trials.

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Droege, Molly E., Suzanne L. Van Fleet, and Eric W. Mueller. "Application of Antibiotic Pharmacodynamics and Dosing Principles in Patients With Sepsis." Critical Care Nurse 36, no. 2 (April 1, 2016): 22–32. http://dx.doi.org/10.4037/ccn2016881.

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Sepsis is associated with marked mortality, which may be reduced by prompt initiation of adequate, appropriate doses of antibiotic. Critically ill patients often have physiological changes that reduce blood and tissue concentrations of antibiotic and high rates of multidrug-resistant pathogens, which may affect patients’ outcomes. All critical care professionals, including critical care nurses, should understand antibiotic pharmacokinetics and pharmacodynamics to ensure sound antibiotic dosing and administration strategies for optimal microbial killing and patients’ outcomes. Effective pathogen eradication occurs when the dose of antibiotic reaches or maintains optimal concentrations relative to the minimum inhibitory concentration for the pathogen. Time-dependent antibiotics, such as β-lactams, can be given as extended or continuous infusions. Concentration-dependent antibiotics such as aminoglycosides are optimized by using high, once-daily dosing strategies with serum concentration monitoring. Vancomycin and fluoroquinolones are dependent on both time and concentration above the minimum inhibitory concentration.

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Shokrollahi, Behnaz, Akram Sadat Tabatabaee Bafroee, and Tayebeh Saleh. "Effect of Zinc Oxide Nanoparticles on Loaded Antibiotics Against Multidrug-Resistant Acinetobacter spp." Avicenna Journal of Clinical Microbiology and Infection 8, no. 2 (June 29, 2021): 51–56. http://dx.doi.org/10.34172/ajcmi.2021.10.

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Background: Metal oxide nanoparticles (NPs) have shown promising efficacy for combating bacterial resistance due to their antibacterial properties. This research investigated the effect of zinc oxide NPs (ZnO-NPs) on the antibacterial activity of conventional antibiotics including ciprofloxacin (CIP), cefotaxime (CTX), and colistin (CST) against multidrug-resistant Acinetobacter isolates. Methods: The disc diffusion method was performed to detect the pattern of antibiotic resistance in isolates. The synthesized ZnO-NPs via the solvothermal method were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). Finally, the broth microdilution technique was conducted to demonstrate the antibacterial activity of CIP, CTX, and CST antibiotics with and without a sub-inhibitory concentration of ZnO-NPs. Results: XRD, EDS, and FESEM results confirmed the crystalline structure of ZnO-NPs, and the average size was 100±58.68 nm. All isolates were discovered to be of multidrug-resistant (MDR) type and fully susceptible to CST. The antibacterial activity of CTX and CIP was restored when combined with a sub-inhibitory level of ZnO-NPs (0.25 mg/L), and the highest activity was obtained at the concentrations of 32 µg/mL CTX and 8 µg/ mL CIP. Eventually, ZnO-NPs showed a synergistic effect on the antibacterial properties of CST against MDR Acinetobacter. Conclusions: This research indicated that the combination of ZnO-NPs with some common antibiotics can be considered as a novel strategy for reducing the spread of antibiotic-resistant bacteria.

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PHAM, Thanh Luu, Thi Hoang Yen TRAN, and Thanh Thai TRAN. "TOXIC EFFECTS OF SULFAMETHOXAZOLE (SMX) ON A TROPICAL FRESHWATER MICROALGA, CHLORELLA SP." Carpathian Journal of Earth and Environmental Sciences 20, no. 1 (February 1, 2025): 161–68. https://doi.org/10.26471/cjees/2025/020/322.

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This study investigates the acute and sub-chronic toxicity of the emerging antibiotic, sulfamethoxazole (SMX) on the tropical freshwater microalga Chlorella sp. under laboratory condition. An acute exposure for 96 h and a sub-chronic exposure for 10 days were conducted to explore the adverse effects, utilizing growth inhibition, pigment content, and cell diameter as endpoints. The calculated half maximal (50 %) effective concentration (EC50) values for SMX after 24 h and 96 h were estimated to be 0.56 mg/L and 0.41 mg/L, respectively. Sub-chronic exposure unveiled a pronounced inhibitory effect of SMX on algal growth, with significant and dose-dependent increases in growth inhibition observed. Across all treatments, exposure to SMX resulted in growth inhibition and a decline in chlorophyll-a (Chl-a) concentration in the test algae. Notably, at a concentration of 1 mg/L, SMX completely inhibited the growth of Chlorella sp. and reduced Chl-a content by up to 98 %. High concentrations of SMX (0.5 and 1.0 mg/L) led to a decrease in cell diameter in the tested algae. This study contributes valuable insights into the acute and sub-chronic toxic effects of environmentally relevant concentrations of antibiotics on tropical freshwater microalgae.

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Bodo, Emily C., Kathryn E. Daffinee, and Kerry LaPlante. "620. Sub-MIC Concentrations of Levofloxacin and Delafloxacin Enhance Staphylococcus aureus Biofilm Formation: Significance of Maximizing Exposure." Open Forum Infectious Diseases 6, Supplement_2 (October 2019): S288. http://dx.doi.org/10.1093/ofid/ofz360.688.

