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United States Department of Agriculture

Agricultural Research Service


item Stanton, Thaddeus
item Stoffregen, William

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.

Last Modified: 10/19/2017
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