Purpose: Temperature and delivery (“plug” versus “spin”) methods were evaluated to determine B. bacteriovorus viability and predatory activity in the presence of Salmonella spp. and Shiga toxin-producing Escherichia coli (STEC).
Methods: Frozen B. bacteriovorus was spotted onto YPSC agar with non-pathogenic E. coli (ATCC 43827) as prey, and 5-mm diameter “plugs” were removed from the resultant plaque. Half of the plugs were suspended in a solution of HEPES buffer containing prey E. coli (“spin”), while the remaining plugs were added to flasks containing HEPES + STEC or Salmonella cocktails (“plug”). The “spin” treatments were allowed to shake for 48 h and then added to HEPES + STEC or Salmonella cocktails. All flasks were held at 4°C, 10°C, 22°C, or 29°C. STEC and Salmonella were enumerated at 1, 2, and 3 d of storage on MacConkey and Xylose-Lysine-Tergitol-4 agar, respectively, while B. bacteriovorus was enumerated at 2 and 3 d by plating on YPSC agar.
Results: Populations of B. bacteriovorus were significant for delivery*day (P=0.0202). Salmonella populations differed by temperature*delivery (P=0.0049) and were greater in “spin” at 22 and 29°C and greater in “plug” at 10°C (P<0.05). STEC populations differed by temperature*delivery (P=0.0078) and day*temp (P=0.0192) and it is worth noting that “plugs” resulted in higher STEC populations at 4 and 10°C (P<0.05).
Significance: Temperature and delivery methods impact how B. bacteriovorus preys on Salmonella and STEC in vitro with reduced predatory activity at temperatures at which many foods are stored. Future research should be conducted to better understand and optimize B. bacteriovorus’s preying capabilities in different food products.