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Abstract Background Fluoroquinolones are utilized in Staphylococcal prosthetic joint infections due to their anti-biofilm activity. When antibiotic dosing is not optimized or antibiotics do not reach the site of infection, additional virulence factors may upregulate. We aimed to determine whether exposure to sub-MIC concentrations of levofloxacin and delafloxacin affect biofilm formation in Staphylococcus aureus. Methods This study utilized 50 diverse methicillin-susceptible S. aureus (MSSA) clinical isolates collected between 2004 and 2018. Sources included blood, skin/tissue, bone, and joint fluid. Minimum inhibitory concentrations and minimum bactericidal concentrations were identified according to CLSI. Biofilm assays were conducted as previously described by our program. Biofilm quantification was categorized as strong (OD570 ≥ 2), moderate (OD570 ≥ 1 and < 2), or weak (OD570 < 1). Prevention assays were conducted with the addition of increasing concentrations of delafloxacin or levofloxacin. We evaluated the amount of isolates that demonstrated increased biofilm formation in the presence of sub-MIC concentrations and extent of biofilm enhancement. Percent change was calculated between OD570 of the isolate growth control without antibiotic exposure and peak biofilm OD570 when exposed to the antibiotic. Results Of the 50 MSSA isolates, 14 (28%) exhibited moderate/strong formation and 36 (32%) exhibited weak biofilm formation. 52% and 58% of the isolates demonstrated a ≥50% increase in formation when exposed to sub-MIC concentrations of delafloxacin and levofloxacin, respectively. None of the strong biofilm formers demonstrated a ≥50% peak increase in formation when exposed to the antibiotics. Of the isolates that demonstrated a ≥50% peak increase, the average percent change was 267% (±29) with levofloxacin and 258% (±33) with delafloxacin. Conclusion Sub-MIC concentrations of delafloxacin and levofloxacin increased biofilm formation in S. aureus isolates that normally exhibit weak or moderate biofilm formation when not in the presence of antibiotics. Maintaining appropriate fluoroquinolone concentrations at the site of action is critical in preventing enhancement of biofilm formation. Further research is needed to identify the mechanism behind this increase. Disclosures All authors: No reported disclosures.

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Kulik, Klaudia, Anna Lenart-Boroń, and Kinga Wyrzykowska. "Impact of Antibiotic Pollution on the Bacterial Population within Surface Water with Special Focus on Mountain Rivers." Water 15, no. 5 (March 3, 2023): 975. http://dx.doi.org/10.3390/w15050975.

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Environmental aquatic pollution with antibiotics is a global challenge that affects even pristine mountain environments. Monitoring the concentration of antibiotics in water is critical to water resource management. In this review, we present the sources and degradation routes of antibiotics polluting surface waters, with particular focus on mountain environments and pristine areas. This pollution is strongly related to anthropopressure resulting from intensive tourism. An important aspect of the threat to the environment is water containing antibiotics at sub-inhibitory concentrations, which affects bacterial populations. Antibiotics are ecological factors driving microbial evolution by changing the bacterial community composition, inhibiting or promoting their ecological functions, and enriching and maintaining drug resistance. We paid attention to the stability of antibiotics and their half-lives in water related to biotic and abiotic degradation, which results from the structures of molecules and environmental conditions. Wastewater treatment combined with advanced treatment techniques significantly increase the efficiency of antibiotic removal from wastewater. Modern methods of wastewater treatment are crucial in reducing the supply of antibiotics to aquatic environments and enhancing the possibility of economic and safe reuse of wastewater for technical purposes. We provide a perspective on current research investigating antibiotic emergence in mountain areas and identify knowledge gaps in this field.

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Nikolic, Isidora, Verica Aleksic Sabo, Damir Gavric, and Petar Knezevic. "Anti-Staphylococcus aureus Activity of Volatile Phytochemicals and Their Combinations with Conventional Antibiotics Against Methicillin-Susceptible S. aureus (MSSA) and Methicillin-Resistant S. aureus (MRSA) Strains." Antibiotics 13, no. 11 (October 31, 2024): 1030. http://dx.doi.org/10.3390/antibiotics13111030.

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Background: MSSA and MRSA strains are challenging human pathogens that can develop resistance to antibiotics, highlighting the need for alternative antimicrobial agents. Plant metabolites, particularly volatile phytochemicals, may offer promising antimicrobial properties. The aim was to evaluate the antimicrobial and antibiofilm efficacy of various commercial volatile phytochemicals from the terpene and terpenoid groups against reference MSSA and MRSA strains, focusing on synergistic effects in both binary combinations and combinations with antibiotics. Methods: The microdilution method was used to determine the minimum inhibitory concentrations (MICs) for antibiotics and phytochemicals. The checkerboard method assessed synergistic interactions between phytochemicals and between phytochemicals and antibiotics, while the time-kill method was used to confirm these results. Biofilm quantification was performed using the microtiter plate method to evaluate the effects of phytochemicals, antibiotics, and their binary combinations on the eradication of 48-h-old biofilms. Results: Carvacrol and thymol demonstrated the strongest anti-staphylococcal activity, while other terpene compounds showed weaker effects. In binary combinations, carvacrol and thymol exhibited synergy against one MSSA strain (FICI = 0.50) and with tetracycline and chloramphenicol (FICI = 0.28–0.50). Synergy was also noted with streptomycin sulfate against one MRSA strain (FICI = 0.31–0.50) and with other antibiotics, including gentamicin (FICI = 0.25–0.50) and oxacillin (FICI = 0.44). Additionally, effective combinations achieved over 50% biofilm removal at both minimum inhibitory and sub-inhibitory concentrations. Conclusions: Results showed that synergy varies based on strain sensitivity to chemical agents, highlighting their potential for personalized therapy. Despite the difficulty in removing preformed biofilms, the findings highlight the importance of combined treatments to enhance antibiotic effectiveness.

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Quansah, Joycelyn, Himabindu Gazula, Da Liu, and Jinru Chen. "Effect of Pre-Exposure to Chlorine Dioxide on the Susceptibility of Fecal Coliforms to Antibiotics." Antibiotics 11, no. 2 (February 8, 2022): 215. http://dx.doi.org/10.3390/antibiotics11020215.

