Antibiotics Classification with Examples

  • In this antibiotics classification with examples post we have briefly explained about history, classification, target group of microorganisms, and mode of action.
  • 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.


  • 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 trials were done in 1940.
  • It is produced by species of Streptomyces, Bacillus, Penicillium and Cephalosporium. Drugs such as the sulfonamides are sometimes called antibiotics although they are synthetic chemotherapeutic agents which are not microbially synthesized.

Antibiotics Classification with Examples

  1. Target group of microorganisms
  2. Antimicrobial spectrum
  3. Mode of action

Target group of microorganisms

  • Classification based on target group of microorganisms Based on the target group, the antibiotics can be classified as antibacterial, antifungal and antiviral.
  • Classification based on Antimicrobial spectrum Antimicrobial spectrum or antibiotic spectrum refers to the range 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,

a. Broad spectrum

  • 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.

b. Narrow spectrum

  • 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.

Mode of Action

  • The mode of action of antibiotics varies as they damage pathogens in several ways. Some of the important actions of therapeutic drugs in microbial pathogens are as follows. Cell wall synthesis Protein synthesis Nucleic acid synthesis Cell membrane disruption metabolic pathways blockage.

a. Inhibition of Cell Wall

  • The most selective therapeutic antibiotics are those that interfere with the synthesis of bacterial cell walls. These drugs possess a high therapeutic index because bacterial cell walls have a unique structure which is not found in eukaryotic cells. The important cell wall attacking drugs are Penicillin, Cephalosporin, Ampicillin, Methicillin and Vancomycin.

b. Inhibition of Protein

  • Many therapeutic antibiotics discriminate between prokaryotic and eukaryotic ribosomes and inhibit protein synthesis. The therapeutic index of these drugs is fairly high, but not as favorable as that of cell wall synthesis inhibitors.
  • Several of these drugs are medically useful and effective research tools because they block individual steps in protein synthesis. Some therapeutic drugs bind to 30S while others attach to 50S ribosomal subunits. Example Streptomycin, Chloramphenicol, Tetracyclin and Erythromycin

c. Nucleic Acid Synthesis

  • Some antimicrobial drugs or antibiotics inhibit nucleic acid synthesis. These are not selectively toxic as other drugs. This is due to the fact that prokaryotic and eukaryotic nucleic acid synthesis mechanisms do not vary greatly. Example Quinolones, Novobiocin, Actinomycin and Rifampin.

d. Disruption Membrane

  • There are some antimicrobial drugs or antibiotics that act as cell membrane disorganizing agents. Polymixins are such drugs of clinical importance. E.g. Polymixin B and Polymixin E (colistin).

e. Blocking Pathways

  • Some therapeutic drugs act as antimetabolites and block the functioning of metabolic pathways. They competitively inhibit the key enzymes in the metabolic pathway. Example Sulfonamides, Trimethoprim, Dapsone and Isoniazid.

Further Readings