Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2009
Publication Date: October 21, 2009
Citation: Karns, J.S. 2009. Salmonella, E. coli and Listeria in raw milk, a tale of 3 dairy farms in the northeast US. Food Science and Nutrition Department, North Carolina Agricultural and Technical State University.
Salmonella enterica, pathogenic forms of Escherichia coli and Listeria monocytogenes are important food borne bacterial pathogens in the United States. Although not generally associated with dairy products there have been occasional cases of outbreaks of foodborne disease due to contaminated dairy products. In addition, cull dairy cattle are a significant source of beef. Our laboratory has been participating in a 5 year longitudinal study of these three organisms on working dairy farms in New York, Pennsylvania, and Vermont as part of a larger study which also studies Mycobacterium avium Paratuberculosis, the causative agent of Johne’s disease in dairy cattle. Environmental samples are taken 4 times a year on each farm and fecal grabs are taken from each cow twice a year. Milk and in-line milk filters are sampled weekly. All samples are subjected to enrichment culture for the selected pathogens and the enrichments are either cultured onto selective media (Listeria) or analyzed by real-time PCR (Salmonella and pathogenic E. coli). Salmonella has been found on all three farms at various times. On two farms the Salmonella outbreaks have been transient events affecting only a few cows however, on one farm we have documented a long-term Salmonella infection by serotypes that seem to act as commensal organisms in cows with as many as 90% of the cows in the herd shedding the organism with no apparent adverse effects. When high numbers of cows are shedding Salmonella the organism is frequently found in the raw milk from the bulk tank. Listeria monocytogenes was found to be a long-term problem on one farm, with frequent isolation from the bulk tank milk and in-line milk filters. The most likely source of the contamination was fecal matter but the persistence seemed to be due to biofilms in the milking equipment. Shiga-toxigenic E. coli have been detected on all three farms but rarely in the raw milk. EHEC serotype O157:H7 has been detected sporadically but does not seem to be a serious issue on there dairy farms. These results are discussed in the context of national surveys of these organisms in bulk tank milk and the safety of raw milk and products made from raw milk.