Naturally occurring isolates of Neisseria gonorrhoea, which display anomalous serovar properties, express PIA/PIB hybrid porins, deletions in PIB or novel PIA molecules

Abstract

The por gene of Neisseria gonorrhoeae encodes the Protein I porin responsible for serovar specificity. In this study the por genes have been sequenced from clinical isolates which exhibited anomalous serovar reactivity. One group of`intermediate' strains differed significantly from both Protein IA and IB strains, were more closely related to IA but appeared to represent a distinct class of Protein I. Another strain was closely related to Protein IB of serovar IB-6 but contained a deletion of six amino acids in surface exposed loop 6 which removed epitopes recognised by IB specific monoclonal antibodies. The third group of strains, which reacted with both IA and IB specific monoclonal antibodies, expressed hybrid Protein I molecules containing both IA and IB epitopes. These strains appeared to originate from a double crossover between Proteins IA and IB with the amino and carboxy terminal residues homologous to IB while the surface exposed loop 6 demonstrated close homology to IA. This is the first demonstration of naturally occurring gonococci expressing a hybrid Protein IA/IB. z 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.

Molecular Typing of Neisseria gonorrhoeae Isolates by Pyrosequencing of Highly Polymorphic Segments of the porB Gene

“…The widely used serovar determination for epidemiological characterization of N. gonorrhoeae has important limitations (10,12,13,17,24,27,28). In addition, for several of the MAbs used in the serovar determination, the precise amino acid residues of PorB that are critical for single-MAb reactivity have been difficult to identify (1,3,4,5,16,27). Consequently, a rapid and stable molecular genetic method for routine use in the characterization of N. gonorrhoeae, and which overcomes the limitations of serovar determination, is definitely needed.…”

“…Individual strains express only one of the two PorB protein groups, either PorB1a or PorB1b (4,6,11,29), which are encoded by the mutually exclusive porB gene alleles, porB1a and porB1b, respectively. Naturally but rarely occurring strains that express PorB1a-PorB1b hybrids have been identified (4,9).…”

“…Individual strains express only one of the two PorB protein groups, either PorB1a or PorB1b (4,6,11,29), which are encoded by the mutually exclusive porB gene alleles, porB1a and porB1b, respectively. Naturally but rarely occurring strains that express PorB1a-PorB1b hybrids have been identified (4,9). Antigenic diversities of PorB between strains form the basis for the widely used serogroup and serovar determination with monoclonal antibodies (MAbs) (14,22), and attempts at identifying the antigenic epitopes of PorB of the serovar-specific MAbs have previously been published (1,3,4,5,16,27).…”

“…The segments of the porB gene encoding the eight surface-exposed amino acid loops of PorB (29) exhibit the highest level of polymorphism (1,4,5,7,12,27,28,29,31). Sequence analysis of four to six of these short, highly polymorphic segments of the porB gene generates discrimination between isolates that is almost identical to that obtained by sequencing of the entire porB allele (27).…”

Molecular Epidemiology of Neisseria gonorrhoeae : Sequence Analysis of the porB Gene Confirms Presence of Two Circulating Strains

“…The antigenic expression of outer membrane protein PorB within a strain is stable; diversities between strains form the basis for serogroup and serovar determination with monoclonal antibodies (MAbs) (16,24). Any individual N. gonorrhoeae strain expresses only one of two different groups of the porin proteins PorB1a and PorB1b, which show high degrees of sequence homology (6,8,13,32). The proteins are encoded by the mutually exclusive alleles of the porB gene, porB1a and porB1b, respectively (8,13).…”