Salmonella, a very important bacterium to study, causes Salmonellosis in animals and poultry, and is one of the main foodborne pathogens associated with meat and meat products. Each year in the U.S., there are approximately 1.4 million cases of human Salmonellosis and 600 reported deaths due to Salmonella-related food poisoning. In swine, clinical Salmonellosis is a common condition, causing great economic loss in the pork industry.
An American study showed that two thirds of swine operations in some states are Salmonella positive. Salmonella typhimurium DT 104 is the type of Salmonella that causes human sickness or even death. Data from the Animal Health Laboratory of the University of Guelph showed that from January to September 1999, there were 19 swine herds in Ontario that were diagnosed with Salmonella typhimurium DT 104. Gut and affiliated lymph tissues are the primary reservoirs for Salmonella in pigs. The bacteria can be passed onto carcasses in packing plants due to fecal spillage during evisceration. Since the gut is a major reservoir for Salmonella, reducing their concentration in pigs at the farm level and before processing is one of many critical control steps that should be taken. Fewer Salmonella in the gut and feces can significantly reduce the chance of carcass contamination in packing plants and therefore result in safer pork.
A recent laboratory study (Journal of Food Protection, 2001), conducted by USDA scientists in Texas, demonstrated that when fed in low doses, sodium chlorate kills Salmonella typhimurium and E. coli O157: H7 in pigs and cows. This finding provides a potential practical approach for reducing on farm concentrations of these pathogens. How does sodium chlorate work to kill the bugs? Salmonella and E. coli O157: H7 contain an enzyme known as a respiratory nitrate reductase. This enzyme coincidentally converts the chlorate (ClO3-), an analog of nitrate, to chlorite (ClO2-), which in turn kills both pathogens. Since beneficial bacteria in the intestinal tract do not have respiratory nitrate reductase, they are not affected by the addition of chlorate.
In two separate experiments, a total of 45 of the 26 to 29 day old weaned pigs were infected orally with 8 x 107 CFU of Salmonella typhimurium. The pigs were randomly placed into respective treatment groups and kept in separated pens. The pigs in each treatment group were then fed up to 0.04 grams of sodium chlorate per kilogram of body weight at 8 hours and again at 16 hours after Salmonella infection. The pigs were put down at 8 hour intervals (five per group) after receiving the last treatment of sodium chlorate. Fecal samples were then collected by necropsy, which were cultured qualitatively and quantitatively for Salmonella and other bacteria.
Results from the experiments showed that treatment with chlorate produced a significantly large effect on Salmonella concentration. Within 16 hours of the last chlorate treatment, a 150-fold reduction in the number of intestinal Salmonella was observed. In addition, a treatment by time interaction was observed, suggesting that the chlorate effect was concentration dependent. The research is still in the early stage and this new approach needs to be approved by the FDA before it can be widely used by the U.S. livestock industry. Possible applications include feeding chlorate to animals before they are transported to slaughter or adding it to drinking water before loading or at lairage.
By Wayne Du - Pork Quality Assurance Program Lead/OMAFRA