Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 27, 2006
Publication Date: July 3, 2006
Citation: Edrington, T.S., Callaway, T.R., Smith, D.J., Genovese, K.J., Anderson, R.C., Nisbet, D.J. 2006. Effects of ractopamine HCl on Escherichia coli O157:H7 and Salmonella in vitro and on intestinal populations and fecal shedding in experimentally infected sheep and pigs. Current Microbiology. 53:82-88. Interpretive Summary: Ractopamine is a compound fed to cattle and swine prior to slaughter to improve performance and carcass quality. Ractopamine is similar to some hormones that have been shown to affect the growth of E. coli O157:H7. The objectives of the present study were to determine if ractopamine affects growth rates of E. coli and Salmonella, and to examine the effect of feeding ractopamine on intestinal populations of E. coli O157:H7 in sheep, and on Salmonella in swine. Results showed that ractopamine had no effect on growth rates of pathogenic E. coli but did influence Salmonella choleraesuis. Feeding ractopamine had mild effects on gut populations and fecal shedding of E. coli O157:H7 in sheep and Salmonella in pigs. These studies provide valuable insight into ongoing efforts to control pathogenic microorganisms in farm animals.
Technical Abstract: The effects of the beta-agonist ractopamine, approved for use in finishing swine and cattle to improve carcass quality and performance, were examined on two important foodborne pathogens, E. coli O157:H7 and Salmonella. Ractopamine, administered to sheep prior to and following oral inoculation with E. coli O157:H7, increased (P < 0.01) fecal shedding and tended to increase (P = 0.08) cecal populations of the challenge strain. Pigs receiving ractopamine in the diet and then experimentally infected with Salmonella Typhimurium, had decreased (P < 0.05) fecal shedding and fewer (P = 0.05) liver tissue samples positive for the challenge strain of Salmonella. Pure cultures of Escherichia coli O157:H7 (used in the present sheep study), E. coli O157:H19 (isolated from pigs with post-weaning diarrhea), Salmonella Typhimurium (used in the present pig study), and Salmonella Choleraesuis, were incubated with varying concentrations of ractopamine to determine if ractopamine has a direct effect on bacterial growth. No differences in growth rate were observed for either strain of E. coli or for Salmonella Typhimurium. The growth rate for Salmonella Choleraesuis was increased with the addition of 2.0 ug ractopamine/ml, compared with the other concentrations examined. Collectively, these results indicate that ractopamine may influence gut populations and fecal shedding of E. coli O157:H7 and Salmonella. As ractopamine is currently approved to be fed to finishing cattle and swine immediately prior to slaughter, any potential for reducing foodborne pathogens has exciting food safety implications.