Repair of Heat-Injured Staphylococcus aureus 196 E on Food Substrates and Additives and at Different Temperatures
1982
Palumbo, Samuel A. | Smith, James L.
Repair of heat-injured Staphylococcus aureus 196E was studied on a newly developed agar medium containing 25% ground beef. The cells were heat-injured at 50 C in 0.1 M potassium phosphate buffer (pH 7.2). After being heated, the cells were surface plated on: Tryptic soy agar (TSA); TSA + 7% NaCl (TSAS); ground beef agar (GBA) with and without various additions; and meat/food agar. Repair is defined as the number of organisms growing on GBA, GBA + addition, or meat/food agar that is greater than the number growing on TSAS by at least one log cycle. The following additives incorporated into GBA permitted repair of heat-injured S. aureus: nitrite (up to 400 ppm), ascorbate (up to 500 ppm), lactic acid (down to pH 5.5), liquid smoke preparations, and water activity-lowering substances including glycerol (10%), NaCl (2.5%), KCl (5%) and sucrose (30%). Cells regained salt tolerance on TSA when incubated at temperatures from 20 to 45 C, but not at 16 or 50 C. Repair was most rapid at 35 C. When ground beef was replaced in the plating medium, repair occurred on frankfurter and chili beef soup agars, but not on pepperoni and Lebanon bologna agars. Repair of heat-injured S. aureus can take place on meat-foods, in the presence of various meat additives, and at temperatures from 20 to 45C.
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