Multilocus sequence typing of Vibrio cholerae strains with differing pandemic importance

Allelic polymorphism of the housekeeping genes (dnaE, lap, recA, pgm, gyrB, cat, chi, and gmd) from Vibrio cholerae strains of differing epidemiological significance (n = 41) isolated in Siberia and the Far East during the seventh cholera pandemic was studied. Irrespective of time and source of isolation, all toxi-genic strains isolated in the period of epidemic complications were characterized by an identical allelic profile and belonged to the same sequence-type. Nine sequence types were detected in nonepidemic isolates. Their dendrogram clustering was associated with the serogroup and, in some cases, with the territory and time of isolation. The structural heterogeneity of the nontoxigenic V. cholerae housekeeping genes was, in most cases, caused by synonymous nucleotide replacements (Dn/Ds < 1). This indicates the prevalence of negative selec-tion at the analyzed genome regions of V. cholerae. The revealed differences in the housekeeping gene struc-tures of V. cholerae of different epidemiological significance can be regarded as evidence of different direc-tions of evolution of these strain groups.