Bacteria that cause disease are called pathogenic bacteria. Bacteria can cause diseases in humans, in other animals, and also in plants. Some bacteria can only make one particular host ill; others cause trouble in a number of hosts, depending on the host specificity of the bacteria. The diseases caused by bacteria are almost as diverse as the bugs themselves and include food poisoning , tooth ache, anthrax , and even certain forms of cancer. It is impossible to sum up all bacterial diseases and it would be pretty boring. The Infectious Diseases fact sheets gives brief descriptions of diseases, including infectious diseases. Some diseases are named after the organisms that cause them, or is it the other way round?
If you want to have a look at pathogenic bacteria under the microscope:
Some pathogenic bacteria have received disproportionate attention in the press, e.g. the 'flesh-eating bacteria' , which in real life are called Streptococci. Indeed they can cause spectacular, but fortunately uncommon symptoms. In the press, pathogenic bacteria are sometimes represented as (deadly) dangerous enemies that lurk in the dark, unseen, ready to attack you. Although that is exaggerated some bacteria can be life treatening, for example Legionella pneumoniae, the causative of Legionnaire's disease. These bacteria survive in moist places like air conditioners or hot-water pipes.
Though potentially life treatening, bacterial infections do not kill all their victims. Some bacteria potentially kill a high percentage of people infected, at least without proper treatment (they have a so-called a high mortality rate), but their relatively inefficient rate of spreading makes up for that. Other bacteria spread very easily, infecting lots of people (this is called a high morbidity), but they don't kill many of the people they infect. Imagine what would happen with a pathogen that could spread very fast and would kill all its victims; it would soon have none left to infect, and would die out together with the species on which it had been dependent. Bacterial pathogens don't eradicate their hosts completely. Although a popular theme for thrillers, this is a 'mission impossible' in real life.
Bacteria have invented many different strategies to make us ill. These strategies, called bacterial pathogenicity, are the subject of an important division of medical microbiology. Understanding how certain bacteria make us ill can result in better treatment, vaccination, or prevention of that infectious disease. In another exhibit some of the common mechanisms of bacterial pathogenicity are explained.
Bacteria and viruses that can cause disease can result in outbreaks. That means a number of patients get sick from a common source. If the number increases, the outbreak grows into an epidemic, which is usually the case when humans infect each other. Epidemics are explained in the exhibit about Epidemiology. In order to keep this information balanced, now that you know what pathogenic bacteria are, why not also check out how commensal bacteria are good for you.