RESOLUTION OF CLONAL SUBGROUPS AMONG NEISSERIA-GONORRHOEAE IB-2 AND IB-6 SEROVARS BY PULSED-FIELD GEL-ELECTROPHORESIS

Objective-Analysis of macrorestriction patterns by PFGE to resolve the relatedness of clonal subgroups amongst N gonorrhoeae IB-2 and IB-6 s erovar strains. Materials and methods-Nineteen IB-2 and eight IB-6 ser ovar strains that differed in either auxotype or penicillin sensitivit y were isolated over a two and a half-year period from patients attend ing several STD clinics in Sydney. During this period, a major clone, Wt/IB-2 (FS), established on epidemiological grounds, was circulating amongst homosexual males. The genetic relation of this major clone to the other strains present in the community was determined by pulsed-fi eld gel electrophoretic (PFGE) analysis of DNA restriction fragments. Genomic DNA from the 27 isolates were prepared, digested with SpeI and Bg/II and the restriction patterns were analysed by contour-clamped h omogeneous electric field electrophoresis (CHEF) in a CHEF DRIII equip ment. Results-Phenotypic characterisation of the 27 isolates by the co mbined use of auxotype, serological characterisation and penicillin se nsitivity indicated the presence of subgroups within each of the two s erovars. In the present study, PFGE analysis of SPeI and Bg/II-generat ed genomic DNA restriction patterns from six of the ten Wt/IB-2 (FS) c orrelated well with phenotypic characterisation of this major clone. F our of the ten Wt/IB-2 (FS) were found to be clonally-derived variants of this major clone as minor genome variations (less than 3 DNA fragm ents) were observed. Distinct clones were represented by three Wt/IB-2 (LS) isolates as the DNA fingerprints generated from these were unrel ated to the major clone. Analysis of PFGE patterns of 6 Pro/IB-2 isola tes showed that one was genotypically identical to the major clone, tw o were clonal variants and three had significantly different patterns to indicate that they were genotypically unrelated. Wt/IB-6 isolates h ad heterogenous PFGE patterns that were clearly unrelated to the Wt/IB -2 serovar strains. Within the IB-6 serovar, there were three isolates with the Wt/IB-6 (FS) phenotype that could be considered as clonal va riants whilst the rest were genotypically distinct. Conclusions-PFGE a nalysis of macrorestriction patterns generated from SpeI- and Bg/II-cl eavage of genomic DNA has enabled the establishment of clonal origins of strains present in the Sydney community during the period of study. The delineation of strains belonging to major A/S groups by PFGE anal ysis presents a clearer epidemiological picture than phenotypic charac terisation alone.