Fatal sepsis caused by multidrug-resistant Bacteroides fragilis, harboring a cfiA gene and an upstream insertion sequence element, in Japan.

Here, we report a case of fatal sepsis resulting from an intra-abdominal infection caused by a Bacteroides fragilis strain containing a CfiA4 metallo-β-lactamase and an upstream insertion sequence (IS) element. Meropenem was used as empiric therapy for septic shock as a result of the intra-abdominal infection, although two rounds of carbapenem treatment had been administered previously. B. fragilis was isolated from two anaerobic blood culture bottles 4 days after the onset of septic shock. Susceptibility testing revealed that the isolate was non-susceptible to all tested agents except metronidazole and tigecycline. The isolate gave a positive result in ethylenediaminetetraacetic acid and carbapenem inactivation tests, but a negative result in a double-disk synergy test using sodium mercaptoacetate. Next-generation whole-genome sequencing indicated the presence of the cfiA4, emrG and emrF genes. PCR indicated the presence of an IS element upstream of the cifA4 gene. Although carbapenem-resistant B. fragilis isolates have previously been reported, clinical sepsis by this organism is considered rare. In Japan, as in most countries worldwide, routine susceptibility testing and the detection of metallo-β-lactamases is not carried out in anaerobic organisms, including B. fragilis. The emergence of carbapenem resistance during therapy should be monitored, as B. fragilis strains containing the cfiA gene show decreased sensitivity during carbapenem therapy. Therefore, susceptibility testing and appropriate antibiotic stewardship are required in cases of anaerobic bacterial infections.

Nakamura I ，Aoki K ，Miura Y ，Yamaguchi T ，Matsumoto T ... -  《-》

Antimicrobial susceptibility and prevalence of resistance genes in Bacteroides fragilis isolated from blood culture bottles in two tertiary care hospitals in Japan.

The in vitro susceptibilities of Bacteroides fragilis to antimicrobial agents, especially to carbapenem, are a major concern in the treatment of patients with bloodstream infections. In this study, 50 isolates of B. fragilis were obtained from positive blood bottles from 2014 to 2019 in Saitama, Japan. Their susceptibility to ampicillin/sulbactam was reduced to 70.0% compared with a previous report, whereas they were still sufficiently susceptible to piperacillin/tazobactam (94.0%). Five cfiA-positive isolates (5/50, 10.0%) were identified that were resistant to doripenem and meropenem, and two of them carried an insertion sequence located upstream of the cfiA-coding region. In particular, imipenem should be considered as a first-line carbapenem for the empirical treatment of B. fragilis infection because only insertion sequence and cfiA double-positive strains showed resistance to imipenem. Thirty-six percent of the isolates had a reduced minimum inhibitory concentration for moxifloxacin. In addition, metronidazole should still be considered as an active agent for B. fragilis because all isolates were susceptible to this antibiotic and the prevalence of the nim gene was low in Japan.

Ogane K ，Tarumoto N ，Kodana M ，Onodera A ，Imai K ，Sakai J ，Kawamura T ，Takeuchi S ，Murakami T ，Mitsutake K ，Ikebuchi K ，Maesaki S ，Maeda T ... -  《-》

Emergence of carbapenem resistance in Bacteroides fragilis in China.

The antimicrobial resistance crisis makes it critically important for laboratories to closely monitor trends and mechanisms of emerging antimicrobial resistance in clinical isolates. Bacteroides fragilis is an anaerobic pathogen that causes several serious infections and is increasingly resistant to antimicrobial agents. However, data from China regarding antimicrobial resistance in B. fragilis are limited. In this work, the mechanism underlying carbapenem resistance in 44 B. fragilis isolates collected from a Chinese hospital was investigated. Antimicrobial susceptibility testing for 13 antimicrobial agents was performed by the agar dilution method, and the contribution of efflux pumps to carbapenem resistance was analysed. Genetic relatedness of the isolates was determined by PFGE. Outer membrane porins were analysed in isolates with reduced carbapenem susceptibility. Potential carbapenemase-encoding genes were identified, and the location and environment of the cfiA gene was analysed. Among the 44 isolates, 18.2%, 29.5%, 22.7%, 100%, 100%, 29.5%, 15.9%, 81.8%, 88.6% and 47.7% were resistant to imipenem, meropenem, ertapenem, penicillin, ampicillin, amoxicillin/clavulanic acid, piperacillin/tazobactam, clindamycin, tetracycline and moxifloxacin, respectively. None of the isolates were resistant to metronidazole, cefoxitin or chloramphenicol. A chromosomally located gene (cfiA) encoding a metallo-β-lactamase was identified in 16 isolates (36.4%). A conserved insertion sequence of IS1187 or IS613 was upstream of cfiA in eight isolates with high-level carbapenem resistance. The insertion sequences were associated with increased carbapenem resistance in B. fragilis by upregulating the expression of cfiA as shown by RT-qPCR. This is the first study to describe a mechanism of carbapenem resistance in B. fragilis in mainland China.

