Micro exam 3

Antibiotics Overview

Spectrum of Activity

  • Narrow-spectrum: Targets specific types of bacteria (e.g., gram-positive or gram-negative).

  • Broad-spectrum: Affects a wide range of bacteria, both gram-positive and gram-negative.

  • Selective Toxicity: Designed to be more harmful to bacteria than to human cells.

Types of Antibiotics and Their Targets

Cell Wall Inhibitors

  • Bacitracin

    • Topical application.

    • Inhibits peptidoglycan synthesis.

  • Beta-Lactams

    • Inhibit cell wall synthesis by targeting penicillin-binding proteins (PBPs).

    • Penicillin

      • Natural beta-lactam.

      • Some forms are only slightly modified.

    • Cephalosporins

      • Modified beta-lactams.

      • Come in multiple generations with increasing gram-negative coverage.

    • Carbapenems

      • Broad-spectrum synthetic antibiotics.

      • Highly resistant to beta-lactamases.

    • Monobactams

      • Single-ring structure.

      • Limited spectrum; primarily gram-negative bacteria.

  • Cycloserine

    • Inhibits formation of the bacterial cell wall by interfering with amino acid configuration (e.g., D-alanine).

  • Glycopeptides (e.g., Vancomycin)

    • Inhibits cell wall synthesis by binding to D-Ala-D-Ala bridge in NAM subunits.

    • Large molecule—ineffective against gram-negative bacteria.

  • Ethambutol

    • Targets arabinogalactan in acid-fast bacteria.

    • Used for tuberculosis and leprosy.

    • Side effect: optic neuritis (can affect color vision).

    • Targets slow-growing bacteria.

  • Isoniazid

    • Blocks mycolic acid synthesis.

    • Used against acid-fast bacteria (TB, leprosy).

    • Inhibits enzyme needed to produce mycolic acid.

Protein Synthesis Inhibitors

  • Aminoglycosides

    • Cause misreading of mRNA → incorrect amino acids in protein synthesis.

    • Bactericidal.

  • Chloramphenicol

    • Inhibits peptidyl transferase → no peptide bond formation.

    • Broad-spectrum.

  • Oxazolidinones (e.g., Linezolid)

    • Prevent assembly of 70S ribosome by blocking 50S/30S subunit binding.

  • Macrolides (e.g., Erythromycin)

    • Bind to 50S subunit → prevent translocation (movement along mRNA).

  • Tetracyclines

    • Block tRNA binding to the A-site on the 30S subunit.

    • Prevents addition of amino acids.

  • Lincosamides

    • Similar to macrolides; bind to 50S and inhibit peptide chain elongation.

  • Mupirocin

    • Inhibits isoleucyl-tRNA synthetase.

    • Specifically blocks isoleucine incorporation.

  • Streptogramins

    • Bind to 50S subunit, block protein elongation.

  • Gramicidin

    • Forms channels in membrane → uncontrolled ion flow → cell death.

Antimetabolites

  • Sulfonamides

    • Mimic PABA → block folic acid synthesis.

  • Dapsone

    • Similar mechanism to sulfonamides.

  • Trimethoprim

    • Inhibits dihydrofolate reductase → blocks later step in folic acid synthesis.

  • Fluoroquinolones (e.g., Ciprofloxacin)

    • Inhibit DNA gyrase and topoisomerase IV → prevent DNA replication.

  • Nitroimidazoles (e.g., Metronidazole)

    • Produce free radicals in anaerobic bacteria → DNA damage.

  • Rifampin (Rifampicin)

    • Inhibits bacterial RNA polymerase → stops transcription.

Vaccines and Immunity

  • "Vacca" = Latin for cow. Origin of the term vaccine from Edward Jenner’s cowpox/smallpox experiments.

What Does a Vaccine Do?

  • Introduces antigens (modified or dead) to stimulate B and T cell memory without causing disease.

Types of Vaccines

  • Whole Cell

    • Live Attenuated: Weakened form of pathogen. Can replicate but doesn't cause illness.

    • Inactivated (Killed): Entire pathogen is killed; cannot replicate but still triggers immunity.

  • Subunit Vaccines

    • Contain only specific parts (antigens) of a pathogen.

    • Cellular: Fragments of the pathogen.

    • Conjugated: Polysaccharide linked to a protein to enhance immune response.

    • Recombinant: Engineered using DNA technology to produce antigens.

  • Contraindication: A medical reason not to receive a vaccine or drug (e.g., allergy, immunosuppression).

  • Herd Immunity: When a large portion of a population is immune, it indirectly protects those who are not.

Fungi and Parasitic Infections

Common Fungal Pathogens

  • Candida albicans

    • Causes thrush (oral), yeast infections (vaginal), and cutaneous/systemic infections.

  • Candida auris

    • Multidrug-resistant; often hospital-acquired.

  • Claviceps purpurea

    • Produces lysergic acid (precursor to LSD).

    • Causes ergotism and hallucinations.

  • Coccidioides immitis

    • Found in alkaline soil; causes Valley Fever.

    • Airborne spores → respiratory infection (not person-to-person).

  • Sporothrix schenckii

    • "Rose gardener's disease."

    • Causes nodular skin lesions; spreads via lymphatics.

  • Mucor spp.

    • Opportunistic fungi in decaying vegetation.

    • Can cause mucormycosis (e.g., rhino-cerebral infections).

Cutaneous Mycoses (Dermatophytes)

  • Tinea capitis: Scalp

  • Tinea barbae: Beard

  • Tinea corporis: Body (ringworm)

  • Tinea cruris: Groin (jock itch)

  • Tinea pedis: Feet (athlete’s foot)

  • Tinea manuum: Hands

  • Tinea unguium: Nails

Protozoa and Helminths

  • Toxoplasma gondii

    • Found in cat feces.

    • Dangerous in pregnancy (can cause miscarriage).

    • Potential mental health links.

  • Naegleria fowleri

    • Brain-eating amoeba.

    • Found in warm freshwater.

    • Inhaled through the nose.

  • Enterobius vermicularis (Pinworm)

    • Itchy anus, especially at night.

    • Common in children.

  • Giardia lamblia

    • "Beaver fever."

    • Causes greasy diarrhea and flatulence.

    • Spread via contaminated water.

  • Loa loa (African Eye Worm)

    • Transmitted by fly.

    • Migrates under the skin and across the eye.