Antibacterials Flashcards
What do class I reactions in bacteria produce?
Precursor molecules & ATP
What do class II reactions in bacteria produce?
Hexosamines, amino acids & nucleotides
What do class III reactions in bacteria produce?
Peptidoglycan, proteins, RNA & DNA
What are the major targets for antibacterial drugs?
- DNA gyrase
- DNA-directed RNA polymerase
- Cell-wall synthesis
- Folic acid metabolism
- Oxazolidinones
- Protein synthesis
- 50s & 30s ribosomes
Which class of bacteria are more sensitive to penicillins?
Gram +Ve
gram -ve
- lipopolysaccharide layer which prevents penicillins getting to the site of action
What is the action of beta-lactams in terms of inhibiting peptidoglycan?
Prevent the cross-linking peptides from binding to the tetrapeptide side-chains
What is the antibacterial activity of Beta-lactams?
Have an ability to bind penicillin binding proteins to inhibit transpeptidases
What is the antibacterial activity of Beta-lactams?
Have an ability to bind penicillin binding proteins to inhibit transpeptidases
How can resistance to beta-lactams develop?
Mutations in transpeptidases & beta-lactamase activity
What is the action of clavulanic acid?
Beta-lactamase inhibitor, no antibacterial effect alone
What is benzylpenicillin most effective against?
Gram positive bacteria & cocci
Why can benzylpenicillin not be administered orally?
Is acid instable so will be broken down in stomach
What is the acid stability of ampicillin?
Medium
What is the acid stability of amoxicillin?
Very good
What is the beta-lactamase stability of ampicillin and amoxicillin?
Susceptible
What is the spectrum of ampicillin and amoxicillin?
G+ cocci and G-
Which antibacterials compete with tRNA for the A site?
Tetracyclines
Which antibacterials inhibit peptide bond formation?
Chloramphenicol and florfenicol
Which antibacterials inhibit translocation?
Macrolides
How do sulphonamides & trimethoprim target bacteria?
Inhibit bacterial folate synthesis
What enzyme do sulphonamides target?
Dihyrdropteroate synthetase
What enzyme does trimethoprim inhibit?
dihydrofolate reductase
What are the biochemical mechanisms of antibiotic resistance?
- Inactivation of the antibacterial drug
- Alteration of the target site
- Decrease drug accumulation in the bacterium
- Upregulate synthesis of target
- Alter metabolic pathway of bacteria
What will happen if the gene for beta-lactamase is encoded on a bacterial chromosome and how is it different to a plasmid?
Chromasomal - Expression inducible, won’t produce beta-lactamase until exposed to the drug
Plasmids - constitutively produced
How can drug binding sites be altered?
- Mutations in proteins
- erythromycin resistance - mutation in 50S subunit
- Quinolones - mutation in DNA gyrase
What do efflux pumps do?
method of decreasing drug accumulation - remove the tetracyline from the bacterium so it cant inhibit protein synthesis
