A study of the prevalence of hydrogen peroxide generating Lactobacilli in bacterial vaginosis: the determination of H2O2 concentrations generated, in vitro , by isolated strains and the levels found in vaginal secretions of women with and without infection.

The concentration of hydrogen peroxide in the vaginal secretions of normal women were compared with levels found in women infected with bacterial vaginosis (BV). The mean concentration found in 90 normal samples was 0.171 microg per ml, whereas in women with BV, the mean level was 0.04 microg per ml (P < 0.001). In vitro culture experiments using TMB agar showed that in normal women, 75% of Lactobacillus strains produced H2O2 and 25% did not, whereas in women 'infected' with BV. 14% of the isolates produced H2O2 and 86% did not (P < 0.001). Quantitative culture tests showed that both anaerobic and facultative strains of Lactobacilli isolated from normal women generated significantly higher levels of H2O2 than strains cultured from women with BV. Anaerobic strains isolated from normal women produced a mean level of 6.8 microg per ml, compared with the mean level of 1.4 microg per ml from women with BV. Facultative strains from normal women produced mean levels of 18.3 microg per ml compared with 2.4 microg per ml produced by strains from BV-infected women, which had been incubated under the same conditions (P < 0.001). There results indicate that Lactobacilli which produce H2O2 probably have a significant role in protecting the vaginal ecosystem from BV infection.