Comparison of quantitative and qualitative methods of detecting hydrogen peroxide produced by human vaginal strains of lactobacilli.

A quantitative method was developed for the measurement of micromolar quantities of H2O2 produced in Rogosa broth and peptonized milk broth by vaginal strains of lactobacilli isolated from women. The production of substantial amounts reproducibly was dependent on the growth of the organisms in acid media (pH less than or equal to 6.0) under anaerobic or micro-aerophilic conditions with continuous agitation. The addition to the media of the enzyme inhibitor, 3-amino-1,2,4-triazole, with or without catalase sometimes induced the production of H2O2 especially in non-agitated cultures. However, other agents such as concanavalin and o-dianisidine had no enhancing effect, and catalase or peroxidase alone completely inhibited H2O2 production. The H2O2 produced in the acid media was stable for more than a month at 5 degrees C but not in media at pH greater than or equal to 7.0. Of five strains of lactobacilli tested by the quantitative method and by a chromogenic qualitative method (Rogosa-catalase or -per-oxidase agar), three consistently produced H2O2 measurable by the former method, but none did so after growth of the organisms on Rogosa-catalase/peroxidase agar which suggested that the qualitative method was unreliable. The fact that H2O2 was produced in substantial quantities by some strains and not at all by others enabled H2O2-producers and non-producers to be distinguished easily.