ARS | Publication request: Prevalence of Salmonella and Listeria monocytogenes in Raw, Bulk Tank Milk From US Dairy Farms

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: March 5, 2008
Publication Date: August 4, 2008
Citation: Van Kessel, J.S., Karns, J.S., Lombard, J.E. 2008. Prevalence of Salmonella and Listeria monocytogenes in Raw, Bulk Tank Milk From US Dairy Farms. 95th Annual Meeting of the International Association for Food Protection (IAFP) August 3-6, 2008, Columbus, Ohio. Paper No. P2-21.

Technical Abstract: Listeria monocytogenes and Salmonella are frequently isolated from dairy cattle and have been identified as bulk milk contaminants. The objective of this study was to determine the prevalence of L. monocytogenes and Salmonella in bulk milk from US dairy farms. As part of the NAHMS Dairy 2007 survey, 541 milk samples and 523 in-line filters were collected from farms in 17 states and shipped overnight to the laboratory. Milk filters were pummeled with an equal weight of buffered peptone water. Filter extract and milk were enriched in selective broths. Listeria enrichments were struck on modified Oxford medium. The presence of Salmonella was determined by real time PCR and positive enrichment broths were struck onto selective agar for isolation of Salmonella. Presumptive Listeria and Salmonella isolates were confirmed on several selective agars. L. monocytogenes was distinguished from other Listeria species via the presence of phosphatidylinositol-specific phospholipase. PCR analysis indicated that Salmonella was present in 13.9% of the milk samples and 33.3% of the filters. Salmonella isolates were obtained from 6.7% of the milk samples and 19.9% of the filters. Twenty-five Salmonella serotypes were identified with the most common being Cerro (34), Kentucky (20), Muenster (14), Newport (10), Anatum (10), Montevideo (8), and Mbandaka (8). Listeria was detected in 7.8% of the milk samples and 26.8% of the filters while L. monocytogenes was detected in 4.3% of the milk samples and 6.5% of the filters. Salmonella prevalence in bulk milk is higher than estimated in the NAHMS 2002 dairy survey (2.6% culture positive; 11.8% PCR positive). L. monocytogenes was more prevalent in the 2002 survey (6.5%). Milk filters were not collected during the 2002 study but results from the current study indicate that milk filter analysis is more sensitive for detecting the presence of Salmonella and L. monocytogenes than bulk milk analysis.