Pilus-mediated co-aggregation with Lactobacillus crispatus increases meningococcal susceptibility to antimicrobial agents by interfering with microcolony formation

Background Neisseria meningitidis asymptomatically colonizes the nasopharyngeal mucosa, but occasionally, the bacteria disseminate to cause sepsis and meningitis. In the epithelial cell layer, the pathogen co-colonizes with other resident inhabitants, such as Lactobacillus species that are part of the nasopharyngeal-oral microbiota. In this study, we investigated the interaction between lactobacilli and meningococci. Results We demonstrated that Lactobacillus crispatus strain MV24 can co-aggregate with meningococci, whereas all other Lactobacillus strains tested did not co-aggregate. The binding ability of L. crispatus was not strain- or serogroup-specific but was dependent on the ability of meningococci to form microcolonies. The finding that N. meningitidis lacking pili did not co-aggregate with L. crispatus , but that hyperpiliated N. meningitidis exhibited strong co-aggregation, led us to examine the interaction between purified meningococcal pili and lactobacilli. Our results showed that L. crispatus MV24 can bind to purified meningococcal Class I and II pili, explaining the aggregative clusters observed under the microscope. Co-aggregation with L. crispatus disrupted microcolony formation, and increased the killing of meningococci by LL-37, hBD2 and cephalexin. Further, co-aggregation had the added effect of impeding motility. Conclusion N. meningitidis pili bind to L. crispatus , which interferes with the meningococcal microcolonies and increases sensitivity to antimicrobial agents. Taken together, our findings suggest that L. crispatus MV24 may have a beneficial effect on the host through co-aggregating with meningococci.