Department of Microbiology, Kasturba Medical College, Manipal Academy of Higher Education, Manipal, Karnataka, India.
Indian J Med Res. 2021 May;154(5):750-756. doi: 10.4103/ijmr.IJMR_2568_19.
BACKGROUND & OBJECTIVE: Bacteroides fragilis is a Gram-negative anaerobic opportunistic pathogen which is managed by empirical anaerobic coverage as a hospital norm. However, with rising reports of resistance among B. fragilis strains, antibiotic susceptibility testing for this pathogen may be the only way to understand the magnitude of the problem. This study aimed to characterize resistance patterns among clinical isolates and identify resistance genes.
A prospective observational study was conducted which included all samples requesting anaerobic cultures within the study period. Minimum inhibitory concentration (MIC) was detected for metronidazole, clindamycin and chloramphenicol by agar dilution. E-test strips were used for imipenem and piperacillin, followed by polymerase chain reaction to detect nim and cfiA genes.
Among a total of 50 isolates, 94 per cent (47/50) were susceptible and six per cent (3/50) showed intermediate resistance to metronidazole. Susceptibility to clindamycin and piperacillin was noted in 70 and 50 per cent of strains; intermediate resistance in 14 and 2 per cent and resistance in 16 and 48 per cent, respectively. No resistance was observed for chloramphenicol and imipenem. Nim gene was found in 26 per cent (13/50) and cfiA gene was found in 52 per cent (26/50) of isolates. Isolates with high metronidazole MIC of 8-16 μg/ml were found to carry nim gene (χ test, P<0.001).
INTERPRETATION & CONCLUSIONS: Rising resistance among B. fragilis is evident and there is a significant association between nim gene and metronidazole resistance. Improving awareness among clinicians is paramount in tackling AMR among these pathogens, as empirical anaerobic coverage may not be effective in all cases.
脆弱拟杆菌是一种革兰氏阴性厌氧菌，是一种机会致病菌，医院常规采用经验性抗厌氧菌覆盖治疗。然而，随着脆弱拟杆菌菌株耐药率的上升报告，对该病原体进行抗生素敏感性测试可能是了解问题严重程度的唯一方法。本研究旨在描述临床分离株的耐药模式并鉴定耐药基因。
进行了一项前瞻性观察性研究，纳入了研究期间所有要求进行厌氧菌培养的样本。采用琼脂稀释法检测甲硝唑、克林霉素和氯霉素的最小抑菌浓度（MIC）。使用 E 试验条检测亚胺培南和哌拉西林，然后通过聚合酶链反应检测 nim 和 cfiA 基因。
在总共 50 株分离株中，94%（47/50）对甲硝唑敏感，6%（3/50）显示中度耐药。70%和 50%的菌株对克林霉素和哌拉西林敏感；14%和 2%的菌株显示中度耐药，16%和 48%的菌株显示耐药。未观察到对氯霉素和亚胺培南的耐药性。26%（13/50）的分离株中发现 nim 基因，52%（26/50）的分离株中发现 cfiA 基因。甲硝唑 MIC 值为 8-16μg/ml 的高耐药株分离株携带 nim 基因（卡方检验，P<0.001）。
脆弱拟杆菌的耐药率正在上升，nim 基因与甲硝唑耐药性之间存在显著关联。提高临床医生的认识对于应对这些病原体的 AMR 至关重要，因为经验性抗厌氧菌覆盖可能并非所有情况下都有效。
