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You would be amazed at the hosts of germs out there waiting to take up residence in your body. One category of germs is bacteria. Known to scientists as prokaryotes, bacteria are the most populous class of creatures on earth, existing in even larger numbers than beetles. They are very simple organisms - single cells with no nucleus. Nevertheless, they eat, are capable of reproducing themselves, and have a membrane or shell that separates their insides from the outside world.
Bacteria, the most familiar of infectious agents, cause 90 percent of hospitalized infections in developing countries, although they compete with viruses for being the most diversified. 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 living off other organisms, but as a class they are complete life forms unto themselves. Smaller living organisms such as viruses cannot survive outside another living system, such as yours.
Bacteria cause most of the serious, short-term infections we get and can be stopped with medications called antibiotics. From bacteria we get urinary tract and kidney infections, strep throat, boils, typhoid, cholera, tetanus, gangrene, diphtheria, whooping cough, anthrax, Lyme disease, and most of the serious cases of dysentery, meningitis and pneumonia.
How bad are bacteria?
Doctors know that bacterial infections can cause stomach ulcers. Bacterial infections can also cause toxic shock syndrome and the potentially lethal E. coli infections children get from contaminated public swimming pools or tainted hamburger meat. Bacteria are responsible for the bubonic plague epidemic that ravaged Europe in the fourteenth century.
Since Alexander Fleming discovered penicillin in 1928, bacteria have encountered a new enemy--the antibiotic--and have responded ingeniously. Within 50 years, nearly all disease-causing bacteria have developed resistance to at least one antibiotic. They have even learned how to pass their resistance on to their relatives. But the most frightening news is that some bacteria have developed resistance to every known antibiotic. Much of this resistance has come from improper use of antibiotics (such as not finishing prescriptions), which is the main reason that these drugs are not available over the counter in the U.S.. Incomplete doses kill all but the hardiest germs, which are then able to develop even stronger resistance through mutation and "natural selection."
The lesson here is "Finish your prescription. Kill them all, or they'll come back to get you, and don't take antibiotics for illnesses caused by viruses." Given the tens of millions of dollars and the years of processing required to get a single new drug on the market, bacteria have a clear advantage when it comes to efficiency.
TB is a classic example of selective development of resistance. It used to be universally susceptible to INH (isonicotinic acid hydrazide, more commonly called isoniazid), a cheap, safe treatment that is used throughout the world. Inadequate dosing was the rule rather than the exception, especially since it takes months, rather than days, to eradicate TB in a patient. Now, TB can be resistant not only to INH, but also to many more expensive and more powerful drugs. Some TB strains are resistant to every drug. TB is now treated initially with four antibiotics to prevent emergence of resistance. With the advent of AIDS, TB is increasing by as much as twenty-fold in African countries heavily stricken with AIDS.
Leprosy, now known as Hansen's disease, is also caused by a mycobacterium.
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External Source
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Centers for Disease Control and Prevention
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This article was reviewed and updated June 2007.
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