Tetracycline Resistant Subtypes Emanating from Beef Cattle Administered Non-Therapeutic Chlortetracycline are Longitudinally Transmitted within the Production Continuum but are Not Detected in Ground Beef.

The impacts of the antimicrobial growth promoter (AGP), chlortetracycline with sulfamethazine (AS700), on the development of antimicrobial resistance and longitudinal transmission of within the beef production continuum were empirically determined. Carriage of tetracycline resistance determinants in the enteric bacterial community increased at a greater rate for AS700-treatment cattle. The majority of the bacteria from animals administered AS700 carried . Densities of shed in feces increased over the confined feeding period, and the administration of AS700 did not conspicuously reduce densities in feces or within the intestine. The majority of isolates recovered were resistant to tetracycline, but the resistance rates to other antibiotics was low (≤20.1%). The richness of subtypes recovered from AS700-treated animals that were either resistant or susceptible to tetracycline was reduced, indicating selection pressure due to AGP administration. Moreover, a degree of subtype-specific resistance to tetracycline was observed. tetO was the primary tetracycline resistance determinant conferring resistance in C. jejuni isolates recovered from cattle and people. Clinically-relevant subtypes (subtypes that represent a risk to human health) that were resistant to tetracycline were isolated from cattle feces, digesta, hides, the abattoir environment, and carcasses, but not from ground beef. Thus, study findings indicate that clinically-relevant subtypes associated with beef cattle, including those resistant to antibiotics, do not represent a significant foodborne risk.