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United States Department of Agriculture

Agricultural Research Service

Research Project: EPIDEMIOLOGY, ECOLOGY, AND MOLECULAR GENETICS OF ANTIMICROBIAL RESISTANCE IN PATHOGENIC AND COMMENSAL BACTERIA FROM FOOD ANIMALS

Location: Bacterial Epidemiology and Antimicrobial Resistance

Title: Effect of Antimicrobial Dosage Regimen on Salmonella and Escherichia Coli Isolats from Feeder Swine

Authors
item Wagner, Bruce - USDA-APHIS
item Straw, Barbara - MICHIGAN STATE UNIV
item Cray, Paula
item Dargatz, David - USDA-APHIS

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 11, 2008
Publication Date: March 3, 2008
Citation: Wagner, B., Straw, B.E., Cray, P.J., Dargatz, D. 2008. Effect of antimicrobial dosage regimen on salmonella and escherichia coli isolats from feeder swine. Applied and Environmental Microbiology. 74(6):1731-1739

Interpretive Summary: Salmonella is a zoonotic pathogen which can be transferred from animals to humans, most often through consumption of contaminated food. Infection with Salmonella can cause mild to severe gastroenteritis in humans while infection in food animals is often with clinical signs of disease. Antimicrobial resistance is a growing concern for public and animal health. Threats to public health could come from the transfer of pathogens from animals to people via indirect contact such as through food or by direct contact. In addition, concern has been raised for the potential transfer of resistance determinants from animals to humans through commensal bacterial flora such as Escherichia coli. In this study 3 different antimicrobial regimes (low-level antimicrobial concentrations given continuously, pulse (in which the antimicrobial is administered then stopped for a period of time prior to re administration), and no antimicrobial) for 2 antimicrobials (chlortetracycline and tylosin) on the presence of Salmonella spp. and on the prevalence of antimicrobial resistance of both Salmonella spp. and E. coli in fecal samples from feeder swine. The prevalence of fecal samples positive for Salmonella spp. significantly decreased between the samples taken from pigs at mid-growth compared to samples taken when the animals were close to market weight. The development of resistance in Salmonella spp. did not appear to be influenced by dosing treatment. However, resistance to the cephalosporin antimicrobial, cephalothin, increased in E. coli under the pulse chlortetracycline treatment. These results suggest that the dosing regime examined in this study did not lead to an increase in the prevalence of Salmonella spp. or the prevalence of resistance to a number of antimicrobials for Salmonella spp. or E. coli. These data are necessary to enable a more informed debate among scientists, commodity groups, government regulators, and animal industry personnel on the impact antimicrobial use has on the development of resistance in zoonotic and commensal bacteria.

Technical Abstract: A body of evidence exists that suggests that antimicrobial use in food animals leads to resistance in both pathogenic and commensal bacteria. This study focused on the impact of 3 different antimicrobial regimes (low-level continuous, pulse, and no antimicrobial) for 2 antimicrobials (chlortetracycline and tylosin) on the presence of Salmonella spp. and on the prevalence of antimicrobial resistance of both Salmonella spp. and non-specific Escherichia coli in fecal samples from feeder swine. The prevalence of fecal samples positive for Salmonella spp. significantly decreased between the samples taken at feeder placement compared to samples taken when the animals were close to market weight. Differences in resistance of Salmonella spp. did not appear to be influenced by dosing treatment including the control. Examination of both susceptible/resistance and minimum inhibitory concentration demonstrated that resistance to cephalothin increased in E. coli under the pulse chlortetracycline treatment. These results suggest that the dosing regime examined in this study did not lead to an increase in the prevalence of Salmonella spp. or the prevalence of resistance to a number of antimicrobials for Salmonella spp. or E. coli.

Last Modified: 7/12/2014