The term ‘antibiotic’ was derived from ‘antibiosis’ which refers to the suppression of microorganisms due to secretion of toxic or inhibitory compounds by other microorganisms. Although antibiosis has been observed by many scientific workers fairly frequently towards the end of the nineteenth century, it was not until the discovery and development of Penicillin that a truly wide ranging search for antibiotics was initiated.
Antibiotics are not effective against viral infections such as the common cold.
The first chemotherapeutic agent, discovered by Paul Ehrlich, was Salvarsan, used to treat syphilis.
Alexander Fleming discovered the first antibiotic, penicillin, in 1929; its first clinical trails were done in 1940.
Antibiotics are produced by species of Streptomyces, Bacillus, Penicillium and Cephalosporium
1904 Ehrlich found that the dye trypan red was active against the trypanosome that causes African sleeping sickness and could be used therapeutically
Drugs such as the sulfonamides are sometimes called antibiotics although they are synthetic chemotherapeutic agents which are not synthesized using microbes.
The antibiotics are usually classified on the basis of:
• Target group of microorganisms
• Antimicrobial spectrum and
• Mode of action
Based on the target group, the antibiotics can be classified as antibacterial, antifungal and antiviral.
Antimicrobial spectrum or antibiotic spectrum refers to the range of effectiveness of antibiotics on different kind of microorganisms, i.e. the range of different kind of microorganisms that can be inhibited, killed, or lysed by a particular type of antibiotic.
The susceptibility of microorganisms to individual antibiotic varies significantly and on account of this, the antibiotics can be classified in two groups as,
These attack different kinds of microbial pathogens and therefore find wider medical use. Antibacterial antibiotics of broad – spectrum are effective against both Gram positive and Gram negative bacteria. They also attack pathogens belonging to Mycobacteria, Rickettsia, and Chlamydia . Similarly, broad – spectrum antifungal antibiotics attack different type of fungal pathogens.
Narrow – spectrum antibiotics are categorized as those that are effective only against a limited variety of microbial pathogens. These antibiotics are quite valuable for the control of microbial pathogens that fail to respond to other antibiotics. For example, vancomycin is a narrow spectrum glycopeptide. It is an effective bactericidal agent for gram – positive penicillin resistant bacterial pathogens belonging to genera Staphylococcus, Bacillus, and Clostridium.