MIIM - Antibiotics I - Week 9 Flashcards
What is the multiplication threshold for disease and what effect do antibiotics have?
It is the level of microbial multiplication within the body required to cause disease. It usually begins in the later phase of being infected. Antibiotics reduces microbial multiplication to be below the threshold so the disease never occurs (or much less severe symptoms)
What are antibiotics (and other drug classes like them) directed at?
Replicating organisms
List the four classifications of antibiotics.
Source
Chemical structure
Spectrum
Mechanism of action
Name two antibiotics classes that are classified by having a B-lactam ring.
Penicillin
Cephalosporin
Name and describe the three key considerations for an antibiotic to be safe and effective in humans (6).
Selective toxicity
-target the organism not humans
Access to the site of infection
-achieve adequate levels where the organism is
Provision of appropriate levels for an appropriate time
-maintain adequate levels to allow inhibition or killing
True or false
Organisms that are resistant to an antibiotic at one site in the body may not be resistant at other sites.
True - organisms resistant at one site may be sensitive at other sites
List 9 major sites of action that a given antibiotic can have.
Nucleic acid replication
Folic acid
RNA synthesis
Peptide synthesis
Nucleotide synthesis
Mycolic acid synthesis
Nicotinamide (antimycobacterial)
Cell membrane synthesis
Peptidoglycan synthesis
Describe how antimicrobial agents enter gram positive and negative bacteria.
Positive - enter easily through the loose outer wall
Negative - must go through narrow porin channels
Briefly describe bacterial cell wall synthesis in 5 steps.
Production of the peptidoglycan monomer in the cytoplasm
Transport across the membrane
Cleavage of the existing peptidoglycan by autolysins
Addition of the new monomer
Peptide crosslinking by transpeptidation by transpeptidases
What is the mechanism of action for a B-lactam antibiotic? What is it a structural analogue of exactly?
It acts as a structural analogue of D-ala - D-ala. They inhibit transpeptidases as well as enzymes that remodel the cell wall.
What are penicillin binding proteins and how do they determine the spectrum a given antibiotic?
Transpeptidases and other enzymes involved in remodelling the cell wall.
Different bacteria may have different kinds of these proteins and will therefore determine the spectrum of the antibiotic
Describe the consequence of an antibiotic binding to terminal D-ala - D-ala residues. Give an example of an antibiotic that does this.
Prevents cross-linking and thus prevents the incorporation of additional NAG-NAM subunits into the growing peptidoglycan chain, weakening the cell wall.
Vancomycin
Briefly describe how bacitracin antibiotics work.
It acts after the NAG-NAM subunit has been added to the chain.
It prevents dephosphrylation of the phospholipid carrier, preventing its regeneration.
What gram type is bacitracin effective against? Considering its mechanism of action, is it significantly toxic to humans or not?
Effective against gram positives and some gram negatives.
Has significant toxicity, so is topical only.
What is the consequence of inhibiting cell wall synthesis?
The bacteria continue to grow, the cell wall weakens, and eventually the bacteria lyses.