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Adaptive exposure to sub-lethal concentrations of sanitizers was previously reported to offer cross-protection to bacteria against antibiotics. This study was undertaken to determine whether the pre-exposure of fecal coliforms to suboptimal concentrations of a chemical sanitizer, chlorine dioxide (ClO2), alters their susceptibility to certain antibiotics. Fecal coliforms isolated from fresh fruit packing facilities (n = 12) were adapted in ½ or ¼ of the manufacturer-recommended concentration of ClO2. The susceptibility of the adapted and non-adapted cells to 13 different antibiotics was determined by observing the changes in their minimal inhibitory concentrations (MICs). The results showed that preadaptation to the suboptimal concentrations of ClO2, in general, either decreased or did not change the MICs of the antibiotics against selected fecal coliform isolates, with only two exceptions; preadaptation increased the MICs of kanamycin against two of the fecal coliform isolates, and of nalidixic acid against one of the fecal coliform isolates. The results suggest that the use of ClO2 has a relatively low risk of inducing the resistance of fecal coliforms to antibiotics.

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Sweedan, Enass, Zina Shehab, and May Flayyih. "Effect of gentamicin and doxycycline on expression of relB and relE genes in Klebsiella pneumonia." Journal of Advanced Biotechnology and Experimental Therapeutics 5, no. 3 (2022): 667. http://dx.doi.org/10.5455/jabet.2022.d145.

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The goal of study was determined that Klebsiella pneumoniae isolates possessed Toxin-Antitoxin II genes such as relE and relB, other than if there was a correlation between the expression of these two genes and antibiotics, and they may participate in increasing the resistance to antibiotics in K. pneumoniae. Fifty-seven urine samples were collected, from Baghdad s’ hospitals, diagnosed and identified by phenotype and biochemical tests, and confirmed with VITEK 2 compact system. Only fifteen isolates which were identified as K. pneumoniae. Antibiotic sensitivity was identified by using twelve antibiotics discs and K. pneumoniae were resisted in 100% to Ceftriaxone, Amoxicillin, Ticarcillin, Ticarcillin+Clavulanic acid, Ceftazidime, Tetracycline, while other antibiotics were showed less percent of resistant. Minimum inhibitory concentrations (MICs) of antibiotics detected by using macro tube dilution method to identify the antimicrobial activity for K. pneumoniae, the MIC of Gentamicin and Doxycycline antibiotics was 1024 Mg/ml, 512 Mg/ml respectively. By polymerase chain reaction detected genes of relB, relE with 115bp. and 136pb. respectively, then gene expression of relB, relE was conducted by using (RT-qPCR) technique with treated sub MIC concentration of (Gentamicin and Doxycycline) antibiotics. This study was found only ten isolates harbored the two genes as well as, value of folding was increased expression fold of relB gene, but in the same time relE gene was decreased its fold change according to control infB1 gene expression results. This means the bacterial cell tolerance antibiotics sub MIC concentrations by maintaining the number of bacteria under stress of antibiotics. Finally, these findings suggest the potential of relB to give K. pneumoniae resistant to antibiotics in their infections when it was being under stress of antibiotics by toxin-antitoxin II system to stay life.

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Sopova, Julia V., Vladimir V. Gostev, Olga S. Kalinogorskaya, Anna N. Lykholay, and Sergey V. Sidorenko. "Proteome dynamics of antibiotic resistant Staphylococcus aureus strains exposed to sub-inhibitory concentrations of beta-lactams." Ecological genetics 16, no. 2 (August 7, 2018): 4–10. http://dx.doi.org/10.17816/ecogen1624-10.

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Background. Ceftaroline is one of the first cephalosporins with activity against methicillin-resistant Staphylococcus aureus (MRSA), it effectively binds to and inhibits penicillin-binding protein 2a (PBP2a). However, isolates with decreased susceptibility to ceftaroline were reported before the commercial release of the antibiotic. The aim of this study was to provide an overview of the proteome changes occurring in MRSA isolates resistant to ceftaroline in response to sub-inhibitory concentrations of cell-wall active antibiotics. Materials and methods. Ceftaroline-resistant mutants were generated from two MRSA SA0077 and SA0422 isolates belonging to ST8-t008-SCCmec IV genetic lineage (sequence type 8, spa type t008, staphylococcal chromosomal cassette mec type IV) and one MRSA isolate SA0085 belonging to ST239-t631-SCCmec III genetic lineage (sequence type 239, spa type t631, staphylococcal chromosomal cassette mec type III). Proteome response of parental and mutant strains to sub-inhibitory concentration of beta-lactams and vancomycin was analyzed. Results. The protein patterns revealed significant increase of 30 кDа band in mutant strains under induction by meropenem, no changes were observed in parental strains or under induction with other antibiotics. According to MS analysis, three proteins represented the band of the mutant strain in absence of meropenem induction. However, under meropenem induction additional protein was detected (BlaZ). Conclusion. The cross talk between two systems with overlapping functions involved in transcription control of PBP2a and BlaZ ensure ceftaroline resistant phenotype.

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MOHAMMED YOUNIS, Khansa, Ghaydaa M. A. ALI, and Ashwaq Hazem NAJEM. "Investigation of the Role of Vitamin C In Enhancing the Activity of Antibacterial Agents and Biofilm Formation." Eurasia Proceedings of Science Technology Engineering and Mathematics 16 (December 31, 2021): 195–203. http://dx.doi.org/10.55549/epstem.1068610.

