Subtherapeutic tylosin phosphate in broiler feed affects Campylobacter on carcasses during processing

Tylosin phosphate is an antimicrobial drug approved for use in broiler feed at subtherapeutic levels for growth promotion. Erythromycin is often the drug of choice for treating humans with campylobacteriosis. Both tylosin and erythromycin are classified as macrolide drugs and cross-resistance between these antimicrobials occurs. Commercial broiler chicks were placed in isolation grow-out chambers and colonized with Campylobacter jejuni. From 14 d of age through grow-out, broilers were fed ad libitim a diet that included 22 ppm of tylosin phosphate (20 g/ton). Control broilers received the same diet without tylosin phosphate. At 42 d of age, broilers were processed in a pilot plant with equipment that closely modeled commercial conditions. Carcass rinses were collected after feather removal, after inside and outside washing, and after immersion chilling. Campylobacter numbers recovered from carcasses after feather removal did not differ according to feed type (3.53 log cfu/mL of rinse for control carcasses, and 3.60 log cfu/mL of rinse for those fed medicated feed). Likewise, medicated feed did not affect Campylobacter numbers on carcasses after inside-outside washing (3.11 and 3.07 log cfu/mL of rinse). However, carcasses of broilers fed tylosin phosphate had lower numbers of Campylobacter after chilling (1.45 log cfu/mL of rinse) than control carcasses (2.31 log cfu/mL of rinse). No Campylobacter isolated from control carcasses were resistant to erythromycin; all Campylobacter recovered from carcasses fed tylosin phosphate were resistant to erythromycin. Application of tylosin phosphate in feed results in lower numbers of Campylobacter on chilled carcasses; however, the Campylobacter that do remain are resistant to erythromycin.