Originally Posted by GB
It is more the heat resistant toxins the bacteria produce than the bacteria itself at that point. The toxins can be deadly and are not killed by heat.
There is a limited number pathogenic bacteria that even produce toxins. Most are in the Clostridium genus and need anaerobic conditions to form and most are not heat resistant. For example botulism toxin is not generally heat resistant.
The only common bacteria that I am aware of that produces a heat resistant toxin would be Staph. It is not uncommon to be on the skin, hair and nose of healthy people. It is not considered deadly and clearly not as deadly as the common flu. In order for that to be present, someone handling the roast would have to be a carrier of the organism, and pass it on to the food.
Heat doesn't kill toxins because they aren't alive in the first place. It destabilizes them.
Most of the concern and regulation about food borne illness is based on commercial food service conditions; many people handling the food, many different bacteria being brought into the establishment and less interest on the part of the workers to be safe then one has in their home.
So home cooked foods are inherently safer that commercially prepared foods just because there is far less opportunity for contamination.
So the best we can say is reheating the roast to 165 degrees might make it "safe". There is no way to know for sure, and that is why some will choose to eat and some will choose to throw.
Bacterial Food Intoxications, Bacterial Toxin, Metabolities, Tuberclosis, Typhoid Fever, Cholera, Salmonella, Bacillus