Antibiotics Lecture Notes

Introduction

• Discussing various types of antibiotics
• Focus on antibiotics affecting the cell wall
• Differences between gram-negative and gram-positive bacteria
  • Gram-negative bacteria: Thin peptidoglycan layer, outer cell membrane with porins, lipopolysaccharides
  • Gram-positive bacteria: Thick peptidoglycan layer, no outer cell membrane

Beta-lactams

• Structure: Beta-lactam ring (cyclic amide)
• Types: Penicillins, Amoxicillin, Cephalosporins

Penicillins

• Mechanism: Binds to penicillin-binding proteins (PBPs), activates autolytic enzymes, inhibits transpeptidase enzymes, disrupts cell wall, leads to cell lysis
• Resistance: Beta-lactamase enzyme breaks beta-lactam ring, rendering penicillin ineffective
• Coverage: Primarily gram-positive, some gram-negative
  • Effective for Streptococcal bacteria, Syphilis

Amoxicillin

• Mechanism: Same as penicillin
• Sensitivity: Susceptible to beta-lactamase
  • Often given with clavulanic acid (beta-lactamase inhibitor)
• Coverage: UTIs, respiratory tract infections, meningitis, salmonella, otitis media

Cephalosporins

• Mechanism: Same as penicillin
• Generations:
  • First Generation (e.g., Cephalexin): Mainly gram-positive
  • Second Generation (e.g., Cefuroxime): Mainly gram-positive
  • Third Generation (e.g., Ceftriaxone): Increased gram-negative coverage
  • Fourth Generation (e.g., Cefepime): Increased gram-negative coverage
• Coverage:
  • First and Second Generation: Staphylococcus aureus, Streptococcus pyogenes
  • Third and Fourth Generation: Pseudomonas aeruginosa, meningitis, Klebsiella, various Enterobacteria

Other Important Beta-lactams

• Pip-Tazo: Treats Pseudomonas
• Carbapenems: Treat problematic abdominal infections

Glycopeptides

• Vancomycin
  • Mechanism: Binds to carboxyl end of peptide chains, inhibits peptide bond formation, disrupts cell wall, causes cell lysis
  • Coverage: Primarily gram-positive (MRSA, C. difficile, resistant coagulase-negative bacteria)

Antibiotics for Mycobacterium (Tuberculosis)

• Isoniazid
  • Mechanism: Inhibits mycolic acid synthase, disrupts mycolic acid synthesis, alters cell wall integrity, leads to bacterial cell death
  • Coverage: Tuberculosis

Conclusion

• Covered antibiotics focusing on cell wall synthesis and structure
• Next topic: antibiotics targeting the folic acid pathway