Abstract
Aims: Bacteroides fragilis is the most common anaerobic bacteria causing infectious diseases in humans. A cfiA gene encoding metallo- β-lactamase, which degrades carbapenem, has been reported as a resistance mechanism against carbapenem. Therefore, the detection of cfiA gene is important for determining appropriate antibiotic therapy. Although cfiA gene is detected via polymerase chain reaction (PCR), simpler and easier methods are required in clinical settings. We compared the detectability of cfiA-positive B. fragilis using multiple methods. Moreover, the isolation frequency of carbapenem-nonsusceptible Bacteroides spp. was evaluated.
Methods: Bacteroides spp. was isolated from clinical specimens at the Kanazawa University Hospital. Antimicrobial susceptibility testing was performed via broth microdilution. We explored whether matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) and modified carbapenem inactivation method (mCIM) can show cfiA gene positivity.
Results: Around 20-50 Bacteroides spp. strains/year were isolated from June 2015 to December 2020. Among these, 0-8 strains exhibited meropenem and/or imipenem nonsusceptibility (intermediate and resistant) in each year. An increased rate of carbapenem resistance, including meropenem- and imipenem-nonsusceptible Bacteroides spp., was observed. All carbapenem-nonsusceptible Bacteroides spp. were susceptible to metronidazole. Four (66.7%) of 6 strains showed cfiA gene positivity based on PCR.
Conclusions: MALDI-TOF MS and mCIM detected cfiA-positive strains. MALDI-TOF MS and mCIM are useful for detecting cfiA-positive B. fragilis. Because the isolation frequency of carbapenem-nonsusceptible Bacteroides spp. is increasing, determining their susceptibility is important for appropriate antimicrobial therapy.