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Resistance to antibiotics is rapidly spreading across the globe, posing a new health-care challenge for all countries. Bacterial biofilms are three-dimensional formations made up of cells encased in a matrix of polymeric, making cells resistant to the drugs and the immune system. As a result, new tactics for inhibiting the production of the EPS matrix may lead to more efficient use of already available antibiotics. The mechanism of vitamins C effect on boosting the effectiveness of several anti-bacterial drugs was investigated in this study, the target isolates were obtained from University of Mosul/ Biology department/ bacterial culture collections and evaluated qualitatively and quantitatively. The isolates involved: Staphylococcus aureus, Escherichia coli ,Klebsiella sp., Serratia marcescens and Pseudomonas aeroginosa. Antibiotic sensitivity tests and biofilm producing assay results revealed that the majority of the isolates were resistant to a range of antibiotics and had a large capacity for biofilm formation when grown on a cover glass surface. Vitamin C is an antioxidant, a scavenger of active metabolites. The Minimum Inhibitory Concentration (MIC) of Vitamin C against selected isolates had been determined, and all further experiments used concentrations below the MIC. Our results showed that Vit.C pre-treatment enhance the bactericidal effect of antibiotic and increases bacterial susceptibility to antibiotics. Using light microscopy, experiments of sub inhibitory doses of Vitamin C revealed good suppression of selected isolates biofilm development on the cover glass surface. Vitamin C can be utilized as an antibiotic adjuvant in combination with antibiotic and has effective biofilm inhibition, caused by multidrug-resistant bacteria, according to evidence.

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Nyambe, S., C. Burgess, P. Whyte, and D. Bolton. "The effect of antimicrobials on verocytotoxin bacteriophage transduction under bovine rumen fluid and broth conditions." Irish Journal of Agricultural and Food Research 56, no. 1 (November 15, 2017): 77–84. http://dx.doi.org/10.1515/ijafr-2017-0008.

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AbstractThe verocytotoxin genes in verocytotoxigenicEscherichia coli(VTEC) are carried by bacteriophages, incorporated into the bacterial genome (prophage). Antibiotics may promote phage replication and release to infect other cells (transduction), thus leading to the emergence of new VTEC strains. This study investigated transduction of a verocytotoxin2-encoding bacteriophage (3538(vtx2::cat)) under laboratory conditions, including the effect of antibiotic treatments. Luria-Bertani Miller broth and rumen fluid (raw and sterilised by irradiation) were inoculated with the donor (C600φ3538(Δvtx2::cat)) and recipient (E. coli C600::kanamycinR) strains (4 log10cfu/mL) and incubated at 38°C. Antibiotic treatments (minimal inhibitory and sub-inhibitory concentrations of ampicillin, cefquinome, oxytetracycline and sodium sulfamethazine) were applied after 3 h. Samples were tested for donor, recipient, cell-free phage and transductants at times t = 0, 3, 4, 6, 27 (24 h post-antibiotic treatment) and 51 h. Free phage was detected in the untreated broth and rumen samples, as were the transductants confirmed by polymerase chain reaction. The antibiotic treatments did not significantly (P > 0.01) increase the concentrations of free phage or transductants detected. It was therefore concluded that, under laboratory conditions, the antibiotics tested did not induce bacteriophage lysis, release and infection of new bacterial cells beyond that constitutively found in the phage population.

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Milenkovic, Marina, Dragana Bozic, Violeta Slavkovska, and Branislava Lakusic. "Synergistic effects of Salvia officinalis L. essential oils and antibiotics against methicillin-resistant Staphylococcus aureus." Archives of Biological Sciences 67, no. 3 (2015): 949–56. http://dx.doi.org/10.2298/abs141119057m.

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Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) due to the acquisition of resistance to current antimicrobials pose a serious challenge for therapy, and new measures to treat and prevent this infectious pathogen are of crucial importance. Plant essential oils (EOs) and their constituents are promising agents with antimicrobial properties. The aim of this study was to evaluate the antistaphylococcal effect of essential oils from Salvia officinalis using the broth-microdilution method. Essential oils of S. officinalis were isolated from the same individual, but at different life stages - young and old leaves. The effects of combinations of sub-inhibitory concentrations of oil and different antibiotics were evaluated by the checkerboard method. The results, expressed as the fractional inhibitory concentration (FIC) and index (FICI), indicate that the essential oil isolated from young leaves potentiated the inhibitory effect of antibiotics against tested MRSA strains.

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Quiñones-Vico, María I., Ana Fernández-González, Ana Ubago-Rodríguez, Kirsten Moll, Anna Norrby-Teglund, Mattias Svensson, José Gutiérrez-Fernández, Jesús M. Torres, and Salvador Arias-Santiago. "Antibiotics against Pseudomonas aeruginosa on Human Skin Cell Lines: Determination of the Highest Non-Cytotoxic Concentrations with Antibiofilm Capacity for Wound Healing Strategies." Pharmaceutics 16, no. 1 (January 17, 2024): 117. http://dx.doi.org/10.3390/pharmaceutics16010117.

