Question

If a cell is dormant and not actively growing dividing, will penicillin have any effect? Is this something to consider when taking antibiotics? Why?

Answer 1

Bactericidal mechanism of pennicillin can be of two types : Bacteriostatic and Bacteriocidal

Bacteriostatic means it just inhibhits or stop the growth of organism and there is no further increase in their numbers.Examples : Tetracyclins , Erythromycin and Chloramphenicol

While bacterocidal antibiotics kills the bacteria and there occurs decrease in their number. Example : Pennicillin ,Cephalosporins , Fluoroquinolones and Aminoglycosides.

Now coming to pennicillin , its mechanism of action :

Bacterial cell wall is made up of peptidoglycan : Muramic acid and N acetylglucosamine. They are synthesized as UDPmuramic acid and UDP N acetylglucosamine. UDP is split off and they attach to form long chains . Finally terminal D-Alanine is removed with transpeptidases and the energy released is used in establishing the cross linkages which provide rigidity to the cell .

Pennicillin binds to transpeptidases and pennicillin binding proteins ( PBPs) and inhibhit them . Therefore Cell wall synthesis is interferred.

When susceptible bacteria multiply in presence of pennicillin , cell wall deficient forms are seen which rupture due to hyperosmotic cytoplasm which pulls in water accounting for bactericidal mechanism of pennicillin.

So, pennicillin will show its action only on actively dividing cell. In the above mentiones condition , pennicillin wont have any effect.

Yes, this is something to consider when taking antibiotics , That is why we never give bacteriostatic and bacteriocidal drugs together.