Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2004
Publication Date: 9/1/2004
Citation: Van Kessel, J.S., Karns, J.S., Gorski, L.A., McCluskey, B.J., Perdue, M.L. 2004. Prevalence of Salmonellae, Listeria monocytogenes and fecal coliforms in bulk tank milk on U.S. dairies. Journal of Dairy Science. p. 2822-2830.
Interpretive Summary: Raw milk may contain bacteria that are pathogenic to humans. Although pasteurization will kill these bacteria, many people still drink raw milk or eat raw milk products. The objective of this study was to determine how often raw milk from U.S. dairies is contaminated with two specific types of bacteria (Salmonellae, and Listeria monocytogenes) and one bacterial group (fecal coliforms). Most (95%) of the samples contained fecal coliforms. Salmonellae were isolated from 2.6% of the raw milk samples and L. monocytogenes was isolated from 6.5% of the samples. Serotypes of the L. monocytogenes isolates were similar to those common in human outbreaks. Although the prevalence of L. monocytogenes and Salmonella were low, these pathogens represent a potential risk to consumers of raw milk and raw milk products.
Technical Abstract: The objective of this study was to determine the prevalence of Salmonella, Listeria monocytogenes, and fecal coliforms in bulk tank milk in the United States. As part of the NAHMS Dairy 2002 survey, 861 bulk tank milk samples were collected from farms in 21 states. Milk was directly plated on selective agars for direct bacterial enumeration and was enriched in selective broths to increase detection sensitivity. Somatic cell counts (SCC) and total bacterial counts (TBC) were also determined. Coliforms were detected in 95% (818/860) of the samples and the average SCC was 295,000 cells/ml. Twenty two samples (2.6%) were culture-positive for Salmonella and nine serotypes were identified: Montevideo (7), Newport (4), Muenster (2), Meleagridis (2), Cerro (2), 44:Z36 (Z38) (2), Dublin (1), Anatum (1), and 9, 12:nonmotile (1). L. monocytogenes were isolated from 56 (6.5%) samples and serotyping of these isolates yielded six serotypes (1/2a, 1/2b, 3b, 4b, 4c, and 4d). Of the L. monocytogenes isolates, 91% were serotypes 1/2a, 1/2b, and 4b, the most common human clinical isolates. Regional differences in L. monocytogenes and Salmonella prevalence were observed but more studies are needed to determine the validity of these differences. There were no apparent relationships between SCC or TBC and incidence of Salmonella or L. monocytogenes. Although the prevalence of L. monocytogenes and Salmonella were low, these pathogens represent a potential risk to consumers of raw milk and raw milk products.