Antiobiotic Action Flashcards
Define antimicrobials/antibiotic
-2 types
Agents that kills microorganisms or stops their growth
2 types:
-antibiotic- microbial origin (commonly made by a bacteria)
-antimicrobial- chemically synthesised
Selective toxicity meaning
-how do bacteria exert selective toxicity
kill or inhibit the infecting organism without damaging the host
-targets something unique to bacteria e.g peptidoglycan of cell wall
2 types of actions of antimicrobials
Bactericidal
-kills bacteria
-is irreversible
-may or may not cause lyses of bacteria
Bacteriostatic
-suppresses bacteria but doesn’t kill it
-reversible
What are the sites of action of main antibiotics
Cell wall
Plasma membrane
Ribosomes
DNA synthesis
Metabolic pathways
Best target for selective toxicity
Cell wall
Peptidoglycan is made up of 2 components:
N-acetylglucosamine (NAG)
N-acetylmuramic (NAM)
Basic subunits of petidoglycan
NAG, NAM, peptide connected together
Describe process of biosynthesis of peptidoglycan
1.Subunit of peptidoglycan made in cytoplasm
2.Transported across cell membrane
3.Once in cell wall added to growing peptidoglycan chain
4.Strength and rigidity of structure provided by cross links of peptide bonds
Name antibiotics which inhibit each step of biosynthesis of peptidoglycan
1.Subunit of peptidoglycan made in cytoplasm—> cycloserine, fosfomycin
2.Transported across cell membrane—> bacitracin
3.Once in cell wall added to growing peptidoglycan chain —> glycopeptides
4.Strength and rigidity of structure provided by cross links of peptide bonds—> beta-lactams e.g penicillin (most important group)
4 types of beta-lactams antibiotics
Penicillin
Cephalosporin
Monobactam
Carbapenem
What do all b-lactams have in common?
All have a b-lactam ring (square shaped ring with double bonded oxygen and single bond nitrogen)
Which of the b-lactam antibiotics is only used in humans- shouldn’t be used in animals
Cephalosporin
B-lactam antibiotics only work on what kind of bacteria?
Growing bacteria
Steps of bacterial replication
-Bacterial cells chromosome replicates and cell elongates (stretches)
-chromosome separates and cytoplasmic membrane and cell wall invaginates
-cross wall formation complete
-daughter cells separate
How does b-lactam antibiotic work
For elongation of bacteria (during bacterial replication), it must make breaks in the peptidoglycan in order to add more peptidoglycan. Whilst it’s doing that peptidoglycan is weak, causing water to enter the cell which drives the elongation of bacteria. However this breakage in cell allows for b-lactam inhibition
Microscopic effect of b-lactam on bacteria
Normal Bacteria—> Cell growth—> bulging of cell—> lysis of cell
Name the protein synthesis inhibitors (PSIs)
Aminoglycosides
Chloramphenicol
Macrolides & Lincosamides
Tetracyclines
Protein synthesis inhibitors (PSI): Aminoglycosides
-what does it do
Inhibits initiation of bacterial protein synthesis
Causes misreading of mRNA
Proetin synthesis inhibitors: Chloramphenicol, macrolides and lincosamides
-function
-All inhibit peptidoglycan transferase which transfers the amino acid from tRNA P site to A site during translation
-macrolides & lincosamides: inhibit translation of ribosome along mRNA
Protein synthesis inhibitor: tetracyclines
Bind to A site and prevent binding of tRNA coming with amino acid
Bacteria DNA must be tightly wound inside cell. Which enzymes activate the super coiling and Which antibiotics inhibit this super coiling of DNA
Topoisomerase II activates
Quinolones and 4-fluoroquinolones inhibit
Antibiotic which disrupts gram negative bacterial membrane
-properties
Polymixins
-cyclic peptide, not made of ribosomes
-have a free fatty acid residue which acts like a detergent
-disrupt cytoplasmic membrane
-very toxic so not used when possible
Antibiotic which disrupts gram positive bacterial membrane
-causes what
Daptomycin
-causes loss of ions from interior of bacteria
3 types of interaction of antibiotics
Synergism- 2 o more drugs work together fora better effect against bacteria
Antagonism- drugs working together causes a worse effect on bacteria (want to avoid this one)
Indifference- drugs working together doesn’t make a difference
