Anti-Biotics

Anti-Biotics

Anti-biotics, chemical substance produced by a living organism, generally a microorganism, that is detrimental to other microorganisms. Antibiotics commonly are produced by soil microorganisms and probably represent a means by which organisms in a complex environment, such as soil, control the growth of competing microorganisms. Microorganisms that produce antibiotics useful in preventing or treating disease include the bacteria and fungi.

Antibiotics came into worldwide prominence with the introduction of penicillin in 1941. Since then they have revolutionized the treatment of bacterial infections in humans and other animals. They are, however, ineffective against viruses.

The first anti-biotics

In 1928 Scottish bacteriologist Alexander Fleming noticed that colonies of bacteria growing on a culture plate had been unfavourably affected by a moldPenicillium notatum, which had contaminated the culture. A decade later British biochemist Ernst Chain, Australian pathologist Howard Florey, and others isolated the ingredient responsible, penicillin, and showed that it was highly effective against many serious bacterial infections. Toward the end of the 1950s scientists experimented with the addition of various chemical groups to the core of the penicillin molecule to generate semisynthetic versions. A range of penicillins thus became available to treat diseases caused by different types of bacteria, including staphylococcistreptococcipneumococci, gonococci, and the spirochaetes of syphilis.

Conspicuously unaffected by penicillin was the tubercle bacillus (Mycobacterium tuberculosis). This organism, however, turned out to be highly sensitive to streptomycin, an antibiotic that was isolated from Streptomyces griseus in 1943. As well as being dramatically effective against tuberculosis, streptomycin demonstrated activity against many other kinds of bacteria, including the typhoid fever bacillus. Two other early discoveries were gramicidin and tyrocidin, which are produced by bacteria of the genus Bacillus. Discovered in 1939 by French-born American microbiologist René Dubos, they were valuable in treating superficial infections but were too toxic for internal use.

Anti-Biotics

Use and administration of anti-biotics

The principle governing the use of antibiotics is to ensure that the patient receives one to which the target bacterium is sensitive, at a high enough concentration to be effective but not cause side effects, and for a sufficient length of time to ensure that the infection is totally eradicated. Antibiotics vary in their range of action. Some are highly specific. Others, such as the tetracyclines, act against a broad spectrum of different bacteria. These are particularly useful in combating mixed infections and in treating infections when there is no time to conduct sensitivity tests. While some antibiotics, such as semisynthetic penicillins and quinolones, can be taken orally, others must be given by intramuscular or intravenous injection.

Categories of anti-biotics

Antibiotics can be categorized by their spectrum of activity—namely, whether they are narrow-, broad-, or extended-spectrum agents. Narrow-spectrum agents (e.g., penicillin G) affect primarily gram-positive bacteriaBroad-spectrum antibiotics, such as tetracyclines and chloramphenicol, affect both gram-positive and some gram-negative bacteria. An extended-spectrum antibiotic is one that, as a result of chemical modification, affects additional types of bacteria, usually those that are gram-negative. (The terms gram-positive and gram-negative are used to distinguish between bacteria that have cell walls consisting of a thick meshwork of peptidoglycan [a peptide-sugar polymer] and bacteria that have cell walls with only a thin peptidoglycan layer, respectively.)

Anti-Biotics