Background: Virulence genes can spread among commensal bacteria through horizontal gene transfer. The bacterium with novel virulence factors may pose a severe threat to public health because of the absence of a management system unlike known pathogens. Especially, when a pathogenic bacterium acquires a new kind of virulence genes, it tends to exhibit stronger virulence. In this study, we analyzed the genomes of the two strains of Escherichia coli that were isolated from the feces of patients with diarrhea and produce Shiga-like toxin.
Results: Phylogenetic analysis of conserved genes and average nucleotide identity values of the draft genome sequences indicate that strains NCCP15655 and NCCP15656, isolated from diarrhea patients, belong to the B1 group of E. coli and form a sister clade with strain E24377A. However, the proportion the genes belonging to the subsystem category "phages, prophages, transposable elements, plasmids" and "virulence, disease and defense" are higher than E24377A. Indeed, in their genomes, genes encoding Shiga toxin type 1, Shiga toxin type 2, and type 1 fimbriae were detected. Moreover, a plasmid encoding hemolysin and entropathogenic E. coli secreted protein C was identified in both genomes.
Conclusions: Through the genome analysis of NCCP15655 and NCCP15656, we identified two types of Shiga-like toxin genes that could be responsible for the manifestation of the diarrhea symptom. However, the LEE island, which is one of the major virulence factors of enterohemorrhagic E. coli, was not detected and they are most similar with non-Shiga-like toxin-producing E. coli at the genomic level. NCCP15655 and NCCP15656 will be good examples of Shiga-like toxin-producing E. coli whose genomes are not as similar with typical enterohemorrhagic E. coli as non-Shiga-like toxin-producing E. coli.
Keywords: Hemolysin; Hemolytic uremic syndrome; Pathogenic E. coli; Shiga toxin; Verotoxin.