Genetic characteristics of <i>Vibrio cholerae</i> non-O1/non-O139 and <i>Vibrio paracholerae</i> strains circulating in the Volga River near Saratov

Introduction. The relevance of this study is determined by the critical necessity for molecular genetic monitoring of major river systems to control the spread of pathogenic non-toxigenic vibrios, including the recently discovered Vibrio paracholerae species in the Russian Federation, against the backdrop of increasing climatic and anthropogenic risks. Objective. To study the genetic characteristics of V. cholerae non-O1/non-O139 and V. paracholerae strains isolated from the Volga River near Saratov. Materials and methods. Twenty-one strains of vibrios isolated in 2024 were studied. Biochemical properties were assessed using the api 20 E kit. Sequencing was performed on the MGI DNBSEQ-G50 platform. Blast v. 2.15.0 and BioEdit v. 7.0.9.0 algorithms were used for bioinformatics analysis. A phylogenetic tree based on the alignment of core genome was constructed using maximum likelihood method with iqtree v. 2.4.0 software. Results. Phylogenetic analysis revealed that five isolates were included in the same cluster as representatives of V. paracholerae, indicating their belonging to this species. V. cholerae non-O1/non-O139 and V. paracholerae strains do not contain the CTXφ and RSIφ prophages, the TLC element, the VPI-1 pathogenicity island, the VSP-I pandemic island, and the ICE SXT element. At the same time, their genomes were found to contain the toxR/toxS genes responsible for the biosynthesis of regulatory proteins that control the production of the main pathogenicity factors; the loci of the type 6 secretion system; the MARTX toxin; mannose-sensitive adhesion pili; the outer membrane protein OmpW; and the hemolysin HlyA. In some strains, altered genes of the type 3 secretion system, the vc0496 gene from the VSP-II pandemicity island, the class 1 CRISPR-cas system, and nanH of the VPI-2 pathogenicity island were detected. Analysis of specific genes confirmed that 5 isolated strains belong to the V. paracholerae species. Conclusion. Not only V. cholerae non-O1/non-O139 strains but also V. paracholerae strains circulate in the Volga River near Saratov. Both groups of strains have similar biochemical properties and genetic makeup. Their genomes lack pathogenicity genes and several pandemic genes, but loci for additional toxins, the presence of which is characteristic of aquatic vibrios, have been identified. Further comparative phenotypic and molecular genetic studies of V. paracholerae are necessary.