Abstract
Similar to ruminants, swine have been shown to be a reservoir for Shiga toxin-producing Escherichia coli (STEC), and pork products have been linked with outbreaks associated with STEC O157 and O111:H-. STEC strains, isolated in a previous study from fecal samples of late-finisher pigs, belonged to a total of 56 serotypes, including O15:H27, O91:H14, and other serogroups previously associated with human illness. The isolates were tested by polymerase chain reaction (PCR) and a high-throughput real-time PCR system to determine the Shiga toxin (Stx) subtype and virulence-associated and putative virulence-associated genes they carried. Select STEC strains were further analyzed using a Minimal Signature E. coli Array Strip. As expected, stx2e (81%) was the most common Stx variant, followed by stx1a (14%), stx2d (3%), and stx1c (1%). The STEC serogroups that carried stx2d were O15:H27, O159:H16 and O159:H-. Similar to stx2a and stx2c, the stx2d variant is associated with development of hemorrhagic colitis and hemolytic uremic syndrome, and reports on the presence of this variant in STEC strains isolated from swine are lacking. Moreover, the genes encoding heat stable toxin (estIa) and enteroaggregative E. coli heat stable enterotoxin-1 (astA) were commonly found in 50 and 44% of isolates, respectively. The hemolysin genes, hlyA and ehxA, were both detected in 7% of the swine STEC strains. Although the eae gene was not found, other genes involved in host cell adhesion, including lpfAO113 and paa were detected in more than 50% of swine STEC strains, and a number of strains also carried iha, lpfAO26, lpfAO157, fedA, orfA, and orfB. The present work provides new insights on the distribution of virulence factors among swine STEC strains and shows that swine may carry Stx1a-, Stx2e-, or Stx2d-producing E. coli with virulence gene profiles associated with human infections.
Highlights
Shiga Toxin-producing Escherichia coli (STEC) are food-borne pathogens responsible for outbreaks and serious illness including hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS)
Selected swine STEC strains were analyzed using the FDAECID microarray, and the resulting serotypes were in agreement with the high-throughput real-time PCR (hrPCR)
Using state-of-the-art DNA-based techniques, this study provides new insights on the distribution of virulence factors in a heterogeneous collection of STEC isolated from the major porkproducing states of the U.S Stx2e-producing E. coli known to provoke mild diarrhea in humans carried different virulence factors than Stx2e-producing E. coli associated with edema disease in pigs; this finding suggests that Stx2e-producing E. coli that cause human illnesses may not have a swine origin (Sonntag et al, 2005)
Summary
Shiga Toxin-producing Escherichia coli (STEC) are food-borne pathogens responsible for outbreaks and serious illness including hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). STEC O157:H7 is the serotype that has most often been associated with outbreaks and severe forms of diarrhea; recently a number of non-O157 STEC serogroups that cause similar illnesses have emerged (Gould et al, 2013). Healthy swine may shed STEC, as demonstrated by several studies in which STEC were detected and isolated from swine fecal samples (Tseng et al, 2014b). Many of the investigations focused on serotype O157:H7; some studies tested for non-O157 STEC serogroups and identified serogroups previously associated with human cases of illness (Fratamico et al, 2004; Kaufmann et al, 2006; Tseng et al, 2014b). The possibility that swine can transmit pathogenic STEC to humans is supported by a few outbreaks linked to the consumption of pork products contaminated with STEC O157:H7, O157:NM, and O111:H- (Tseng et al, 2014b)
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