Profile of metronidazole resistance among subgingival anaerobic bacteria

Abstract

Objectives: Metronidazole resistance among subgingival anaerobic bacteria has been demonstrated phenotypically and genotypically in various populations. This study aimed to screen for metronidazole resistance among anaerobic clinical culture collection from human subgingival plaque in a southern Chinese population and to detect the prevalence of nimA gene of the metronidazole resistant strains. Methods: 47 subgingival periodontal isolates were cultured on blood agar and incubated anaerobically. Pure colonies were used for antimicrobial susceptibility testing by broth microdilution in metronidazole concentrations of 0.25-to-512µg/ml. The presence of nimA gene in resistance strains as determined using PCR method. Identification of metronidazole resistant strains was confirmed by 16SrDNA sequencing. Results: Majority of presumptive identified Fusobacterium spp. (7/10) and Propionibacterium spp. (8/9) were found to be highly resistant to metronidazole (>128 µg/ml). A few of Bacteroides spp. (5/17) were found to be metronidazole resistant. Nearly all of Peptostreptococcus spp. (6/7) and Prevotella spp. (3/4) were susceptible to metronidazole. None of the resistance strains were positive upon PCR-based nimA gene detection. Conclusion: Fusobacterium and Propionibacterium from subgingival periodontal isolates were found to be highly resistant to metronidazole. However, none of these resistant strains were found to possess nimA gene. Reasons for metronidazole resistance in these clinical isolates, remains to be determined.