Experimental human gonococcal urethritis: 250 Neisseria gonorrhoeae MS11mkC are infective.

Neisseria gonorrhoeae MS11mkA (mkA) expresses one 3.6-kDa lipooligosaccharide (LOS). Variant MS11mkC (mkC), expressing four larger LOSs, occurs in vitro among mkA at a frequency of 10(-3). Infectivity of these variants was compared in 2 groups of volunteers inoculated with approximately 40,000 piliated, Opa- gonococci of either strain. The mkC variant infected 5 of 5 while mkA infected only 2 (40%) of 5. Gonococci recovered from the mkA infections showed a transition toward the mkC LOS phenotype. The mkA inoculum contained approximately 40 mkC gonococci. These data confirmed earlier studies and suggested that small numbers of mkC gonococci would be infective. This hypothesis was tested in three more experiments. In two, volunteers were inoculated with 250 or 1250 mkC, infecting 3 of 7 in each group, and in the third, 1600 mkC infected 2 of 6, resulting in a total of 8 of 20 infected by < or = 1600 mkC. Gonococci shed by infected volunteers maintained the mkC LOS phenotype but shifted from Opa- to Opa+. Thus, LOS and opacity protein, as well as pilus, are gonococcal virulence factors.