Abstract
Six visits were conducted to four dairy farms to collect swab, liquid, and solid dairy farm environmental samples (165 to 180/farm; 15 sample types). The objective of the study was to determine on-farm sources of Campylobacter jejuni, Salmonella spp., Listeria monocytogenes, and Shiga toxin-producing Escherichia coli (STEC), which might serve as reservoirs for transmission of pathogens. Samples were analyzed using mostly U.S. Food and Drug Administration's Bacteriological Analytical Manual protocols; however, Salmonella spp., L. monocytogenes and STEC were co-enriched in universal pre-enrichment broth. Campylobacter jejuni were enriched in Bolton broth containing Bolton broth supplement. Pathogens were isolated on agar media, typed biochemically, and confirmed using multiplex polymerase chain reaction protocols. Campylobacter jejuni, Salmonella spp., L. monocytogenes, Sorbitol-negative (SN)-STEC O157:H7, and sorbitol-positive (SP)-STEC, respectively, were isolated from 5.06%, 3.76%, 6.51%, 0.72%, and 17.3% of samples evaluated. Whereas other pathogens were isolated from all four farms, SN-STEC O157:H7 were isolated from only two farms. Diverse serotypes of SP-STEC including O157:H7, O26:H11, O111, and O103 were isolated. None of the five pathogen groups studied were isolated from bulk tank milk (BTM). Most pathogens (44.2%) were isolated directly from fecal samples. Bovine fecal samples, lagoon water, bedding, bird droppings, and rat intestinal contents constituted areas of major concern on dairy farms. Although in-line milk filters from two farms tested positive for Salmonella or L. monocytogenes, none of the pathogens were detected in the corresponding BTM samples. Good manure management practices, including control of feral animals, are critical in assuring dairy farm hygiene. Identification of on-farm pathogen reservoirs could aid with implementation of farm-specific pathogen reduction programs.
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