What are antibiotics ? 

These are chemical compounds may be of natural origin or synthetically formed and are used to kill or stop the growth of bacteria.

Mechanism Based Classification


These antibiotics are used to stop the growth of bacteria.


These antibiotics are used to kill the bacteria.

Spectrum Based Classification

1- Narrow Spectrum:

These antibiotics only act either gram positive or gram negative bacteria.

2- Broad Spectrum:

These antibiotics are effective against both gram positive and gram negative bacteria at the same time.

Mode of Action Based Classification

1- Protein Synthesis Inhibition:

These antibiotics stops the synthesis of proteins in bacteria which are responsible for their growth and internal functions of their cells. When these proteins are not synthesized the bacterial cell is unable to grow or multiply and can’t perform its functions. In bacterial cell ribosomes play an important role for protein synthesis. It has two components named as 50 S and 30 S. Some antibiotics bind 30 S to stop protein synthesis and some bind 50 S for this purpose. Those antibiotics which play their role in protein inhibition are bacteriostatic.

2- DNA Gyrase Inhibitor:

Antibiotics also inhibit the formation of DNA gyrase topoisomerase which is responsible for the super coiling during DNA replication. Inhibition of DNA gyrase disturb the DNA replication and bacterial cell can not multiply.

3- Cell Membrane Inhibitor:

Antibiotics also disrupt the cell membrane of the bacteria. When cell membrane is not develop properly the cytosol in the bacterial cell release and the cell death takes place.

4- Cell Wall Inhibitor:

Cell wall is the outer covering of many bacteria for their protection. Some antibiotics stop the formation of cell wall and the cell bursts due to internal pressure and cell death takes place.

5- Folic Acid Inhibitors:

Nucleic acid in bacterial genome is main part and folic acid is the precursor for this. Antibiotics takes part in mechanism of the folic acid synthesis and stop its production.

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Major Groups of Antibiotics are following

1- Tetracyclines

2- Aminoglycosides

3- Macrolides

4- Chloremphenicol

5- Fluoroqunolones

6- Polymyxins

7- Lincosamides

8- Sulfonamides

9- Penicillin

10- Streptogrammins

11- Diaminopyrimidines