Antibiotics describe a class of medications that prevent the growth of bacteria in a living body while having minimal effect on other tissues or body functions. The development of the first antibiotics in the 1940s is considered to be one of the greatest medical breakthroughs of all time, and allowed previously untreatable infections not only to be treated but cured.

It was known from the middle of the 19th century that certain substances, such as bleach and carbolic acid, killed bacteria on contact. The work of Lister in the late 19th century determined that infection during surgery could be almost eliminated by working in an antiseptic environment. However, once an infection was established in the body, the only available treatment was to drain the wound of pus in the hope that the body's immune system would be able to fight off the infection. However, infections in certain parts of the body, such as the brain, could not be treated in this manner, and such a diagnosis inevitably meant the death of the patient.

In addition, several bacteria transmitted diseases, such as scarlet fever, gonorrhea and syphilis, were often fatal, and the only treatment available was rest and treatment of symptoms to relieve such complications as fever and dehydration.

Alexander Fleming noted that penicillium mold that had contaminated one of his culture plates eliminated the growth of bacteria. Fleming was uncertain that this discovery would have more than an antiseptic use, but it was soon discovered that the active chemical, dubbed penicillin, would kill bacteria in the bloodstream without harming the patient.

Penicillin was a narrow spectrum antibiotic. The first broad spectrum antibiotic, streptomycin, which affected all known bacteria was developed a few years later.

Today, there are several dozen different antibiotics. Each antibiotic kills bacteria in a different method. For example, penicillin prevents bacteria from forming new cell walls when it divides.

Most antibiotics have manageable side effects, such as stomach upset or diarrhea. However, many people are allergic to certain antibiotics, and death can result from anaphylactic shock in such patients.

One other complication is that many strains of bacteria have become resistant to certain antibiotics. Tuberculosis, for example, usually has to be treated for six months with three different broad spectrum antibiotics to assure that all resistant forms of the bacteria are eliminated. For this reason, it is usually vital that patients finish their entire dose of medicine, even after they start feeling better.

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