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Title: Related antimicrobial resistance genes detected in different bacterial species co-isolated from swine fecal samples

Author
item Frye, Jonathan
item Lindsey, Rebecca
item Meinersmann, Richard - Rick
item Berrang, Mark
item Jackson, Charlene
item Englen, Mark
item Turpin, Jennifer
item Cray, Paula

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2011
Publication Date: 5/25/2011
Citation: Frye, J.G., Lindsey, R.L., Meinersmann, R.J., Berrang, M.E., Jackson, C.R., Englen, M.D., Turpin, J.B., Cray, P.J. 2011. Related antimicrobial resistance genes detected in different bacterial species co-isolated from swine fecal samples. Foodborne Pathogens and Disease. 8(6):663-679.

Interpretive Summary: Antimicrobial resistance (AR) is a major concern to animal and human health. The spread of AR in bacteria may be caused by the transfer of resistance genes between bacteria. To investigate this possibility, fecal samples were collected and cultured for Salmonella, Escherichia coli, Campylobacter coli and Enterococcus, from finisher swine. All four bacteria were recovered from 49 samples yielding a total of 196 isolates for use in this study. Isolates were tested for AR and were tested on a microarray test designed to detect hundreds of AR related genes. AR genes were detected in the isolates and were consistent with their AR phenotypes. Salmonella and E. coli isolated from the same fecal sample had the same AR genes. The genes detected indicated the possible presence of multi-drug resistance plasmids and integrons which are small pieces of genetic material capable of moving genes between bacteria. These genes encoded resistance to common antimicrobials including: aminoglycosides, '-lactams, chloramphenicols, sulfanillic acid, tetracyclines, and trimethoprime. These data suggests there may be horizontal exchange of AR genes in swine or a common source of AR genes in the swine environment for Salmonella and E. coli. This information is important for commodity groups and scientists as we design mitigation strategies to reduce AR in bacteria found in food animals.

Technical Abstract: A possible factor leading to the spread of antimicrobial resistance (AR) in bacteria is the horizontal transfer of resistance genes between bacteria in animals or their environment. To investigate this, swine fecal samples were collected on-farm and cultured for Salmonella, Escherichia coli, Campylobacter coli and Enterococcus spp. which are commonly found in swine. All four bacteria were recovered from 49 samples yielding a total of 196 isolates for use in this study. Isolates were tested for antimicrobial susceptibility followed by hybridization to a DNA microarray designed to detect 775 AR related genes. Positive hybridizations to AR gene probes were detected generally consistent with the AR phenotypes for each isolate. Salmonella and E. coli isolated from the same fecal sample shared the most gene probe hybridizations. The genes were indicative of MDR plasmids and integrons and encoded resistance to aminoglycosides (aac(3), aadA1, aadB, and strA-B), beta-lactams (ampC, ampR, and blaTEM), chloramphenicols (cat and floR), sulfanillic acids (sul1and sulI), tetracyclines (tet(A), tet(D), tet(C), and tet(R)), and trimethoprimes (dfrA1and dfh). Enterococcus and C. coli isolated from the same sample often shared tet(O) and aphA-3 gene probe hybridizations. Almost half (47%) of Salmonella and E. coli isolated from the same fecal sample shared resistance genes at a significant level (x2 p < 0.0000001). These data suggests there may be horizontal exchange of AR genes in swine or a common source of AR genes in the swine environment for Salmonella and E. coli.