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In vitro activities of 36 antimicrobial agents against clinically isolated Bacteroides fragilis
1School of Medical Technology, College of Medicine, National Taiwan University, Taipei, R.O.C.
Abstract:
Thirty-six antimicrobial agents were evaluated for in vitro activities against 100 clinical isolates of Bacteroides fragilis. The minimal inhibitory concentration (MIC) of each agent for each isolate was determined by the agar dilution method. Among 25 beta-lactam antibiotics, the most active agent was imipenem with an MIC90 and a geometric mean of 1 and 0.15 micrograms/ml, respectively; followed by ticarcillin-clavulanic acid, and amoxicillin-clavulanic acid. Ampicillin-sulbactam, piperacillin-tazobactam, moxalactam, and flomoxef were the next most active agents. Piperacillin, ticarcillin, ceftizoxime, cefotaxime, cefuzonam, cefoxitin, and cefmetazole were equally active with the MIC50s ranging from 4 to 16 micrograms/ml, and MIC90s ranging from 32 to greater than or equal to 256 micrograms/ml. The remaining 10 beta-lactam antibiotics, ampicillin, amoxicillin, cefazolin, cefuroxime, cefoperazone, cefmenoxime, ceftazidime, cefpirome, aztreonam, and carumonam were less active. All isolates were resistant to cefotiam at a low breakpoint. Among 6 quinolones, ciprofloxacin was the most active agent with an MIC50 and an MIC90 of 4 and 16 micrograms/ml, respectively. All isolates were resistant to nalidixic acid, pipemidic acid, cinoxacin, enoxacin, and norfloxacin. Among 5 frequently used agents, chloramphenicol, ornidazole, and metronidazole were the most effective agents which inhibited 100% of the isolates at 8, 2, and 2 micrograms/ml, respectively; while clindamycin and minocycline had less activity.
Insights
Imipenem demonstrated potent in vitro activity against Bacteroides fragilis. Metronidazole, ornidazole, and chloramphenicol also showed effectiveness, while many other agents displayed resistance.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Bacteroides fragilis is a significant opportunistic pathogen.
- Antimicrobial resistance in B. fragilis necessitates ongoing surveillance.
- Understanding the in vitro activity of various agents is crucial for effective treatment.
Purpose of the Study:
- To evaluate the in vitro activity of 36 antimicrobial agents against 100 clinical isolates of Bacteroides fragilis.
- To identify the most effective agents for treating B. fragilis infections.
Main Methods:
- Agar dilution method was employed to determine the minimal inhibitory concentration (MIC) for each agent.
- Thirty-six antimicrobial agents were tested against 100 clinical isolates of B. fragilis.
Main Results:
- Imipenem exhibited the highest in vitro activity among beta-lactam antibiotics against B. fragilis.
- Ticarcillin-clavulanic acid and amoxicillin-clavulanic acid also showed significant activity.
- Ciprofloxacin was the most active quinolone; metronidazole, ornidazole, and chloramphenicol were effective among frequently used agents.
Conclusions:
- Imipenem is a highly effective agent against B. fragilis.
- Metronidazole, ornidazole, and chloramphenicol remain valuable treatment options.
- Resistance patterns highlight the need for careful antimicrobial selection.