Effects of H2O2-producing lactobacilli on Neisseria gonorrhoeae growth and catalase activity.

In the vagina and endocervix, Neisseria gonorrhoeae must interact with complex microflora. Among these are lactobacilli, which may inhibit the growth of gonococci. Lactobacillus acidophilus, which produce H2O2 (LB+), and L. acidophilus and Lactobacillus casei, which do not produce H2O2 (LB-), were coincubated with catalase-positive and -deficient strains of N. gonorrhoeae. When the incubation medium was maintained at pH 7.3, neither LB+ nor LB- affected gonococcal growth. However, LB+ caused a significant increase in expression of gonococcal catalase, which could be offset by exposure of the bacteria to exogenous catalase. When coincubation medium was at lower pH (4.8-5.0), there was a significant decrease in gonococcal survival and catalase activity, which was only partly reversed by exogenous catalase. Lysates of LB+ also effectively inhibited gonococcal catalase. This inhibition was retained upon heating of the lysate to 100 degrees C for 15 min but was lost with proteinase K treatment. Thus, LB+ may inhibit growth of gonococci by acidification of the environment, secretion of H2O2, and production of protein inhibitors.