Competitive exclusion Escherichia coli cultures on E. coli O157 growth in batch culture ruminal or fecal microbial...

The purpose of this study was to determine the efficacy of competitive exclusion (CE) Escherichia coli cultures (ATCC 202018 and 202019) for reducing E. coli O157 in batch culture fermentations with ruminal or fecal microbial inoculum derived from a cannulated feedlot steer fed a corn-grain-based, high-grain diet. A non-CE (NCE) E. coli strain (ATCC 25922) was included as a control. Anaerobic fermentations (50 mL) were set up in serum bottles with a 2:1 mineral buffer to microbial inoculum ratio and with or without gluconic acid, a component of intestinal mucus, which has been shown to be stimulatory to the growth of E. coli O157 in vitro. A five-strain mixture of E. coli O157 made resistant to nalidixic acid (50 microg/mL; Nal(R)) was added to each fermentation, and concentrations of Nal(R) E. coli O157 were determined after 0, 6, 12, and 24 h of fermentation. In ruminal microbial fermentation, the CE treatment had a lower (0.6 log; p < 0.01) concentration of Nal(R) E. coli O157 than the NCE control at 24 h, regardless of gluconic acid inclusion. In fecal microbial fermentation, the CE treatment did not affect Nal(R) E. coli O157 concentrations in fermentations without gluconic acid; but with gluconic acid inclusion, Nal(R) E. coli O157 concentrations were lower in the CE treatment than in NCE controls at 12 h (1.7 log CFU/mL lower) and 24 h (1.9 log CFU/mL lower). In vitro fermentation with ruminal or fecal microbial inoculum could be a simple and inexpensive initial approach to assess efficacy of CE cultures for reducing E. coli O157.