Climate control of terrestrial carbon exchange across biomes and continents

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Antimicrobial activity of Fosfomycin and Tobramycin in combination against cystic fibrosis pathogens under aerobic and anaerobic conditions

Antimicrobial therapy has been a major contributor to the increased life expectancy of CF patients since CF was first describe<! in 1938. However, the high antimicrobial consumption in this patient population means that resistance has become a major problem in CF. As such, there is a need for new antimicrobials or combinations of antimicrobials for use in CF patients. It is also apparent that there are anaerobic niches in the lungs of CF patients; therefore, a new antibiotic which retains its effect under such conditions would be particularly beneficial. The aim of this study was to investigate the activity of a new antibiotic combination consisting of fosfomycin and tobramycin in a 4: I (w/w) ratio (F:T) under aerobic and anaerobic conditions by susceptibility, synergy, resistance development and microarray studies. Results of this study have shown that F:T has good activity against P. aeruginosa and MRSA cultured from CF patients, with enhanced activity under anaerobic conditions. The combination was more likely to be synergistic under anaerobic conditions where it exhibited synergy against 45% of isolates tested compared to 20% under aerobic conditions. F:T also prevented or delayed the emergence of resistance compared to either fosfomycin or tobrarnycin alone under aerobic and anaerobic conditions. In addition, F:T remained active against isolates which developed resistance to either fosfomycin or tobramycin alone. F:T \\-Wi also found to downregulate nitrate reductase genes essential for the anaerobic growth of P. aeruginosa and was able to reverse nitrate utilisation in this organism. As increased nitrate utilisation confers a selective advantage to P. aeruginosa in the Cf lung, this may be particularly beneficial in CF patients. Overall, this study has shown that F:T is a potentially promising new treatment option for CF lung infections caused by P. aeruginosa and MRSA.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Antimicrobial activity of fosfomycin and tobramycin in combination against cystic fibrosis pathogens under aerobic and anaerobic conditions

AbstractBackgroundThere is a need for new antibiotics or combination of antibiotics that possess activity against increasingly resistant cystic fibrosis (CF) respiratory pathogens such as Pseudomonas aeruginosa and MRSA.MethodsThe antimicrobial activity of a novel 4:1 (w/w) fosfomycin:tobramycin (F:T) combination against CF respiratory pathogens under both aerobic and anaerobic conditions was determined by MIC, time-kill and biofilm studies, and compared with activity of fosfomycin and tobramycin, individually.ResultsF:T and fosfomycin had excellent activity against P. aeruginosa and were more active than tobramycin against P. aeruginosa under anaerobic conditions with lower MIC50, MIC90 and geometric mean values. F:T (p<0.001) and fosfomycin (p<0.001) MICs for P. aeruginosa were significantly lower under anaerobic conditions with tobramycin MICs significantly higher (p<0.001). F:T and fosfomycin also had high activity against MRSA with both being more active than tobramycin. In time–kill studies, F:T was rapidly bactericidal against all 15 P. aeruginosa and 3/5 MRSA isolates tested. F:T also demonstrated bactericidal activity against P. aeruginosa grown in biofilm under both aerobic and anaerobic conditions.ConclusionsF:T has promising in vitro antimicrobial activity against MRSA and P. aeruginosa with greater activity under anaerobic conditions similar to those found in the CF lung

Fosfomycin, tobramycin and F∶T MICs for MRSA isolate CFP8 following serial passage in sub-inhibitory antibiotic concentrations under both aerobic and anaerobic conditions.

<p>Exposure to (A) Fosfomycin aerobic, (B) Fosfomycin anaerobic, (C) Tobramycin aerobic, (D) Tobramycin anaerobic, (E) F∶T aerobic, (F) F∶T anaerobic. Filled circle (•) Fosfomycin MIC; filled square (▪) Tobramycin MIC; filled triangle (▴)F∶T MIC.</p

Fosfomycin, tobramycin and F∶T MICs for <i>P. aeruginosa</i> isolate W050 following serial passage in sub-inhibitory antibiotic concentrations under both aerobic and anaerobic conditions.