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Pseudomonas aeruginosa is one of the most common microorganisms causing infections of severe skin wounds. Antibiotic or antiseptic treatments are crucial to prevent and curb these infections. Antiseptics have been reported to be cytotoxic to skin cells and few studies evaluate the impact of commonly used antibiotics. This study evaluates how clinical antibiotics affect skin cells’ viability, proliferation, migration, and cytokine secretion and defines the highest non-cytotoxic concentrations that maintain antibacterial activity. Cell proliferation, viability, and migration were evaluated on cell monolayers. Cytokines related to the wound healing process were determined. The minimum inhibitory concentrations and the impact on bacterial biofilm were assessed. Results showed that 0.02 mg/mL ciprofloxacin and 1 mg/mL meropenem are the highest non-cytotoxic concentrations for fibroblasts and keratinocytes while 1.25 mg/mL amikacin and 0.034 mg/mL colistin do not affect fibroblasts’ viability and cytokine secretion but have an impact on keratinocytes. These concentrations are above the minimum inhibitory concentration but only amikacin could eradicate the biofilm. For the other antibiotics, cytotoxic concentrations are needed to eradicate the biofilm. Combinations with colistin at non-cytotoxic concentrations effectively eliminate the biofilm. These results provide information about the concentrations required when administering topical antibiotic treatments on skin lesions, and how these antibiotics affect wound management therapies. This study set the basis for the development of novel antibacterial wound healing strategies such as antibiotic artificial skin substitutes.

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Shenkutie, Abebe Mekuria, Jiaying Zhang, Mianzhi Yao, Daniel Asrat, Franklin W. N. Chow, and Polly H. M. Leung. "Effects of Sub-Minimum Inhibitory Concentrations of Imipenem and Colistin on Expression of Biofilm-Specific Antibiotic Resistance and Virulence Genes in Acinetobacter baumannii Sequence Type 1894." International Journal of Molecular Sciences 23, no. 20 (October 21, 2022): 12705. http://dx.doi.org/10.3390/ijms232012705.

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Antibiotics at suboptimal doses promote biofilm formation and the development of antibiotic resistance. The underlying molecular mechanisms, however, were not investigated. Here, we report the effects of sub-minimum inhibitory concentrations (sub-MICs) of imipenem and colistin on genes associated with biofilm formation and biofilm-specific antibiotic resistance in a multidrug-tolerant clinical strain of Acinetobacter baumannii Sequence Type (ST) 1894. Comparative transcriptome analysis was performed in untreated biofilm and biofilm treated with sub-MIC doses of imipenem and colistin. RNA sequencing data showed that 78 and 285 genes were differentially expressed in imipenem and colistin-treated biofilm cells, respectively. Among the differentially expressed genes (DEGs), 48 and 197 genes were upregulated exclusively in imipenem and colistin-treated biofilm cells, respectively. The upregulated genes included those encoding matrix synthesis (pgaB), multidrug efflux pump (novel00738), fimbrial proteins, and homoserine lactone synthase (AbaI). Upregulation of biofilm-associated genes might enhance biofilm formation when treated with sub-MICs of antibiotics. The downregulated genes include those encoding DNA gyrase (novel00171), 30S ribosomal protein S20 (novel00584), and ribosome releasing factor (RRF) were downregulated when the biofilm cells were treated with imipenem and colistin. Downregulation of these genes affects protein synthesis, which in turn slows down cell metabolism and makes biofilm cells more tolerant to antibiotics. In this investigation, we also found that 5 of 138 small RNAs (sRNAs) were differentially expressed in biofilm regardless of antibiotic treatment or not. Of these, sRNA00203 showed the highest expression levels in biofilm. sRNAs regulate gene expression and are associated with biofilm formation, which may in turn affect the expression of biofilm-specific antibiotic resistance. In summary, when biofilm cells were exposed to sub-MIC doses of colistin and imipenem, coordinated gene responses result in increased biofilm production, multidrug efflux pump expression, and the slowdown of metabolism, which leads to drug tolerance in biofilm. Targeting antibiotic-induced or repressed biofilm-specific genes represents a new strategy for the development of innovative and effective treatments for biofilm-associated infections caused by A. baumannii.

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van Leuven, Nicole, Ralf Lucassen, Anna Dicks, Patrick Braß, André Lipski, and Dirk Bockmühl. "Does Antibiotic Use Contribute to Biofilm Resistance in Sink Drains? A Case Study from Four German Hospital Wards." Antibiotics 13, no. 12 (December 1, 2024): 1148. https://doi.org/10.3390/antibiotics13121148.

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Backgound. As biofilms are known to harbour (multi-)resistant species, their presence in health settings must be considered critical. Although there is evidence that bacteria spread from drains to the outside, there is still a lack of research data focusing on drain biofilms from hospitals. Methods. We sampled biofilms from various wards of Helios Hospital Krefeld (Germany), where comprehensive antibiotic consumption data were available. Biofilms were analysed by cell counting, isolation of relevant bacterial groups and genetic and phenotypical resistance parameters. Data were correlated with the prescribed antibiotics of the respective ward. Furthermore, an ex situ biofilm model was employed to investigate the influence of sub-inhibitory antibiotics on the bacterial community and the prevalence of class 1 integrons. Results. Our results show that every ward harboured medically relevant bacterial species. While no significant differences were found in cell counts, the median prevalence of the resistance marker gene intI1 correlated with the amount of prescribed antibiotics. In contrast, phenotypical resistances showed no similar tendency. In addition, melting curve analysis data and changes in intI1 prevalence show that the composition of the bacterial community shifted depending on the biofilm and antibiotic. Conclusions. To the best of our knowledge, our study is the first considering possible correlations between the consumption data of hospital wards and resistances in drain biofilms the way we did. Based on our results, we conclude that sub-inhibitory concentrations of antibiotics have no general effect on biofilms in terms of bacterial community shift and occurrence of antibiotic-resistant species. Amongst other things, the effect depends on the initial composition of the bacterial community, the antibiotic used and the intrinsic bacterial resistance, e.g., prevalence of class 1 integrons.

