BIOL 251 Chapter 22 Study Points

Immune defense mechanisms of Respiratory Tract

• Mucociliary escalator: Cilia move mucus and trapped particles upward to be expelled.

• Lysozyme in mucus: Breaks down bacterial cell walls.

• IgA antibodies: In mucus, prevent microbial adherence.

• Resident macrophages: Found in alveoli; phagocytize pathogens.

• Normal microbiota: Competes with pathogens for space/nutrients.

What is Pneumonia

• Infection of the alveoli causing inflammation and fluid accumulation.

• Disrupts gas exchange and oxygen uptake.

• Can be caused by bacteria, viruses, or fungi.

Three bacterial pathogens that cause pneumonia

• Streptococcus pneumoniae: most common

• Klebsiella pneumoniae: common in immunocompromised patients

• Mycoplasma pneumoniae: cause atypical/ walking pneumonia

Characteristics of Streptococcus pneumoniae

• Gram-positive, lancet-shaped diplococcus.

• Symptoms: Fever, chest pain, productive cough with rust-colored sputum.

• Pathology: Lobar pneumonia; inflammatory exudate fills alveoli.

• Treatment: Penicillin or cephalosporins; vaccine-preventable.

• Susceptible Groups: Elderly, young children, immunocompromised.

• Serotypes: Over 90 serotypes based on capsular polysaccharide.

Virulence factors of Streptococcus pneumoniae

• Virulence Factors:

  • Capsule: Inhibits phagocytosis.

  • Pneumolysin: Damages respiratory epithelium.

  • IgA protease: Degrades secretory IgA.

Streptococcus pneumoniae vaccines

• • PCV13 (children & elderly): Covers 13 serotypes.

  • PPSV23 (adults): Covers 23 serotypes.

Characteristics of Klebsiella pneumoniae

• Symptoms: High fever, chills, thick and bloody sputum ("currant jelly").

• Pathology: Necrotizing pneumonia with lung abscess formation.

• Treatment: Antibiotics, though many strains are resistant (e.g., CRE).

• Susceptible: Alcoholics, diabetics, hospitalized/immunocompromised.

• Characteristics: Gram-negative rod, large capsule.

Virulence factors of Klebsiella pneumoniae

• • Capsule: Prevents phagocytosis.

  • Endotoxin: Triggers inflammation.

Characteristics of Mycoplasma pneumoniae

• Symptoms: Gradual onset dry cough, sore throat, mild fever (walking pneumonia).

• Pathology: Atypical pneumonia; interstitial inflammation.

• Treatment: Macrolides (e.g., azithromycin); penicillin ineffective (no cell wall).

• Susceptible: School-age children, college students, military recruits.

• Characteristics:

  • Lacks a cell wall.

  • Smallest known self-replicating organism.

Characteristics of Streptococcus pyogenes

• Sore throat, fever, swollen lymph nodes, white exudates on tonsils.

• Pathogenesis: Colonizes throat, releases toxins, triggers inflammation.

• Treatment: Penicillin or amoxicillin.

• Lancefield Groups: Classification by cell wall carbohydrate antigens (Group A = S. pyogenes).

• Characteristics: Gram-positive cocci in chains, beta-hemolytic.

• Virulence Factors:

  • M protein: Inhibits phagocytosis.

  • Streptolysins: Damage cells.

  • Hyaluronidase: Spreads through tissues.

Influenza

• Risk Factors: Elderly, infants, pregnant women, chronic illnesses.

• Symptoms: Sudden fever, headache, muscle aches, fatigue, cough.

• Structure:

  • Envelope: Contains Hemagglutinin (HA) and Neuraminidase (NA).

  • HA binds to sialic acid receptors to enter cells.

  • NA cleaves sialic acid to release new virions.

Types of Influenza

• Influenza A: Most severe, zoonotic, causes pandemics.

• Influenza B: Milder, seasonal epidemics.

• Influenza C: Rare and mild.

Antigenic drift vs. Shift

• Drift: Minor mutations in HA/NA → seasonal outbreaks.

• Shift: Major reassortment of RNA segments → pandemics.

Characteristics of Mycobacterium tuberculosis

• Acid-fast bacillus, waxy mycolic acid-rich cell wall.

• Susceptible: Immunocompromised (HIV+), elderly, those in crowded living conditions.

• Signs & Symptoms:

  • Chronic cough, weight loss, night sweats, fever, hemoptysis.

Mycobacterium Tuberculosis treatment

• 6–9 month course of multiple antibiotics (e.g., isoniazid, rifampin).

• MDR-TB: Resistant to isoniazid and rifampin → harder to treat, longer regimens.

Pathogenesis of Mycobacterium tuberculosis

• Inhaled bacteria infect alveoli → phagocytosed by macrophages → granuloma formation.

• Two Stages:

  • Latent TB: Bacteria dormant in granulomas; asymptomatic, not infectious.

  • Active TB: Bacteria multiply; symptoms present; infectious.