Characteristics and virulence genes of Escherichia coli isolated from septicemic calves in southeast of Iran.

Virulence factors are associated with the capacity of E. coli strains to cause intestinal and extraintestinal infections. Thirty one E. coli isolates were obtained from heart blood or internal organs of septicemic calves. The O serogroups of isolates were determined. PCR assays were performed to determine the phylogenetic groups and presence of specific virulence genes. Fourteen (45.16%) isolates belonged to seven O serogroups (O8, O15, O20, O45, O78, O101 and O103) and 17 (54.83%) isolates were O-nontypeable. E. coli isolates fall into three phylogenetic groups included 15 isolates belonged to B1, 9 to A and 7 to D phylogenetic groups. Nineteen (61.29%) isolates exhibited at least one of the virulence genes. F17 family (5 isolates f17b, 3 isolates f17c, 1 isolate f17a) genes and aerobactin encoding gene of iucD (5 isolates) were the two most prevalent virulence genes. Three isolates were positive for cnf2 and cdtIII genes in combination and they were O-nontypeable. AfaE-VIII, CS31A gene (clpG) and hemolysin encoding gene (hly) were detected in 3, 4 and 3 isolates respectively. None of the isolates contained the ipaH sequences and the genes encoding fimbria (F5, F41, S, P), AfaI adesin, toxins (LT-I, ST-I, SLT-I, SLT-II, CNF1 and CDT-IV) and intimin.