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United States Department of Agriculture

Agricultural Research Service

Title: Bactericidial Effect of Sodium Chlorate on Esherichia Coli 0157: H7 and Salmonella Typhimurium Dt104 in Rumen Contents

Authors
item Anderson, Robin
item Buckley, Sandra
item Kubena, Leon
item Stanker, Larry
item Harvey, Roger
item Nisbet, David

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 2000
Publication Date: N/A

Interpretive Summary: Escherichia coli O157: H7 and Salmonella Typhimurium DT104 are important food borne pathogens affecting the beef and dairy industries and strategies are sought to rid these from cattle at slaughter. Both of these pathogens possess a certain enzyme that is not contained in many other species of beneficial bacteria. This particular enzyme just so happens to convert chlorate to chlorite. Chlorate is relatively nontoxic, but chlorite, the active agent in bleach, is toxic to bacteria. We conducted an experiment to test the effect of chlorate on populations of gut bacteria. We found that chlorate, at environmentally safe levels, did indeed kill Escherichia coli O157: H7 and Salmonella Typhimurium DT104, but did not kill beneficial bacteria. These results show that chlorate may be a useful chemical to feed to animals just before slaughter to reduce levels of pathogenic bacteria.

Technical Abstract: Escherichia coli O157: H7 and Salmonella Typhimurium DT104 are important food borne pathogens affecting the beef and dairy industries and strategies are sought to rid these from cattle at slaughter. Both pathogens possess respiratory nitrate reductase, long known to also reduce chlorate to the lethal chlorite ion. Since most anaerobes lack respiratory nitrate reductase, we hypothesized that chlorate may selectively kill Escherichia coli O157:H7 and Salmonella Typhimurium DT104 but not potentially beneficial anaerobes. In support of this hypothesis, we found that concentrations of Escherichia coli O157: H7 and Salmonella Typhimurium DT104 were reduced from approximately 1,000,000 colony forming units (CFU) to below our level of detection (<10 CFU) following in vitro incubation (24 hr) in buffered ruminal contents (pH 6.8) containing 5 mM added chlorate. In contrast, chlorate had little effect on the most probable number (mean +/- SD) of total culturable anaerobes (ranging from 9.9 +/- 0.72 to 10.7 +/- 0.01 log base 10 cells/ml). Thus, chlorate was bactericidal to E. coli O157: H7 and Salmonella Typhimurium DT104 but not to potentially beneficial bacteria. The bactericidal effect of chlorate was concentration dependent (less at 1.25 mM) and markedly effected by pH (more bactericidal at pH 6.8 than pH 5.6).

Last Modified: 11/25/2014