IMMUNOLOGY - Antibiotic Action Flashcards
What is selective toxicity?
An agent which harms the invading organism without harming the host
Define bactericidal antibiotics
Antibiotics which kill the bacteria
Define bacteriostatic antibiotics
Antibiotics which inhibit the growth of bacteria. This action is reversible
Which category of antibiotics target peptidoglycan within the bacterial cell wall?
β-lactams
Give three examples of β-lactam drugs classes
- Penicillin
- Cephalosporin
- Monobactam
How do β-lactam drugs kill bacteria?
β-lactam drugs inhibit the action of transpeptidase enzymes which cross-link the peptide bonds between the NAG-NAM dimers that make up the peptidoglycan layer of the cell wall. This occurs during bacterial replication causing the bacteria to lose its structure and rigidity and eventually bulge and lyse due to the bacteria’s high internal oncotic pressure
How is penicillin G and penicillin V administered?
Penicillin G is administered via the parenteral route and penicillin V is administered orally
What are the benefits of ampicillin and amoxicillin drugs compared to penicillin?
- Target G+ and more G- bacteria than penicillin
- Parenteral AND oral administration
What is the advantage of using methicillin drugs?
Targets G+ bacteria including β-lactamase producing bacteria
What are the main drug classes which disrupt bacteria protein synthesis?
- Aminoglycosides
- Chloramphenicol
- Tetracyclines
- Macrolides and Lincosamides
What is unique about aminoglycoside drugs compared with other drug classes which disrupt bacteria protein synthesis?
Aminoglycosides are bactericidal
How do aminoglycoside drugs inhibit protein synthesis in bacteria?
Aminoglycosides inhibit the initiation of translation
How do chloramphenicol drugs inhibit protein synthesis in bacteria?
Inhibit the enzyme peptidase transferase which is involved in forming peptide bonds between the amino acids of the developing protein
How do macrolide and lincosamide drugs inhibit protein synthesis in bacteria?
- Inhibit the enzyme peptidase transferase which is involved in forming peptide bonds between the amino acids of the developing protein OR Inhibit translocation of the ribosome along the mRNA
How do tetracycline drugs inhibit protein synthesis in bacteria?
Block the ‘A’ site, preventing the binding of tRNA to the mRNA
What are the main drug classes which inhibit the biosynthesis of folic acid in bacteria?
- Sulphomanides
- Trimethoprim
Why is folic acid biosynthesis essential for bacteria to survive?
Folic acid is requires for 1-carbon metabolism (which is required for nucleic acid synthesis). Bacteria have to carry out folic acid biosynthesis as unlike vertebrates, bacteria cannot gain folate as a vitamin and instead have to synthesis their own
Which enzyme involved in folic acid biosynthesis is inhibited by sulphomanide drugs?
Dihydropteroate synthase (DHPS)
Which enzyme involved in folic acid biosynthesis is inhibited by trimethoprim drugs?
Dihydrofolate reductase (DHFR)
Sulphonamide drugs and trimethoprim drugs are often clinically used together. What is the collective term for these drugs?
Potentiated sulphonamides
(T/F) Sulphonamides and trimethoprim drugs are chemically made
TRUE
What is the main drug class which inhibits DNA replication in bacteria?
4-fluoroquinolones
Give an example of one of the most commonly used 4-fluroquinolones
Enrofloxacin
How do 4-fluoroquinolone drugs inhibit DNA replication in bacteria?
Inhibition of topoisomerase enzymes involved in coiling bacterial DNA
What is the main drug class that damages bacterial DNA?
Nitromidazoles
Give an example of a nitromidazole drug
Metronidazole
What is a unique feature of selective toxicity in nitromidazoles?
Nitromidazoles need to be reduced within anaerobic bacteria in order to activate and cause DNA damage, ultimately killing the bacteria (bacteriacidal)
(T/F) The use of metronidazole is prohibited in food-producing animals
TRUE. The use of metronidazole in animals has proven to be genotoxic, carcinogenic and mutagenic
What is the main class of drugs which disrupts the cytoplasmic membrane of Gram negative bacteria?
Polymyxins
What is the main class of drugs which disrupts the cytoplasmic membrane of Gram positive bacteria?
Depatomycin
Sometimes different antibiotics need to be given at the same time. Describe the different possible interactions between antibiotics
Synergism: combined antibiotics have a greater effect
Antagonism: combined antibiotics have a negative effect on one another
Indifferent: combined antibiotics have no effect on one another
