Harmful bacteria are microorganisms that can cause disease in humans and animals. Two examples of harmful bacteria are Streptococcus, commonly known as Strep, and Escherichia coli, or E. coli. Strep is a type of bacteria that can cause a range of illnesses, including strep throat, scarlet fever, and pneumonia. E. coli is a type of bacteria that can cause food poisoning, urinary tract infections, and other illnesses. Both Strep and E. coli can be spread through contact with an infected person or contaminated food or water.