The role of Lactobacillus species in the female urogenital tract as a barrier to infection is of considerable interest. These organisms are believed to contribute to the control of vaginal microbiota by competing with other microorganisms for adherence to epithelial cells and by producing antimicrobial compounds. These bactericidal compounds include organic acid, which lowers the vaginal pH, hydrogen peroxide, bacteriocin-like substances and possibly biosurfactants.