Lactobacilli are the predominant organisms in the healthy vagina whereas there are few or none in the vagina of women with bacterial vaginosis (BV). In a study of 155 women, these organisms were isolated from the vagina of 47 (88 . 6 per cent) of 53 healthy women, and from 30 (29 . 4 per cent) of 102 women with BV, the dominant species being L. acidophilus and L. plantarum. The proportion of hydrogen peroxide (H2O2)-producing strains of these two species, 31 (72 per cent) of 43 isolated from healthy women, was similar to the proportion of such strains, 14 (77 per cent) of 18 isolated from women with BV. Furthermore, the total number of H2O2-producing lactobacilli isolated from the healthy women, that is 38 (61 per cent) of 62 isolates of H2O2-producers, was not greatly different from 31 (73 per cent) of 42 isolates recovered from the women with BV. Overall, the number of colonies of lactobacilli isolated on Rogosa agar and the amount of H2O2 produced by them were not much different whether the organisms were recovered from healthy women or women with BV.Bacteria-free supernates containing H2O2 produced by growth of several strains of lactobacilli, in addition to micro-molar solutions of H2O2 and known concentrations of lactic acid and urea, had no inhibitory effect on Bacteroides ureolyticus, Pievotella melaninogenica (B. melaninogenicus) and Bifidobacterium spp. However, Gardnerella vaginalis and Mobiluncus spp. were weakly-inhibited by the cell-free supernates and G. vaginalis by solutions of nitrate and catalase. As these organisms were also resistant to known concentrations of analytical H2O2, the positive inhibitory reaction from these fluids was probably due to an inhibitory substance in the supernate other than H2O2 which deserves further investigation. These observations suggest that H2O2 per se may be less bactericidal than previously thought in the control of intra-vaginal proliferation by BV-related bacteria in vivo.
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