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United States Department of Agriculture

Agricultural Research Service

Research Project: DAIRY MANAGEMENT PRACTICES AND THE TRANSMISSION OF ZOONOTIC PATHOGENS IN MILK
2008 Annual Report


1a.Objectives (from AD-416)
Objective 1 - Determine the environmental compartments within dairy farming systems that support the survival of the zoonotic pathogens Salmonella enterica, Escherichia coli, and Listeria monocytogenes and characterize their contribution to the pathogen content of milk.

Objective 2 - Characterize the role of management practices in the introduction and maintenance of Salmonella enterica, Escherichia coli, and Listeria monocytogenes on dairy farms and evaluate changes in management practices that might reduce or eliminate pathogens.

Objective 3 - Use molecular typing methods to determine the relationship between isolates of Listeria, Salmonella, and pathogenic E. coli from dairy cows, the farm environment, and from bulk tank milk with those known to have caused human disease.

Objective 4 - Develop new methods for the rapid and sensitive detection of Bacillus anthracis and Listeria monocytogenes in bulk tank milk and milk products.


1b.Approach (from AD-416)
Although pasteurization and regulations controlling the processing of any products made with unpasteurized milk have an excellent record of assuring the biological safety of dairy products marketed in the US, there is increasing concern about the presence of zoonotic pathogenic microorganisms in raw milk. For various cultural and economic reasons the consumption of raw milk and desire for products made from raw milk seems to be increasing and outbreaks of food-borne gastrointestinal disease due to contamination of dairy products have been documented. This project focuses on the ecology of the zoonotic bacterial pathogens Salmonella, Listeria monocytogenes, and Escherichia coli on dairy farms in the Northeastern United States, and the relationship of the pathogens found in farm animals and the farm environment with those found in bulk tank milk from those farms. Intensive longitudinal sampling will be performed on three ‘typical’ farms with collection of milk, milk filters, blood, feces, and various environmental samples. We will analyze samples for the three pathogens by both molecular and culture techniques; collaborators will analyze samples for MAP, Campylobacter, and enterococci. Molecular characterization techniques will be used to equate any pathogens found in bulk tank milk with those found on the farm. Management changes will be suggested to the farmers and the results of those changes will be documented. The relationships between Listeria monocytogenes from the farm and those associated with human disease will be investigated. Methods will be developed for improved detection of bacterial pathogens in milk and environmental samples.


3.Progress Report
The past year has seen the use of sophisticated molecular tracking techniques to identify and characterize farm isolates of Listeria, Salmonella and E. coli. The longitudinal study of Salmonella, E. coli, and Listeria monocytogenes has continued with samplings adjusted as required to fully define outbreaks. A backlog of E. coli samples have been analyzed by real time PCR for the presence of virulence factors. Results indicate that unique shiga-toxin producing strains may populate each farm. The enterohemorrhagic strain O157:H7 was isolated from several samples. This, along with participation in the NAHMS 2007 dairy survey has helped to provide a national view of these pathogens on US dairy farms. It has also provided a mechanism to track pathogens in their various niches on farms. With access to three specific farms through our collaboration with four northeastern universities, the laboratory is in a position to become a leader in characterizing molecular epidemiological relationships among a host of important dairy pathogens. The samples taken from these three farms have been simultaneously analyzed by our university collaborators for the presence of Mycobacterium avium subsp. paratuberculosis (MAP). From these analyses, supershedder cows that excrete extremely large quantities of this organism have been identified. The progression of cows from a low shedding through a moderate shedding to the supershedder state has been documented. The major contribution of supershedders of MAP to the environmental load of this organism was documented as was the effect of culling these animals on the reduction of these loads. Samples from this study were used to validate a rapid PCR assay for the detection of Mycobacterium avium subsp. paratuberculosis in feces and manure which will dramatically reduce the time required to identify animals shedding the bacterium. Under National Program 108 (Food Safety) the following Component 1 topics apply to the current research plan: 1.1 Pathogens, Toxins and Chemical Contaminants Preharvest, 1.1.1 Methodology, 1.1.2 Epidemiology, 1.1.3 Ecology, Host Pathogen and Chemical Contaminants Relationships, and 1.1.4 Intervention Strategies.


4.Accomplishments
1. Pulsed Field Gel Electrophoresis (PFGE) was used to characterize Listeria monocytogenes found in feces, milk and environmental samples from a participant farm. Results suggested a role for biofilms in milking equipment as a source of persistent Listeria contamination in the bulk tank. Addresses National Program 108 component Ia i, ii,iii, and iv.

2. Supershedder cows that excrete extremely large quantities of Mycobacterium avium subsp. paratuberculosis have been identified. The progression of cows from a low shedding through a moderate shedding to the supershedder state has been documented. The major contribution of supeshedders of M. avium subsp. paratuberculosis to the environmental load of this organism was documented as was the effect of culling these animals on the reduction of these loads. Addresses National Program 108 component Ia i, ii, iii, and iv.


5.Significant Activities that Support Special Target Populations
None.


6.Technology Transfer

Number of Non-Peer Reviewed Presentations and Proceedings9

Review Publications
Van Kessel, J.S., Karns, J.S., Wolfgang, D.R., Hovingh, E., Schukken, Y. 2007. Longitudinal study of a clonal, sub-clinical outbreak of Salmonella enterica subsp. enterica Serovar Cerro in a US dairy herd. Foodborne Pathogens and Disease. 4(4):449-461.

Lu, Z., Mitchell, R.M., Smith, R.L., Van Kessel, J.S., Chapagain, P.P., Schukken, Y.H., Grohn, Y.T. 2008. The Importance of Culling in Johne’s Disease Control. Journal of Theoretical Biology. 254(2008):135-146.

Hang, J., Sundaram, A.K., Zhu, P., Shelton, D.R., Karns, J.S., Martin, P.A., Li, S., Amstutz, P., Tang, C.M. 2008. Development of a Rapid and Sensitive Immunoassay for Detection and Subsequent Recovery of Bacillus anthracis Spores in Environmental Samples. Journal of Microbial Methods. 73:242–246.

Last Modified: 7/28/2014
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