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Zuo, Jing, Qingying Fan, Jinpeng Li, Baobao Liu, Bingqian Xue, Xiaoling Zhang, Li Yi, and Yang Wang. "Sub-Inhibitory Concentrations of Amoxicillin and Tylosin Affect the Biofilm Formation and Virulence of Streptococcus suis." International Journal of Environmental Research and Public Health 19, no. 14 (July 8, 2022): 8359. http://dx.doi.org/10.3390/ijerph19148359.

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Streptococcus suis (S. suis) can form a protective biofilm during infection and lead to prolonged disease. Oral antibiotics are often used for treatment in clinical practice, but sub-inhibitory concentration levels often exist due to low oral absorption rate, resulting in disease deterioration. The purpose of this study was to investigate the effects of Amoxicillin and Tylosin on the biofilm formation and virulence of S. suis HA9801 at sub-inhibitory concentration. We first determined that the test groups (1/4MIC Amoxicillin and Tylosin) could significantly increase the amount of biofilm formation without affecting bacterial growth. The LD50 value of the test groups was significantly higher than that of the control group in the mouse infection model. In the mouse infection model, the LD50 value of the experimental group was significantly increased, but the tissue bacterial load was significantly decreased. Further RT-PCR analysis showed that the expression levels of virulence-related genes in the experimental group were significantly reduced. Our study suggests that both Amoxicillin and Tylosin at sub-inhibitory concentrations could enhance the biofilm formation ability of S. suis HA9801 and reduce its virulence to form persistent infection.

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Whelan, Shane, Mary Claire O’Grady, Gerard Daniel Corcoran, Karen Finn, and Brigid Lucey. "Effect of Sub-Inhibitory Concentrations of Nitrofurantoin, Ciprofloxacin, and Trimethoprim on In Vitro Biofilm Formation in Uropathogenic Escherichia coli (UPEC)." Medical Sciences 11, no. 1 (December 20, 2022): 1. http://dx.doi.org/10.3390/medsci11010001.

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The purpose of this study was to determine the effect of sublethal concentrations of nitrofurantoin, ciprofloxacin, and trimethoprim on biofilm formation in 57 uropathogenic Escherichia coli strains (UPEC). The minimum inhibitory concentration of nitrofurantoin, ciprofloxacin, and trimethoprim was determined and the biofilm formation for each isolate with and without sub-lethal concentrations of each antibiotic was then quantified. The statistical significance of changes in biofilm formation was ascertained by way of a Dunnett’s test. A total of 22.8% of strains were induced to form stronger biofilms by nitrofurantoin, 12% by ciprofloxacin, and 19% by trimethoprim; conversely 36.8% of strains had inhibited biofilm formation with nitrofurantoin, 52.6% with ciprofloxacin, and 38.5% with trimethoprim. A key finding was that even in cases where the isolate was resistant to an antibiotic as defined by EUCAST, many were induced to form a stronger biofilm when grown with sub-MIC concentrations of antibiotics, especially trimethoprim, where six of the 22 trimethoprim resistant strains were induced to form stronger biofilms. These findings suggest that the use of empirical treatment with trimethoprim without first establishing susceptibility may in fact potentiate infection in cases where a patient who is suffering from a urinary tract infection (UTI) caused by trimethoprim resistant UPEC is administered trimethoprim. This emphasizes the need for laboratory-guided treatment of UTI.

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Harshaw, Nathaniel S., Nicholas A. Stella, Kara M. Lehner, Eric G. Romanowski, Regis P. Kowalski, and Robert M. Q. Shanks. "Antibiotics Used in Empiric Treatment of Ocular Infections Trigger the Bacterial Rcs Stress Response System Independent of Antibiotic Susceptibility." Antibiotics 10, no. 9 (August 25, 2021): 1033. http://dx.doi.org/10.3390/antibiotics10091033.

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The Rcs phosphorelay is a bacterial stress response system that responds to envelope stresses and in turn controls several virulence-associated pathways, including capsule, flagella, and toxin biosynthesis, of numerous bacterial species. The Rcs system also affects antibiotic tolerance, biofilm formation, and horizontal gene transfer. The Rcs system of the ocular bacterial pathogen Serratia marcescens was recently demonstrated to influence ocular pathogenesis in a rabbit model of keratitis, with Rcs-defective mutants causing greater pathology and Rcs-activated strains demonstrating reduced inflammation. The Rcs system is activated by a variety of insults, including β-lactam antibiotics and polymyxin B. In this study, we developed three luminescence-based transcriptional reporters for Rcs system activity and used them to test whether antibiotics used for empiric treatment of ocular infections influence Rcs system activity in a keratitis isolate of S. marcescens. These included antibiotics to which the bacteria were susceptible and resistant. Results indicate that cefazolin, ceftazidime, polymyxin B, and vancomycin activate the Rcs system to varying degrees in an RcsB-dependent manner, whereas ciprofloxacin and tobramycin activated the promoter fusions, but in an Rcs-independent manner. Although minimum inhibitory concentration (MIC) analysis demonstrated resistance of the test bacteria to polymyxin B and vancomycin, the Rcs system was activated by sub-inhibitory concentrations of these antibiotics. Together, these data indicate that a bacterial stress system that influences numerous pathogenic phenotypes and drug-tolerance is influenced by different classes of antibiotics despite the susceptibility status of the bacterium.

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Anderson, Jasmine R., Nghi B. Lam, Jazmyne L. Jackson, Sean M. Dorenkott, Taylor Ticer, Emir Maldosevic, Amanda Velez, Megan R. Camden, and Terri N. Ellis. "Progressive Sub-MIC Exposure of Klebsiella pneumoniae 43816 to Cephalothin Induces the Evolution of Beta-Lactam Resistance without Acquisition of Beta-Lactamase Genes." Antibiotics 12, no. 5 (May 10, 2023): 887. http://dx.doi.org/10.3390/antibiotics12050887.

