P. F. Sparling

Construction of isogenic gonococci with variable porin structure : effects on susceptibility to human serum and antibiotics

Protein I (PI) is the most abundant protein on the gonococcal cell surface and besides its porin function it may have important properties contributing to pathogenicity. By allelic exchange using cloned PI genes from FA19 (PIA) and MS11 (PIB) and a selectable marker introduced closely downstream of these genes, we constructed sets of isogenic gonococcal strains that differ only in their PI gene. Analysis revealed that PI has a major effect on stable resistance to normal human serum, and a slight effect on low‐level resistance to antibiotics. All PIA/B hybrids were hypersusceptible to serum, suggesting a possible explanation for why such hybrids do not occur in nature.

IMMUNOBIOLOGY OF PURIFIED RECOMBINANT OUTER MEMBRANE PORIN PROTEIN I OF NEISSERIA GONORRHOEAE

Gonococcal porins (Por) from strains FA19 (Por‐1, serogroup A), MS11 (Por‐2, serogroup B) and FA6434 (Por‐5, a hybrid porin containing epitopes from both serogroups), were expressed in Escherichia coli and purified under non‐denaturing conditions. Porins were inserted into liposomes, and they were bound by monoclonal antibodies which bind native Por and intact gonococci, but not denatured Por. All three recombinant porins (rPor) were highly immunogenic in rabbits without additional adjuvant. The rPor antisera were specific for Por by Western blotting and whole‐cell radioimmunoprecipitation and were broadly cross‐reactive within serogroups. Post‐immune, but not pre‐immune, sera bound to intact gonococci, induced deposition of complement components C3 and C9 onto gonococcal membranes and increased association with and activation of human neutrophils. Gonococci were not killed in bactericidal assays, and there was no phagocytic killing with gonococci opsonized with recombinant antisera. Lack of killing in bactericidal assays was not caused by the presence of blocking antibodies to the outermembrane protein Rmp.