Cefoxitin inactivation by Bacteroides fragilis

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Clinical Science

Background:

• The Bacteroides fragilis group is a common cause of anaerobic infections.
• Assessing antimicrobial susceptibility is crucial for effective treatment.
• Cefoxitin is a key antibiotic used against anaerobic bacteria.

Purpose of the Study:

• To determine the prevalence of cefoxitin resistance in clinical isolates of the Bacteroides fragilis group.
• To investigate the mechanisms underlying cefoxitin resistance in these isolates.

Main Methods:

• Surveyed 1,575 clinical isolates of the Bacteroides fragilis group for antimicrobial susceptibility.
• Identified cefoxitin-resistant isolates and characterized their resistance patterns.
• Utilized microbiological and high-pressure liquid chromatography (HPLC) assays to detect cefoxitin inactivation.
• Analyzed cefoxitin breakdown products using HPLC.

Main Results:

• Eleven isolates (0.7%) exhibited high cefoxitin resistance (MIC ≥ 64 µg/ml) and cross-resistance to other beta-lactams.
• Four of these isolates demonstrated cefoxitin inactivation capabilities.
• HPLC analysis revealed two distinct patterns of cefoxitin degradation products.
• Beta-lactamase inhibitors (clavulanic acid, sulbactam) did not show synergistic effects with cefoxitin.

Conclusions:

• Members of the Bacteroides fragilis group have acquired a novel mechanism to inactivate cefoxitin.
• This inactivation mechanism represents a significant challenge to cefoxitin efficacy.
• Further research is needed to understand and combat this emerging resistance in anaerobic bacteria.