Background:Bacteroides fragilis is the most common anaerobic pathogen isolated from
surgical site infections (SSIs).
Metronidazole resistance is increasing and the mechanisms of resistance are not clear in some isolates. The aim of the present study was to investigate the
metronidazole susceptibility prevalence, and detect nim genes in B. fragilis isolates from SSIs. Methods: This study included 100 surgery patients with signs and symptoms indicative of SSIs. Syringe aspiration of the infected site was used to collect specimens. All specimens were cultured on BBA (Brucella blood
agar), KVLB (
kanamycin-
vancomycin laked blood), and BBE (Bacteroides bile
esculin)
agar. The MIC (minimum inhibitory concentration) of
metronidazole was determined by the
agar dilution method according to the Clinical and Laboratory Standard Institute (CLSI). Then the PCR method was used to determine the presence of the nim gene. Results: In the present study, 26 B. fragilis were isolated from 100 SSIs specimens. Eight isolates were
metronidazole resistant; the
metronidazole MIC was 32 µg/mL for 7 isolates and 64 µg/mL for one isolate. All isolates were nim gene negative. Conclusion: The emergence of
metronidazole-resistant B. fragilis limits the application of this
drug for treatment and prophylaxis of SSIs. Thus, rapid identification of
metronidazole-resistant B. fragilis is essential to restrict inappropriate, superfluous administration. In spite of various
metronidazole resistance mechanisms other than that depending on the nim gene, detection of nim by PCR is unsuitable for identifying resistant isolates. Therefore, phenotypic methods are better to screen for and identify
metronidazole-resistant B. fragilis.