Survival of a Salmonella typhimurium experimental contaminant during cooking of beef roasts

Twenty-one raw boneless beef roasts were experimentally injected with 2 X 10(7) cells of a nalidixic acid-resistant strain of Salmonella typhimurium per roast. Contaminated roasts were cooked to center internal temperatures of 137.0 to 147.5 degrees F (58.3 to 64.1 degrees C) in a gas-fired pilot plant food-processing oven. Viable experimental contaminants were recovered from two core samples of the 21 roasts (one cooked to 137.0 degrees F [58.3 degrees C] and one cooked to 141.5 degrees F [ca 60.8 degrees C]). All of 17 cooking net samples taken from the contaminant injection side of roasts were salmonella positive, whereas 7 of 9 net samples from the side opposite injection were positive and all of 11 net samples from the bottom of roasts were positive. The implications of these results are discussed in relation to salmonella contamination of precooked beef roasts.