Dogs and cats are carnivores, and evolved eating raw meat. Their systems can handle a certain amount of bacteria; indeed, they were designed for it. So, a dog will not get sick from e.coli or salmonella poisoning if he eats raw meat. This is because the dogs digestive tract is different from a humans in some important ways that prevent this. The dogs have strong hydrochloric acid in their stomach to digest meat and even bones. The acid is about 10 times stronger in concentration than what we have in our stomach. The acid kills any bacteria that might come its way. Also, the overall length of the gastrointestinal tract of a dog is much shorter in comparison to a humans. This means that rapidly decaying food passes through the system much more quickly, in hours rather than days.

Bacteria don't have a chance to get a foothold. This does not mean that a dog can ever possibly contract e.coli or salmonella poisoning. However, such rare incidences are usually the result of a dog that was raised on a lifetime of commercial food and suddenly is raiding the garbage can one day.