Recovery of injured organisms inoculated into ground beef at various cooking temperatures

The objective of this study was to determine whether sublethally injured organisms could be recovered from a substrate of ground beef heated to three different temperatures. Three organisms, Escherichia coli, Staphylococcus aureus, and Salmonella enteritidis, were injected uniformly into lots of ground beef and allowed to propagate at 4°C over three days of storage. Each day samples were procured and subjected to one of the three cooking temperatures, 60.0°C, 65.6°C or 71.1°C. After each heat treatment the patties were analyzed for total viable population (injured and uninjured organisms), injured organisms, and aerobic plate count. In addition, counts were obtained on the raw ground beef over the three days of storage at 4°C. The data obtained were subjected to analysis of variance. Recovery of sublethally injured Escherichia coli and Staphylococcus aureus occurred at all three temperatures, but the variation was insignificant. Recovery of sublethally injured Salmonella enteritidis showed significance in storage-temperature interaction. Survival of total bacterial population, after heat exposure, showed only significance in replication. With the third set of samples, storage time had a significant effect, as well as temperature. Over three days storage, the number of Escherichia coli and Staphylococcus aureus did not change significantly. The counts of Salmonella enteritidis decreased throughout storage. The percentages of Escherichia coli and Salmonella enteritidis killed continually decreased as the cooking temperature increased. The percentage of Staphylococcus aureus appeared to follow no obvious trend.