Shiga Toxin-Producing Escherichia coli in Food

Abstract

Shiga toxin-producing Escherichia coli (STEC) strains are important food-borne pathogens responsible for a number of human gastrointestinal diseases, including watery or bloody diarrhea and hemorrhagic colitis (HC). In a proportion of individuals, mainly children and the elderly, these symptoms may be complicated by neurological and renal sequelae, including hemolytic-uremic syndrome (HUS). Most outbreaks and sporadic cases of HC and HUS have been attributed to STEC strains of serotype O157:H7. However, especially in continental Europe, STEC strains belonging to serotypes O26:H11/H-, O91:H21/H-, O103:H2, O111:H-, O113:H21, O121:H19, O128:H2/H, and O145:H28/H- are increasingly reported as causes of HC and HUS. In general, these STEC strains are termed non-O157. Clinical laboratories historically screened only for serogroup O157, leading to possible underreporting of non-O157 STEC-associated diseases. The main virulence factor of STEC is the production of Shiga toxin 1 (Stx1) and/or Stx2 or its variants. Since the minimal infectious dose of STEC is very low, usually qualitative procedures with enrichment steps are established. Due to significant differences in methods for detection of STEC O157 and non-O157, these two groups are discussed separately. Cultural methods for detection of STEC O157:H7 in food samples basically comprise a combination of an enrichment step and a serogroup-specific concentration with plating on selective agar and/or chromogenic solid media, followed by confirmation of presumptive positive colonies by biochemical and serological testing as well as by molecular methods. The detection methods of non-O157 STEC include culture methods, enzyme-linked immunosorbent assay (ELISA), and PCR.