Article

Shiga Toxin Subtypes Display Dramatic Differences in Potency

Molecular Genetics, Biochemistry, and Microbiology, Room 3109, 231 Albert Sabin Way, ML 524, University of Cincinnati, Cincinnati, OH 45267-0524, USA.
Infection and immunity (Impact Factor: 3.73). 03/2011; 79(3):1329-37. DOI: 10.1128/IAI.01182-10
Source: PubMed

ABSTRACT

Purified Shiga toxin (Stx) alone is capable of producing systemic complications, including hemolytic-uremic syndrome (HUS),
in animal models of disease. Stx includes two major antigenic forms (Stx1 and Stx2), with minor variants of Stx2 (Stx2a to
-h). Stx2a is more potent than Stx1. Epidemiologic studies suggest that Stx2 subtypes also differ in potency, but these differences
have not been well documented for purified toxin. The relative potencies of five purified Stx2 subtypes, Stx2a, Stx2b, Stx2c,
Stx2d, and activated (elastase-cleaved) Stx2d, were studied in vitro by examining protein synthesis inhibition using Vero monkey kidney cells and inhibition of metabolic activity (reduction
of resazurin to fluorescent resorufin) using primary human renal proximal tubule epithelial cells (RPTECs). In both RPTECs
and Vero cells, Stx2a, Stx2d, and elastase-cleaved Stx2d were at least 25 times more potent than Stx2b and Stx2c. In vivo potency in mice was also assessed. Stx2b and Stx2c had potencies similar to that of Stx1, while Stx2a, Stx2d, and elastase-cleaved
Stx2d were 40 to 400 times more potent than Stx1.

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    • "STEC strains that produce Stx2d are virulent in a mouse oral challenge model (Wadolkowski et al., 1990). According to the Fuller et al. (2011), Stx2a and Stx2d displayed similar potencies but were significantly more potent than other Stx2 subtypes. Indeed, the culture supernatant of these two strains demonstrated distinct cytotoxicity towards Vero cells (data not shown). "
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    ABSTRACT: The objectives of this study were to investigate prevalence and pathogenic potential of Escherichia coli contaminating raw milk and its products in Egypt. Out of 187 dairy products including 72 raw milk samples, 55 Karish cheese and 60 Ras cheese, 222 E. coli isolates including 111, 89 and 22 were obtained from 55 raw milk samples (76.4%), 41 Karish cheese (74.5%), and 13 Ras cheese (21.7%), respectively. Isolated E. coli strains were examined for 24 representative virulence genes present in diarrheagenic E. coli (DEC) and extraintestinal pathogenic E. coli (ExPEC). Among DEC and ExPEC virulence factors, genes for enteropathogenic E. coli (eaeA, bfpA, EAF), enterohemorrhagic E. coli (stx1, stx2, eaeA), enterotoxigenic E. coli (elt, est), enteroinvasive E. coli (invE), enteroaggregative E. coli (Eagg, astA), diffusely adherent E. coli (daaD), ExPEC (cdt-I to cdt-V, cnf1, cnf2, hlyA) and putative adhesins (efa1, iha, ehaA, saa, and lpfAO113) were screened by colony hybridization assay. Out of 222 E. coli strains, 104 (46.8%) isolated from 69 (36.9%) samples carried one or more virulence genes. The most prevalent gene detected was lpfAO113 (40.5%), followed by ehaA (32.4%,), astA (3.15%,), iha (1.80%), hlyA (1.35%), stx1 (0.90%), stx2 (0.90%), eaeA (0.45%), cdt-III (0.45%) and cnf2 (0.45%). Two strains isolated from Karish cheese harbored 5 virulence genes (stx1, stx2, iha, ehaA, lpfAO113). Stx subtype was determined to be stx1 (not stx1c or stx1d) and stx2d. Indeed, expression of hemolysin A, CDT-III, CNF-II, Stx1 and Stx2d was confirmed by blood agar plate, cytotoxicity assay and Western blotting, respectively. Among the 222 E. coli strains, 54 (48.6%), 38 (42.6%) and 12 (54.7%) isolated from raw milk, Karish cheese and Ras cheese were potentially virulent, respectively. O-genotyping indicated that most of the potentially virulent E. coli isolates did not belong to clinically important O serogroups except O75, O91 and O166, which have been associated with human diseases. Phylogenetic grouping revealed that 150 (67.6%), 67 (30.2%) and 5 (2.30%) strains were clustered into A, B1 and D groups, respectively, which are considered to be associated with intestinal infection, indicating that these E. coli strains might have a potential to cause gastroenteritis. To the best of our knowledge, this is the first comprehensive study regarding prevalence and pathogenic potential of E. coli in dairy products in Egypt. Raw milk, Karish cheese and Ras cheese in Egypt are highly contaminated with E. coli including potentially pathogenic strains, which may impose a public health threat.
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    • "The B-subunits of Stx recognize cell surface glycolipid globotriaosylceramide (Gb3) [33] and to a lesser extent globotetraosylceramide (Gb4) as receptors [27], [34] (Table 1). Gb3 is composed of a tri-saccharide (Galα1-4Galβ1-4Glc), called Pk trisaccharide, which is attached to the lipid, ceramide. "
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    Full-text · Article · Jul 2014 · PLoS ONE
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    • "Many studies have underlined the potential key role of the Stx2 subtypes in the severity of disease. Although Stx2e is not a potent subtype [47], strains harboring Stx2e have been isolated from patients with diarrhea [48]. Intimin contributes to the development of A/E lesions and is a key virulence for some STEC serotypes [49], while ehxA can be found in many STEC serotypes, such as O157:H7 and O26:H11 that are associated with diarrheal disease and HUS [7,50]. "
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