Non-toxigenic Vibrio cholerae O1 strains that caused gastroenterocolitis in the Zaporizhia and Kherson regions: case reports and pathogen molecular genetic characteristics

In 2023–2024, two cases of gastroenterocolitis caused by non-toxigenic Vibrio cholerae O1 were documented in Zaporizhzhia and Kherson regions. Previously, diseases of this etiology had not been detected in Russia over the last 18 years, although CTX– strains were isolated from water bodies. The aim of the study was to determine the molecular genetic characteristics of clinical strains of V. cholerae O1 isolated in Russia and comparative bioinformatics analysis of their whole genome sequences (WGSs). Materials and methods. The strains were identified in accordance with MUK 4.2.3745-22, sequencing was performed on the MiSeq Illumina platform, bioinformatics analysis — using BioEdit, Vector NTI, CARD and author’s software. Results. A patient from Zaporizhzhia region fell ill after consumption of market foods, and from the Kherson region — after bathing in the sea. Both were diagnosed with acute gastroenterocolitis, in the second case rotavirus was detected along with vibrio. The isolated cultures with identical PCR genotypes were identified as non-toxigenic V. cholerae O1. Both patogens belonged to Ogawa serotype. The WGSs of both strains lacked prophages CTX, preCTX, islands VPI and VSP-II, genes of heat-stable and cholix toxins, proteins OmpT and OmpU, but shared RTX and msh clusters, genes of hemolysin, metallo- and serine proteases; cytotonic factor Cef, represented in two pathogens by different alleles. Significant differences included the presence in the 2024 pathogen of VSP-I island, T3SS cluster integrated into VPI-3, ompW and β-lactamase varG genes which were absent in the 2023 one. The latter contained an incomplete VPI-2 and significantly altered genes rtxA, as well as genes encoding proteases VesC and VchC. On the dendrogram, the isolates formed 2 distant clusters, which also included environmental waterborne strains isolated in other Russian territories in different years; in each cluster all genes had the same repertoires of genetic determinants and gene alleles. These data evidence an opportunity for their long-term preservation in water reservoirs and the absence of importations from abroad. Conclusion. Two new clonal complexes of CTX– V. cholerae O1 have been identified in the territory of Russian Federation. Non-toxigenic strains usually do not cause large-scale epidemiological complications, and the diseases caused by representatives of each complex could be associated with compromised immunity of patients.