Comparative virulence of opacity variants of Neisseria gonorrhoeae strain P9

The invasive properties of nine variants of Neisseria gonorrhoeae strain P9 known to vary in their surface composition have been investigated. Relative virulence was evaluated by their cytotoxic effect on Chang epithelial cell monolayers. Piliated variants P9-2 (with alpha pili) and P9-20 (with beta pili plus protein II) showed increased ability to kill the target cells compared with the prototype P9-1 (lacking pili and additional outer membrane proteins). Two nonpiliated variants, P9-11 (with proteins IIa and IId) and P9-19 (with proteins II and IIc), were also relatively more virulent compared with P9-1. Enhanced attachment was exhibited by both piliated and some nonpiliated variants: beta-piliated P9-20 (with protein II; molecular weight, 29,000) and nonpiliated P9-16 (with protein IIb; molecular weight, 28,000) were the most effective in adherence to the target monolayers.