Pathogenicity Islands Distribution in Non-O157 Shiga Toxin-Producing Escherichia coli (STEC).

Shiga toxin-producing Escherichia coli (STEC) are foodborne pathogens associated with outbreaks and hemolytic-uremic syndrome. Cattle and meat foods are the main reservoir and infection source, respectively. Pathogenicity islands (PAIs) play an important role in STEC pathogenicity, and non-locus of the enterocyte effacement(LEE) effector ( nle ) genes present on them encode translocated substrates of the type III secretion system. A molecular risk assessment based on the evaluation of the nle content has been used to predict which STEC strains pose a risk to humans. The goal was to investigate the distribution of the PAIs OI (O-island)-36 (nleB2 , nleC , nleH1-1 , nleD ), OI-57 ( nleG2-3 , nleG5-2 , nleG6-2 ), OI-71 ( nleA , nleF , nleG , nleG2-1 , nleG9 , nleH1-2 ) and OI-122 ( ent/espL2 , nleB , nleE , Z4321, Z4326, Z4332, Z4333) among 204 clinical, food and animal isolates belonging to 52 non-O157:H7 serotypes. Differences in the frequencies of genetic markers and a wide spectrum of PAI virulence profiles were found. In most LEE-negative strains, only module 1 (Z4321) of OI-122 was present. However, some unusual eae -negative strains were detected, which carried other PAI genes. The cluster analysis, excluding isolates that presented no genes, defined two major groups: eae -negative (determined as seropathotypes (SPTs) D, E or without determination, isolated from cattle or food) and eae -positive (mostly identified as SPTs B, C, or not determined).