Defense factors of vaginal lactobacilli

OBJECTIVE: To determine the antagonistic relationship between vaginal lacto bacilli and endogenous vaginal microflora. STUDY DESIGN: Twenty-two Lactobacillus strains were studied for the product ion of lactic acid, hydrogen peroxide, and bacteriocin. RESULTS: Under standardized growth conditions, most strains increased their biomass by more than 4 times, Lactobacillus species grew best at a pH grea ter than or equal to 4.5, and growth was retarded at a pH < 4.5. Lactic aci d levels were 0.68 to 2.518 mg/mL and were not related to the number of cel ls or the pH of media. The pH of the media was caused by the secretion of l actic and other organic acids. Approximately 80% of the strains produced H2 O2 and were graded as 2+ in one third of the strains and 1+ in others. No s tatistical correlation was found between H2O2 lactic acid and bacteriocin p roduction. Bacteriocin activity was tested on 4 strains of Gardnerella vagi nalis. Approximately 80% of the lactobacilli tested produced bacteriocin th at inhibited growth of G vaginalis. Six of the strains did not produce bact eriocin. Thirteen strains produced all 3 defense factors, whereas the other s lacked 1 or 2 properties. CONCLUSIONS: Lactobacillus, species grow best at a pH > 4.5. The pH of the media is dependent on the cell mass and on all organic acids produced by La ctobacillus species. Although all species produce organic acids, not all pr oduce H2O2 and bacteriocin. Not all strains of G vaginalis can be inhibited by lactobacilli-producing bacteriocin.