Gao Q ，Wu S ，Xu T ，Zhao X ，Huang H ，Hu F ... -  《-》

[Can meropenem E-test be used to estimate the presence of carbapenem resistance gene cfiA among Bacteroides fragilis strains?].

Bacteroides fragilis, which is found in normal colon flora, is the most commonly encountered pathogen in anaerobic infections and more resistant to antimicrobial agents than the other anaerobes. Limited number of antibiotics; such as carbapenems, beta-lactam/beta-lactamase inhibitors and nitroimidazoles are the most effective antibiotics against Bacteroides, however resistant isolates to these antimicrobials have been reported recently. Resistance against carbapenems occurs due to a metallo-beta-lactamase enzyme expressed by cfiA gene. While agar dilution method is used to test the antimicrobial susceptibility of anaerobic organisms, E-test is recommended for susceptibility testing of anaerobes associated with life-threatening infections with high mortality and morbidity. In this study, meropenem E-test was used to determine the carbapenem resistance of B.fragilis strains and to estimate the presence of cfiA gene. A total of 63 B.fragilis strains that were previously isolated from clinical samples (of which 16 were from stool samples) in our laboratory, were enrolled in the study. Minimum inhibitory concentration (MIC) values were determined by meropenem E test (AB Biodisk, Sweden) and presence of cfiA genes were investigated by in-house polymerase chain reaction. The MIC ranges of meropenem were < 0.002 - > 32 µg/ml and the resistance rate was 9.5% (6/63). Thirty-three percent (21/63) of strains harboured cfiA gene. A statistically significant relation (p< 0.0001) was determined between presence of cfiA gene and high MIC value (MIC 0.5 µg/ml). The proportion of cfiA-positive isolates detected in this study was substantially higher than that reported in other countries. This might be attributed to the frequent use of carbapenems in our hospital. The results of this study indicated that meropenem E-test method could be useful to estimate the presence of cfiA gene in B.fragilis strains and thus to detect the resistant strains.

Toprak Ülger N ，Ilki A ，Ozel N ，Balkan N ，Söyletir G ... -  《MIKROBIYOLOJI BULTENI》

Examination of cfiA-mediated carbapenem resistance in Bacteroides fragilis strains from a European antibiotic susceptibility survey.

Of 1284 Bacteroides strains collected in Europe in 2000 for antibiotic susceptibility surveillance, 65 isolates displayed imipenem minimum inhibitory concentrations (MICs) > or =1 mg/L and were chosen for a thorough analysis of their resistance mechanism. Twenty-five of the isolates were positive for the cfiA carbapenem resistance gene. The resistance rates were 0.8% and 1.3% for imipenem and meropenem, respectively. In six of the strains, insertion sequence (IS) elements (IS613, IS614B, IS1186 and IS1187) activated the cfiA gene. However, other strains displayed at least elevated carbapenem MICs or were carbapenem resistant and produced measurable carbapenemase activities but did not harbour IS elements in the region upstream of the cfiA gene. The major determinant of carbapenem resistance in Bacteroides fragilis is production of CfiA metallo-beta-lactamase via activation of the cfiA gene by IS elements (higher level resistance) or by activation of its putative own promoter.

Sóki J ，Edwards R ，Hedberg M ，Fang H ，Nagy E ，Nord CE ，ESCMID Study Group on Antimicrobial Resistance in Anaerobic Bacteria ... -  《INTERNATIONAL JOURNAL OF ANTIMICROBIAL AGENTS》