Incidence of Escherichia coli 0157:H7, Listeria monocytogenes, and Salmonella species on a Tennessee dairy farm

Author

Theresa L. Ervin

Date of Award

8-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

Ronald E. Yoder

Committee Members

F. Ann Draughon, Raj Raman, Robert T. Burns

Abstract

In response to public awareness of foodbome pathogens due to recent outbreaks of illness, and to the call for control of pathogens to begin on the dairy farm, a study was conducted on the survival and movement of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella species on a dairy farm in middle Tennessee. Samples were taken from various locations around the farm, including water samples from up- and down-stream in a creek running through the farm. Samples were also collected from free stall bedding, silage, separator liquids, separator solids, pumped liquid from a holding pond, feed, and bulk tank milk. Three samples were taken monthly at each location for 12 months. These samples were evaluated to determine possible sources and reservoirs of the pathogens on the dairy farm and to identify seasonal trends in pathogen presence. No Escherichia coli O157:H7 was found in any of the samples. Listeria monocytogenes was present most often in the pumped holding pond liquid and the separator liquid, with each producing positives in 31% of the samples. The bedding and silage samples were negative for the pathogen for the entire testing period. The up- and downstream samples each produced one positive sample, in December and September respectively. Listeria monocytogenes was found in the November sample of irrigated pasture soil; irrigated soil samples were also collected during September. A possible seasonal trend was identified in Listeria monocytogenes, with more positive samples collected during cooler months. In contrast to Listeria monocytogenes, Salmonella were found widely across the farm. Pumped liquid exhibited the highest incidence of Salmonella occurrence with 34 (94%) of the 36 samples testing positive. The manure solids separator was also identified as a potential control point with separator liquid and separator solid samples returning Salmonella,/em> positives on 72% and 81%, respectively. The downstream samples yielded 27% positives, whereas the upstream samples identified isolates in 42% of the samples collected. All of the sampling locations yielded at least two positive Salmonella samples. Three times within the testing period comparative samples were collected from within a nearby city to supply a reference for pathogen presence. The comparative stream samples from the city yielded one Listeria monocytogenes positive sample for each location in September. Comparative samples collected below a waste treatment discharge provided 44% positive Salmonella isolates. After testing was completed, locations associated with waste, such as the manure solids separator and the holding pond, were identified as potential control points for Listeria monocytogenes and Salmonella. Based on these findings, possible methods for reducing pathogen presence on the farm include composting the separator solids prior to being used for bedding and possibly irrigating silage corn with holding pond water. The farm will never be a sterile environment, but pathogen concentrations can possibly be reduced by setting up critical points throughout the farm and controlling the use of the products at these points.