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Bacterial exposure to antibiotic concentrations below the minimum inhibitory concentration (MIC) may result in a selection window allowing for the rapid evolution of resistance. These sub-MIC concentrations are commonly found in soils and water supplies in the greater environment. This study aimed to evaluate the adaptive genetic changes in Klebsiella pneumoniae 43816 after prolonged but increasing sub-MIC levels of the common antibiotic cephalothin over a fourteen-day period. Over the course of the experiment, antibiotic concentrations increased from 0.5 μg/mL to 7.5 μg/mL. At the end of this extended exposure, the final adapted bacterial culture exhibited clinical resistance to both cephalothin and tetracycline, altered cellular and colony morphology, and a highly mucoid phenotype. Cephalothin resistance exceeded 125 μg/mL without the acquisition of beta-lactamase genes. Whole genome sequencing identified a series of genetic changes that could be mapped over the fourteen-day exposure period to the onset of antibiotic resistance. Specifically, mutations in the rpoB subunit of RNA Polymerase, the tetR/acrR regulator, and the wcaJ sugar transferase each fix at specific timepoints in the exposure regimen where the MIC susceptibility dramatically increased. These mutations indicate that alterations in the secretion of colanic acid and attachment of colonic acid to LPS may contribute to the resistant phenotype. These data demonstrate that very low sub-MIC concentrations of antibiotics can have dramatic impacts on the bacterial evolution of resistance. Additionally, this study demonstrates that beta-lactam resistance can be achieved through sequential accumulation of specific mutations without the acquisition of a beta-lactamase gene.

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Iseppi, Ramona, Martina Mariani, Carla Condò, Carla Sabia, and Patrizia Messi. "Essential Oils: A Natural Weapon against Antibiotic-Resistant Bacteria Responsible for Nosocomial Infections." Antibiotics 10, no. 4 (April 10, 2021): 417. http://dx.doi.org/10.3390/antibiotics10040417.

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The emergence of antibiotic-resistant bacteria has become a major concern worldwide. This trend indicates the need for alternative agents to antibiotics, such as natural compounds of plant origin. Using agar disc diffusion and minimum inhibitory concentration (MIC) assays, we investigated the antimicrobial activity of Citrus aurantium (AEO), Citrus x limon (LEO), Eucalyptus globulus (EEO), Melaleuca alternifolia (TTO), and Cupressus sempervirens (CEO) essential oils (EOs) against three representatives of antibiotic-resistant pathogens and respective biofilms: vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. Using the checkerboard method, the efficacy of the EOs alone, in an association with each other, or in combination with the reference antibiotics was quantified by calculating fractional inhibitory concentrations (FICs). All the EOs displayed antibacterial activity against all strains to different extents, and TTO was the most effective. The results of the EO–EO associations and EO–antibiotic combinations clearly showed a synergistic outcome in most tests. Lastly, the effectiveness of EOs both alone and in association or combination against biofilm formed by the antibiotic-resistant strains was comparable to, and sometimes better than, that of the reference antibiotics. In conclusion, the combination of EOs and antibiotics represents a promising therapeutic strategy against antibiotic-resistant bacteria, even protected inside biofilms, which can allow decreasing the concentrations of antibiotics used.

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44

Chen, Juan, Huyue Zhou, Jingbin Huang, Rong Zhang, and Xiancai Rao. "Virulence alterations in staphylococcus aureus upon treatment with the sub-inhibitory concentrations of antibiotics." Journal of Advanced Research 31 (July 2021): 165–75. http://dx.doi.org/10.1016/j.jare.2021.01.008.

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Majtán, J., L. Majtánová, and V. Majtán. "P613 Infiuence of sub-inhibitory concentrations of antibiotics on biofilm formation by Salmonella typhimurium." International Journal of Antimicrobial Agents 29 (March 2007): S143. http://dx.doi.org/10.1016/s0924-8579(07)70456-9.

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Quinn, Brettni, Jasmine Martinez, Christine Liu, Meaghan Nguyen, and Maria Soledad Ramirez. "The effect of sub-inhibitory concentrations of antibiotics on natural transformation in Acinetobacter baumannii." International Journal of Antimicrobial Agents 51, no. 5 (May 2018): 809–10. http://dx.doi.org/10.1016/j.ijantimicag.2018.01.026.

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Piatti, Gioia. "Bacterial adhesion to respiratory mucosa and its modulation by antibiotics at sub-inhibitory concentrations." Pharmacological Research 30, no. 4 (December 1994): 289–99. http://dx.doi.org/10.1016/1043-6618(94)80009-x.

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48

Mâ€™hamedi, Imane, Hafida Hassaine, Leila Dalaa, Saadia Benelhadj-Djelloul, and Mohammed Ziane. "Effect of subinhibitory antibiotics concentrations on biofilm formation by clinical Acinetobacter baumannii isolated from endotracheal tubes in ventilator-associated pneumonia." South Asian Journal of Experimental Biology 11, no. 3 (May 24, 2021): 242–48. http://dx.doi.org/10.38150/sajeb.11(3).p242-248.

