The acquisition of new mobile genetic elements contributes to the genetic diversity of Vibrio cholerae strains. An important role in this process belongs to the genetic material obtained from phages. The aim of this work was to identify phage-induced PLE islands in strains of V. cholerae O1 serogroup and to determine the resistance of isolates with and without those mobile genetic elements to the lytic activity of the diagnostic cholera El Tor bacteriophage. Materials and methods. Whole genomes nucleotide sequences of toxigenic and non-toxigenic V. cholerae O1 strains presented in the NCBI GenBank were used for the work. Bioinformatic analysis was performed using the BLAST algorithm, MEGA X (or BioEdit v. 7.0.9.0). The test with phages was carried out according A. Gratia technique. Results and discussion. The analysis of 39 toxigenic strains imported to the territory of the Russian Federation and neighboring countries has revealed one strain of V. cholerae O1 of the classical biovar containing the PLE5 island, and 13 strains of V. cholerae O1 of the El Tor biovar containing the PLE4 island. PLE islands have not been found in non-toxigenic strains. It is shown that strains with PLE4 belong to V. cholerae O1 genovariants of the El Tor biovar and have the ctxB1 gene allele. Isolates with this mobile element caused sporadic cases of the disease in 1994–1999, as well as cholera outbreaks in the Russian Federation (in 1993–1994, in 1998 – Dagestan, and 1993 – Tatarstan) and Ukraine (1994–1995). It has been suggested that, perhaps, the presence of the PLE4 island makes a certain contribution to the resistance of V. cholerae O1 strains of the El Tor biovar to the diagnostic cholera El Tor phage (55.6 % of phage-resistant isolates were detected), but there are other mechanisms that have not yet been identified. Thus, the data on the presence of new mobile genetic elements in the genome of earlier imported toxigenic strains of V. cholerae O1, biovar El Tor have been obtained, which expands information about their genetic organization.
Objective. The comparative analysis of the structure of the regulatory gene vasH of the type VI secretion system and its expression in toxigenic and non-toxigenic V. cholerae O1, biovar El Tor strains. Materials and methods. We used 35 strains isolated from patients and from the environmental samples in the territory of Russia and Ukraine between 1970 and 2017. Analysis of the structure of the vasH gene and the amino acid sequence of the protein was carried out using Ugene 1.32, Mega X, and Bioedit v. 7.0.9.0. The relative level of vasH expression was studied by 2Ct. Results. The The structure of the vasH gene and the amino acid sequence of VasH protein in toxigenic typical strains and genovariants of V. cholerae O1, El Tor biovar (genotype ctxA+tcpA+) have been shown to be identical to the reference V. cholerae n16961 O1, El Tor biovar strain. The vasH sequence is variable in isolates lacking ctxA and tcpA genes (ctxAtcpA), and does not differ from the reference in ctxAtcpA+ (with the exception of one strain). The studied toxigenic typical strains and the genovariants have a similar relative level of expression of the vasH gene. In isolates that do not contain the ctxA and tcpA genes, the expression of this gene is comparable to toxigenic strains, and is 3.1 times higher in ctxAtcpA+ strains than that of ctxAtcpA and 2.142.6 times higher than that of toxigenic ones. Conclusion. The analysis of toxigenic and non-toxigenic V. cholerae O1, biovar El Tor strains isolated in Russia and Ukraine in different periods of the current cholera pandemic confirmed the data of foreign researchers on vasH gene being intact in toxigenic isolates and variable in isolates lacking ctxA and tcpA genes. Meanwhile, the structure of vasH gene has been shown to be identical to that of toxigenic ones in 99% of the studied ctxAtcpA+ strains. The expression of the vasH gene has been detected in all studied strains, being the highest in ctxATtcpA+ strains. Only two non-toxigenic strains presumably synthesizing the functionally inactive VasH protein have been identified.
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