Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 8, 2007
Publication Date: November 1, 2007
Citation: Harhay, D.M., Arthur, T.M., Bosilevac, J.M., Guerini, M.N., Kalchayanand, N., Koohmaraie, M. 2007. Enumeration of Salmonella and Escherichia coli O157:H7 in ground beef, cattle carcass, hide and faecal samples using direct plating methods. Journal of Applied Microbiology 103(5):1657-1668. Interpretive Summary: Assuring the microbiological safety of beef is of great importance to consumers and to the beef processing industry. Prevalence of pathogens is routinely determined by industry and researchers. However, economical and high-throughput methods for assessing the levels of pathogens such as Salmonella and E. coli O157:H7 at steps throughout the beef production process have not been available. It would greatly increase the processing industry's ability to ensure safe product if they could routinely determine not only whether pathogens are present, but if so, at what level. Thus, we have developed and validated two rapid methods for the enumeration of Salmonella and E. coli O157:H7 from ground beef, carcass, hide and fecal samples. These methods can be performed in a fraction of the time and at a fraction of the cost of other methods. Consequently, their use would allow for more routine quantification data collection, thus providing additional information about the effectiveness of beef processing intervention strategies and aiding those involved in food safety research.
Technical Abstract: Aim: To develop and validate high throughput methods for the direct enumeration of viable and culturable Salmonella and Escherichia coli O157:H7 in ground beef, carcass, hide and fecal (GCHF) samples from cattle. Methods and Results: The hydrophobic grid membrane filtration (HGMF) method and the spiral plate count method (SPCM) were evaluated as rapid tools for the estimation of pathogen load using GCHF samples spiked with known levels of Salmonella Typhimurium. Validation studies showed that for a single determination of each sample type the low end of the detection limits was approximately 2.0 x 100 CFU g-1 for ground beef, 5.0 x 10-1 CFU (100 cm2) -1 for Salmonella and 8.0 x 10-1 CFU (100 cm2) -1 for E. coli O157:H7 on carcasses, 4.0 x 101 CFU (100 cm2) -1 for hide and 2.0 x 102 CFU g-1 for fecal samples. In addition, ground beef (n=609), carcass (n=1520) and hide (n=3038) samples were collected from beef processing plants and fecal samples (n=3190) were collected from feedlot cattle, and these samples were tested for the presence of Salmonella and E. coli O157:H7 by enrichment and enumeration methods. Conclusions: The direct enumeration methods described here are amenable to high throughput sample processing and were found to be cost effective alternatives to other enumeration methods for the estimation of Salmonella and E. coli O157:H7, in samples collected during cattle production and beef processing. Significance and Impact of the Study: Use of the methods described here would allow for more routine testing and quantification data collection, providing useful information about the effectiveness of beef processing intervention strategies.