Antibiotics Lecture Overview

Antibiotics Lecture

• Writer: Abdulhamid Al-Abadi
• Reviewer: Eithar zaki
• Notes: 221-222-223
• Lecture Title: Antibiotics
• Date: 2024-2025

Bacterial Cell Structure

• Human cells differ from bacterial cells in having no nucleus; bacterial DNA is in the cytoplasm
• Bacterial cells have a cell wall, which is the outer layer covering the cell membrane
• The cell wall protects bacteria, and its destruction can kill bacteria
• The lecture includes a diagram of a typical prokaryote cell, highlighting components like cytoplasm, ribosomes, DNA, cell membrane, and cell wall.

Bacterial Cell Wall

• The cell wall structure differs in Gram-positive and Gram-negative bacteria
• Gram-positive bacteria have a thick cell wall with many layers of peptidoglycan and teichoic acid
• Gram-negative bacteria have a thin cell wall with peptidoglycan between two membranes (outer and inner)
• Peptidoglycan is a polymer of alternating NAM and NAG.

Synthesis of Bacterial Cell Wall

• NAM and NAG are produced inside the cell and then move to form the cell wall
• Antibiotics target transpeptidases, enzymes crucial for linking peptidoglycan to build the cell wall
• Inhibition of these enzymes stops the synthesis of the cell wall, thus inhibiting bacterial growth.

Classification of Antimicrobial Agents

• Bacteriostatic: Stop bacterial growth (e.g., Erythromycin, Isoniazid)
• Bactericidal: Kill bacteria (e.g., Aminoglycosides, Beta-lactams)
• Some antibiotics can act as either bacteriostatic or bactericidal, depending on the dose.

Bactericidal vs Bacteriostatic

• Bactericidal kill bacteria directly.
• Bacteriostatic weaken bacteria by slowing their growth
• Bacteriostatic is used for mild infections and not for patients with immune deficiency
• Bactericidal is used to directly kill bacteria

Classification of Antimicrobials

• Broad Spectrum: Active against both Gram-positive and Gram-negative bacteria (e.g., Cephalosporins)
• Narrow Spectrum: Active against either Gram-positive or Gram-negative bacteria (e.g., Penicillin G)
• Extended Spectrum: Effective against strains resistant to other antibiotics (e.g., Pseudomonas aeruginosa).

Mechanism of Action of Antimicrobial Agents

• Antibiotics have different mechanisms of action:
• Targeting cell wall synthesis
• Targeting DNA synthesis
• Targeting ribosomes
• Targeting other cellular processes.

Inhibitors of Cell Wall Synthesis

• β-Lactam Antibiotics: Block the synthesis of peptidoglycans
  • Penicillin
  • Cephalosporins
• Vancomycin: Also interferes with peptidoglycan synthesis.

Penicillin

• Preparations:
  • Penicillin G: Natural form, short duration of action (6 hours), Acid-sensitive, not effective orally.
  • Penicillinase-resistant penicillin: Effective orally, treats staph infections
  • Broad-spectrum penicillins: Effective against Gram-negative bacteria, e.g., Amoxicillin, Ampicillin (can be affected by food and not fully absorbed).
  • Extended spectrum penicillin: More active against gram negative bacteria (e.g., Piperacillin, Ticarcillin).
• Indications: Subacute bacterial endocarditis prophylaxis.
• Side Effects: Allergic reactions (urticaria, angioedema, and anaphylaxis), diarrhea (due to superinfection), and dose-related nephrotoxicity.

Cephalosporins

• Similar to Penicillin, but more resistant to β-lactamases
• Broad-spectrum activity in 1st generation and Gram -ve in later generations
• NOT effective against meningitis in 1st generation
• Increased activity and resistance in later generations (2nd-5th)
• Uses: Infections resistant to penicillin, anaerobic infections, respiratory tract infections, urinary tract infections (especially Gram -ve), and meningitis.
• Side Effects: Allergic reactions (similar to penicillin), GI upsets, diarrhea, possible nephrotoxicity, and thrombophlebitis

Inhibitors of DNA Replication (Fluoroquinolones)

• Mechanism of Action: Inhibit bacterial DNA gyrase (topoisomerase II), preventing DNA replication
• Types: Norfloxacin, Ciprofloxacin, and gatifloxacin
• Broad Spectrum: Effective against Gram-positive and Gram-negative bacteria (including Pseudomonas, strep pneumoniae, and chlamydia)
• Uses: Urinary tract infections, sexually transmitted diseases, respiratory tract infections, and others.
• Side Effects: Hypersensitivity reactions, photo-sensitivity, nephrotoxicity, chondrolytic arthropathy.

Quiz Questions & Answers

• Provide the answers to the quiz questions as bullet points. (Please provide the questions to get the answers)