Which substances in the stomach destroys the bacteria?
The stomach contains a highly acidic mixture of enzymes, acids, etc. Specifically, the inside of the stomach is acidic to allow the enzyme pepsin to work at its maximum efficiency. The use of hydrochloric acid (HCl) acidifies to stomach juices to around a pH of 2. This highly acidic environment allows the destruction of bacteria. The acidic nature of the stomach contents can denature bacterial enzymes, DNA, etc. Therefore, I would say that the acidity of the stomach is what helps destroy bacteria, and prevent infections from said bacteria.