Biosynthesis and degradation of H2O2 by vaginal lactobacilli.

Hydrogen peroxide production by vaginal lactobacilli represents one of the most important defense mechanisms against vaginal colonization by undesirable microorganisms. To quantify the ability of a collection of 45 vaginal Lactobacillus strains to generate H(2)O(2), we first compared three published colorimetric methods. It was found that the use of DA-64 as a substrate rendered the highest sensitivity, while tetramethyl-benzidine (TMB) maintained its linearity from nanomolar to millimolar H(2)O(2) concentrations. Generation of H(2)O(2) was found to be especially common and strong for L. jensenii strains, while it was variable among L. crispatus and L. gasseri strains. Biosynthesis of H(2)O(2) only occurred upon agitation of the cultures, but the H(2)O(2)-producing machinery was already present in them before aeration started. Calcium, magnesium, manganese, and zinc ions did not affect H(2)O(2) production, while Cu(2+) inhibited the growth of Lactobacillus jensenii CECT 4306, which was chosen as a model strain. Cultures with Fe(3+), hemin, and hemoglobin did not accumulate H(2)O(2). Fe(3+) activated an extracellular peroxidase that destroyed the H(2)O(2) being produced by the cultures. This protected the lactobacilli against its antimicrobial effect. The production of the enzyme appears to be constitutive, the Fe(3+) ions being a necessary cofactor of the reaction.