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Title: Prevalence of nontyphoidal Salmonella and Salmonella strains with conjugative antimicrobial-resistant serovars contaminating animal feed in Texas

item HSIEH, YI-CHENG - Texas A&M University
item Poole, Toni
item RUNYON, MICK - Texas A&M University
item Hume, Michael
item HERRMAN, TIMOTHY - Texas A&M University

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2015
Publication Date: 2/1/2016
Publication URL:
Citation: Hsieh, Y., Poole, T.L., Runyon, M., Hume, M.E., Herrman, T.J. 2016. Prevalence of nontyphoidal Salmonella and Salmonella strains with conjugative antimicrobial-resistant serovars contaminating animal feed in Texas. Journal of Food Protection. 79(2):194-204.

Interpretive Summary: Bacteria that cause disease (pathogens) in humans and animals are of major public health concern because diseases once thought under control are reappearing. Many public health officials blame the food animal industry for the emergence of pathogenic bacteria and down play the role of human medicine. Poultry and livestock producers have long been under pressure to limit the presence of pathogenic bacteria that are often present on retail meat products. However, with the emergence of multi-drug resistant pathogens there are new pressures to limit the use of antimicrobial agents. There is evidence that the reduction in antibiotic use alone is not sufficient to reduce antimicrobial resistant bacterial populations. The limitation of antimicrobial use poses an additional dilemma for producers for the maintenance of food animals as well as preventing the presence of pathogens on retail meat. There is an effort to determine the source of pathogens and antimicrobial resistant pathogens in food animal production. This study characterizes the antimicrobial resistance traits of 365 Salmonella isolates that were found in animal feed to determine if feed is a possible source of antimicrobial resistance contamination.

Technical Abstract: The objective of this study was to characterize 365 nontyphoidal Salmonella enterica isolates from animal feed. Among the 365 isolates, 78 serovars were identified. Twenty-four isolates (7.0%) were recovered from three of six medicated feed types. Three of these isolates derived from the medicated feed, Salmonella Newport, Salmonella Typhimurium var. O 5-(Copenhagen),and Salmonella Lexington var. 15þ (Manila), displayed antimicrobial resistance. Susceptibility testing revealed that only 3.0% (12) of the 365 isolates displayed resistance to any of the antimicrobial agents. These 12 isolates were recovered from unmedicated dry beef feed (n ¼ 3), medicated dry beef feed (n ¼ 3), cabbage culls (n ¼ 2), animal protein products (n ¼ 2), dry dairy cattle feed (n¼1), and fish meal (n¼1). Only Salmonella Newport and Salmonella Typhimurium var. O 5_(Copenhagen) were multidrug resistant. Both isolates possessed the IncA/C replicon and the blaCMY-2 gene associated with cephalosporin resistance. Plasmid replicons were amplified from 4 of 12 resistant isolates. Plasmids (40 kb) were Salmonella Montevideo and Salmonella Kentucky. Conjugation experiments were done using 7 of the 12 resistant isolates as donors. Only Salmonella Montevideo, possessing a plasmid and amplifying IncN, produced transconjugants. Transconjugants displayed the same antimicrobial resistance profile as did the donor isolate. Three isolates that amplified replicons corresponding to IncA/C or IncHI2 did not produce transconjugants at 30 or 378C. The results of this study suggest that the prevalence of antimicrobial-resistant Salmonella contaminating animal feed is low in Texas. However, Salmonella was more prevalent in feed by-products; fish meal had the highest prevalence (84%) followed by animal protein products (48%). Ten of the 35 feed types had no Salmonella contamination. Further investigation is needed to understand the possible role of specific feed types in the dissemination of antimicrobial resistant bacteria.