Non-toxigenic strains of Vibrio cholerae biovar El Tor, isolated in the territory of Russia: molecular-genetic peculiarities and pathogenic properties

Abstract

Aim. Comparative analysis of the sequenced on our own effort genomes of non-toxigenic strains with different set of pathogenicity genes and assessment of their virulence on the model of intestinal inoculation of newborn rabbits. Materials and methods. Whole-genome DNA sequencing of 26 strains was carried out using semiconductor sequencing technology. Haemolysin and hemagglutinin-protease production was evaluated applying conventional methods. Virulence of the strains for newborn rabbits was determined through intraluminal inoculation at the dose of 107 CFU/ml. Results. On the basis of whole genome analysis of ctxA-tcpA+ and ctxA-tcpA- non-toxigenic strains, differences in composition and structure stability of mobile elements associated with pathogenicity have been identified. Significant differences in nucleotide sequences of hlyA, hapA, and rtxA genes, encoding production of additional pathogenicity factors, have also been detected. The paper provides the results of assessment of their phylogenetic relations. Experiments on animal models have confirmed the inability of non-toxigenic ctxA-tcpA+ and ctxA-tcpA- strains to cause the development of typical cholera infection. Conclusion. New data on the genome structure of different non-toxigenic strains and their phylogenetic relations have been obtained. Based on the results of inoculation of animal models with cells of non-toxigenic strains with the studied genome the inference is drawn on their inability to cause the development of typical cholera infection.