Antibiotics and antibiotic resistance

• What are antibiotics?

  Naturally occurring antimicrobials
• What results from the modification of natural antibiotics?

  Semi-synthetic antibiotics are produced
• What are aminoglycosides?

  Antibiotics with amino sugars linked by glycosidic bonds
• Why are aminoglycosides considered reserve antibiotics?

  They are used when other antibiotics fail
• What are macrolides characterized by?

  Lactone rings bonded to sugars
• What is the target of erythromycin?

  The 50S subunit of the ribosome
• What do tetracyclines contain?

  Four rings in their structure
• What is the primary use of tetracyclines?

  Broad spectrum inhibition of protein synthesis
• Which ribosomal subunit do tetracyclines inhibit?

  The 30S ribosomal subunit
• What is the beta-lactam group known for?

  It includes penicillins, cephamycins and cephalosporins
• What percentage of antibiotics used worldwide are beta-lactams?

  Over half of all antibiotics
• Who discovered penicillins?

  Alexander Fleming
• What type of bacteria are penicillins primarily effective against?

  Gram-positive bacteria
• How do penicillins target bacteria?

  By targeting cell wall synthesis

  • bind covalently and irreversibly to the active site of PBPs necessary for peptide crosslinks
  • causes weakening of peptidoglycan layer and cell rupture
• What do quinolones inhibit?

  DNA gyrase
• How is resistance to quinolones mediated?

  By decreased binding to DNA gyrase
• What does vancomycin inhibit?

  Cell wall biosynthesis
• What is a limitation of vancomycin?

  Poor bioavailability and activity against gram-negative
• Why are gram-negative pathogens difficult to treat with vancomycin?

  Due to their outer membrane acting as a barrier

  • OM in gram- is a fundamental diffusive barrier that renders whole classes of antibiotics useless to treat gram-
  • antibiotics against gram- can either diffuse freely across OM or exploit OMPs to reach cell interior
• What is methicillin's mechanism of action?

  Inhibits cell wall biosynthesis
• Why is methicillin no longer used?

  It has become ineffective against bacteria
• examples of aminoglycosides

  • kanamycin
  • neomycin
  • amikacin
• why arent aminoglycosides used today

  neurotoxicity and nephrotoxicity