Graduate Thesis Or Dissertation
 

Salmonella and other Enterobacteriaceae in dairy cow feed ingredients and their antimicrobial resistance

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ww72bf933

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  • Antimicrobial resistant Enterobacteriaceae might be introduced into dairy cows through the consumption of feeds and the microbes may eventually enter the human food supply. Thirty-two farms were selected at random from 43 commodity feeding dairy farms. Of the 32 farms selected, 12 farms agreed to participate in the study. In the prevalence survey, 50 feed ingredient piles were sampled for the presence of bacteria. In the repeated samples survey, 10 of the original 50 piles were sampled over time. Presumptive Salmonella positives (Assurance EIA Salmonella kit) were evaluated further using cultural methods and the Enterobacteriaceae Micro-ID system. The Kirby-Bauer technique was used to identify chloramphenicol, ciprofloxacin, ampicillin, streptomycin and tetracycline resistance. In addition, the repeated samples were tested for bacterial counts using the aerobic plate count method. In the prevalence study, 42.0% (21/50) of the 50 feed ingredient piles were presumptive positive for Salmonella. By the culture method and Enterobacteriaceae Micro-ID system, 2.0% (1/50) was confirmed as Salmonella el11eritidis and serogrouped as poly Group B, Group C₁. In the repeated samples study, 60.0% (6/10) of the piles were presumptive positive for Salmonella. By the culture method and the Enterobacteriaceae Micro-ID system, 20.0% (2/10) were confirmed as Salmonella enteritidis and serogrouped as poly Group B, Group C₁. In addition, 80.0% (8/10) feed ingredient piles showed an increase of bacterial counts during the two and three-week sampling periods. Fifty bacterial isolates were tested for antimicrobial resistance. Sixty-two percent (31/50) of the isolates demonstrated ampicillin resistance while 10.0% (5/50) displayed tetracycline resistance. The presence of antimicrobial resistant Enterobacteriaceae in feed ingredients raise concerns about health risks to food-producing animals such as dairy cows and subsequently to the consumer. Removal of aged feed ingredient piles should be frequent because of the observed increase in bacterial counts over a short period of time. The practice of frequent removal of aged feed ingredients may improve the overall hygiene of feed bins.
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