Antibiotic Drugs
Antibiotic drugs (frequently referred to as antibiotics) are substances, usually obtained from microorganisms, that inhibit the growth of or destroy other microorganisms, particularly bacteria. Synthetic antibiotics also exist but the majority are analogs of naturally occurring antibiotics or their derivatives.
Antibiotics were first discovered in the nineteenth century when French chemist and bacteriologist Louis Pasteur demonstrated that one species of microorganism is capable of killing another. This idea was further developed by German bacteriologist Paul Ehrlich, who realized that selective toxicity was possible. Selective toxicity implies that a chemical can be toxic to one set of organisms, but leave others entirely unaffected. Many antibiotics come from bacteria, actinomycetes, and fungi. The most widely known antibiotic is penicillin, and its derivatives. Penicillin is produced by the mold Penicillium chrysogenum and the fact that it produces a substance capable of killing bacterial cultures was first noted by Scottish bacteriologist Alexander Fleming (1881- 1955) in 1928 (the discovery was made using a related species, Penicillium notatum). Fleming was unable to purify the active ingredient and it was left to Australian biochemist Howard Florey (1898-1968) and German biochemist Ernst Chain to isolate, characterize, and mass produce the antibiotic some ten years later.
Antibiotics are generally produced by fermentation in large vats of nutritive media. Other techniques are also used, such as de novo chemical synthesis and modification of natural products.
There are several different classification systems for antibiotics, based on chemical structure, origin, range, or action. Some antibiotics are broad spectrum and can be used against a wide variety of microorganisms, while others are very specific in their action and kill only microorganisms of one species or group.
Within naturally occurring populations of bacteria there are generally antibiotic-resistant strains. Once an antibiotic is used, resistant strains of the bacteria develop, and new antibiotics must be formulated to combat them. For this reason, it is important that antibiotics are not overused, since overuse ultimately will make them less effective. Antibiotics are frequently given to livestock animals to enhance their growth. Regarded a poor practice by some, the use of antibiotics encourages the growth of resistant bacteria in the animals and may lead to disease epidemics for which there are no treatments. When people consume meat or other products from antibiotic-treated livestock, they are exposed to low levels of these antibiotics. This can lead to sensitization, making individuals who consumed these food products unable to take that type of antibiotic when it is needed to treat a disease. Some antibiotics are useful for human diseases, while others are used only on other animals, and others still are generally only used in laboratories because their toxicity is so high to living organisms.
Humans take antibiotics orally, by injection, or topically (applied to the skin). The method of administration is governed by where the antibiotic needs to be to work, its stability, and its mode of action. Some antibiotics have side effects, e.g. they may produce rashes or send a patient into shock. An individual can be allergic to specific antibiotics and, in such a case, administration of these antibiotics can be fatal. Some antibiotics, such as the tetracycline group, are broad spectrum and kill useful bacteria as well as harmful ones. This can lead to an opportunistic infection by fungi or other microorganisms.
Tetracycline is a broad spectrum antibiotic that kills bacteria from both the gram-negative and gram-positive groups. It is isolated from bacteria in the genus Streptomyces and the active compound is based on a napthacene skeleton--an aromatic structure with four benzene-type rings. Erythromycin is active only against gram-positive bacteria. It is used for individuals who are allergic to penicillin and tetracycline and has the chemical formula C37H67NO13.
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