A bacterial infection is a proliferation of a harmful strain of bacteria on or inside the body. Bacteria can infect any area of the body. Pneumonia, meningitis, and food poisoning are just a few illnesses that may be caused by harmful bacteria.armful bacteria can affect almost any area of the body. Other types of bacterial infections include: 1  Bacterial meningitis is a severe infection of the meninges, the lining of the brain. 2  Otitis media is the official name for an infection or inflammation of the middle ear.