Antibiotic susceptibility of Atopobium vaginae

Background: Previous studies have indicated that a recently described anaerobic bacterium, Atopobium vaginae is associated with bacterial vaginosis (BV). Thus far the four isolates of this fastidious micro-organism were found to be highly resistant to metronidazole and susceptible for clindamycin, two antibiotics preferred for the treatment of BV. Methods: Nine strains of Atopobium vaginae, four strains of Gardnerella vaginalis, two strains of Lactobacillus iners and one strain each of Bifidobacterium breve, B. longum, L. crispatus, L. gasseri and L. jensenii were tested against 15 antimicrobial agents using the Etest. Results: All nine strains of A. vaginae were highly resistant to nalidixic acid and colistin while being inhibited by low concentrations of clindamycin (range: <0.016 mu g/ml), rifampicin (<0.002 mu g/ml), azithromycin (<0.016-0.32 mu g/ml), penicillin (0.008-0.25 mu g/ml), ampicillin (<0.016-0.94 mu g/ml), ciprofloxacin (0.023-0.25 mu g/ml) and linezolid (0.016-0.125 mu g/ml). We found a variable susceptibility for metronidazole, ranging from 2 to more than 256 mu g/ml. The four G. vaginalis strains were also susceptible for clindamycin (<0.016-0.047 mu g/ml) and three strains were susceptible to less than 1 mu g/ml of metronidazole. All lactobacilli were resistant to metronidazole (>256 mu g/ml) but susceptible to clindamycin (0.023-0.125 mu g/ml). Conclusion: Clindamycin has higher activity against G. vaginalis and A. vaginae than metronidazole, but not all A. vaginae isolates are metronidazole resistant, as seemed to be a straightforward conclusion from previous studies on a more limited number of strains.