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Frequencies of variants resistant to different aminoglycosides in Pseudomonas aeruginosa
L Nilsson1, L Sörén, G Rådberg
1Department of Clinical Bacteriology, University Hospital, Linköping, Sweden.
Abstract:
The MICs of aminoglycosides for Pseudomonas aeruginosa are higher than those for Enterobacteriaceae and the number of variants resistant to high concentrations of aminoglycosides is greater in P. aeruginosa than in Escherichia coli. However, when the frequencies of resistant variants at different multiples of the MIC were calculated, these frequencies were similar in P. aeruginosa and E. coli. When large inocula of strains of P. aeruginosa, which were classified as sensitive in conventional MIC determinations, were incubated with amikacin, gentamicin, netilmicin or tobramycin at the break-point concentrations between sensitivity and resistance, 82%, 90%, 90% and 15%, respectively, of the strains regrew. The corresponding percentages for Enterobacteriaceae were much lower. The clinical relevance of this pronounced regrowth of P. aeruginosa is discussed.
Insights
Pseudomonas aeruginosa exhibits higher aminoglycoside resistance than E. coli. Despite similar resistant variant frequencies, P. aeruginosa shows significant regrowth at critical concentrations, impacting treatment efficacy.
Area of Science:
- Microbiology
- Antimicrobial Resistance
- Pharmacology
Background:
- Aminoglycosides are crucial antibiotics for treating Gram-negative bacterial infections.
- Pseudomonas aeruginosa and Enterobacteriaceae are common pathogens with varying susceptibility profiles.
- Understanding resistance mechanisms is vital for effective antimicrobial therapy.
Purpose of the Study:
- To compare the frequency and characteristics of aminoglycoside-resistant variants in Pseudomonas aeruginosa and Escherichia coli.
- To investigate the regrowth of P. aeruginosa strains classified as sensitive at clinically relevant aminoglycoside concentrations.
Main Methods:
- Minimum Inhibitory Concentrations (MICs) were determined for various aminoglycosides against P. aeruginosa and Enterobacteriaceae.
- Frequencies of resistant variants were calculated at different multiples of the MIC.
- Large inocula of sensitive P. aeruginosa strains were incubated with breakpoint concentrations of amikacin, gentamicin, netilmicin, and tobramycin.
Main Results:
- P. aeruginosa demonstrated higher MICs and a greater number of resistant variants compared to Enterobacteriaceae.
- However, the frequencies of resistant variants at multiples of the MIC were similar between P. aeruginosa and E. coli.
- Significant regrowth (82-90%) was observed for P. aeruginosa strains incubated with amikacin, gentamicin, and netilmicin at breakpoint concentrations, unlike Enterobacteriaceae.
Conclusions:
- Despite similar resistant variant frequencies, P. aeruginosa exhibits a pronounced regrowth phenomenon at critical aminoglycoside concentrations.
- This regrowth suggests potential challenges in achieving effective bacterial killing and clinical cure in P. aeruginosa infections.
- Further investigation into the clinical relevance of this P. aeruginosa regrowth is warranted for optimizing aminoglycoside therapy.