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Title: SURVEY OF BULK TANK MILK IN THE UNITED STATES FOR FOOD-BORNE BACTERIAL PATHOGENS

Author
item Van Kessel, Jo Ann
item Karns, Jeffrey
item MCCLUSKEY, B. - USDA, APHIS, FT. COLLINS
item Perdue, Michael

Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 6/25/2003
Publication Date: 6/25/2003
Citation: Van Kessel, J.S., Karns, J.S., McCluskey, B.J., Perdue, M.L. 2003. Survey of bulk tank milk in the United States for food-borne bacterial pathogens. [Abstract]. Joint Abstracts of the American Dairy Science and Society of Animal Science. p.369.

Interpretive Summary:

Technical Abstract: The consumption of raw milk and raw milk products has led to periodic disease outbreaks in the United States and more information is needed to assess the incidence of food-borne pathogens in bulk tank milk. The objective of this study was to determine the prevalence of Salmonella spp., Listeria monocytogenes, and Escherichia coli 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 and, when possible, shipped overnight on ice to the USDA-ARS laboratories in Beltsville, MD. Milk was directly plated on selective agars (MacConkey, Sorbitol MacConkey, XLT4, and Modified Oxford media) for direct bacterial enumeration and was enriched in selective broths (EC, tetrathionate, and modified Listeria enrichment broth) to increase detection sensitivity. After enrichment, cultures were streaked on selective media as above. Coliforms are often used as a general indicator of fecal contamination and coliforms were detected in 798 (92.7%) of the milk samples. Twenty two samples (2.6%) were culture-positive for Salmonella. When the Salmonella enterica isolates were serotyped, nine different serotypes were represented. The most common serotype was Montevideo which was found in seven milk samples. S. enterica Newport was isolated from four samples, S. enterica Muenster, S. enterica Meleagridis, S. enterica Cerro, and Salmonella 44:Z36, (Z38) were identified in each of two milk samples, and S. enterica Dublin, S. enterica Anatum and Salmonella Sal9,12:nonmotile were identified in one milk sample each. Listeria was detected in 90 milk samples (10.4%) and, based on hemolysis, approximately 50% of these were Listeria monocytogenes, the only species of Listeria pathogenic to humans. The results of this survey demonstrate that Listeria and Salmonella contamination of bulk milk is relatively low and infrequent. Although their presence presents a risk to consumers of raw milk and raw milk products, pasteurization kills each of these species.