Identification and detection of subtypes in LEE-negative Shiga toxin-producing (STEC) strains isolated from humans, cattle and food.

LEE-negative Shiga toxin-producing (STEC) strains are important cause of infection in humans and they should be included in the public health surveillance systems. Some isolates have been associated with haemolytic uremic syndrome (HUS) but the mechanisms of pathogenicity are is a field continuos broadening of knowledge. The IrgA homologue adhesin (Iha), encoded by , is an adherence-conferring protein and also a siderophore receptor distributed among LEE-negative STEC strains. This study reports the presence of different subtypes of in LEE-negative STEC strains. We used genomic analyses to design PCR assays for detecting each of the different subtypes and also, all the subtypes simultaneously. LEE-negative STEC strains were designed and different localizations of this gene in STEC subgroups were examinated. Genomic analysis detected in a high percentage of LEE-negative STEC strains. These strains generally carried sequences similar to those harbored by the Locus of Adhesion and Autoaggregation (LAA) or by the plasmid pO113. Besides, almost half of the strains carried both subtypes. Similar results were observed by PCR, detecting LAA in 87% of the strains (117/135) and pO113 in 32% of strains (43/135). Thus, we designed PCR assays that allow rapid detection of subtypes harbored by LEE-negative strains. These results highlight the need to investigate the individual and orchestrated role of virulence genes that determine the STEC capacity of causing serious disease, which would allow for identification of target candidates to develop therapies against HUS.