Penicillin G Overview Quiz

Antibiotics Lecture Notes

• Course Information:
  • Block 1.2 Lectures
  • 2024-2025
  • Antibiotics lecture
  • Presented by Abdulhamid Al-Abadi
  • Reviewed by Eithar zaki
  • Notes 221-222-223
  • References and student explanations also covered
  • Topics include bacterial infection treatment, bacterial cell structure, antibiotic classification, mechanisms of action, resistance, and side effects of penicillin and cephalosporins

Bacterial Cell Structure

• Key Differences from Human Cells: Bacterial cells lack a nucleus and possess a cell wall, distinguishing them from human cells.
• Cell Wall: This outer layer covers the cell membrane, crucial for bacterial survival; its destruction leads to bacterial death.
• Bacterial cell wall's Function: protection
• Importance of Cell Wall: Cell wall destruction is the primary target of many antibiotics.

Bacterial Cell Wall

• Gram-Positive: The cell wall is thick and composed of multiple layers of peptidoglycan, which are polymer of alternating NAM and NAG.
• Gram-Negative: The cell wall is thinner, sandwiched between two membranes (outer and inner); it also contains peptidoglycan, and lipoproteins & lipopolysaccharide.
• Peptidoglycan: A polymer composed of alternating N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) subunits. Cross-links between these layers give the cell wall strength.

Synthesis of Bacterial Cell Wall

• NAM & NAG Production & Assembly: Synthesized inside the cell and then assembled to form the bacterial cell wall.
• Transpeptidases: Enzymes crucial in cross-linking peptidoglycan for cell wall formation. Antibiotics targeting these enzymes impede bacterial reproduction by inhibiting cell wall synthesis.
• Antibiotics Target: Antibiotics target transpeptidase enzymes to inhibit cell wall synthesis, preventing or halting bacterial growth and replication.

Classification of Antimicrobials

• Bacteriostatic:
  • Inhibits bacterial growth but does not kill them.
  • Examples: Erythromycin and Isoniazid
• Bactericidal:
  • Kills bacteria directly.
  • Examples: Aminoglycosides, Beta-lactams, Vancomycin, Quinolones, Rifampin, Metronidazole
• Classification by Concentration:
  • Bacteriostatic or bactericidal effects depend on concentration.

Penicillin

• Preparations:
  • Penicillin G: Natural form of penicillin, short duration of action (6 hours), acid-sensitive (not effective orally).
  • Acid sensitive
  • ß-Lactamase sensitive (enzyme degrades the penicillin).
• Mechanism of Action:
  • Binds to penicillin-binding proteins (PBPs)
  • Inhibits cell wall synthesis
  • Activates autolytic enzymes (leads to cell lysis).
• Side Effects:
  • Allergy (cross-reactivity with other beta-lactams), gastrointestinal upset (diarrhea).

Penicillin: Resistant Strains

• Beta-Lactamase Production: Some bacteria produce beta-lactamases, which destroy penicillin. Resistance can be overcome by combining penicillin with a beta-lactamase inhibitor.

Cephalosporins

• Mechanism:
  • Similar to penicillin, inhibiting cell wall synthesis.
  • More resistant to beta-lactamases
• Generations:
  • 1st generation: Active against mainly gram-positive organisms
  • 2nd generation: less effective against gram-positive, more effective against gram-negative
  • 3rd generation: broad spectrum, more effective against gram-negative, can cross the blood-brain barrier (BBB)
  • 4th generation: more resistant to beta-lactamases, effective against gram-negative bacteria
  • 5th generation: most advanced generation of cephalosporins, highly effective against serious infections
• Uses: Infections resistant to penicillin, anaerobic infections, respiratory tract infections, urinary tract infections, meningitis
• Side Effects: Allergies, gastrointestinal distress, and nephrotoxicity (kidney damage)

Fluoroquinolones

• Mechanism of Action: Inhibit bacterial DNA synthesis, specifically targeting topoisomerase enzymes.
• Use: Urinary tract infections, sexually transmitted diseases (e.g., gonorrhea, chlamydia), typhoid fever, intra-abdominal infections, osteomyelitis, and septicemia.
• Side Effects: Hypersensitivity reactions, photosensitivity, nephrotoxicity, joint damage.
• Antimicrobial Classes and Their Functions:
  • Categorization of antibiotics according to their target in bacteria.

Quiz Questions & Answers

• Question 1: Which type of antibiotic primarily works by inhibiting cell wall synthesis in bacteria?
  • Answer: Penicillin
• Question 2: Which class of antibiotics works by inhibiting bacterial DNA synthesis?
  • Answer: Fluoroquinolones
• Question 3: What is the primary mechanism of resistance to penicillin in some bacterial strains?
  • Answer: Production of beta-lactamas enzyme
• Question 4: Which generation of cephalosporins is primarily effective against Gram-negative bacteria and can cross the blood-brain barrier, making it useful in treating meningitis?
  • Answer: Third generation
• Question 5: What is the difference between bactericidal and bacteriostatic antibiotics?
  • Answer: Bactericidal antibiotics kill bacteria directly, while bacteriostatic antibiotics inhibit bacterial growth.