Effect of subminimal inhibitory concentrations of antimicrobial agents on the piliation and adherence of Neisseria meningitidis.

Neisseria meningitidis is known to be highly resistant to lincomycin (minimum inhibitory concentration greater than 32 micrograms/ml). However, during studies on meningococcal piliation, we noticed a significant reduction in the number of pili after cultivation on lincomycin-containing selective media. This observation was followed up by in vitro and in vivo studies on the relation between lincomycin and meningococcal adherence to human epithelial cells. We found a remarkable decrease in in vitro piliation and adherence after exposure to lincomycin at concentrations as low as 0.05 micrograms/ml. By giving four healthy meningococcal carriers lincomycin orally for 3 to 6 days, the possible in vivo effect of lincomycin was studied. A marked decrease in the meningococcal counts of the pharyngeal secretion was observed. One person completely lost his meningococcal strain during the observation period.