Hydrogen peroxide production and resistance to nonoxinol-9 in Lactobacillus spp. isolated from the vagina of reproductive-age women.

Lactic acid production is considered to be the major protection mechanism of lactobacilli against vaginal infections due to genital pathogens. However, some species of Lactobacillus are also hydrogen peroxide-producers. Women, who usually use intrauterine dispositive (IUD) and spermicides such as nonoxinol-9 (N-9) as contraceptive methods, increase the risk of acquiring an urinary tract infection and a bacterial vaginosis; some studies have demonstrated that these compounds alter the normal vaginal biota. It is known that they inhibit lactobacilli in vitro at concentrations of 0.1% to 1% and that they do not have an effect on the growth of Escherichia coli. It is probable that the presence of nonoxinol-9 affects the ecological balance of the vagina by inhibiting the protector lactobacilli. In this study, we identified Lactobacillus acidophilus, L. brevis, L. crispatus, L. fermentii and L. jensenii as the species most frequently isolated from women. Seventy-one hydrogen peroxide-producer strains and 48 strains resistant to the inhibitory effect of nonoxinol-9 were detected. L. brevis showed the highest number of resistant strains.