Purpose: This study was conducted to gain knowledge of Bdellovibrio bacteriovorus efficacy as a pre-harvest intervention to control Salmonella and Escherichia coli O157:H7 in cattle using an in vitro model to simulate the digestive tract of the animal host.
Methods: Cattle rumen fluid and feces were inoculated with antimicrobial susceptible or resistant strains of Salmonella or Escherichia coli O157:H7. HEPES was added to control samples while experimental samples were supplemented with HEPES containing Bdellovibrio bacteriovorus and all samples were incubated anaerobically at 38.6°C and 50 rpm. At 0, 24, 48, and 72 hours, samples were plated onto Sorbitol MacConkey Agar with Cefixime and Tellurite (CT-SMAC) to enumerate Escherichia coli O157:H7 and subjected to Most Probable Number (MPN) before streaking to Xylose Lysine Tergitol-4 (XLT-4) to enumerate Salmonella.
Results: Bdellovibrio bacteriovorus did not significantly reduce antimicrobial susceptible and resistant populations of Escherichia coli O157:H7 in either rumen or fecal environments. Significant reductions in Salmonella populations in rumen fluid were also not observed. In comparison to control fecal samples, Bdellovibrio bacteriovorus decreased resistant Salmonella by 3.79 (P = < 0.0001) and 2.24 (P = 0.0013) log MPN/g following 24 and 48 hour incubations, respectively, and susceptible Salmonella by 2.02 log MPN/g (P = 0.0005) when time was held constant.
Significance: The significant decrease in Salmonella populations achieved in cattle feces in vitro suggests that Bdellovibrio bacteriovorus may be able to predate within the gastrointestinal tract of cattle. These data suggest that future in vivo research is warranted.