<p>Exposure to (A) Fosfomycin aerobic, (B) Fosfomycin anaerobic, (C) Tobramycin aerobic, (D) Tobramycin anaerobic, (E) F∶T aerobic, (F) F∶T anaerobic. Filled circle (•) Fosfomycin MIC; filled square (▪) Tobramycin MIC; filled triangle (▴)F∶T MIC.</p

Fosfomycin, tobramycin and F∶T MICs for MRSA and <i>P. aeruginosa</i> strains used in this study.

<p>Fosfomycin, tobramycin and F∶T MICs for MRSA and <i>P. aeruginosa</i> strains used in this study.</p

Fosfomycin, tobramycin and F∶T MICs for <i>P. aeruginosa</i> isolates following serial passage in sub-inhibitory antibiotic concentrations and subsequent removal of antibiotic pressure following 12 passages.

<p>(A) AY4 FOS aerobic, (B) AY4 FOS anaerobic and (C) W050 TOB aerobic. Filled circle (•) Fosfomycin MIC; filled square (▪) Tobramycin MIC; filled triangle (▴)F∶T MIC; broken line, antibiotic pressure removed.</p

Mean^a (S.D.) frequency of spontaneous MRSA (n = 6) and <i>P. aeruginosa</i> (n = 6) mutants with increased fosfomycin (FOF), tobramycin (TOB) and F∶T MICs under aerobic and anaerobic conditions at 2×, 4× and 8× MIC.

a<p>Where the spontaneous mutation frequency was above or below the limit of detection, the limit of detection was used to calculate the mean e.g. if spontaneous mutation frequency was <4.4×10⁻⁸ then 4.4×10⁻⁸ was used.</p

Growth curves showing total viable counts of parent MRSA and <i>P. aeruginosa</i> isolates and resistant mutants which developed following exposure to fosfomycin and tobramycin.

<p>(A) MRSA CFP13, aerobic, (B) MRSA CFP13 anaerobic, (C) <i>P. aeruginosa</i> W050 aerobic and (D) <i>P. aeruginosa</i> W050 anaerobic. Filled circle (•) Parent strain; filled square (▪) Fosfomycin resistant mutant; filled triangle (▴) Tobramycin resistant mutant.</p

Fosfomycin and tobramycin in combination downregulate nitrate reductase genes narG and narH, resulting in increased activity against Pseudomonas aeruginosa under anaerobic conditions

The activity of aminoglycosides, which are used to treat Pseudomonas aeruginosa respiratory infection in cystic fibrosis (CF) patients, is reduced under the anaerobic conditions that reflect the CF lung in vivo. In contrast, a 4:1 (wt/wt) combination of fosfomycin and tobramycin (F:T), which is under investigation for use in the treatment of CF lung infection, has increased activity against P. aeruginosa under anaerobic conditions. The aim of this study was to elucidate the mechanisms underlying the increased activity of F:T under anaerobic conditions. Microarray analysis was used to identify the transcriptional basis of increased F:T activity under anaerobic conditions, and key findings were confirmed by microbiological tests, including nitrate utilization assays, growth curves, and susceptibility testing. Notably, growth in subinhibitory concentrations of F:T, but not tobramycin or fosfomycin alone, significantly downregulated (P < 0.05) nitrate reductase genes narG and narH, which are essential for normal anaerobic growth of P. aeruginosa. Under anaerobic conditions, F:T significantly decreased (P < 0.001) nitrate utilization in P. aeruginosa strains PAO1, PA14, and PA14 lasR::Gm, a mutant known to exhibit increased nitrate utilization. A similar effect was observed with two clinical P. aeruginosa isolates. Growth curves indicate that nitrate reductase transposon mutants had reduced growth under anaerobic conditions, with these mutants also having increased susceptibility to F:T compared to the wild type under similar conditions. The results of this study suggest that downregulation of nitrate reductase genes resulting in reduced nitrate utilization is the mechanism underlying the increased activity of F:T under anaerobic conditions