University of Guelph Researchers Characterize E. coli O157:H7 from Pigs in Ontario

October 5, 2005 — Dr. George Charbonneau

Dr. George Charbonneau provides the following summary of a survey conducted by Dr. Carlton Gyles and Dr. Robert Friendship at the Ontario Veterinary College at the University of Guelph. Although cattle are the major reservoir of E. coli O157:H7 there has been evidence of the presence of E. coli O157:H7 in a low percentage of pigs in Ontario.

The original survey was carried out in 2000-2002 . The study, which was supported by grants from the Ontario Ministry of Agriculture and Food, and the Natural Sciences and Engineering Research Council, was designed to determine whether the prevalence of E. coli O157:H7 in pig feces varied between warm and cold months. In addition, the concentrations of the bacteria shed by pigs were estimated and the E. coli O157:H7 isolates were characterized so that they could be compared with those implicated in disease in humans.

The results of the study were that E. coli O157:H7 was isolated from pigs on 7 of 88 farms. One of these farms yielded a nontoxigenic E. coli O157:H7. Of the 7 positive farms 6 were positive in the warm months from July to September while only 1 herd was positive in the month of February. When the samples that were positive for E. coli O157:H7 were tested quantitatively 13 had E. coli O157:H7 at a concentration of less than 50 organisms per gram of feces and 13 had the bacterium at 0.5 to 5.9 x 100 per gram of feces.

The characterization of the toxigenic E. coli O157:H7 isolates revealed that all had the stx2, eae, and ehx genes that are characteristic of E. coli O157:H7 that have been implicated in human disease. Most isolates also had the stx1 gene. Phage type 14 was most common.

Dr. Gyles and Friendship concluded from this study that E. coli O157:H7 is excreted in low concentrations by pigs on some farms and that the prevalence is higher in the warmer months. Some of the E. coli O157:H7 that were isolated are nontoxigenic and therefore of low public health significance. Other isolates, however, are similar to the E. coli O157:H7 that cause disease in humans. Pork has not been implicated as a source of infection in humans but a low level of environmental contamination may occur from swine feces.

Full Story: http://www.aps.uoguelph.ca/Swine-Report2005/Article-11.pdf