Atypicity of <i>Vibrio cholerae </i> O1 strains based on agglutability

The review analyzes literature data on the phenotypic variability of Vibrio cholerae of the O1 serogroup. Three types of polysaccharide structures are distinguished in the cholera pathogen: lipopolysaccharide, or O-antigen, capsular polysaccharide and exopolysaccharide. The rugous form of V. cholerae strains is able to synthesize exopolysaccharide which is highly resistant to antimicrobials, and to form wrinkled colonies that can be agglutinated with cholera sera in various combinations. Serological classification of V. cholerae is based on the specificity of the lipopolysaccharide. V. cholerae of serogroups O1 and O139 causes cholera epidemics, although strains from non-O1/non-O139 serogroups with the main virulence factors are known. Upon transition from the Sto the R-form, lipopolysaccharide loses the O-polysaccharide, and the central region begins to fulfill the function of somatic antigen, exhibiting R-specificity. The serological differences in the strains of V. cholerae are based on a change in the regulation or structural organization of genes encoding the biosynthesis of O-antigen (rfb). From 1988 to 2019, 168 strains of V. cholerae that are atypical for agglutinability and were isolated from the R variant were isolated from environmental objects in the territory of the former USSR and subjects of the Russian Federation; the genetic organization of these strains has not been fully studied. The evolutionary relationships of atypical strains of cholera vibrios isolated from environmental objects in Siberia and the Far East are determined on the basis of a comparative analysis of housekeeping genes. The analysis of the results of basic and applied research indicates that the problem of variability in agglutinability of V. cholerae strains isolated from humans and from environmental objects remains relevant at the current stage of development of the seventh cholera pandemic. The atypicality of strains of V. cholerae O1 on this basis is considered in aspects of the environmental conditions of their existence and the conditionality of phenotypic manifestations by molecular biological determination