Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/20/2007
Publication Date: 8/1/2007
Citation: Ladely, S.R., Harrison, M.A., Cray, P.J., Berrang, M.E., Englen, M.D., Meinersmann, R.J. 2007. Development of Macrolide Resistant Campylobacter in Broilers Administered Subtherapeutic or Therapeutic Levels of Tylosin. Journal of Food Protection. 70(8):1945-1951. Interpretive Summary: The use of antimicrobials, particularly those commonly used to treat infections in humans, in food animal production has become a source of debate in recent years. Concerns regarding the emergence of resistant bacterial pathogens resulting from the use of antimicrobials in animals, and the potential transfer of resistant strains from food products to humans has led to changes in antimicrobial use in food animal production worldwide. However, limited data are available regarding the development of resistance from administration of antimicrobials for growth promotion (subtherapeutic) or disease control (therapeutic) in food animal production. The effect of tylosin administration (FDA approved levels) on susceptibility of C. jejuni and C. coli isolated from ceca of treated broilers was evaluated. Macrolide resistance was observed at a higher frequency among C. coli (70.8%) compared to C. jejuni (36.8%), recovered from medicated broilers. In addition, macrolide resistance was observed at a significantly higher frequency when tylosin was administered at subtherapeutic levels (62.7 %), compared to administration of therapeutic levels (11.4%). These data will aid animal production scientists and public health officials in evaluating the ramifications of various antimicrobial administration options, and facilitate the development of risk assessment models addressing antimicrobial use in food animal production.
Technical Abstract: The use of antimicrobials in food animal production, particularly those commonly used to treat infections in humans, has become a source of debate in recent years. However, limited data are available regarding the development of resistance following subtherapeutic or therapeutic administration of antimicrobials in animal production. The objective of this study was to evaluate the effect of administration of therapeutic and subtherapeutic levels of tylosin on erythromycin susceptibility of C. jejuni and C. coli isolated from ceca of treated broilers. In three replicate studies, day-of-hatch chicks were exposed to macrolide susceptible C. jejuni or C. coli. At two weeks of age, tylosin was administered at subtherapeutic (22 ppm, continuously in the diet) or therapeutic levels (529 ppm in drinking water for 5 days). Broilers were sacrificed weekly. Total and erythromycin resistant Campylobacter were enumerated from individual ceca with contents. Overall erythromycin resistance was observed at a higher frequency (P<0.01) among C. coli isolates 70.8% compared to C. jejuni isolates 36.8% following tylosin administration. Across Campylobacter species erythromycin resistance was observed at a higher frequency (P<0.001) when tylosin was administered at subtherapeutic (62.7%), compared to therapeutic levels (11.4%). Subtherapeutic administration resulted in recovery of 83.3% and 56.1% erythromycin resistant isolates compared to only 33.3% and 7.9% of the isolates expressing erythromycin resistance following administration of therapeutic levels, for C. coli and C. jejuni, respectively. Further studies are needed to determine the factors involved in the apparent difference in the acquisition of macrolide resistance in C. coli compared to C. jejuni.