MICI: RTI Pt 1

Overview of Respiratory System Infections

• Respiratory infections affect both upper and lower respiratory tracts with different pathogens.
• Upper Respiratory Tract (URT) infections include pharyngitis, often caused by Streptococcus pyogenes.
• Normal microbiota in the URT can become opportunistic pathogens.
• Lower Respiratory Tract (LRT) is usually free of microbes but can lead to serious conditions like pneumonia.
• Common bacterial causes of pneumonia include Streptococcus pneumoniae, Haemophilus influenzae, and Mycoplasma pneumoniae.

Common Pathogens in Respiratory Tract Infections

• Streptococcus pneumoniae: Leading cause of bacterial pneumonia, characterized as an opportunistic pathogen with a virulent capsule.
• Haemophilus influenzae: Particularly affects children and immunocompromised individuals, causing pneumonia.
• Mycoplasma pneumoniae: Causes atypical pneumonia ("walking pneumonia"); resistant to beta-lactam antibiotics due to the absence of a cell wall.
• Chlamydia pneumoniae: Also causes atypical pneumonia and is resistant to beta-lactam antibiotics because of its unique cell wall structure.
• Legionella pneumophila: Causes Legionnaires' disease associated with water sources; a gram-negative intracellular organism.

Mechanisms of Pathogen Virulence and Immune Evasion

• Virulence factors help bacteria colonize and cause disease, vital for treatment and prevention strategies.
• Streptococcus pyogenes: Produces streptolysins that kill leukocytes and has a capsule and M protein to evade phagocytosis.
• Complications from untreated strep throat can include rheumatic fever and glomerulonephritis.
• Streptococcus pneumoniae: Its capsule enables rapid lung multiplication and secretes pneumolysin to destroy host cells.
• Mycoplasma pneumoniae: Lack of cell wall confers resistance to beta-lactam antibiotics.
• Chlamydia pneumoniae: Inhibits phagolysosome fusion in immune cells, allowing survival inside human cells.

Diagnosis and Treatment of Respiratory Infections

• Diagnostic Methods:
  • Sputum culture is critical for pneumonia diagnosis, analyzed based on epithelial cell content.
  • Rapid antigen tests facilitate quick determination of infections like strep throat.
• Antibiotic Treatment:
  • Streptococcus pyogenes and S.pneumoniae are typically treated with penicillin or amoxicillin; resistant cases may require alternatives.
  • Mycoplasma pneumoniae treated with erythromycin or doxycycline due to beta-lactam resistance.
  • Legionella pneumophila is best treated with quinolones or macrolides.

Pathogen Transmission and Preventive Measures

• Streptococcus pneumoniae and Mycoplasma pneumoniae spread via respiratory droplets, allowing person-to-person transmission.
• Legionella pneumophila is transmitted through contaminated water sources, emphasizing the need for effective water treatment.
• Vaccination with pneumococcal vaccines such as Pneumovax is recommended for high-risk populations, including the elderly and immunocompromised individuals.

Key Concepts for Review

• Understand the differences between viruses, bacteria, and eukaryotic pathogens.
• Review the Gram stain process and the distinction between Gram-positive and Gram-negative bacteria.
• Familiarize with antibiotic mechanisms, particularly how beta-lactam antibiotics target bacterial cell walls, and why certain bacteria are resistant.
• Identify key pathogens and their transmission methods, including Streptococcus pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila.
• Learn about antibiotic resistance mechanisms and understand the distinction between broad-spectrum and narrow-spectrum antibiotics.