USMLE1-Anti Bacterial Pharmacology

Antibacterial agents: substance that destroy bacteria or prevent their growth or replication.

Antibiotics: the general class of medications that are used against bacteria and also some parasites.

Anti microbial drugs can be either:

• Bactericidal: kill infecting organisms
• Bacteriostatic: slow their growth

Bactericidal drugs: Penicillin, Cephalosporins, Aminoglycosides, Quinolones/Fluoroquinolones
Bacteriostatic drugs: Sulfonamides, Tetracyclines, Erythromycin

Mechanism of Action of antimicrobial agents:

Inhibition of Bacterial Cell wall synthesis: Penicillins,Cephalosporins,Imipenem,Vancomycin

Inhibition of Bacterial protein synthesis: Aminoglycosides,chloramphenicol,macrolides,tetracyclines3.Inhibition of 3.Nucleic acid synthesis: Fluoroquinolones,Rifampicin

Inhibition of Folic acid synthesis: Sulfonamides,Trimethoprim,Pyrimethamine
Disruption of cell membrane function: Azoles and Polyene Anti fungal agents.

Bacterial Cell Wall - Basics:
Gram positive:

• Presence of Teichoic and lipoteichoic acids
• Have thick peptidoglycan layer, embeded in them is teichoic acid and lipoteichoic acid, most of the Antibiotics works on the peptidoglycans.

Gram negative:

• Thin peptidoglycan layer
• Outer membrane containing lipopolysaccharide (LPS), phospholipids and protiens
• It has periplasmic space which is btw cytoplasmic membrane and outer membrane.
• Gram -ve bacteria is resistance to antibiotic due to enzymes in periplasmic space.

Microbial Resistance to drugs

• Mutation: A stable and heritable genetic change that occurs spontaneously and randomly among microorganism e.g., Rifampicin resistant mycobacterium tuberculosis.

Resistance due to Gene transfer by:

• Conjugation: R factor transferred
• Transduction : transfer of resistance gene by bacteriophage (virus that infect bacteria)
• Transformation: by release of the resistance carrying DNA into the medium.

Due to alteration of expression of proteins in drug resistant organism:

• Lack or alteration of binding site: Penicillin (PBP)
• Lowered penetration/permeability:Beta lactams
• Increased efflux:Tetracycline, Fluoroquinolones
• Antibiotic inactivating enzyme: Beta lactams

Anti Bacterial Agents:

• Beta-Lactam Antibiotics : Pc, Cephalosporine

Three other classes of beta-lactam antibiotics are available
These are:

• Carbapenems/Imipenem
• Carbacephems
• Monobactams. 

 All beta-lactam antibiotics have the same bactericidal mechanism of action.- bacterial cell wall synthesis