How Antibiotics Work?
All the antibiotics work in two different ways or in combination of the two(source:medicalnewstoday.com).
Bactericidal - This type of antibiotic kills the bacteria by interfering with the formation of cell wall or the cell contents. Penicillin is an example of this type of antibiotic.
Bacteriostatic - The definition of bacteriostatic implies that it inhibits the growth of bacteria by multiplying. This type of antibiotic keeps the bacteria in a stationary growth phase.
Many antibiotics, like penicillin, act by attacking the bacterial cell. These drugs specifically prevent synthesis of peptidoglycan, a macromolecule that is made up of amino sugars and peptides, which provides strength to the cell wall of bacteria, in order to survive in the human body. Other antibiotics of this class which prevent the assembly of peptidoglycan, include Cephalosporins, Carbapenems, Vancomycin, Polymycin, and Bacitracin.(source:medicalnewstoday.com)
Polymixin B and colistin are inhibitors of cell membrane function. But their clinical usage is limited to topical applications, because of their non-selective action which could result in host toxicity.
Their mode of action is by preventing DNA replication, protein synthesis or other cellular mechanisms, vital in reproduction. Ciprofloxacin and other antibiotics which are in the class quinolones, act against DNA gyrase, which is an important enzyme in DNA replication, thus inhibiting the multiplication of bacteria.
The antibiotics that inhibit protein synthesis include tetracyline, chloramphenicol, and erythromycin. These types of drugs prevent protein synthesis by inhibiting the binding of key molecules on ribosomes, the place where protein synthesis occurs.
Some antibiotics like Rifamycin, which are treated for tuberculosis, provide bacteriostatic effect by inhibiting the RNA synthesis, thus preventing the translation of DNA into proteins.
Some other antibiotics act against infections by preventing the bacterial production of folic acid, which is essential for growth and reproduction. Some examples are sulfonamides and trimethoprim.
It is also important to note that the selective action of antibiotics against bacteria, not against the host cells is what makes them useful in the treatment of infections.
Due to their different modes of action, when choosing an antibiotic for the treatment of bacterial infection, physicians may either select a bactericidal drug, a bacteriostatic drug or a combination of the two (source:news-medical.net). Since an antibiotic that is effective for one strain of bacteria may only cause the growth inhibition of another strain, the selection will not be always impeccable.
A Book on Amazon : Antibiotics and Antibiotic Resistance by Ola Sköld. The book provides an in depth discussion of antibiotics.
Written by: Anila J., United States (Post Graduate in Biology).
Edited by: Rajesh Bihani ( Find me on Google+ )