Molecular Analysis of Shiga Toxin-Producing Escherichia coli Strains Isolated from Hemolytic-Uremic Syndrome Patients and Dairy Samples in France

Abstract

Shiga toxin-producing Escherichia coli (STEC) has been associated with food-borne diseases ranging from uncomplicated diarrhea to hemolytic-uremic syndrome (HUS). While most outbreaks are associated with E. coli O157:H7, about half of the sporadic cases may be due to non-O157:H7 serotypes. To assess the pathogenicity of STEC isolated from dairy foods in France, 40 strains isolated from 1,130 raw-milk and cheese samples were compared with 15 STEC strains isolated from patients suffering from severe disease. The presence of genes encoding Shiga toxins (stx 1 , stx 2 , and variants), intimin (eae and variants), adhesins (bfp, efa1), enterohemolysin (ehxA), serine protease (espP), and catalase-peroxidase (katP) was determined by PCR and/or hybridization. Plasmid profiling, ribotyping, and pulsed-field gel electrophoresis (PFGE) were used to further compare the strains at the molecular level. A new stx 2 variant, stx 2-CH013 , associated with an O91:H10 clinical isolate was identified. The presence of the stx 2 , eae, and katP genes, together with a combination of several stx 2 variants, was clearly associated with human-pathogenic strains. In contrast, dairy food STEC strains were characterized by a predominance of stx 1 , with a minority of isolates harboring eae, espP, and/or katP. These associations may help to differentiate less virulent STEC strains from those more likely to cause disease in humans. Only one dairy O5 isolate had a virulence gene panel identical to that of an HUS-associated strain. However, the ribotype and PFGE profiles were not identical. In conclusion, most STEC strains isolated from dairy products in France showed characteristics different from those of strains isolated from patients.

Prevalence of Shiga toxin-producing Escherichia coli in food products of animal origin as determined by molecular methods

“…This is of particular importance since it has been previously proposed that the Stx2 is the most common virulence factor associated with severe human disease (Pradel et a., 2008). No correlation could be observed between source of isolation (dairy or meat) and the presence of the stx 2 gene.…”

“…Pradel et al (2008) compared the genotypes of STEC strains isolated from dairy products and from patients. Based on their findings the authors concluded that there was a statistical association between strains isolated from human disease and the presence of the stx 2 gene while the dairy STEC strains were characterized by the predominance of stx 1 , with a limited number of strains carrying the eaeA gene.…”

“…Information regarding the prevalence and distribution of STEC in foodstuffs is only recently becoming available. Studies conducted so far (Brooks et al, 2001;Doyle and Schoeni, 1987;Fantelli and Stephan, 2001;Pradel et al, 2000), particularly those investigating STEC strains with different virulence genotypes (Pradel et al, 2008;Slanec et al, 2009), highlight the need for determination of a possible association of certain STEC genotype profiles with specific food types in order to assess their possible risk to human health.…”

Molecular screening of bovine raw milk for the presence of Shiga toxin-producing Escherichia coli (STEC) on dairy farms

“…Bovine milk and other dairy products such as yogurt and cheese have been associated with diseases caused by STEC (Chapman et al, 1993;Prandel et al, 2008;Martin & Beutin, 2011). Outbreaks of milk-borne diseases associated with STEC, including pasteurized dairy products, have been reported worldwide emphasizing the importance of STEC control for public health (Morgan et al, 1993;Upton & Coia, 1994;Seghal et al, 2008).…”

Shiga Toxin-Producing Serogroup O91 Escherichia coli Strains Isolated from Food and Environmental Samples

“…Surveys of nonclinical sources have shown that STEC serogroup O91 strains are also present in foods. These strains have been isolated from raw milk and cheeses in France (17) and Switzerland (18), from minced beef in France (19), and from cattle feces in Argentina (20), and they are the second most common STEC serogroup found in various types of meats and dairy products in Germany (16). In the United States, STEC O91 strains have been isolated from ground beef (21), from the production environments of other food animals, and also from fresh produce (22).…”