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Title: EFFECT OF PORCINE-DERIVED MUCOSAL COMPETITIVE EXCLUSION CULTURE ON ANTIMICROBIAL RESISTANCE IN ESCHERICHIA COLI FROM GROWING PIGLETS

Author
item Kim, L
item GRAY, JEFFERY - UNIV OF GUELPH
item BAILEY, JOSEPH - 6612-05-05
item JONES, RICHARD - UNIV OF GEORGIA
item Cray, Paula

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2005
Publication Date: 12/1/2005
Citation: Kim, L., Gray, J.T., Bailey, J.S., Jones, R.D., Cray, P.J. 2005. Effect of porcine-derived mucosal competitive exclusion culture on antimicrobial resistance in escherichia coli from growing piglets. Foodborne Pathogens and Disease. 2(4):317-329.

Interpretive Summary: Antimicrobial are used in both human and veterinary medicine and the emergence of antimicrobial resistance has become a global problem. In veterinary medicine, antimicrobials are used to treat ill animals, for prevention of disease and for growth promotion. Although use of antimicrobials has been shown to improve the growth of animals, its use in this manner is thought to contribute significantly to the development and maintenance of antimicrobial resistant bacteria in food animal production. In this study, we determined the effect of three antimicrobial feed additives (apramycin, carbadox, and chlortetracycline) on the development of antimicrobial resistance in Escherichia coli recovered from growing piglets as well as their effect on animal growth. Three replicate trials were conducted using growing piglets fed standard diets with and without antimicrobials in the feed. Fecal samples were cultured for E. coli at regular intervals from all piglets from birth to market weight. Antimicrobial susceptibility testing of recovered E. coli isolates was performed to determine if resistance had developed. Animal growth was also measured. Resistance to tetracycline in E. coli varied widely by sample, group, and trial. However, a significant increase in the percentage of resistant isolates was observed in piglets receiving antimicrobials in the feed when compared to controls (P is less than 0.0001). Resistance to apramycin increased significantly in E. coli from piglets fed apramycin when compared to controls (P is less than 0.0001). However, unlike the other antimicrobials, upon removal of apramycin, resistance in E. coli declined to baseline levels by Day 75. Piglets receiving antimicrobials in their feed grew significantly better than piglets without antimicrobials in their feed (P is less than 0.001). These data suggest that antimicrobial resistance as a result of using antimicrobials for growth promotion is drug dependent and indicates that some antimicrobials may be suitable for use as growth promotants. These data are critical as scientists, commodity groups, government regulators, and animal industry personnel debate the use of antimicrobials for growth promotion in animals and its potential effect on the development and maintenance of antimicrobial resistant bacteria.

Technical Abstract: Objectives: To determine the effect of three antimicrobial feed additives (apramycin, carbadox, and chlortetracycline) on the antimicrobial susceptibility of E. coli in growing piglets and on animal performance. Materials and Methods: Three replicate trials were conducted using growing piglets fed standard diets with and without antimicrobial feed additives (AFAs). Fecal samples were cultured selectively for E. coli at regular intervals from all piglets from birth to market. Antimicrobial susceptibility testing of recovered E. coli isolates was performed using a replica-plate screening method and a broth microdilution method. Animal performance was also measured. Results: Resistance to tetracycline in E. coli varied widely by sample, group, and trial. However, a significant increase in the percentage of resistant isolates was observed in piglets receiving AFAs when compared to controls (P is less than 0.0001). Resistance to apramycin increased in E. coli from piglets fed apramycin when compared to controls (P is less than 0.0001). However, upon removal of apramycin, resistance in E. coli declined to baseline levels by Day 75. Piglets receiving AFAs demonstrated improved feed efficiency during Phase 4 (P is less than 0.001), and higher average daily gains in Phases 3 and 4 (P is less than 0.0001). Discussion: This study highlights the complex network of factors involved in the development of antimicrobial resistance in E. coli. While tetracycline resistance was highly variable throughout the study, selective pressure exerted in animals receiving AFAs had a measurable effect on resistant populations, indicating that tetracycline-resistant populations may not only persist, but increase. Conversely, use of apramycin in feed resulted in a transient increase in resistance that declined rapidly to baseline levels following its removal. These data suggest that antimicrobial resistance to AFAs is drug dependent and that some antimicrobials may be suitable for use as feed additives.