OBJECTIVE: Our purpose was to Investigate the bacteriocin susceptibility of Gardnerella vaginalis and its relationship to biotype, genotype, and resistance to metronidazole. STUDY DESIGN: Bacteriocin susceptibility of 36 G vaginalis clinical Isolates was tested against a vaginal strain of Lactobacillus acidophilus by a growth-inhibition method. The relationship to biotype, genotype, and resistance to metronidazole were analyzed by the chi (2) test and Fisher exact test. RESULTS: Eight G vaginalis strains (22%) were bacteriocin-resistant. Biotypes 5 and 7 were found to be the most frequent among these resistant strains. Eight (42%) of the 19 isolates classified as biotype 5, 6, or 7 were bacteriocin-resistant compared with none of the isolates that were classified as other biotypes (P < .01). Biotype 5 was found in higher prevalence among the isolates resistant to bacteriocin (62%) than among the susceptible isolates (14%) (P=.01). Genotype B was found more frequently among the bacteriocin-resistant strains, but this finding was not statistically significant (P=.71). Seven (88%) bacteriocin-resistant strains were also resistant to metronidazole. CONCLUSION: An association between biotype and an increased resistance to bacteriocin was found. The ability of G vaginalis to resist the antibacterial activity of Lactobacillus bacteriocin may be a pivotal factor in understanding bacterial vaginosis.185511861190