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Beta-lactamase induction and aminoglycoside susceptibility in Pseudomonas aeruginosa
Abstract:
Recent clinical reports have described the emergence of cross-resistance to aminoglycosides during beta-lactam therapy. We therefore studied the effect of imipenem-mediated beta-lactamase induction on the susceptibilities of 92 clinical isolates of Pseudomonas aeruginosa to gentamicin, tobramycin, and amikacin. We performed a disc approximation test to look for truncation by imipenem of the inhibitory zone sizes of the aminoglycosides. We also compared aminoglycoside inhibitory zone sizes of strains grown in the presence and absence of subinhibitory concentrations of imipenem. Finally, we compared aminoglycoside MIC values determined with and without subinhibitory concentrations of imipenem. The results showed that simultaneous emergence of resistance to beta-lactams and aminoglycosides is very rare.
Insights
Cross-resistance to aminoglycoside antibiotics during beta-lactam therapy is rare. This study found that imipenem induction of beta-lactamase in Pseudomonas aeruginosa did not significantly increase resistance to gentamicin, tobramycin, or amikacin.
Area of Science:
- Microbiology
- Clinical Pharmacy
- Antibiotic Resistance
Background:
- Emerging clinical reports suggest cross-resistance between beta-lactam and aminoglycoside antibiotics.
- Understanding this phenomenon is crucial for effective antimicrobial stewardship.
Purpose of the Study:
- To investigate the impact of imipenem-induced beta-lactamase production on the susceptibility of Pseudomonas aeruginosa to key aminoglycosides.
- To determine the frequency of simultaneous resistance to beta-lactams and aminoglycosides.
Main Methods:
- Disc approximation tests were used to assess changes in inhibitory zone sizes for gentamicin, tobramycin, and amikacin.
- Minimum Inhibitory Concentration (MIC) values for aminoglycosides were determined in the presence and absence of subinhibitory imipenem concentrations.
- Ninety-two clinical isolates of Pseudomonas aeruginosa were analyzed.
Main Results:
- Imipenem-mediated beta-lactamase induction did not significantly alter the susceptibility of Pseudomonas aeruginosa to gentamicin, tobramycin, and amikacin.
- Zone sizes and MIC values showed minimal changes, indicating limited cross-resistance.
- The simultaneous emergence of resistance to both beta-lactams and aminoglycosides was found to be very rare.
Conclusions:
- Beta-lactam therapy, specifically with imipenem, does not appear to commonly induce cross-resistance to aminoglycosides in Pseudomonas aeruginosa.
- The study provides evidence against a widespread mechanism for combined resistance, supporting the continued use of these antibiotic classes in combination therapy when indicated.