What is bacteriocidal and bacteriostatic mean in relation to site of drug action?

[scilearner]

Hello everyone,

 

Bacteriocidal- Example quinolones who inhibit DNA synthesis

Bacteriostatic- like aminoglycosides which inhibit protein synthesis

 

Now my question is bacteriocidal means bacteria must be killed, now if DNA synthesis is inhibited, the bacteria won't be able to replicate and create proteins. Ok the lack of protein would kill the bacteria.

 

Now bacteriostatic means prevention of bacterial growth. How can inhibiting protein synthesis not kill the bacteria, and how does it prevent bacterial replication.

 

Also what category does beta lactamases which inhibit cell wall syntheis fall into.

 

Thanks

[CharonY]

The important bit regarding bacteriostatics is that they reversibly inhibit growth. If, at any point, it result in cell death, they are generally classified as bacteriocides. Note that lethality not only depends on the molecular target of the antibiotics but also the physiological context of the cell.

 

Quinolones have different ways to interact with DNA, resulting in cell death. Generally intefering with DNA replication is not necessarily lethal, however, interference of certain quinolones as trovafloxacin during dvision will mess up the replication so much, that the division does not work and the cells die. Other quinolones act upon RNA synthesis, for instance and are lethal under different conditions. Bet lactams inhibit cell wall synthesis, thus cells that are actively growing will be killed (i.e. it is bacteriocidal), however it is ineffective against cells that are not actively growing.

Edited January 15, 2012 by CharonY

[scilearner]

The important bit regarding bacteriostatics is that they reversibly inhibit growth. If, at any point, it result in cell death, they are generally classified as bacteriocides. Note that lethality not only depends on the molecular target of the antibiotics but also the physiological context of the cell.

 

Quinolones have different ways to interact with DNA, resulting in cell death. Generally intefering with DNA replication is not necessarily lethal, however, interference of certain quinolones as trovafloxacin during dvision will mess up the replication so much, that the division does not work and the cells die. Other quinolones act upon RNA synthesis, for instance and are lethal under different conditions. Bet lactams inhibit cell wall synthesis, thus cells that are actively growing will be killed (i.e. it is bacteriocidal), however it is ineffective against cells that are not actively growing.

 

Thanks for your reply . I understood the bactericidal part now but I still have a question about bacteriostatic drugs. Now definition of bacteriostatic means reversibly inhibit bacterial growth. . Now my question is even though protein synthesis is inhibited, the bacteria can still replicate and divide using DNA replication, they won't be able to cause damage but they will still increase. So isn't this contradictory with the definition. So when the drug is removed, you will suddenly find lot of bacteria who are now free to attack with full potential. Also I wished I asked this earlier, since your last bit was exactly the question asked in the mini test which I couldn't answer. Why are beta lactams not effective against resting organims.

Edited January 15, 2012 by scilearner

[CharonY]

the bacteria can still replicate and divide using DNA replication

 

Nope. All replication is protein-dependent. Think of the mechanisms of cell growth and DNA replication. Would a protein-free cell be able to do any of this? If you inhibit novel protein synthesis, the cell would have to rely on what it already has. Depending on what it is doing it could kill it, or just inhibit further growth.

 

For the latter question I advise you to look up precisely the function of beta lactams. Then think about what happens to the cell walls of actively growing cells as opposed to resting ones.