Association of EnterohemorrhagicEscherichia coliHemolysin with Serotypes of Shiga-Like-Toxin-ProducingEscherichia coliof Human and Bovine Origins

Abstract

In this study we investigated whether the enterohemorrhagicEscherichia coli (EHEC) hemolysin gene ehxAcould be used as an indicator of pathogenicity in Shiga-like-toxin-producing Escherichia coli (SLTEC) isolates. The isolates in a collection of 770 SLTEC strains of human and bovine origins were assigned to group 1 (230 human and 138 bovine SLTEC isolates belonging to serotypes frequently implicated in human disease), group 2 (85 human and 183 bovine isolates belonging to serotypes less frequently implicated in disease), and group 3 (134 bovine isolates belonging to serotypes not implicated in disease). PCR amplification was used to examine all of the SLTEC isolates for the presence of ehxA and the virulence-associated geneseae, slt-I, and slt-II. The percentages of human isolates in groups 1 and 2 that were positive forehxA were 89 and 46%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive forehxA were 89, 51, and 52%, respectively. The percentages of human isolates in groups 1 and 2 that were positive foreae were 92 and 27%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive for eaewere 78, 15, and 19%, respectively. The frequencies of bothehxA and eae were significantly higher for group 1 isolates than for group 2 isolates. The presence of the ehxA gene was associated with serotype, as was the presence of the eae gene. Some serotypes, such as O117:H4, lacked both eae and ehxA and have been associated with severe disease, but only infrequently. Theslt-I genes were more frequent in group 1 isolates than in group 2 isolates, and the slt-II genes were more frequent in group 2 isolates than in group 1 isolates. In a second experiment we determined the occurrence of the ehxA andslt genes in E. coli isolated from bovine feces. Fecal samples from 175 animals were streaked onto washed sheep erythrocyte agar plates. Eight E. coli-like colonies representing all of the morphological types were transferred to MacConkey agar. A total of 1,080 E. coli isolates were examined, and the ehxA gene was detected in 12 independent strains, only 3 of which were positive for slt. We concluded that the ehxA gene was less correlated with virulence than the eae gene was and that EHEC hemolysin alone has limited value for screening bovine feces for pathogenic SLTEC because of presence of the ehxA gene in bovine isolates that are not SLTEC.

High numbers of Shiga toxin-producing found in bovine faeces collected at slaughter in Japan

“…These STEC isolates belonging to 40 different O:H serotypes and five non-typeable strains were separated into three pathogenic groups according to the grouping by Gyles et al [11] (Table 3). Group 1, which included stx1-and/or stx2-and eae-and hlyA-positive strains, consisted of 31 strains isolated from 25 beef cattle (5.2%) and 6 cows (6.2%).…”

“…Events related to slaughtered cattle significantly impact public health, although differences in the STEC 0378 prevalence rates in previous studies could be due to different seasonal and/or detection methods. Healthy cattle can be transient reservoirs of food-borne pathogens and many human infections result from ingestion of contaminated bovine food products [2,[8][9][10][11][12][13]. Therefore, data on the prevalence and concentration of STEC in animals at slaughter are critical for the design of risk-based hazard analysis for critical control point programs in order to control pathogens.…”

Virulence factors of Escherichia coli O157 and other Shiga toxin-producing E. coli

“…Although the majority of strains of E. coli O157 produce Stx2 only, amongst non-O157 STEC the toxin phenotype is much more variable with isolates producing Stx1alone occurring commonly. Isolates of serogroup O26 usually produce Stx1 ), isolates of serogroup O111 produce Stx1 and some produce Stx2 in addition (Willshaw et al 1992;Gyles et al 1998). There is considerable epidemiological evidence to indicate that STEC isolates producing Stx2 are more commonly associated with serious disease than isolates producing Stx1 or Stx1 and Stx2 (Kleanthous et al1990;Boerlin et al 1999).…”

PRODUCTION OF SHIGA‐LIKE TOXINS BY ESCHERICHIA COLI O157 : H7: EFFECTS OF OTHER BACTERIA AND ANALOGS OF QUORUM SENSING MOLECULES

“…In the U.S.A. and Canada, the majority of STEC infections have been caused by E. coli O157 : H7 or O157:H-minus, with 20-25% of HUS caused by non-O157 serotypes (Gyles et al 1998). STEC produces one or both of two toxic proteins known as SLT I and II, also referred to as verotoxins (VT-I and VT-2) or Shiga toxins (stx1 and stx2) (Smith and Scotland 1988;Gyles et al 1998).…”