Antimicrobial resistance in the Bacteroides fragilis group in faecal samples from patients receiving broad-spectrum antibiotics.

Members of the Bacteroides fragilis group are opportunistic pathogens and cause severe infections including bacteraemia. As increased levels of antimicrobial resistance in B. fragilis group bacteria can be detected years after administration of specific antibiotics, monitoring antimicrobial susceptibility in the gut microbiota could be important. The objectives of this study were to 1) investigate the distribution of species and the occurrence of reduced antimicrobial susceptibility in the B. fragilis group from patients treated at departments with a high level of antibiotic use, 2) to determine the prevalence of the carbapenem resistance gene cfiA in B. fragilis in this patient group, and 3) to determine the association between previous antibiotic treatment and reduced susceptibility to clindamycin, meropenem, metronidazole, and piperacillin-tazobactam. Consecutive faecal samples (n = 197) were collected from patients at the departments of haematology, oncology, and infectious diseases at Odense University Hospital, Denmark. Three colonies from each sample were identified by Matrix Assisted Lazer Desorption Ionization Time of Flight Mass Spectrometry and isolates were screened for resistance to clindamycin, meropenem, metronidazole, and piperacillin-tazobactam. B. fragilis isolates were tested for the cfiA metallo-beta-lactamase gene. Fisher's Exact test was used to test for correlation between antimicrobial exposure and reduced susceptibility. A total of 359 isolates were tested for reduced susceptibility. Of these 28%, 5%, <1%, and 11% were intermediate susceptible or resistant to clindamycin, meropenem, metronidazole, and piperacillin-tazobactam respectively. Three metronidazole resistant Bacteroides spp. were isolated. The proportion of B. fragilis belonging to division II (cfiA+) was 5.3%. Previous exposure to meropenem was associated with reduced susceptibility to meropenem (p= 0.001). In conclusion, antimicrobial resistance is prevalent and the distribution of species appears to be affected in the B. fragilis group from patients receiving broad-spectrum antibiotics, with meropenem exposure being associated with meropenem resistance.

Prevalence of antimicrobial resistance and the cfiA resistance gene in Danish Bacteroides fragilis group isolates since 1973.

OBJECTIVES: The purpose of this study was to determine the prevalence of resistance and the cfiA carbapenemase-producing gene in historical Bacteroides fragilis group isolates. METHODS: Danish clinical B. fragilis group isolates (n = 444) from 1973 to 2015 were identified with Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) on the Biotyper platform. Antimicrobial resistance was determined using a disk diffusion screening method and commercial antibiotic gradient strips. Division I (cfiA-negative) and division II (cfiA-positive) B. fragilis strains were differentiated using MALDI-TOF MS and real-time polymerase chain reaction (PCR). RESULTS: From 1973-1980 to 2010-2015 the prevalence of antimicrobial resistance rose from 0% to 21.2%, 2.5%, and 1% for clindamycin, meropenem, and metronidazole, respectively. MALDI-TOF MS and real-time PCR identified 16 of 266 (6.0%) B. fragilis strains as division II, of which 4 strains, isolated between 2010 and 2015, were resistant to meropenem. CONCLUSIONS: Substantial increases in resistance were found throughout this study. This supports the general perception that antimicrobial resistance in the B. fragilis group has been established in the recent decades in Europe. Resistance to meropenem, facilitated by expression of the cfiA resistance gene, seems to be increasing; therefore, it is imperative to monitor the occurrence of this gene, e.g. using MALDI-TOF MS.