Introduction to Antibiotics and Resistance
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Questions and Answers

What type of antibiotics specifically target a limited group of bacteria?

  • Narrow spectrum antibiotics (correct)
  • Broad spectrum antibiotics
  • Antivirals
  • Bactericidal antibiotics
  • Which of the following is an example of a bactericidal antibiotic?

  • Chloramphenicol
  • Clindamycin
  • Aminoglycosides (correct)
  • Erythromycin
  • Which antibiotics disrupt the cell membrane of bacteria?

  • Glycopeptides
  • Tetracyclines
  • Beta Lactams
  • Polymyxins (correct)
  • What is the primary action of bacteriostatic antibiotics?

    <p>Inhibit bacterial growth and replication</p> Signup and view all the answers

    Which class of antibiotics specifically inhibits DNA gyrase?

    <p>Quinolones</p> Signup and view all the answers

    What mechanism of resistance involves bacteria developing unresponsiveness after exposure to antibiotics?

    <p>Acquired resistance</p> Signup and view all the answers

    Which antibiotic is classified as narrow spectrum and specifically effective against mycobacteria?

    <p>Isoniazid</p> Signup and view all the answers

    Which antibiotic class acts on the 30S ribosomal subunit to inhibit protein synthesis?

    <p>Tetracyclines</p> Signup and view all the answers

    What is the primary action of beta-lactams in bacteria?

    <p>Inhibit peptidoglycan cross-linking</p> Signup and view all the answers

    Which of the following statements is true regarding vancomycin?

    <p>It inhibits cell wall synthesis in Gram-positive bacteria.</p> Signup and view all the answers

    What mechanism allows the transfer of resistance genes among bacteria through direct cell-to-cell contact?

    <p>Conjugation</p> Signup and view all the answers

    Which antibiotic does Salmonella typhi become resistant to due to modification of DNA gyrase?

    <p>Quinolones</p> Signup and view all the answers

    What is the encoded gene responsible for the resistance of Methicillin-resistant Staphylococcus aureus (MRSA) to beta-lactam antibiotics?

    <p>mecA</p> Signup and view all the answers

    Which of the following mechanisms involves bacteria pumping antibiotics outside their cells to diminish drug effectiveness?

    <p>Increased Drug Efflux</p> Signup and view all the answers

    Which of the following is a method by which bacteria can inactivate antibiotics?

    <p>Drug inactivation through enzyme production</p> Signup and view all the answers

    Study Notes

    Introduction to Antibiotics and Antibiotic Resistance

    • Antimicrobial agents are chemical substances that kill or inhibit the growth of microorganisms.
    • These include antibiotics, antivirals, antifungals, and antiparasitic drugs.
    • Antimicrobials are toxic to microbes but not to human cells.

    Classifications of Antibiotics

    • Spectrum of activity:

      • Broad spectrum: effective against a wide variety of bacterial species. Examples include: Carbepenams, Chloramphenicol, 2nd/3rd/4th gen Cephalosporins, 3rd gen Fluoroquinolones, Broad spectrum penicillins, and Tetracyclines.
      • Narrow spectrum: effective only against a single or a limited group of bacteria. Examples include: Isoniazid (active only against mycobacteria), Penicillin V and G, Lincosamides (Clindamycin), Glycopeptides (Vancomycin and Teicoplanin), and Isoniazid.
    • Mode of action:

      • Bacteriostatic: inhibits the growth and replication of bacteria. Examples include: Chloramphenicol, Erythromycin, Clindamycin, Sulfonamides, Trimethoprim, and Tetracyclines.
      • Bactericidal: kills the bacteria. Examples include: Aminoglycosides, Beta-lactams, Vancomycin, Quinolones, Rifampin, and Metronidazole.
    • Site of action:

      • Inhibition of cell wall (e.g., Glycopeptides, Beta-lactams).
      • Disturbance of cell membrane (e.g., Polymyxins, Daptomycin).
      • Inhibition of protein synthesis (e.g., Aminoglycosides, Macrolides, Tetracyclines).
      • Inhibition of nucleic acid (e.g., Fluoroquinolones, Rifampicin).

