Submitted to: American Society of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/14/1999
Publication Date: N/A
Technical Abstract: Escherichia coli O157:H7 (EC) and Salmonella typhimurium DT104 (ST) are important food borne pathogens affecting the beef industry, and strategies are sought to rid these from slaughter cattle. As members of the family Enterobacteriaceae, both pathogens possess respiratory nitrate reductase. Since most ruminal anaerobes lack nitrate reductase, and since most known respiratory nitrate reductases also reduce chlorate to cytotoxic chlorite, we hypothesized that chlorate may selectively inhibit EC and ST. To test this, ruminal fluid, collected from a cannulated cow maintained on pasture (predominantly rye grass), was mixed 1:1 with phosphate buffer (pH 6.8) containing cellobiose, glucose, soluble starch, and xylose (1% wt/vol each). The buffered ruminal fluid was incubated anaerobically (39C) with or without 5 mM sodium chlorate and either 7.3 x 10**5 colony forming units/ml (cfu/ml) of a novobiocin (NO) and nalidixic acid (NA) resistant EC or 2.5 x 10**5 cfu/ml of ST. Colony counts for EC were determined via direct plating on MacConkey agar containing 25 ug NO/ml and 20 ug NA/ml and for ST via plating on Brilliant Green agar containing NO and chloramphenicol (25 ug/ml each). Concentrations of EC declined slightly to 1.3 x 10**5 cfu/ml following 24 hr culture in ruminal fluid without added chlorate but declined rapidly (to = 10 cfu/ml by 6 hr) when incubated with added chlorate. Concentrations of ST declined more when incubated 24 hr with added chlorate than without (1.5 x 10**3 vs 1.3 x 10**4 cfu/ml, respectively) but the chlorate effect was not as dramatic as that observed with EC. Sodium nitrate (2.5 mM), when added to ruminal fluid containing chlorate, caused ST concentrations to decline to = 10 cfu/ml following 24 hr incubation, presumably by inducing expression of nitrate reductase.