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The treatment of ventilator-associated pneumonia caused by Acinetobacter baumanii requires a probabilistic antibiotic therapy followed by a specific antibiotic therapy. However, this treatment is faced with two problems; first, the great ability of A. bauamnii to form a biofilm on the surface of endotra-cheal tube, and second the exposure of bacteria to a sub-minimal inhibitory concentration (Sub-MIC) of antibiotics due to their weak diffusion through the tissues. The purpose of the present study was to determine the effects of Sub-MICs of ceftazidime (CAZ), piperacillin/tazobactam (PIP/TAZ), imipenem (IMP) and colistin (CST) on biofilm formation of six A. baumanii clinical iso-lates and as well as on its representative strain ATCC 19606. Sub-MIC of ceftazidime was found to increase biofilm formation in all six isolates. Alt-hough, in the presence of Sub-MIC of PIP/TAZ, biofilm formation of three isolates was reduced. Also, Sub-MIC of CST had a stimulating effect on bio-film formation in three isolates and a reducing effect on one single isolate. While, no impact was noted on all isolates in the presence of Sub-MIC of IMP. The ATCC 19606 biofilm formation exhibited no significant change in the presence of Sub-MIC of IMP. However, it decreased in the presence of Sub-MIC of PIP / TAZ and CST and increased in the presence of Sub-MIC of CAZ Finally, an inappropriate choice of antibiotic therapy, combined with a lower concentration can in some cases stimulate the potential of clinical A. baumanii strains to form a biofilm in ventilator-associated pneumonia (VAP).

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Tapia-Rodriguez, Melvin Roberto, Ernesto Uriel Cantu-Soto, Francisco Javier Vazquez-Armenta, Ariadna Thalia Bernal-Mercado, and Jesus Fernando Ayala-Zavala. "Inhibition of Acinetobacter baumannii Biofilm Formation by Terpenes from Oregano (Lippia graveolens) Essential Oil." Antibiotics 12, no. 10 (October 14, 2023): 1539. http://dx.doi.org/10.3390/antibiotics12101539.

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Acinetobacter baumannii is a nosocomial pathogen known for its ability to form biofilms, leading to persistent infections and antibiotic resistance. The limited effective antibiotics have encouraged the development of innovative strategies such as using essential oils and their constituents. This study evaluated the efficacy of oregano (Lippia graveolens) essential oil (OEO) and its terpene compounds, carvacrol and thymol, in inhibiting A. baumannii biofilms. These treatments showed a minimum inhibitory concentration of 0.6, 0.3, and 2.5 mg/mL and a minimum bactericidal concentration of 1.2, 0.6, and 5 mg/mL, respectively. Sub-inhibitory doses of each treatment and the OEO significantly reduced biofilm biomass and the covered area of A. baumannii biofilms as measured by fluorescence microscopy. Carvacrol at 0.15 mg/mL exhibited the most potent efficacy, achieving a remarkable 95% reduction. Sub-inhibitory concentrations of carvacrol significantly reduced the biofilm formation of A. baumannii in stainless steel surfaces by up to 1.15 log CFU/cm2 compared to untreated bacteria. The OEO and thymol exhibited reductions of 0.6 log CFU/cm2 and 0.4 log CFU/cm2, respectively, without affecting cell viability. Moreover, the terpenes inhibited twitching motility, a crucial step in biofilm establishment, with carvacrol exhibiting the highest inhibition, followed by OEO and thymol. The study provides valuable insights into the potential of terpenes as effective agents against A. baumannii biofilms, offering promising avenues for developing novel strategies to prevent persistent infections and overcome antibiotic resistance.

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Atshan, Salman Sahab, Rukman Awang Hamat, Marco J. L. Coolen, Gary Dykes, Zamberi Sekawi, Benjamin J. Mullins, Leslie Thian Lung Than, Salwa A. Abduljaleel, and Anthony Kicic. "The Role of Subinhibitory Concentrations of Daptomycin and Tigecycline in Modulating Virulence in Staphylococcus aureus." Antibiotics 10, no. 1 (January 3, 2021): 39. http://dx.doi.org/10.3390/antibiotics10010039.

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Staphylococcus aureus (S. aureus) infections are notoriously complicated by the ability of the organism to grow in biofilms and are difficult to eradicate with antimicrobial therapy. The purpose of the current study was to clarify the influence of sub-inhibitory concentrations (sub-MICs) of daptomycin and tigecycline antibiotics on biofilm adhesion factors and exoproteins expressions by S. aureus clinical isolates. Six clinical isolates representing positive biofilm S. aureus clones (3 methicillin-sensitive S. aureus (MSSA) and 3 methicillin-resistant S. aureus (MRSA)) were grown with sub-MICs (0.5 MIC) of two antibiotics (daptomycin and tigecycline) for 12 h of incubation. RNA extracted from culture pellets was used via relative quantitative real-time-PCR (qRT-PCR) to determine expression of specific adhesion (fnbA, fnbB, clfA, clfB, fib, ebps, cna, eno) and biofilm (icaADBC) genes. To examine the effect of sub-MIC of these antibiotics on the expression of extracellular proteins, samples from the culture supernatants of six isolates were collected after 12 h of treatment with or without tigecycline in order to profile protein production via 2D gel sodium dodecyl sulfate-polyacrylamide gel electrophoresis (2D gel-SDS-PAGE). Sub-MIC treatment of all clinical MRSA and MSSA strains with daptomycin or tigecycline dramatically induced or suppressed fnbA, fnbB, clfA, clfB, fib, ebps, cna, eno, and icaADBC gene expression. Furthermore, sub-MIC use of tigecycline significantly reduced the total number of separated protein spots across all the isolates, as well as decreasing production of certain individual proteins. Collectively, this study showed very different responses in terms of both gene expression and protein secretion across the various isolates. In addition, our results suggest that sub-MIC usage of daptomycin and tigecycline could signal virulence induction by S. aureus via the regulation of biofilm adhesion factor genes and exoproteins. If translating findings to the clinical treatment of S. aureus, the therapeutic regimen should be adapted depending on antibiotic, the virulence factor and strain type.

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Journal articles on the topic 'Sub-Inhibitory concentrations of antibiotics'

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