Low Prevalence of Salmonella and Shiga Toxin–Producing Escherichia coli in Lymph Nodes of Australian Beef Cattle

Abstract

Salmonella contamination of ground beef has been viewed as originating from the surface of carcasses. Recent studies have identified lymph nodes as a potential source of Salmonella contamination because these tissues play an active role in containment of pathogens in the live animal and because some lymph nodes are unavoidably present in manufacturing beef trimmings or primal cuts that may be incorporated into ground beef. A survey was conducted of the microbiological status of lymph nodes from Australian cattle at the time of slaughter to determine the prevalence of microbiological contamination. Sets of lymph nodes (n = 197), consisting of the superficial cervical (prescapular), prepectoral, axillary, presternal, popliteal, ischiatic, subiliac (precrural), coxalis, and iliofemoralis (deep inguinal), were collected from five geographically separated Australian abattoirs over a period of 14 months. Samples were tested for the presence of Salmonella spp. and Shiga toxin-producing Escherichia coli by BAX PCR assay. Aerobic plate count, E. coli, and coliforms were enumerated with a lower limit of detection of 80 CFU per node. The observed prevalence of Salmonella within peripheral lymph nodes was 0.48% (7 of 1,464). Two of the seven lymph nodes in which Salmonella organisms were detected came from the same animal. Grass-fed, grain-fed, and cull dairy cattle were all found to have detectable Salmonella in lymph nodes. All Salmonella detections occurred during cooler months of the year. No Shiga toxin-producing E. coli were detected. Aerobic microorganisms were detected above the limit of quantification in 3.2% of nodes (median count 2.24 log per node), and E. coli was detected in 0.8% of nodes (median count 3.05 log per node). The low prevalence of Salmonella and low concentration of aerobic microorganisms in Salmonella-positive lymph nodes of Australian cattle at the time of slaughter suggest that the likelihood of lymph nodes contributing significantly to the presence of Salmonella in ground beef is low.

Non-Typhoidal Salmonella at the Human-Food-of-Animal-Origin Interface in Australia

“…According to recent investigations, lymph nodes are recognised as a potential reservoir of Salmonella, not only because of their active role in the containment of pathogens in animals, but also as a result of their unavoidable presence on carcasses during the trimming process at abattoirs [112]. A recent study of 1464 lymph nodes randomly selected from chilled cattle carcasses in five processing facilities in different Australian states (QLD, NSW, VIC, TAS and SA) found a low carriage of Salmonella (0.48%) amongst tested samples, with S. Typhimurium and S. Virchow being the predominant serovars [112]. Salmonella spp.…”

Metaphylactic antimicrobial effects on occurrences of antimicrobial resistance in Salmonella enterica, Escherichia coli and Enterococcus spp. measured longitudinally from feedlot arrival to harvest in high-risk beef cattle

“…Numerous studies have reported relatively low prevalence of Salmonella isolated from lymph nodes in cattle (Arthur et al, 2008; Bailey et al, 2017; Smith et al, 2021; Webb et al, 2017). Results from the current study support these findings as the average Salmonella prevalence isolated from lymph nodes was 8.4% (0.0–14.0%).…”

“…Furthermore, pathogenic E. coli are responsible for approximately 205,000 infections, 2500 hospitalizations and 20 deaths per year in the United States (Scallan et al, 2011). Both Salmonella and E. coli can contaminate carcasses from hides during processing; however, Salmonella is also able to colonize the lymphatic system and contaminate ground beef via trimmings (Arthur et al, 2008; Bailey, Huynh, Govenlock, Jordan, & Jenson, 2017). Therefore, the objective of this study was to investigate the link between concentrations of antimicrobial‐resistant Salmonella , Enterococcus and E. coli resulting from common metaphylactic antimicrobials.…”

Assessment of Microbiological Load of Small Ruminant Carcasses, Livers, Some Lymph Nodes, Tools and Knife Samples in Slaughterhouse

“…Besides, the studies conducted on carcass lymph nodes have shown that those nodes may harbor pathogenic microorganisms such as Salmonella spp. (4). It is known that completely removing lymph nodes from the carcass is impossible.…”