Date Full Report Received


Date Abstract Report Received


There is increasing scrutiny regarding the use of antimicrobials in animals as a result of increasing antimicrobial resistance in human pathogens, and in particular foodborne outbreaks caused by multiple resistant foodborne pathogens (for example Salmonella Typhimurium DT104). The perceived risk of transfer of resistance from bacteria colonizing animals to pathogens of humans has led to the ban of sub-therapeutic antimicrobials in animal feeds in many European countries and has prompted suggestions for a moratorium on use in the US. The overall objective of this research was to evaluate, in a controlled manner, the effect of sub-therapeutic chlortetracycline on antimicrobial resistance and pig performance on commercial swine farms. In this study, there was no effect of sub-therapeutic chlortetracycline on the prevalence or antimicrobial resistance of Salmonella isolated from swine. There was a small, but statistically significant increase in the proportion of fecal flora isolates resistant to tetracycline, ampicillin and ceftriaxone in the fecal flora of swine that received sub-therapeutic chlortetracycline in their diets, but no effect was seen in resistance to gentamycin. The public health implication of this change in resistance is uncertain and unanswerable by this project. Further efforts to measure the risk attributable to antimicrobial use on farms to antimicrobial resistant infections in humans is necessary.