    Target Sites for Antibiotics in Bacteria

    • Cell wall synthesis inhibitors:

      • Beta-lactams: bind to penicillin-binding proteins (transpeptidases), inhibiting peptidoglycan cross-linking. Examples include Penicillins (e.g., Penicillin G, Ampicillin), Cephalosporins (e.g., 1st to 5th generation), Carbapenems (e.g., Imipenem, Meropenem), and Monobactam.
      • Glycopeptides (e.g., Vancomycin): narrow spectrum, effective against Gram-positive bacteria.
    • Cell membrane inhibitors:

      • Polymyxins: narrow spectrum, effective against Gram-negative bacteria.
    • Protein synthesis inhibitors:

      • Bind to 30S or 50S ribosomes, inhibiting protein synthesis. Examples include Macrolides (e.g., erythromycin, azithromycin), Aminoglycosides (e.g., gentamycin), and Tetracyclines (e.g., tetracycline, doxycycline).
    • Nucleic acid inhibitors:

      • Fluoroquinolones: inhibit DNA gyrase or topoisomerase. Examples include Ciprofloxacin.
    • Rifampicin: inhibits RNA polymerase.

    • Sulfonamides and trimethoprim: inhibit folic acid pathway.

    Causes of Antibiotic Therapy Failure

    • Antibiotic .1:

      • Inadequate dose
      • Inadequate duration
      • Wrong route of administration
      • Wrong choice of antibiotics
      • Use of antagonistic antibiotic combination
    • Bacteria .2:

      • Viral infection
      • Mixed bacterial infection
      • Antimicrobial resistance

    Drug Resistance

    • Natural (Intrinsic) Resistance: Bacteria naturally resist the antibiotic without previous exposure. They lack the target site of the antibiotic agent.

      • Examples: Mycoplasma, Chlamydia (resist beta-lactams due to lack of cell wall peptidoglycan), and Gram-negative bacteria (resistant to Vancomycin).
    • Acquired Resistance: Resistance mechanisms developed after exposure to antibiotics. Resistance mechanisms include mutation of existing genes, or acquisition of new resistance genes.

      • Gene transfer mechanisms like conjugation (sex pili), transduction (bacteriophage), transformation.

    Modification of target sites of antibiotics

    • Examples: Salmonella typhi (modified DNA gyrase → quinolones resistance), Methicillin-resistant Staphylococcus aureus (MRSA) (modified penicillin-binding protein (PBP) encoded by the mecA gene).

    Increased Drug Efflux

    • Pumping antibiotics out of the bacterial cell, making the drug unable to reach its target site.
      • Examples: Gram-negative bacteria (e.g., E. coli, Pseudomonas aeruginosa) efflux beta-lactam antibiotics and tetracyclines.

    Drug Inactivation

    • Some bacteria produce enzymes that inactivate antibiotics.
      • Examples: β-lactamases (inactivate penicillin) and cephalosporinases, adenyl transferases (inactivate aminoglycosides)

    Cross Resistance

    • Bacteria resistant to a certain antibiotic may also be resistant to other antibiotics having similar mechanism of action or chemical structure.
      • Example: Macrolides (e.g., azithromycin) and Lincosamides (e.g., clindamycin).

    How to Decrease Antibiotic Resistance

    • Avoid unnecessary antibiotic prescriptions (for viral infections).
    • Proper antibiotic selection.
    • Give empirical antibiotic first and then modify based on culture and sensitivity results.
    • Use antibiotics in proper route, dose, and duration.
    • Antibiotic recycling (stopping use for a period, then re-evaluate potency).
    • Establish antibiotic stewardship programs.

    Antibiotic Stewardship Programs

    • Designed to improve how antibiotics are prescribed and used.
    • Ministry of health prepares guidelines for treatment and prophylaxis of infections.
    • List of restricted antimicrobials.
    • Aims: treat infections effectively (type, dose, duration, and route), protect patients from unnecessary antibiotic use, decrease antibiotic resistance.

    Antibiotic Combination

    • Indication: Mixed infection, severe life-threatening infections (e.g., meningitis), and resistant bacteria.
    • Aims: Synergism—combined effect greater than individual effects (High cost, more adverse reactions).
    • Disadvantages: High cost, potential for more adverse effects.
    • Antagonism—combined effect is less than individual effects.

    Questions

    • Q1: Aminoglycosides
    • Q2: Macrolides.

    Reference

    • Lippincott Illustrated Microbiology 4th edition, Chapter 5.

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    Description

    This quiz covers the basics of antibiotics and their classifications, including spectrum of activity and modes of action. Understand the differences between broad and narrow-spectrum antibiotics, and learn about their effects on microbial growth. Test your knowledge on antimicrobial agents and their significance in medicine.

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