Experimental rapid infection in market swine following exposure to a Salmonella contaminated environment

The objective of these experiments was to evaluate the possibility of swine becoming infected with Salmonella Typhimurium after a short time interval in a contaminated environment. Two experiments were conducted. Experiment 1 consisted of five trials with eight market weight swine. Pigs were necrops ied at 2 (n = 10), 3 (n = 10) and 6 (n = 5) hours after continuous exposure to an environment contaminated with feces shed by swine intranasally inocu lated with nalidixic acid-resistant Salmonella Typhimurium (chi 4232). In E xperiment 2, pigs were necropsied after 30 minutes (n = 6), 60 minutes (n = 6), 2 hours (n = 6), and 6 hours (n = 3). In addition, control animals wit h no exposure were also necropsied in both experiments. At necropsy, the su perficial inguinal, ileocecal. and mandibular lymph nodes, as well as cecal contents, distal ileum portion, and feces were evaluated. All samples were cultured for the presence of the nalidixic acid-resistant Salmonella. Fece s deposited on the floor by intranasally inoculated swine were mixed with w ater to form slurry with a resulting load of 10(3)-10(5) Salmonella Typhimu rium CFU per gram. In Experiment 1, 80% percent of animals with a 2-hour, 6 0% of animals with a 3-hour, and 100% of animals with a 6-hour exposure to this slurry had at least one sample test positive for the marked Salmonella Typhimurium strain. In Experiment 2, 50% of the 30 minute. 50% of the 60 m inute, and 33% of the 2-hour exposed pigs had at least one sample test posi tive. These experiments show that market swine can become infected during r outine resting or holding periods when exposed to relatively low levels (10 (3) CFU) of Salmonella in the simulated pre-slaughter environment, and that exposure times as short as 30 minutes are sufficient to produce contaminat ed gastrointestinal tracts. They also demonstrate the high risk of holding pigs longer than six hours. Intervention at this step in the swine producti on process may have a significant impact on the safety of pork products.