Detection and Enumeration of Clostridium difficile Spores in Retail Beef and Pork

Recent studies have identified Clostridium difficile in food animals and retail meat, and concern has been raised about the potential for food to act as a source of C. difficile infection in humans. Previous studies of retail meat have relied on enrichment culture alone, thereby preventing any assessment of the level of contamination in meat. This study evaluated the prevalence of C. difficile contamination of retail ground beef and ground pork in Canada. Ground beef and ground pork were purchased from retail outlets in four Canadian provinces. Quantitative and enrichment culture was performed. Clostridium difficile was isolated from 28/230 (12%) samples overall: 14/115 (12%) ground beef samples and 14/115 (12%) ground pork samples (P = 1.0). For ground beef, 10/14 samples (71%) were positive by enrichment culture only. Of the 4 ground beef samples that were positive by direct culture, 20 spores/g were present in 2 while 120 and 240 spores/g were present in 1 each. For ground pork, 10/14 (71%) samples were positive by enrichment culture only. Of the 4 ground pork samples that were positive by direct culture, 20 spores/g were present in 3 while 60 spores/g were present in 1. Ribotype 078 predominated, consistent with some previous studies of C. difficile in food animals. Ribotype 027/North American pulsotype 1 was also identified in both retail beef and pork. This study has identified relatively common contamination of retail ground beef and pork with C. difficile spores; however, the levels of contamination were very low.Clostridium difficile is an important cause of enteric disease in humans. It is the most commonly diagnosed cause of hospital- and antimicrobial agent-associated diarrhea in people, and recent evidence suggests that it may be emerging as an important community-associated pathogen (2, 5). In addition to humans, C. difficile can be found in the intestinal tracts of a variety of animal species, including food animals, such as cattle and pigs (7, 10, 13). Clostridium difficile has also been found in retail meat (11, 12, 17), and concerns about the role of food in the epidemiology of community-associated C. difficile infection (CA-CDI) have been expressed (5, 8, 15).Initial studies have reported isolation of C. difficile from 4.6 to 45% of retail meat samples (11, 12, 17). However, all studies have used broth enrichment protocols, which could detect very low spore numbers and provide no information about the number of organisms present in a sample. No studies have evaluated numbers of C. difficile spores in food. While the infectious dose is not known, an understanding of the level of contamination may be an important factor in determining the relevance of contamination of food. Additionally, the use of different methods between studies hampers comparison of results. Recently a study was performed to evaluate different methods for qualitative and quantitative detection of C. difficile (21). This study determined that the detection threshold of enrichment culture could be at least as low as 10 spores/g of meat. It also determined that quantitative culture can accurately determine the level of contamination in experimentally inoculated meat samples, albeit with a higher detection threshold. The objective of this study was to determine the prevalence of C. difficile contamination of retail ground beef and ground pork using both qualitative and quantitative methods.