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Recent experience with antimicrobial susceptibility of anaerobic bacteria: increasing resistance to penicillin
Abstract:
Results of antimicrobial susceptibility testing of anaerobes were reviewed for the last 5 years and compared with two previous surveys from this institution. Allowing for differences in methodology, there appears to be a striking increase in penicillin resistance by the "non-fragilis" Bacteroides. Penicillin concentrations of 50 microgram/ml were required to inhibit 70% of 43 strains tested. The clinical implications of this observation are not known, but isolated reports of therapeutic failure when penicillin was used against the non-fragilis Bacteroides have appeared. Penicillin resistance among Clostridium other than C. perfringens was also noted in the current study. Several strains of clindamycin-resistant Bacteroides fragilis have been observed during the last 2 years, and whether this represents a true increase in resistance will require close scrutiny of clindamycin susceptibility in the future. Future surveillance of antimicrobial susceptibility of anaerobic bacteria will be useful in the detection of any major changes in susceptibility profiles. This knowledge will potentially affect the choice of antimicrobial agent in patients with serious infections caused by anaerobes.
Insights
Antimicrobial resistance is increasing in anaerobic bacteria. Penicillin resistance in non-fragilis Bacteroides has significantly risen, potentially impacting treatment outcomes for serious infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Clinical Pharmacy
Background:
- Antimicrobial resistance is a growing global health concern.
- Anaerobic bacteria are significant pathogens in various infections.
- Monitoring antimicrobial susceptibility is crucial for effective treatment.
Purpose of the Study:
- To assess trends in antimicrobial resistance among anaerobic bacteria.
- To compare current resistance patterns with historical data.
- To identify emerging resistance mechanisms in clinically relevant anaerobes.
Main Methods:
- Retrospective review of antimicrobial susceptibility testing results.
- Analysis of data spanning five years.
- Comparison with two prior institutional surveys.
Main Results:
- A notable increase in penicillin resistance among non-fragilis Bacteroides species observed.
- Penicillin MIC90 for non-fragilis Bacteroides reached 50 µg/ml.
- Emergence of clindamycin resistance in Bacteroides fragilis noted.
- Increased penicillin resistance in Clostridium species (excluding C. perfringens).
Conclusions:
- Significant rise in penicillin resistance in non-fragilis Bacteroides strains.
- Potential clinical implications of increased resistance, including therapeutic failures.
- Need for ongoing surveillance of anaerobic bacterial susceptibility to guide antimicrobial therapy.