Bacterial Structure and Antibiotic Resistance

Structural Components of Bacteria

• Cell Membrane
  • Surrounded by a cell wall
  • Some bacteria have an additional outer layer
• Internal Components
  • Cytoplasm contains ribosomes, nuclear region, and sometimes granules or vesicles
• External Structures
  • May include capsule, flagella, and pili

Gram-negative vs Gram-positive Bacteria

• Gram-negative Bacteria
  • Have a periplasmic space between cell membrane and cell wall
• Gram-positive Bacteria
  • Generally lack a periplasmic space but have periplasm
  • Thick cell wall due to multiple layers of peptidoglycan

Peptidoglycan Synthesis

• Structure
  • Polymer of N-acetylmuramic acid and N-acetylglucosamine
  • Cross-linked by a chain of four amino acids
• Function
  • Maintains bacterial shape
  • Prevents bursting from osmotic pressure
• Synthesis Stages
  • Addition of five amino acids to N-acetylmuramic acid
  • Formation of peptidoglycan precursor with N-acetylglucosamine
  • Transport and cross-linking in the periplasm
• Enzymes Involved
  • Transpeptidase and D-alanilcarboxypeptidase (penicillin-binding proteins)

Beta-lactam Antibiotics

• Mechanism of Action
  • Bind to penicillin-binding proteins
  • Inhibit peptidoglycan cross-linking
  • Lead to bacterial cell damage and lysis
• Effectiveness
  • Particularly effective against gram-positive bacteria due to high internal osmotic pressure

Mechanisms of Bacterial Resistance

• Transformation
  • Transfer of chromosomal genes between bacteria
  • Uptake of naked DNA containing resistance genes
  • Homologous transformation incorporating resistance genes into host DNA
  • Leads to altered penicillin-binding proteins with reduced affinity for beta-lactams
• Enzyme Production
  • Beta-lactamase enzymes inactivate or modify beta-lactams
  • Gram-positive Bacteria
    • Inducible enzyme production
    • Release beta-lactamase into extracellular environment
  • Gram-negative Bacteria
    • Constitutive enzyme production
    • Retain beta-lactamase in periplasmic space

Resistance Gene Transfer

• Conjugation
  • Transfer of resistance plasmids between bacteria via small channel
  • Plasmids encode beta-lactamase enzymes

Conclusion

• Resistance to beta-lactam antibiotics poses significant challenges
• Understanding bacterial structures and resistance mechanisms is crucial for developing effective treatments