Bactericidal activity:
Ability of a drug to directly kill bacteria leading to decreased number of
viable bacteria.
Bacteriostatic activity:
Ability of a drug to inhibit bacterial growth without killing the
organisms
Bacteriostatic drug withdrawn Bacteria resume growing.
These drugs depend entirely on patient’s host defense mechanisms
to actually destroy bacteria e.g. phagocytosis.
Distinction b/w both
Bactericidal required for:
immediate life threatening infection
Patient with severely compromised immune system.
Necessary for endocarditis; where fibrinous network of vegetations limits
ability of phagocytes to clear the bacteria
Bacteriostatic required for:
Competent immune system with functional phagocytes
Phagocytes eliminate bacteria once the replication has stopped.
MOA of antibacterial drugs:
Operate on principle of selective toxicity
They exploit the structural and metabolic differences b/w bacterial
and human cells to inhibit microorganism growth w/o damaging the host.
They target 1 out of 4 possible sites.
1. Inhibition of cell wall synthesis:
a. Humans lack peptidoglycan cell walls thus highly selective
b. Penicillin and cephalosporins (β-lactams)
i. Bind to PBPs
ii. Inhibit transpeptidases
iii. No crosslinking in synthesis of peptidoglycan
c. Vancomycin
i. Binds directly to D-alanyl-D-alanine portion of pentapeptide
ii. Physically blocks transpeptidase enzyme from making
cross links
d. Cycloserine and bacitracin:
Ability of a drug to directly kill bacteria leading to decreased number of
viable bacteria.
Bacteriostatic activity:
Ability of a drug to inhibit bacterial growth without killing the
organisms
Bacteriostatic drug withdrawn Bacteria resume growing.
These drugs depend entirely on patient’s host defense mechanisms
to actually destroy bacteria e.g. phagocytosis.
Distinction b/w both
Bactericidal required for:
immediate life threatening infection
Patient with severely compromised immune system.
Necessary for endocarditis; where fibrinous network of vegetations limits
ability of phagocytes to clear the bacteria
Bacteriostatic required for:
Competent immune system with functional phagocytes
Phagocytes eliminate bacteria once the replication has stopped.
MOA of antibacterial drugs:
Operate on principle of selective toxicity
They exploit the structural and metabolic differences b/w bacterial
and human cells to inhibit microorganism growth w/o damaging the host.
They target 1 out of 4 possible sites.
1. Inhibition of cell wall synthesis:
a. Humans lack peptidoglycan cell walls thus highly selective
b. Penicillin and cephalosporins (β-lactams)
i. Bind to PBPs
ii. Inhibit transpeptidases
iii. No crosslinking in synthesis of peptidoglycan
c. Vancomycin
i. Binds directly to D-alanyl-D-alanine portion of pentapeptide
ii. Physically blocks transpeptidase enzyme from making
cross links
d. Cycloserine and bacitracin:
