Masters Theses

Date of Award

8-2002

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

F. Ann Draughon

Committee Members

P. Michael Davidson, Alan G. Mathew

Abstract

This research was conducted as two separate studies. The objective of the first study was to determine the major sources of Listeria monocytogenes and Listeria spp. associated with dairy cows, calves, and the farm environment. Isolation and confirmation of Listeria spp. was performed according to the Food and Drug Administration's Bacteriological Analytical Manual(AOAC). Modifications in isolation protocol were made to determine the prevalence and optimal isolation media (MOX or PALCAM) for the detection of L. monocytogenes (LM) and other Listeria spp. from dairy farm cattle and environmental samples. Cows( n=30)( foremilk, hair,oral, rectal, and teats) and calves (n=30) (hair, oral, and rectal) were sampled over a six-month period. The environmental samples (n=20) included bulk tank milk, air, trough water (n=22),feed, bedding, farmyard soil, grain, silage, insects, milking equipment (cups, hoses, inflations), and river water (n=10) adjacent to the dairy farm. LM was more frequently isolated from the dairy farm environment (17.3%) than from dairy cows (13.1%) or calves (12.2%). All dairy cow, calf, and farm environmental sites, except for air, tested positive for the presence of LM. Based on the enrichment and isolation protocols evaluated in this research, the authors recommend that MOX be used for all sample types associated with dairy farms with the exception of soil, rectal, and trough water in which PALCAM gives better isolation of L. monocytogenes. The development of a stepwise "on-farm" pathogen reduction program to control LM in dairy cows and calves will be a challenge due to the frequent occurrence of LM in the environment of dairy cows. Protocols for sampling should be selected which can consistently detect the presence of LM. In the second study, Listeria isolates (n=48) from a total of 548 cow, 454 calf, and 1,556 University of Tennessee Dairy Farm environmental isolates obtained during a 1999-2001 survey were submitted for automated ribotype analysis utilizing the Riboprinter microbial characterization system, alpha version (E. 1. Du Pont de Nemours & Co., Inc.). This investigation compared Listeria ribotypes (RTs) obtained from dairy cows, calves, and farm environmental isolates to a database of clinical isolates of Listeria associated with animal miscarriages and foodbome listeriosis. Riboprint patterns of 17 of the 48 isolates confirmed the identity as Listeria spp. based upon the Du Font (EcoRI) database. Fourteen Listeria RTs were discriminated. The 14 RTs were identified as 5 L. monocytogenes RTs (1029, 1041, 1051, 1052, and 1XXXX, a confidential isolate held by Du Font), 5 L innocua RTs (1005, 1006, 1009, 1010, and 1019), and 4 L. welshimeri RTs (1072, 1073, 1074, and 1079). Of the isolates selected for ribotyping, L. monocytogenes was detected phenotypically from grain, feedbunk, corn silage, raw bulk tank milk, air, soil, bedding, river water adjacent to the midpoint of the farm, milking equipment, calf oral and hair samples, as well as cow anal, oral, and teat samples. According to ribotype analysis, optimal detection sites for the presence of L. monocytogenes were from the cows' teats, the oral cavity of calves, com silage, raw bulk tank milk, and from the river water adjacent to the midpoint of the farm. Knowledge of the agricultural ecosystem, the taxonomy of Listeria strains, and careful attention to detailed isolation and confirmation protocols were essential to prevent misidentification of Listeria spp. when initiating and conducting an on-farm pathogen-reduction program.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS