ARS | Publication request: Chlortetracycline - resistant intestinal bacteria in organically-raised and feral swine

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 25, 2011
Publication Date: October 15, 2011
Citation: Stanton, T.B., Humphrey, S.B., Stoffregen, W.C. 2011. Chlortetracycline - resistant intestinal bacteria in organically-raised and feral swine. Applied and Environmental Microbiology. 77(20):7167-7170.

Interpretive Summary: Swine that were obtained from two Iowa farms practicing USDA certified organic practices for the last four years, nevertheless, had high fecal levels of tetracycline resistant bacteria. These bacteria were Escherichia coli, Megasphaera elsdenii and different bacteria that can only be cultivated in the absence of oxygen. By comparison, swine that were wild and living on an island near South Carolina had low levels of tetracycline resistant bacteria in their feces (over 1000-fold fewer than the organically raised swine). Even in the absence of farm use of antibiotics, antibiotic resistance persisted in the organically raised swine. The reasons for the persistence of antibiotic resistance are likely to be multiple. These findings suggest approaches in addition to prudent antibiotic use will be important in effectively reducing resistant bacterial populations in swine.

Technical Abstract: Organically-raised swine had high fecal populations of chlortetracycline (CTC)-resistant (growing at 64 micro g CTC/ml) Escherichia coli, Megasphaera elsdenii and anaerobe populations. By comparison, predominant CTC-resistant bacteria in feral swine feces were over 1000-fold fewer and exhibited lower taxonomic diversity.