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United States Department of Agriculture

Agricultural Research Service

Title: Biofilm in milking equipment on a dairy farm as a potential source of bulk tank milk contamination with Listeria monocytogenes

item Latorre, A
item Van Kessel, Jo Ann
item Karns, Jeffrey
item Zurakowski, M
item Pradhan, A
item Boor, K
item Jayarao, B
item Houser, B
item Daugherty, C
item Schukken, Y

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2010
Publication Date: 5/20/2010
Publication URL:
Citation: Latorre, A.A., Van Kessel, J.S., Karns, J.S., Zurakowski, M.J., Pradhan, A.K., Boor, K.J., Jayarao, B.M., Houser, B.A., Daugherty, C.S., Schukken, Y.H. 2010. Biofilm in milking equipment on a dairy farm as a potential source of bulk tank milk contamination with Listeria monocytogenes. Journal of Dairy Science. 93:2792-2802.

Interpretive Summary: Listeria monocytogenes can cause listeriosis in humans. This illness, despite being underreported, is an important public health concern in the United States and worldwide. Listeria are ubiquitious in the environment and are frequently isolated from various locations in and around dairy farms. As a result, raw milk is occasionally contaminated with Listeria monocytogenes. Pasteurization is effective at destroying these organisms in the milk. Regular testing of milk, animals, and the environment of a dairy farm identified the presence of Listeria monocytogenes on the farm and frequently in the milk that was shipped from the farm. The data suggested that a bacterial biofilm was persisting in the milking equipment. The objective of this study was to determine if there was a L. monocytogenes-containing biofilm in the milking equipment that was the a source of this pathogenic bacterium in the milk. Samples were collected from the bulk milk tank, milking equipment, and milk room and tested for the presence of Listeria monocytogenes. Pieces were cut out of the milking equipment (plastic meters and rubber liners) and were scanned with high power microscopes. We observed numerous isolated bacteria and bacteria in a biofilm matrix on the milk meter surfaces. Our results are suggestive of a L. monocytogenes-containing biofilm. Hygiene in milking routine, adequate cleaning, and regular replacement of plastic and rubber materials in milking equipment would help dairy producers to prevent biofilms and subsequent milk contamination. Pasteurization of the milk would prevent exposure of the consumer to Listeria monocytogenes and other potential pathogens in milk.

Technical Abstract: The quality and safety of raw milk are important attributes for consumers of milk and dairy products. The objective of this study was to assess the presence of a L. monocytogenes biofilm in milking equipment as a potential source of bulk tank milk contamination on a dairy farm. Weekly tests to monitor somatic cell count, standard plate count, and preliminary incubation count in bulk tank milk samples were conducted from February 2004 to April 2008. Samples were collected from milking equipment and milking parlor premises in May 2007 and January, February, and March 2008 and analyzed for the presence of L. monocytogenes. Pulsed-field gel electrophoresis typing was conducted on L. monocytogenes isolates from the milking equipment, parlor and storage room floors, bulk tank milk, and in-line milk filters. In March 2008, pieces from milk meters and rubber liners from the milking line of the dairy farm were obtained to assess the presence of a biofilm using Scanning Electron Microscopy. The geometric mean of somatic cell counts, standard plate count, and preliminary incubation count in bulk tank milk samples during a 4 year-2 mo period was 233,301 cells/mL, 5,109 cfu/mL, and 18,778 cfu/mL, respectively. A total of 6 samples (15%) collected from milking equipment and the parlor were positive for L. monocytogenes in May 2007. Four (25%) and 1 (6%) of milk meters were L. monocytogenes-positive in January and February 2008, respectively. Two samples from milk meters collected in March 2008 were L. monocytogenes hly PCR positive, but were culture-negative. Combined AscI and ApaI restriction analysis yielded 6 PFGE types for 15 L. monocytogenes isolates obtained from milking equipment, parlor, bulk tank milk, and milk filters. Scanning Electron Microscopy of samples from the bottom cover of 2 milk meters, showed the presence of individual and clusters of bacteria, mainly associated with scratches on the surface. The presence of a bacterial biofilm was observed on the bottom covers of the two milk meters analyzed. These results are highly suggestive of the presence of a L. monocytogenes-containing biofilm. Prevention of the establishment of biofilms in milking equipment is a crucial step in fulfilling the requirement of safe, high-quality milk.

Last Modified: 07/22/2017
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