Presence of pathogenicity island related and plasmid encoded virulence genes in cytolethal distending toxin producing Escherichia coli isolates from diarrheal cases

CONTEXT: Mobile genetic elements such as plasmids, bacteriophages, insertion elements, and genomic islands play a critical role in virulence of bacterial pathogens. These elements transfer horizontally and could play an important role in the evolution and virulence of many pathogens. A broad spectrum of gram-negative bacterial species has been shown to produce a cytolethal distending toxin (CDT). On the other hand, Shiga toxin producing Escherichia coli are the one carry virulence genes such as stx 1 and stx 2 (Shiga toxin) and these genes can be acquired by horizontal gene transfer. AIM: The aim of this study was to investigate the presence of other virulence associated genes among CDT producing E. coli strains. MATERIALS AND METHODS: Thirty CDT positive strains isolated from patients with diarrhea were characterized. Thereafter, the association with virulent genetic elements in known pathogenicity islands (PAIs) was assessed by polymerase chain reaction. RESULTS: In this study, it was shown that the most CDT producing E. coli isolates express Shiga toxin. Moreover, the presence of prophages framing cdt genes (like P2 phage) was also identified in each cdt-type genomic group. Flanked regions of cdt-I, cdt-IV, and cdt-V-type was similar to plasmid sequences while cdt-II and cdt-III-type regions similarity with hypothetical protein (orf3) was observed. CONCLUSION: The occurrence of each cdt-type groups with specific virulence genes and PAI genetic elements is indicative of horizontal gene transfer by these mobile genetic elements, which could lead to diversity among the isolates.