KEY TAKEAWAYS
- After collecting six different types of beef cattle peripheral lymph nodes from twelve harvest establishments in the eight BIFSCo regions, over the course of four seasons, it was learned that Salmonella risk (prevalence and quantity) was highest in the spring, in BIFSCo Region 3 (Arizona, New Mexico, Texas), and in superficial inguinal lymph nodes.
- Risk varies with season, region, and peripheral lymph node type.
- With further development of mathematical models, establishments in different regions will be able to quantitatively evaluate the Salmonella risk they have for including peripheral lymph nodes as raw materials for ground beef at different times of the year.
BACKGROUND
Bovine peripheral lymph nodes (PLNs) have been shown to be a source of
Salmonella contamination in beef carcasses. Since PLNs are encased in muscle and adipose tissue,
Salmonella cells that reside in them do not come into contact with surface interventions. Thus, when beef trim containing contaminated PLNs is processed into ground beef,
Salmonella cells from PLNs are exposed and are distributed throughout the ground beef. It has been shown to a limited extent that prevalence of
Salmonella in PLNs may vary by season, geography, and PLN type. Furthermore, it has been shown that the quantity of
Salmonella in PLNs may also vary by each of these factors. This leads to different risk profiles for
Salmonella in PLNs when season, geography, and lymph node type are considered. However, prior to this study, no comprehensive nationwide surveys of
Salmonella carriage in PLNs had occurred.
Six major PLNs (axillary, coxalis, popliteal, prescapular, superficial inguinal, and subiliac) were collected from beef cattle at twelve harvest establishments located across the eight BIFSCo regions in the United States. The study was conducted over the course of one year, with sampling performed at each facility in each of four different seasons. A total of fifteen samples were collected for each PLN type in each facility during each of the four different seasons. At the laboratory, each PLN was trimmed to remove excess fat and fascia, and was sterilized on the exterior using boiling water. The PLN was then pulverized inside of a bag and was enriched and incubated for
Salmonella growth. The enrichments were then analyzed for
Salmonella prevalence and quantity using the Hygiena BAX® System Real-Time PCR Assay for
Salmonella and its BAX® SalQuant™ application, which is able to produce a CFU/PLN value from a standard curve based on the strength of the CT value obtained from the Hygiena BAX® System Real-Time PCR Assay for
Salmonella. All presence/absence and quantity data were organized and analyzed by lymph node type, establishment, and season.
Overall, 4.26% of all PLNs collected were positive for
Salmonella prevalence, while only 1.98% produced a measurable quantity of
Salmonella. Within each PLN type, the percentage of samples that were positive for
Salmonella prevalence and the percentage of samples that had a measurable quantity of
Salmonella, respectively, were 0.85% and 0.00% for axillary PLNs, 2.65% and 1.53% for coxalis PLNs, 5.56% and 3.19% for popliteal PLNs, 6.23% and 2.23% for prescapular PLNs, 3.61% and 2.08% for subiliac PLNs, and 6.67% and 2.78% for superficial inguinal PLNs. Within each BIFSCo region, the percentage of samples that were positive for
Salmonella prevalence and the percentage of samples that had a measurable quantity of
Salmonella, respectively, were 2.22% and 0.28% for Region 1, 5.85% and 2.23% in Region 2, 8.51 and 4.40% for Region 3, 3.61% and 2.36% for Region 4, 3.49% and 2.51% for Region 5, 2.64% and 0.69% for Region 6, 1.94% and 0.28% for Region 7, and 4.72% and 1.11% for Region 8. Within each season, the percentage of samples that were positive for
Salmonella prevalence and the percentage of samples that had a measurable quantity of
Salmonella, respectively, were 3.80% and 1.11% for Winter, 5.73% and 3.00% for Spring, 5.25% and 2.73% for Summer, and 2.49% and 1.20% for Fall.
Implications
The data collected from this study are ultimately intended to be used for modeling the
Salmonella risk that is associated with including various PLNs into beef trim that is destined for use in producing ground beef. However, cursory analysis of the data from the study already indicate which regions, seasons, and PLN types had the highest prevalence of
Salmonella and highest percentage of PLNs with a measurable amount of
Salmonella present. Thus, establishments can already take this information and begin to assess what conditions will put them at highest risk. However, with further development of mathematical models, establishments will be able to perform quantitative assessments of risk for different combinations of regions, seasons, and lymph node types. These quantitative assessments of risk will then be able to be used in the future as justification for decisions made regarding removal or retention of PLNs. This study also employed the novel concept of using the Hygiena BAX® System Real-Time PCR Assay for
Salmonella SalQuant™ application to provide simple and fast quantification of
Salmonella in PLNs, which enabled a large amount of PLNs to be tested in this study in order to provide greater statistical relevance.