Hydrogen Peroxide–Producing Lactobacilli Inhibit Gonococci In Vitro but Not during Experimental Genital Tract Infection

Commensal lactobacilli that produce hydrogen peroxide (H 2 O 2 ) inhibit Neisseria gonorrhoeae in vitro, and clinical data suggest that they are associated with a reduced risk of gonorrhea. We precolonized mice with Lactobacillus crispatus and then challenged them with N. gonorrhoeae, to measure the effects of H 2 O 2 -producing lactobacilli on gonococcal infection. We found no difference in the duration of infection or the number of gonococci recovered from untreated mice and mice colonized with L. crispatus. A gonococcal catalase mutant and a catalase, cytochrome C peroxidase mutant exhibited greater susceptibility to L. crispatus in vitro than did wild-type bacteria; however, recovery of these mutants from mice was not affected by L. crispatus. We also found no evidence that utilization of lactobacillus-produced lactate by N. gonorrhoeae balances the detrimental effects of H 2 O 2 during infection. We conclude that the association between lactobacilli and gonococci is complex and may be subject to factors that have not been reproduced in vitro.