ANTIBIOTIC-RESISTANCE OF BACTERIAL LITTER ISOLATES

Use of antibiotics in subtherapeutic doses as growth-promoting feed ad ditives for animal production is widespread in the U.S. and throughout the world. Previous studies by our research group concluded that size fractionation of poultry (broiler) litter followed by storage facilit ated reutilization of litter as a soil amendment or bedding supplement . However, litter microbial contamination, including antibiotic-resist ant populations, and accumulation of metals and other elements may lim it litter reutilization. Litter from four broiler houses was separated into a fine fraction for use as a soil amendment, and a coarse fracti on for reutilization as a bedding supplement in growing subsequent flo cks of broilers. Fractions and whole litter were stored in indoor pile s simulating farm storage conditions for 4 mo with periodic analysis f or metals, other elements, and culturable bacteria (including total an d fecal coliform, Aeromonas hydrophila, Pseudomonas aeruginosa, Yersin ia enterocolitica, and Campylobacter jejuni). Representative bacterial isolates were tested for their sensitivity to 12 common antibiotics ( ampicillin, bacitracin, cephalothin, erythromycin, gentamicin, kanamyc in, nalidixic acid, neomycin, penicillin, streptomycin, sulfisoxazole, and tetracycline) using the Kirby-Bauer technique. Pathogens and indi cator bacteria tested were found to be resistant to multiple antibioti cs. Data suggest that microbial contamination of litter should be redu ced or eliminated prior to reutilization to minimize environmental hea lth risks related to transfer of antibiotic-resistant bacteria to huma ns or other animals.