Test 3-4 (antibiotics) Flashcards
-Define the terms “bacteriocidal” and “bacteriostatic” and be able to give some antibiotic examples that would fall into each of these categories. In a general sense, know what types of infections are treated with bacteriocidal and bacteriostatic antibiotics. -Describe the specific mechanism of action of the drugs for whom specific examples were given. -Know the definition of broad spectrum and narrow spectrum antibiotics, as well the advantages and disadvantages of each. -Describe specific b
Bacteriocidal drugs
kills the bacteria
ex: Aminoglycosides; Beta-Lactams; Quinolones
Bacteriostatic drugs
inhibits the growth of bacteria (no killing)
ex) Tetracyclines; Sulfonamides; Clindamycin; Chloramphenicol
Antibiotic therapy is
the treatment of bacterial infections using drugs that either kill microbes or interfere with bacterial growth. Whether a drug is bacteriocidal or bacteriostatic can depend on the bacteria treated and the antibiotic used.
when are bacteriocidal drugs used?
invasive infections such as bacteremia, meningitis, and bacterial endocarditis
when are bacteriostatic drugs used?
when the host defenses can be counted on to eliminate the bacteria
Cell wall inhibitors - antibiotics:
Penicillins, cephalosporins, vancomycin
Protein synthesis inhibitors - antibiotics
Aminoglycosides, macrolides, tetracyclines, chloramphenicol,erythromycin
Nucleic acid synthesis inhibitors - antibiotics
Quinolones, rifampin,Metronidazole
Folic acid synthesis inhibitors (anti-metabolites) - antibiotics
Sulfonamides (targets DNA), trimethoprim (targets RNA)
Steps in cell wall synthesis:
- The bacterial cell wall consists of strands of repeating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) subunits. The NAM subunits have short peptide chains attached to them. The proximal alanine is usually L-ala and the distal two are usually D-ala. These chains, in turn, are bound to chains of 5 glycine residues that will be used in cross-linking.
- The penicillin-binding protein (PBP) forms a bond with the peptide side chain at the second most distal alanine residue. This displaces the most distal alanine residue.
- Another strand of bacterial cell wall arrives. The free end of one of the pentaglycine chains displaces the PBP and forms a bond with the terminal alanine on the other strand.
- After being displaced, the PBP diffuses away.
- The formation of one cross-link is complete.
Penicillin-mediated inhibition:
-Penicillin enters the active site of the PBP and reacts with the serine group that is important in its enzymatic activity (Step 3).
-The beta-lactam ring of penicillin (represented here as the top of the “P”) is irreversibly opened during the reaction with the PBP. Penicillin remains covalently linked to the PBP and permanently blocks the active site (Step 4).
last line of defense to treat highly resistant bacteria?
vancomycin
Vancomycin mechanism:
1) Vancomycin recognizes and binds to the two D-ala residues on the end of the peptide chains.
2) Vancomycin binds to the peptide chains and prevents them from interacting properly with the cell wall cross-linking enzyme.
3) Cross-links cannot be formed and the cell wall falls apart.
bacteria that are resistant to vancomycin have…
-The last D-ala residue has been replaced by a D-lactate, so vancomycin cannot bind.
-Stable cross links are formed and cell wall is successfully made.
aminoglycside mechanism
-protein synth inh
-bind to multiple sites on both 30S and 50S== prevents the tRNA from forming initiation complexes
tetracycline mechanism
-protein synth inh
-bind to 30S ribosomes and prevent tRNA from forming initiation complexes
chloramphenicol mechanism
-protein synth inh
-blocks formation of the peptide bond bw the amino acids
erythromycin mechanism
-protein synth inh
-blocks the translocation of tRNA from the acceptor to the donor side on the ribosome
