Detection of Shiga Toxin-Producing Escherichia coli from Nonhuman Sources and Strain Typing

Abstract

Shiga toxin-producing Escherichia coli (STEC) strains are commonly found in the intestine of ruminant species of wild and domestic animals. Excretion of STEC with animal feces results in a broad contamination of food and the environment. Humans get infected with STEC through ingestion of contaminated food, by contact with the environment, and from STEC-excreting animals and humans. STEC strains can behave as human pathogens, and some of them, called enterohemorrhagic E. coli (EHEC), may cause hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Because of the diversity of STEC types, detection strategies for STEC and EHEC are based on the identification of Shiga toxins or the underlying genes. Cultural enrichment of STEC from test samples is needed for identification, and different protocols were developed for this purpose. Multiplex real-time PCR protocols (ISO/CEN TS13136 and USDA/FSIS MLG5B.01) have been developed to specifically identify EHEC by targeting the LEE (locus of enterocyte effacement)-encoded eae gene and genes for EHEC-associated O groups. The employment of more genetic markers (nle and CRISPR) is a future challenge for better identification of EHEC from any kinds of samples. The isolation of STEC or EHEC from a sample is required for confirmation, and different cultivation protocols and media for this purpose have been developed. Most STEC strains present in food, animals, and the environment are eae negative, but some of these strains can cause HC and HUS in humans as well. Phenotypic assays and molecular tools for typing EHEC and STEC strains are used to detect and characterize human pathogenic strains among members of the STEC group.

Identification of Shiga toxin-producing (STEC) and enteropathogenic (EPEC) Escherichia coli in diarrhoeic calves and comparative genomics of O5 bovine and human STEC

“…However, those AE-STEC from young calves receive much less attention today and they are seldom included in comparative studies of isolates from healthy cattle and from humans (Beutin and Fach, 2015;Caprioli et al, 2015). Therefore their actual prevalence, virulotypes and host specificity are largely unknown.…”

“…(haemorrhagic) colitis (HC) and (bloody) diarrhoea, followed by the HUS in 10% of the cases (Davis et al, 2015;Kaper and O'Brien, 2015). However some debate exists about the EHEC name because not all of Stxand AE-positive strains are associated with HC in humans (Tozzoli and Scheutz, 2014;Beutin and Fach, 2015). Therefore two of us recently proposed to rename them AE-STEC and this nomenclature will be followed in this manuscript.…”

“…Therefore their actual prevalence, virulotypes and host specificity are largely unknown. According to the latest review by Mainil and Fairbrother (2014), several AE-STEC from diarrhoeic calves belong to some of the most frequent and pathogenic serotypes in humans such as O26:H11 and O111:H-, while others belong to subdominant serotypes that are quite rarely isolated from diseased humans and/or healthy cattle, though some of them such as O5:H-and O118:H16 are listed as emerging AE-STEC serotypes in humans (Beutin and Fach, 2015). Moreover if the genome analyses of several non-O157 AE-STEC have been or are being conducted by different means Lindsey et al, 2014;Sadiq et al, 2015), the genomics of the O5:H-and O118:H16 AE-STEC from diarrhoeic calves has not been.…”

“…Numerous studies have been published about the prevalence of the carrier state, the incidence of faecal shedding and the virulotypes of AE-STEC present in asymptomatic cattle (Mekata et al, 2014;Beutin and Fach, 2015;Persad and Lejeune, 2015). Besides the O157: H7 serotype, that is the most frequently responsible for large outbreaks and the most pathogenic to humans, AE-STEC can belong to scores of serotypes (Tozzoli and Scheutz, 2014;Beutin and Fach, 2015). Of these, 5 have been frequently identified worldwide and are most pathogenic for humans together with O157:H7: O26:H11, O103:H2, O111:H-, O121:H19, and O145:H-.…”

“…Of these, 5 have been frequently identified worldwide and are most pathogenic for humans together with O157:H7: O26:H11, O103:H2, O111:H-, O121:H19, and O145:H-. In addition to the phage-located stx1 and stx2 genes, those AE-STEC can harbour several other genes coding for virulence-associated factors: a set of genes on a pathogenicity island named the Locus of Enterocyte Effacement (LEE) code for a type three secretion system (T3SS), T3-secreted effectors and the outer membrane intimin adhesin (the eae gene); different chromosomal non LEE-located genes code for other T3-secreted effectors and for other adhesins or toxins; and still other genes located on a plasmid (pO157 plasmid) code for several virulence markers, including one enterohaemolysin (Ehly) (Mainil and Daube, 2005;Bugarel et al, 2010;Beutin and Fach, 2015;McWilliams and Torres, 2015;Stevens and Frankel, 2015).…”