Shiga-toxin Producing Escherichia coli: Pathogenicity, Supershedding, Diagnostic Methods, Occurrence, and Foodborne Outbreaks.

Historically, Escherichia coli is among the most studied organisms and serves as the basis for understanding many fundamental biochemical and genetic concepts. In addition, it displays 9 pathogenesis groups, with the Shiga toxin-producing (STEC) group being the main representative regarding foodborne pathogenesis. Its typical characteristic is the presence of 2 distinct toxins and variants: stx1 (stx1a, stx1c, and stx1d), and stx2 (stx2a, stx2b, stx2c, stx2d, stx2e, stx2f, and stx2g). The main challenge regarding the study of E. coli is the standardization of a high sensitivity method including all pathotypes, that allows for enrichment of STEC cells and a decrease of background microbiota. The ability of some E. coli cells belonging to other pathogenic groups, such as O104:H4, to acquire genes unique to the STEC group, increases the pathogenic power and the risk of new outbreaks related to these bacteria. In addition, animals with a high concentration of pathogenic E. coli cells present in feces (above 104 CFU/g), designated as supershedding animals, may be the primary transmission factor among ruminants. Therefore, the purpose of this review is to address pathogenicity factors and the importance of supershedding animals in the transmission of this pathogen, discussing the main methods currently applied, to focus on the occurrence of STEC in beef.