The Distribution of Cytotoxic Necrotizing Factors (CNF-1, CNF-2, CNF-3) and Cytolethal Distending Toxins (CDT-1, CDT-2, CDT-3, CDT-4) in Escherichia coli Strains Isolated from Extraintestinal Infections and The Determination of Their Philogenetic Relationship by PFGE

Abstract Background: Determinants of extraintestinal infection in Escherichia coli (E. coli) remain unclear. Virulence factors making Extraintestinal pathogenic E. coli (ExPEC) different from other E. coli strains are the host cell adhesion, invasion, and two important factors/toxins, Cytotoxic Necrotizing Factor (CNF) and Cytolethal Distending Toxin (CDT) that are responsible for cell death. In the present study, prevalence of CNF-CDT genotypes was investigated in 645 E. coli strains isolated from patients. This prevalence was analyzed regarding clinical origins, phylogroups and putative phylogenetic relationships.Results: At least one virulence gene identified for ExPEC was found in 156 (24%) of 645 E. coli strains. 78, 12, 20 of ExPEC strains contained cnf1, cnf2, cnf3, respectively. Genes of cdt1, cdt2, cdt3 and cdt4 were detected as 20, 4, 4, 4. Finally, two factors were detected cnf1-cnf3 (n=6), cnf1- cdt1 (n=4), cdt1-cdt4 (n=4). These 156 strains were found to be distributed in 106 large clusters by Pulsed-Field Gel Electrophoresis (PFGE). Virulent ExPEC was primarily related to the groups B2 (60%) and D (32%). Conclusions: The CNF gene family is believed to enhance colonization of E. coli especially in the urinary system and the genes of E. coli gene pool gain the ability to survive in new environments, such as the human urinary tract. The widespread diffusion of the CNF gene in E. coli helps to distinguish ExPEC from commensal strains and these genes may be used as specific marker for non-commensal E. coli. It was concluded that different strains of E. coli gained ExPEC properties by acquiring different virulence genes resulting in deletion and recombination mutations, and it was thought that the infections caused by these strains were more likely community-acquired rather than hospital-acquired. Furthermore, in this study, cnf2, cnf3, cdt1, cdt2, cdt3 and cdt4 genes were demonstrated in Turkey for the first time.