Differentiation of Neisseria gonorrhoeae IB-3 and IB-7 serovars by direct sequencing of protein IB gene and pulsed-field gel electrophoresis.

Serotyping of Neisseria gonorrhoeae based on the differential recognition by a panel of six monoclonal antibodies (MAbs) against Protein IB (PIB) is a valuable tool for studying the epidemiology of gonorrhoea. However, the predominance of certain serovars in specific geographic regions necessitates the development of new MAbs or new genotyping approaches. Nucleotide and amino-acid sequence analysis of PIB from strains within the IB-3 and IB-7 serovars revealed strain differences within the same serovar. Based on the generation of PIB nucleotide and deduced amino-acid sequences that centred on amino-acid residues 196 and 237, eight serovar IB-3 strains and nine serovar IB-7 strains were separately subdivided into five groups. Intra-serovar differences were also established by pulsed-field gel electrophoresis (PFGE) of macro-restriction fragments generated by SpeI- and NheI-cleavage of genomic DNA. There was good correlation between the results based on PIB gene PCR-sequencing and those based on PFGE analysis of macro-restriction fragment patterns. These data demonstrate the high precision of PFGE analysis and indicate that this approach can be used as a rapid epidemiological subtyping system for major serovars of N. gonorrhoeae.