This project is supported by an FDA Office of Women's Health Grant. The predominant proteins in the outer membranes of N. gonorrhoeae are trimeric porin proteins (PI). They are considered good vaccine candidates because porin protein is expressed by all strains, they are surface exposed, and, although antigenic variation exists between different strains, there is no phase variation during an infection as there is for both pilin and lipooligosaccharide (LOS). A model of these neisserial porin proteins predicts eight surface exposed loops. Regions of variability between serotypes in the genes coding for these proteins have been mapped to several surface exposed loops and it is predicted that these variable region (VR)loops form the epitopes for both serotyping and bactericidal antibodies. A genotyping method utilizing oligonucleotide hybridization and chemiluminescence detection to differentiate VRs of PIB strains of N. gonorrhoeae has been developed. Comparative sequence analysis of PIB porin genes from GenBank revealed that the predicted surface-exposed loops 2, 4, and 8 are widely conserved among strains, while loops 5 and 6 exhibit the greatest sequence variation, particularly in the apex region. Five collections of gonococcal isolates have been typed using this method: (1) 24 endemic Korean strains from experimental vaccinees, (2) a panel of 17 temporally and geographically diverse strains, (3) a group of partner strains from a Baltimore STD clinic, (4) additional partner strains, (5) strains with published sequences for reference (Dr, M. Hobbs, North Carolina). The results suggest that in a group of temporally and geographically related strains there is a limited degree of variation in regions of the PI protein that are of suspected immunologic importance. In the group of diverse strains, this typing system differentiated the 12 PIB strains into 9 groups which is similar to the discriminatory ability of serovar testing. Differences between strains of the same serovar and similarities between strains of different serovar were found illustrating that a variable region specific typing system is preferable in studies designed to address questions about the antigenicity and protective potential of the PI gonococcal protein. This system correlated with the current serological method in instances where serotyping PIB monoclonal antibodies have been epitope mapped. Sexual contact pairs from Baltimore and the U.K. showed identical hybridizations for each variable region typed except for one discordant (PIA _ PIB)pair. Comparison of hybridization results with PIB sequence data for the Baltimore contact pair isolates showed the variable region sequence was identical to the hybridizing probe in > 50% of cases, and the greatest difference seen between actual sequence and probe sequence was 2 base pairs. This work was presented at the 1999 ASM General meeting, May 1999, and at the gonococcal typing workshop following the International Society for Sexually Transmitted Diseases Research meeting, July 1999, in Denver, CO.
