Date Full Report Received


Date Abstract Report Received



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Recent research has reported that if superficial lymph nodes from cattle carcasses were included into ground beef, there was an increased risk of Salmonella contamination of ground beef. This increased risk of contamination is because Salmonella is often at a higher prevalence in lymph nodes compared to other tissues. Pork products, particularly the head trim and other trim destined for ground pork, may contain lymph nodes. It is not unreasonable to speculate that pork, like beef, could be at increased risk of Salmonella contamination if lymph nodes are present in ground pork. To date, there has been limited to no research on Salmonella prevalence for chops and roasts, head trim, or trim intended for ground. We had preliminary data from a pork processing plant to indicate that a high percentage (98%) of cheek meat can be contaminated with Salmonella. The objectives of the present study were to: 1) determine the prevalence of Salmonella in head meat and trim intended for ground; 2) determine the serotypes (genetics) of isolates; 3) determine the antibiotic resistance of isolates; and 4) if justified, use molecular techniques to determine the relatedness of isolates that are of the same serotype, but display differences in antimicrobial patterns.

In this study, a large pork processing plant in the United States was sampled every other month for 11 months from January to November of 2015 to determine the prevalence, seasonality, diversity of serotypes, and antimicrobial susceptibility of Salmonella enterica isolated from cheek meat and head trim of swine carcasses. Each cheek meat and head trim collection period (January, March, May, July, September, and November) consisted of 25 samples collected on a Monday a.m., 25 on Monday p.m., 25 on Tuesday a.m., and 25 on Tuesday p.m., for a total of 100 cheek meat and 100 head trim samples (total of 200 for each period, total of 1200 for 6 periods). Tissues were cultured for Salmonella by described procedures using restrictive media and enrichment techniques. Salmonella isolates were serotyped by the National Veterinary Services Laboratories, Ames, IA, USA.

For the six sample periods, the percentages of SE-positive sample totals were 63% for cheek meat and 66% for head trim for a total of 774 isolates. The following were the results of isolations from cheek meat and head trim: January 94%; March 80%; May 53.5%; July 58.5%; September 46.5%; and November 55%. There was a large diversity of serotypes (25) which included isolates commonly found in swine and others that have rarely seen in swine. We identified 218 isolates (99 [58.8%] cheek meat and 119 [66.8%] head trim) that were multi-drug resistant (greater than 3 classes of antibiotics). Of the multi-drug resistant isolates, 90 were the type identified by a national program (National Antimicrobial Monitoring System) as Salmonella (ACSSuT phenotype) of increasing concern. Additionally, increased resistance to ciprofloxacin, a broad spectrum antibiotic used in human medicine, was observed in isolates and was attributed to genetic elements within the bacteria.
The results from this study suggest that pork products from the head have a high carriage rate of Salmonella which includes a diverse population of serotypes with a substantial number of isolates with elevated multi-drug resistance. Based on our results, there appears to be an effect of season with increased prevalence of Salmonella in cooler months (Jan., Mar., Nov. = 76.3%) compared to warmer ones (May, Jul., Sept. = 52.8%). The results from this study are beneficial to the industry because now there is a knowledge base of the extent of the Salmonella prevalence, the level of antibiotic resistance in Salmonella from swine products, the potential seasonality of Salmonella carriage in swine, and the wide range of serotypes and genetic diversity of Salmonella in swine products. With an increased knowledge of a problem comes the search for solutions. Intervention methods to reduce Salmonella in head products of swine processing plants are warranted and will be forthcoming. Overall pork wholesomeness will be improved and thus a “value added product”.
Roger B. Harvey, DVM, MS
2881 F&B Road
College Station, TX 77845
979-260-9259 (voice)