Isolation and virulence factors of vero cyto toxinproducing Escherichia coli in human stool samples

Abstract

OBJECTIVE: To evaluate the isolation rate of O157 and non-O157 verocytotoxin-producing Escherichia coli (VTEC) strains, to study the occurrence of additional virulence factors and to correlate these with clinical symptoms. METHODS: Over more than 5 years, 17 296 unduplicated fecal samples submitted for routine culture were screened for VTEC by a single PCR detecting VT1, VT2 and its variants. Verocytotoxin B subunit genotypes of the isolates obtained by testing individual colonies in positive samples were determined by a polymerase chain reaction---restriction fragment length polymorphism (PCR---RFLP) technique, the eaeA gene and the 60-MDa virulence plasmid by PCR, and the hemolytic phenotype by using CaCl2-washed blood agar. RESULTS: Verocytotoxin genes were found in 1.02% of the samples. Non-O157 VTEC strains were isolated in 0.66% and O157 in 0.17%. Overall, VTEC was less frequently isolated than Campylobacter and Salmonella but more frequently than Yersinia and Shigella. All cases except two siblings were epidemiologically unrelated. Cases of hemolytic uremic syndrome (HUS) were only observed in association with serogroup O157, which seems to be more pathogenic than the non-O157 strains. Among non-O157 VTEC strains, eaeA-positive strains are more frequently associated with clinical symptoms than are eaeA-negative strains. Other virulence factors correlate less closely with the presence of symptoms. CONCLUSIONS: VTEC is the third bacterial intestinal pathogen in our study population. All stool samples from patients with diarrhea should be screened for the most frequent serogroup, O157, or, if this is not possible, at least those from patients with bloody diarrhea. Non-O157 VTEC strains, especially if they are eaeA positive, are also associated with diarrhea, more often non-bloody. PCR or the new commercially available immunoassays could be used in selected cases, e.g. in patients suffering from HUS and in cases of outbreaks.

Prevalence and Characterization of Shiga Toxin-Producing Escherichia coli in Swine Feces Recovered in the National Animal Health Monitoring System's Swine 2000 Study

“…Thus, these strains are potential human pathogens (Table 2). Furthermore, most of the STEC serogroups that were isolated have been associated with human illnesses (15,16,20,28,33,43,49). For example, E. coli strains of serotypes O91:H(Ϫ), O91:H10, O91: H21, and O91:H40 have been associated with cases of bloody diarrhea and HUS (7,28,43).…”

“…Furthermore, most of the STEC serogroups that were isolated have been associated with human illnesses (15,16,20,28,33,43,49). For example, E. coli strains of serotypes O91:H(Ϫ), O91:H10, O91: H21, and O91:H40 have been associated with cases of bloody diarrhea and HUS (7,28,43). E. coli O121 has also been reported in cases of human illness, and E. coli O121:H19 was associated with an outbreak of HUS at a lake in Connecticut in 1999 (20,31).…”

The Common Ovine Shiga Toxin 2-Containing Escherichia coli Serotypes and Human Isolates of the Same Serotypes Possess a Stx2d Toxin Type

“…stx c was isolated from E. coli O157:H Ϫ strain E32511 and is closely related to stx 2 and stx 2vha (30). The stx 2d cluster as defined by Pierard et al (26) comprises stx 2d-O111 (24), stx 2d-OX3a (25), and stx 2d-Ount variants, and these subtypes were identified in non-O157 STEC strains isolated from humans and meat (26,27). However, stx 2d -positive STEC strains are not observed in the most virulent serogroups for humans, including O157, O26, O103, O111, and O145 and have been reported to be less frequently associated with diarrhea and hemolytic uremic syndrome (HUS) (26).…”

Characterization of stx2 and its variants in Escherichia coli O157:H7 isolated from patients and animals

“…Two main stx 2 subtypes were detected (stx 2 and stx 2c ) and no combination of these two subtypes was detected. Two pairs of primers (stx2-F and stx2-R, VT2-c and VT2-d) can amplify stx 2 and stx 2c , though the amplicons amplified by primers VT2-c and VT2-d can be further subtyped by using Tyler's PCR-RFLP method (Piérard et al, 1997;Piérard et al, 1998). Stx 2 genotype isolates caused more severe symptoms (two with HUS and 1 with bloody diarrhea) than stx 2c harboring isolates (three with watery diarrhea), though the case load was shortage.…”

“…Stx2 shares approximately 56% amino acid homology with stx1 but is relatively more heterogeneous (Jackson et al, 1987). Several related variants of stx2 have been described that include stx2c, stx2d, stx2e, stx2f and stx2g, moreover, stx2c can be classified into two groups: stx 2vha , and stx 2vhb (Weinstein et al, 1988;Gannon et al, 1990;Ito et al, 1990;Schmitt et al, 1991;Tyler et al 1991;Piérard et al, 1998;Schmidt et al, 2000;Teel et al, 2002;Leung et al, 2003;Beutin et al, 2008;Vu-Khac and Cornick, 2008;Prager et al, 2009).…”