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Title: Evaluation of the potential antimicrobial resistance transfer from a multi-drug resistant Escherichia coli to Salmonella in dairy calves

item Edrington, Thomas
item FARROW, RUSSELL - Texas A&M University
item Hume, Michael
item ANDERSON, P - Texas A&M University
item HAGEVOORT, G - New Mexico State University
item CALDWELL, DAVID - Texas A&M University
item Callaway, Todd
item Anderson, Robin
item Nisbet, David

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2012
Publication Date: 10/20/2012
Citation: Edrington, T.S., Farrow, R.L., Hume, M.E., Anderson, P.N., Hagevoort, G.R., Caldwell, D.J., Callaway, T.R., Anderson, R.C., Nisbet, D.J. 2012. Evaluation of the potential antimicrobial resistance transfer from a multi-drug resistant Escherichia coli to Salmonella in dairy calves. Current Microbiology. 66:132-137.

Interpretive Summary: Young dairy calves contain E. coli that are resistant to multiple antibiotics and may transfer this resistance to other bacteria such as Salmonella. We conducted two studies to determine if resistance would transfer from E. coli to Salmonella in dairy calves and to examine the effects of modifying rumen bacterial and protozoal populations on resistance dissemination. Results from the first study indicate that resistance does transfer from E. coli to Salmonella, however the Salmonella appeared to change serotypes with the acquisition of resistance, and further research is warranted. Modifying the rumen bacterial and protozoal communities did not appear to affect resistance transfer. Understanding the mechanisms of antibiotic resistance transfer to pathogenic bacteria may lead to practical interventions to prevent the same.

Technical Abstract: Previous research conducted by our laboratory investigated the incidence of multi-drug resistant (MDR) Salmonella in dairy cattle and reported that individual cattle, and most often calves, shed multiple Salmonella serotypes that vary in the degree of antibiotic resistance. More recently, we investigated the high incidence of an MDR E. coli in dairy calves and found that it disappears with increasing age. Taken together, this suggests the MDR E. coli population may be an important reservoir for resistance elements that could potentially transfer to Salmonella. Therefore, the objective of the current research was to determine if resistance transfers from MDR E. coli to susceptible strains of Salmonella (Experiment I) and to examine the effect of modifying the rumen microbial ecosystem on resistance transfer (Experiment II). Both experiments utilized Holstein calves (approx. 3 weeks old) naturally colonized with MDR E. coli and fecal culture negative for Salmonella. Fecal samples were collected for culture of Salmonella and MDR E. coli throughout both experiments following experimental inoculation with the susceptible Salmonella strains. Results from Experiment I suggest that resistance did transfer from the MDR E. coli to the inoculated strains of Salmonella, with these strains demonstrating multiple antibiotic resistance following in vivo exposure to MDR E. coli. However, serogrouping and serotyping results of a portion of the Salmonella isolates recovered from the calves indicated two new strains of Salmonella, confounding interpretation of the results. In the second experiment, all fecal samples in all treatments were Salmonella negative when plated on antibiotic-supplemented media, indicating that resistance did not transfer to the inoculated Salmonella under these experimental conditions. These results suggest that antimicrobial resistance can transfer from MDR E. coli to Salmonella in vivo, however further research confirming these results is warranted.