Submitted to: American Society for Microbiology
Publication Type: Abstract only
Publication Acceptance Date: 2/27/2004
Publication Date: 5/23/2004
Citation: Stanton, T.B., Stoffregen, W.C. 2004. Tetracycline resistant bacteria in organically raised and feral swine [abstract]. American Society for Microbiology. p. 673. Interpretive Summary:
Technical Abstract: Important to the success of efforts to reduce antibiotic-resistant bacteria in farm animals is establishing baseline levels of "naturally occurring" resistant bacteria. To that end our research focuses on tetracycline-resistance characteristics of bacteria from swine not fed antibiotics. Fecal samples were obtained from swine from farmers practicing organic management policies for the past four years and from free-ranging feral swine remote from farm contact. Chlortetracycline (CTC)-resistant (capable of growth at 64 'g CTC/ml) populations of E. coli, Megasphaera elsdenii, and total anaerobes were determined. CTC-resistant anaerobe isolates were presumptively identified from sequences of their 16S rRNA V3 regions and were screened in PCR assays for various tet gene classes. Organic swine feces contained 6.7 x 10**6 E. coli cfu/gm, and 27% of the colonies were CTC-resistant. Feral feces contained similar E. coli concentrations, however, CTC-resistant E. coli were undetectable (< 5,000 cfu /gm). Many M. elsdenii isolates (46% or 264/540) from organic swine were CTC-resistant, whereas none (0/91), from feral swine were resistant. Sixteen percent (9 x 10**9 cfu/gm) of the anaerobic bacteria from organic swine were CTC-resistant, whereas 0.3% (3.2 x 10**6 cfu/gm), from feral swine were resistant. CTC-resistant anaerobes from organic swine represented numerous and diverse species. Most of the tested isolates (46/54) carried known tet genes, mainly of classes W, O, and Q. By contrast, species and tet gene diversity among CTC-resistant feral isolates were limited. Most isolates (38/44) were identical strains of Lactobacillus or Streptococcus and those examined carried tet genes of classes O or M. These results indicate organically-raised swine, not exposed to antibiotics, shed high numbers of CTC-resistant fecal bacteria. By comparison, CTC-resistant bacteria in feral swine feces are, at least, 1,000-fold fewer and, although present, exhibit lower species diversity. These findings suggest management approaches other than restricted antibiotic use will be important in effectively reducing resistant bacterial populations in swine.