Analysis of changes in the genome of Vibrio cholerae O1 El Tor genovariants during the current period of the cholera pandemic

Abstract

Introduction. The genome variability of genetic variants of El Tor cholera agent has led to the emergence of strains carrying mutations in various genes associated with epidemically important pathogen properties. This situation requires an assessment of the trends in these changes in order to predict the pathogenic potential of previously unknown variants and promptly develop new tools for their diagnostics and prevention. The purpose of this work was to analyze the dynamic changes in pathogenicity and drug resistance genes of V. cholerae El Tor genetic variants from endemic countries and Russia. Materials and methods. We analyzed complete genome nucleotide sequences of 104 V. cholerae El Tor strains from the NCBI Gen Bank and European Nucleotide Archive databases, as well as those obtained by us. The nucleotide sequences were analyzed using the UGEN v. 45.1 software. The dendrogram was constructed using maximum parsimony algorithm in BioNumerics v.7.6 software package based on the multiple alignment generated using the Snippy 4.6.0 program. Results. Genomic sequences of 103 strain genovariants isolated on the territory of nine endemic countries of Asia and Africa, as well as in Russia in 1991-2022, have been compared. It is shown that the process of genovariant genome changing was multistage and occurred due to the continuous accumulation of point mutations in key (ctxB and tcpA) and additional (rtxA) genes of pathogenicity and core genes of antibiotic resistance (gyrA, parC and carR), as well as a deletion in SXT element. The most important was the change in the ctxB gene and the emergence of new genovariants with the ctxB7 allele, which replaced the previously prevalent strains. Analysis of altered genome regions of 83 strains from endemic regions has revealed eight genotypes, while the strains (21 isolates) imported to Russia belonged to only five of them including highly virulent strains with the ctxB7 allele and lost PolR biovar-specific feature due to carR gene mutation. The established close phylogenetic relatedness of genovariants from Russia with strains from endemic Asian countries confirms their importation from this region. Conclusion. The sequential occurrence and accumulation of mutations in the pathogenicity and drug resistance genes in the genome of genovariants in endemic regions have been shown, which leads to a change in their epidemically important features. The importation of new highly virulent genovariants into Russia has been established, which indicates the need for an ongoing assessment of changes in the genome of this pathogen for the timely development of adequate means of gene diagnostics and prevention.

Keywords

• v. cholerae
• genovariants
• variability
• virulence
• drug resistance
• phylogenetic relations