Bacteria cause disease by secreting or excreting toxins (as in botulism), by producing toxins internally, which are released when the bacteria disintegrate (as in typhoid), or by inducing sensitivity to their antigenic properties (as in tuberculosis).

Do most bacteria cause disease?

Not all bacteria are harmful, and some bacteria that live in your body are helpful. For instance, Lactobacillus acidophilus — a harmless bacterium that resides in your intestines — helps you digest food, destroys some disease-causing organisms and provides nutrients.

Why do bacterial infections occur?

Direct contact occurs when an individual comes into contact with the reservoir via touching infected bodily fluid; sharing beverages containing infectious bacteria; being bitten by an insect or other animal that is carrying the bacteria; or inhaling bacterial particles, often emitted by sneezing or coughing.