From bacteria we get urinary and kidney infections, strep throats, pink eye, boils, typhoid, cholera, tetanus, gas gangrene, diphtheria, whooping cough, anthrax, Lyme disease, tsutsugamuchi fever, Delhi belly, Montezuma's revenge, Turkey trots, and most of the serious cases of dysentery, meningitis, and pneumonia. Because it is so important, we'll also call tuberculosis a bacterium, even if it we are not quite accurate in that classification. For the most part, bacteria are the smallest free-living organisms in nature, having all the genetic material necessary to live independently. This is not to say that many of them don't enjoy the parasitic life, but as a class they are complete life forms unto themselves. Smaller living organisms such as viruses are obligate parasites, unable to survive outside another living system yours, for example.
Bacterial infections fill the space between pimples and plague.
Recently doctors have discovered that they even cause stomach ulcers. They also cause toxic shock syndrome and the recently publicized E. Coli infections children get from contaminated public swimming pools or hamburger meat. Bacteria are responsible for the bubonic plagues that ravaged Europe throughout much of the last two millennia. Since Alexander Fleming discovered penicillin midway through the 20 th century, bacteria have encountered a new enemy, and have responded very ingeniously. In the space of 50 years, nearly all disease-causing bacteria have developed resistance to at least one antibiotic.