ANTIBIOTICS

Antibiotics

Antibiotics are chemical substances produced by a microorganism that has the capability, in low concentration, to inhibit selectively or even to destroy bacteria and other microorganisms through an antimetabolic mechanism.

An antibiotic (from Latin anti, "against" and Greek biotikos, "fit for life") is a chemotherapeutic agent that inhibits or abolishes the growth of micro-organisms, such as bacteria, fungi, or protozoa. The term originally referred to any agent with biological activity against living organisms; however, "antibiotic" now refers to substances with anti-bacterial, anti-fungal, or anti-parasitical activity. The first widely used antibiotic compounds used in modern medicine were produced and isolated from living organisms, such as the penicillin class produced by fungi in the genus Penicillium, or streptomycin from bacteria of the genus Streptomyces. With advances in organic chemistry many antibiotics are now also obtained by chemical synthesis, such as the sulfa drugs. Many antibiotics are relatively small molecules with a molecular weight less than 2000 Da.

Testing the susceptibility of Staphylococcus aureus to antibiotics by the Kirby-Bauer disk diffusion method. Antibiotics diffuse out from antibiotic-containing disks and inhibit growth of S. aureus resulting in a zone of inhibition.


Classification

Antibiotics can be classified on the basis of the biosynthetic origin of the antiobiotic molecule.

1) Antibiotics derived form amino acid metabolism.
Example- Penicillin, Amoxicillin, Cephalosporin, Chlorampheniclol, Dactomycin etc.
2) Antibiotics derived from acetate metabolism.
Example- Tetracyclines, 2- macrolides, griseofulvin etc.
3) Antibiotics derived from carbohydrate metabolism.
Example- Amkacin, gentamicin, kanamycin etc.