Monday, November 13, 2006

Evaluation of Antibiotic Resistant Profiles of Enteric Bacteria in Swine Manure Before and After Manure Management.

Leilei Qian, Alexandria Graves, and Emily Norris. Dept. Soil Science, North Carolina State University, 100 Derieux Street, Raleigh, NC 27695

Benefits of antibiotic use in livestock production include the therapeutic value in the treatment of diseases, improvement of feed efficiency and growth, decreased pathogen loads, etc.  These benefits have helped sustain intensive animal production to meet consumer demands for food products.  However, contrasting the above benefits are suggestions that agricultural use of antibiotics may be partly responsible for the emergence of antibiotic-resistant organisms.  As a result there is a great need to determine the effect of manure management on antibiotic resistance of enteric bacteria, especially considering that there is a significant amount of managed manure land applied, thus opening the door for the spread of antibiotic resistance in the environment.  The goal of this project was to evaluate the effects of manure management (lagoon treatment) on the persistence of antibiotic resistance in enteric bacteria isolated from swine.  A total of 1152 Escherichia coli isolates and 1152 Enterococcus isolates were collected from a swine nursery facility and 1152 Escherichia coli isolates and 1152 Enterococcus were collected from a swine finishing facility.  Both swine facilities are located in Sampson County, North Carolina.  For each 1152 set of isolates, 576 isolates were collected from the respective lagoons.   The antibiotic resistance profiles were determined using a combined battery of antibiotics (Escherichia coli: cephalothin, erythromycin, neomycin, oxytetracycline, rifampicin, streptomycin and tetracycline; Enterococcus: cephalothin, erythromycin, neomycin, oxytetracycline, streptomycin, tetracycline, chloratetracycline, vancomycin and amxocillin).  One hundred percent of all the isolates displayed multi-drug resistance with resistance to up to seven of the antibiotic treatments at all sampling locations (Nursery, Nursery Lagoon, Finishing, and Finishing Lagoon).  The results suggest that antibiotic resistance is not confined to one particular stage of livestock production and that the enteric bacteria that persist after manure management continue to exhibit antibiotic resistance.