Characteristics of Unique Imported Vibrio cholerae Strains Which Caused Cases of Acute Intestinal Infection in Moscow in 2023

BACKGROUND: In 2023, two cases of acute intestinal infection caused by identical strains of Vibrio cholerae El Tor carrying the preCTX prophage and the classical allele of the tcpA gene were reported in Russia for the first time. The patients had recently visited Asian countries (Indonesia, Bangladesh, and India). A detailed molecular genetic characterization of the pathogens was required to assess their pathogenic potential. AIM: To provide phenotypic and genotypic characteristics of Vibrio cholerae O1 strains imported to Moscow in 2023 and isolated from patients with acute intestinal infection. METHODS: In this study, whole-genome sequences (WGSs) were obtained using the MiSeq Illumina platform. Bioinformatics analysis was performed using Vector NTI Advance, BioEdit, BLASTN, BLASTP, and CARD, as well as the pygenomeviz and biopython packages. RESULTS: The studied strains belonged to the biovar El Tor, serovar Ogawa, and had identical antibiotic resistance profiles. Their genomes contained the preCTX and RS1 prophages with a unique gene composition. RS1 harbored the rstRcalc gene (Calcutta variant), while the RS2 element of preCTX contained the rstRclass gene (classical variant), as well as an additional orfX gene of unknown function. Within the complete VPI-1 pathogenicity island, the tcp cluster — responsible for the production of toxin-coregulated pili — demonstrated significant differences from prototypes in the tcpF and toxT genes, although their products retained characteristic active domains. The tcpA gene was of the classical type but differed from the prototype by three single nucleotide polymorphisms. The strains also possessed a wide array of intact genetic determinants of pathogenicity factors characteristic for the biovar El Tor, sufficient to express its full pathogenic potential. CONCLUSION: The analyzed Vibrio cholerae strains were imported from India, Bangladesh, or Indonesia and are linked by a common source of infection and a transmission pathway. The risk of further importation of such or similar strains persists, and the characterized isolates can be used as reference strains for cholera surveillance studies in the Russian Federation.