Location: Food and Feed Safety Research
Title: Development of a transdermal Salmonella challenge model in calves Authors
|Loneragan, Guy -|
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2013
Publication Date: July 10, 2013
Citation: Edrington, T.S., Loneragan, G.H., Hill, J.E., Genovese, K.J., He, L.H., Callaway, T.R., Anderson, R.C., Brichta-Harhay, D.M., Nisbet, D.J. 2013. Development of a transdermal Salmonella challenge model in calves. Journal of Food Protection. 76:1255-1258. Interpretive Summary: Cattle may contain the bacteria Salmonella that can make people sick. Peripheral lymph nodes in these cattle may contain Salmonella that protects it from interventions in the slaughter plant. Salmonella in these lymph nodes is more prevalent in the summer months and declines in the winter, suggesting flies may be a vector for transmission. However it was unknown if the lymph nodes could acquire Salmonella through fly bites. Results of this research demonstrated that Salmonella can be transferred to the peripheral lymph nodes following a mimicked fly bite. Further research tested a Salmonella vaccine to prevent lymph node uptake following dermal challenge. The results indicate some effectiveness of the vaccine, but further research is warranted. Prior to expensive live animal field studies, our experimental model may be used to pre-screen likely intervention strategies.
Technical Abstract: The peripheral lymph nodes (PLN) in cattle may contain Salmonella and thus are a potential source of contamination for ground beef. Research on the prevalence of Salmonella in these lymph nodes suggests that regional and seasonal differences occur with the seasonal fluctuations, a reflection of fly populations. However, it is not known if Salmonella-positive PLN arise from transdermal Salmonella inoculation. Therefore, three pilot studies were conducted to develop a cattle model in which mimicked fly bites could be examined for their potential to transmit Salmonella to the PLN. In the first study, Holstein steers were administered Salmonella via needle and syringe intra-dermally above the metacarpus and metatarsus. Salmonella-positive PLN were cultured from the inoculated animals while the control steers were all Salmonella-negative. Swelling and lameness in the treated steers indicated some of the Salmonella was delivered subcutaneously, therefore the second and third pilot studies utilized an allergy skin testing device for Salmonella inoculation. Steers were administered the Salmonella in the lower legs as above and necropsied up to 8 days later. Superficial cervical and popliteal lymph nodes were Salmonella-positive in both studies and no swelling or lameness was observed in any of the treated steers. The final experiment examined the ability of a commercially-available SRP Salmonella vaccine to prevent Salmonella-positive PLN following intradermal inoculation. Sixteen steers were allotted to control or vaccine treatments and within each treatment, inoculated intra-dermally with either Salmonella, Montevideo, or Newport 14 days following the administration of the vaccine booster. Three and six days following Salmonella inoculation, steers were necropsied and PLN cultured. No treatment differences were observed in calves inoculated with Salmonella Montevideo except for a reduction (P < 0.05) in the percentage of right sub-iliac lymph nodes that were culture-positive in the vaccine treatment. The vaccine treatment decreased (P < 0.05) the percentage of left superficial cervical lymph nodes that were positive compared to control steers inoculated with Salmonella Newport. When lymph node data was combined and analyzed as a percentage of all PLN Salmonella-positive, the vaccine treatment tended (P < 0.10) to lower the percentage that were Salmonella-positive. No swelling or lameness was observed in any of the cattle. Results herein demonstrate the transdermal uptake and transmission of Salmonella to the PLN in cattle and present an animal model for the evaluation of potential pre-harvest interventions to prevent and/or eliminate lymph node acquisition of Salmonella.