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Abstract
Some authorities question the use of antimicrobials in food production based on data that suggests usage may lead to an increase in multiple drug resistance among food-borne pathogens. The purpose of this study was to investigate the influence of antibiotic administration on the ecology of antibiotic resistance. We detected a high prevalence of resistance to antibiotics that were not used on the chicken farms, suggesting that antibiotic usage patterns may not be predictive based on phenotypic data. Sarafloxacin administration did affect the E. coli strain population in a flock. However, we discovered that other factors such as physiological status and the environment might also affect the ecology of resistance. Overall, our data indicated that multiple drug resistance may occur at a high prevalence without an accompanying antibiotic administration selective pressure. This data also revealed the many factors that influence multiple drug resistance among commensal bacteria in the chicken intestine.