Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/21/2006
Publication Date: 11/8/2006
Citation: Garland, J.E., Frye, J.G., Gray, J.T., Berrang, M.E., Harrison, M.A., Cray, P.J. Transmission of salmonella enterica serotype typhimurium in poultry with and without antimicrobial selective pressure. Journal of Applied Microbiology. 101(6):1301-1308 Interpretive Summary: Some studies have reported that antimicrobial resistant Salmonella are more virulent and others have shown that resistance may reduce fitness. This study was done to determine if antimicrobial resistant Salmonella has an advantage during transmission from chick to chick under antimicrobial treatment. In four pens, each with 12 broiler chicks two were inoculated with a Salmonella resistant to 12 antimicrobials including tetracycline while four identical pens were inoculated with a sensitive strain. Two pens inoculated with each strain were treated with chlortetracycline and two were not. At day seven, the intestines of chicks exposed to infected pen mates were cultured for Salmonella. The multi drug resistant Salmonella strain had significantly increased transmission with treatment (90% Vs 60%); however, transmission of the sensitive strain was unaffected by tetracycline (95% Vs 90%). This data is useful in understanding the complex effect that antimicrobials have on the transmission of Salmonella in poultry.
Technical Abstract: Aims: To determine the effect of antimicrobial selective pressure on the transmission of antimicrobial resistant and sensitive strains of Salmonella in poultry. Methods and Results: Two out of 12 broiler chicks in each of four pens were inoculated with a Salm. Typhimurium strain resistant to 12 antimicrobials, including tetracycline. Two out of 12 chicks in each of four other pens were inoculated with a strain sensitive to all antimicrobials tested. Two pens inoculated with each strain were treated with chlortetracycline and two were not. Experiments were performed independently twice. Chicks were sacrificed on day 7 and ceca were cultured for Salmonella. Chicks exposed to pen mates inoculated with the resistant strain and treated with tetracycline were 90% positive; where as 60% of chicks in untreated pens were positive. Chicks exposed to the sensitive strain were 95% positive with tetracycline treatment and 90% positive without. Conclusions: A multi drug resistant Salm. Typhimurium strain had increased transmission when chicks were treated with tetracycline. Transmission of a sensitive strain was not inhibited by antimicrobial selective pressure at MIC levels. Significance and Impact of the Study: This study demonstrates that antimicrobial usage may influence the transmission of antimicrobial resistant pathogens in poultry.