Fundamentals of Antibiotics Flashcards
Two groups of antibiotic agents?
Bacteriostatic and Bactericidal
What are bacteriostatic antibiotics?
They stop bacteria replication but don’t kill bacteria
What are Bactericidal antibiotics?
They kill bacteria
What do ‘folic acid synthesis’ inhibitors do?
They inhibit the synthesis of dihydrofolic (DHF) acid by competing with para-aminobenzoic acid (PABA). They also block the production of tetrahydrofolic acid (THF) by reversibly binding to dihydrofolate reductase enzymes required for the conversion of DHF to THF.
Why is THF so important?
Essential in the formation of DNA bases (guanine, adenine and thymine)
What do DNA topoisomerase inhibitors do?
Topoisomerase is used to unravel DNA strands to enable transcription and replication. However, topoisomerase enzymes e.g. fluoroquinolones bind to two nuclear enzymes which then inhibits DNA replication. Topoisomerase inhibitors prevent the enzyme from uncoiling the DNA strands so that transcription and replication can’t take place.
How is bacterial DNA damaged by antibiotics?
1) Forms Reactive Oxygen Species resulting in oxidative damage of DNA.
2) Antibiotic forms covalent adduct with proteins involved in antioxidant defence making the cells more vulnerable to oxidative stress.
How is bacterial mRNA synthesis inhibited?
Antibiotic targets RpoB of the RNA polymerase enzyme. This inhibits transcription.
How do macrolides inhibit protein synthesis?
They bind reversibly to the 50S subunit preventing the transfer of peptidyl-tRNA from the A-site to the P-site (prevents translocation). So the amino acids can’t join to form a polypeptide.
Role of tetracycline in inhibiting protein synthesis?
Inhibits aminoacyl-tRNA binding to mRNA-ribosome complex. Tetracycline binds to the 30s ribosome in the mRNA translation complex. So inhibits translation.
Role of aminoglycosides in inhibiting protein synthesis?
Bind to 30s ribosomal sub-unit and cause the mis-reading of the genetic code. This means faulty proteins will be made as it interrupts normal bacterial protein synthesis.
Role of vancomycin in inhibiting cell wall synthesis?
It inhibits the 2nd stage of cell wall synthesis of susceptible bacteria. It also alters cell membrane permeability and selectively inhibits RNA synthesis.
Why are bacteria with beta-lactamase enzymes dangerous?
Because they can break the bond in the beta-lactam ring in penicillin hence inactivating the drug. This makes these bacteria resistant to penicillin.
Effect of Ergosterol synthesis inhibitors on fungus?
Causes fungal cell death!
Role of Caspofungin antibiotic?
Blocks the synthesis of beta (1,3)-d-glucan of fungal cell wall by non-competitive inhibition of beta(1,3)-d-glucan synthase. -Glucan is an essential component of fungal cell walls.