Search

Lactobacilli are believed to contribute to the control of the vaginal microflora by different mechanisms such as production of antagonistic substances like lactic acid, bacteriocins, and H2O2. This paper describes the selection of H2O2-generating lactobacilli among 35 hydrophobic isolates from the human vagina. Lactobacillus crispatus F117, which generated the highest H2O2 level, was chosen to study: (a) the kinetics of H2O2 production considering different culture conditions, and (b) the effect of this metabolite on the growth of urogenital tract pathogens. The levels of H2O2 in L. crispatus supernatant increased during its growth and were maximum at the early stationary phase (3.29 mmol H2O2 L-1) under aerated conditions (agitated cultures). In nonagitated cultures there were no detectable levels of H2O2. L. crispatus F117 spent supernatant inhibited Staphylococcus aureus growth in plaque assay. Inhibition was due to H2O2 since catalase treatment of the supernatant suppressed inhibition. In mixed cultures performed with L. crispatus and S. aureus a significant decrease in pathogen growth was observed. The inhibitory effect depended on the initial inoculum of S. aureus. Further evaluation of the properties of L. crispatus F117 will be performed to consider its inclusion in a probiotic for local use in the vaginal tract.

Lactobacillus leichmanii growing in complex medium supplemented with decanoic acid accumulated high concentrations of hydrogen peroxide in the culture. The H2O2-generating system was specifically induced by one of the saturated fatty acids from 4:0 to 16:0 or oleic acid. The induction of this system was associated with the presence of a fatty acyl-CoA-dependent H2O2-generating activity in the cell-free extracts. This activity is shown for the first time in a procaryote organism.