Bacterial infections are caused by ingesting:

Bacterial infections are indeed caused by ingesting sufficient numbers of harmful bacteria. When these bacteria enter the body, they can multiply and cause illness. The infectious dose, the number of bacteria required to establish an infection, can vary widely among different bacteria.

This is distinct from pre-formed bacterial toxins, which are toxins produced by bacteria that may already be present in food before it is consumed, leading to foodborne illnesses without the necessity of the bacteria being ingested. Chemical additives are substances that are added to food to preserve flavor or enhance its taste, appearance, or other qualities, and do not cause bacterial infections. Harmful parasites involve different pathogens and do not fall under bacterial infections specifically. Therefore, the correct answer focuses explicitly on the direct relationship between ingesting harmful bacteria and the resulting infections.