Nitroimidazole resistance genes (nimB) in anaerobic Gram-positive cocci (previously Peptostreptococcus spp.)

To investigate metronidazole resistance and the prevalence of nitroimidazole (nim) genes in clinically isolated anaerobic Gram-positive cocci.

Metronidazole susceptibility was determined in 99 strains of anaerobic Gram-positive cocci and PCR amplification for the nim gene carried out on 61 strains (metronidazole MIC > or =0.5 mg/L).

The nimB gene was detected in 34% (21/61) of the strains. These included two highly resistant Finegoldia magna strains (MICs >128 mg/L). The nimB gene was, however, also demonstrated in 90% (19/21) of susceptible strains.

Although the nimB gene may be implicated in the high-level metronidazole resistance in 2 F. magna strains, the alarmingly high prevalence of the nimB gene in anaerobic Gram-positive cocci cannot be directly associated with resistance and the possibility of a silent nimB gene should be considered.