11 May 2012

3 minute read

The presence of indistinguishable strains of Clostridium difficile in humans, food animals and food, as well as the apparent emergence of the food-animal-associated ribotype 078/toxinotype V as a cause of community–associated C. difficile infection have created concerns about the potential for foodborne infection.

In a paper published in BMC Veterinary Research recently, Marcio C. Costa of the University of Guelph and co–authors there and at the Public Health Agency of Canada, Guelph and Saskatoon, Feedlot Health Management Services Ltd. and Colorado State University in the US report that C. difficile infection (CDI) in humans is a serious and increasingly problematic disease. Its epidemiology has changed over the last 10 years, with increasing incidence, mortality and relapse rates in humans. Furthermore, while it is classically a hospital–associated pathogen predominantly affecting elderly individuals, there are increasing reports of community–associated CDI, including disease in younger individuals and people with few or no traditional risk factors.

The source of infection for community-associated cases of CDI remains uncertain, the researchers say. However, foodborne infection has been suggested and there are reasonable concerns about zoonotic and foodborne transmission following reports of isolation of C. difficile from animals. Concern has been raised by the apparent increase in CDI in humans caused by the C. difficile ribotype 078, since this is the dominant strain among food animals and it has been recovered from meat products.

Costa and co-authors report that while studies have reported C. difficile in calves, studies of cattle closer to the age of harvest are required.

Four commercial feedlots in Alberta (Canada) were enrolled for their study. Faecal samples were collected at the time of arrival and after acclimatisation (less than 62, 62 to 71 or more than 71 days on feed). Selective culture for C. difficile was performed, and isolates were characterised by ribotyping and pulsed-field gel electrophoresis. A logistic regression model was built to investigate the effect of exposure to antimicrobial drugs on the presence of C. difficile.

C. difficile was isolated from 18 of 539 animals at the time of feedlot arrival (CI=2.3-6.1) and from 18 of 335 cattle at mid-feeding period (CI=2.9-13.1).

Overall, there was no significant difference in the prevalence of C. difficile shedding on arrival versus mid-feeding period (P=0.47). No association between shedding of the bacterium and antimicrobial administration was found (P=0.33). All the isolates recovered were ribotype 078, a toxinotype V strain with genes encoding toxins A, B and CDT. In addition, all strains were classified as NAP7 by pulsed field gel electrophoresis (PFGE) and had the characteristic 39 base pairs deletion and upstream truncating mutation on the tcdC gene.

It is apparent that C. difficile is carried in the intestinal tracts of a small percentage of feedlot cattle arriving and later in the feeding period and that ribotype 078/NAP7 is the dominant strain in these animals, concluded Costa and co–authors.

They added that herd management practices associated with C. difficile shedding were not identified and that further studies of the potential role of antimicrobials on C. difficile acquisition and shedding are required.