MICROBIAL DISEASES OF RESPIRATORY SYSTEM

• Respiratory system infections

  • Infections of the upper respiratory system are the most common type of infection
  • Pathogens that enter the respiratory system can infect other parts of the body
• Upper respiratory system


  • Nose
  • Pharynx (throat)
  • Sinus
  • Nasal cavity
  • Oral cavity
  • Middle ear
  • Tongue
  • Epiglottis
  • Larynx (voice box)
  • Trachea (windpipe)
  • Eustachian tubes
• Nose

  • Coarse hairs filter large particles from air entering the respiratory tract
• Nose and throat

  • Ciliated mucous membranes trap airborne particles and remove them from the body
• Lymphoid tissue, tonsils, and adenoids


  • Provide immunity to certain infections
• Lower respiratory system

  • Larynx
  • Trachea
  • Bronchial tubes
  • Alveoli
  • Pleura
• Lower respiratory system

  • Ciliary escalator helps prevent microorganisms from reaching the lungs
  • Normal microbiota can include pathogenic microorganisms
  • Alveolar macrophages phagocytize microbes
  • Respiratory mucus contains IgA antibodies
• The lower respiratory system is usually sterile because of the action of the ciliary escalator
• Upper respiratory system diseases

  • Pharyngitis
  • Laryngitis
  • Tonsillitis
  • Sinusitis
  • Epiglottitis
• Streptococcal pharyngitis (strep throat)


  • Caused by Streptococcus pyogenes, a gram positive cocci in chains
  • Resistant to phagocytosis
  • Produces streptokinases that lyse clots and streptolysins that are cytotoxic
  • Diagnosed by enzyme immunoassay (EIA) tests
• Scarlet fever


  • Caused by Streptococcus pyogenes
  • Produces erythrogenic toxin that causes a red rash, high fever, and red enlarged tongue
• Diphtheria


  • Caused by Corynebacterium diphtheriae, a gram-positive rod
  • Produces a membrane containing fibrin, dead human and bacterial cells that can block the airway
  • Diphtheria toxin inhibits protein synthesis, leading to heart, kidney or nerve damage
  • Prevented by DTaP vaccine
• Otitis media


  • Earache caused by infections, often as a complication of nose and throat infections
  • Common pathogens include Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pyogenes, and Staphylococcus aureus
• Common cold


  • Caused by over 200 different viruses, with rhinoviruses causing about 50%
  • Symptoms include sneezing, nasal secretions, and congestion
  • Incidence increases in cold weather, possibly due to increased indoor contact or physiological changes
  • Antibodies are produced against the specific viruses
• Diphtheria was a leading infectious killer of children in the US in 1935, and is still common in developing countries without routine immunizations
• Lower respiratory system diseases

  • Bronchitis
  • Bronchiolitis
  • Pneumonia
• Pertussis (whooping cough)


  • Caused by Bordetella pertussis, a gram-negative coccobacillus
  • Tracheal cytotoxin damages ciliated cells, and pertussis toxin is also produced
  • Transmitted through the air from human to human
  • Prevented by DTaP vaccine
• Tuberculosis


  • Caused by Mycobacterium tuberculosis, an acid-fast rod
  • Transmitted from human to human via the gastrointestinal route
  • Mycolic acids in the cell wall are an important pathogenicity factor and provide resistance to drying and disinfectants
  • Lesions called tubercles form, which may calcify into a Ghon's complex visible on X-ray
• Pathogenesis of tuberculosis


  1. Tubercle bacilli reach alveoli and are ingested by macrophages, some survive

  2. Macrophages and other cells form an early tubercle, but many die releasing bacilli

  3. A mature tubercle forms with a caseous center, some bacilli remain dormant

  4. Liquefaction causes the tubercle to rupture, allowing bacilli to spread through the lungs and body
• Tuberculosis treatment


  • Prolonged treatment with multiple antibiotics
  • BCG vaccine, live, avirulent M. bovis, not widely used in US
• Tuberculosis diagnosis


  • Positive tuberculin skin test indicates current or prior infection, vaccine and immunity to the disease
  • Followed by X-ray, CT, acid-fast staining, and bacterial culture
• Pneumococcal pneumonia

  • Caused by Streptococcus pneumoniae, a gram-positive encapsulated diplococcus
  • Infected alveoli fill with fluid, interfering with oxygen uptake
  • Diagnosed by optochin-inhibition or bile solubility tests, and serological typing
  • Treated with penicillin or fluoroquinolones, prevented by pneumococcal vaccine
• Haemophilus influenzae pneumonia


  • Caused by a gram-negative coccobacillus
  • Predisposing factors include alcoholism, poor nutrition, cancer, or diabetes
  • Symptoms resemble pneumococcal pneumonia
  • Diagnosed by isolation, requires special chocolate agar media
  • Treated with cephalosporins
• Mycoplasmal pneumonia


  • Caused by Mycoplasma pneumoniae, a pleomorphic wall-less bacterium
  • Common in children and young adults
  • Symptoms are mild but persistent, with low fever, cough, and headache
  • Diagnosed by PCR and serological testing
  • Treated with tetracyclines
• Onia


  Gram-negative coccobacillus
• Predisposing factors


  • Alcoholism
  • Poor nutrition
  • Cancer
  • Diabetes
• Symptoms

  Resemble those of pneumococcal pneumonia
• Diagnosis

  Isolation; special media for nutritional requirements (chocolate agar)
• Mycoplasmal Pneumonia


  Primary atypical pneumonia; walking pneumonia
• Mycoplasma pneumoniae


  Pleomorphic, wall-less bacteria
• Mycoplasma pneumoniae


  • Common in children and young adults
  • 0.5 mm
• Mycoplasma pneumoniae


  • Individual cells
  • Filamentous growth
• Symptoms

  Mild but persistent respiratory symptoms; low fever, cough, headache
• Diagnosis

  PCR and serological testing
• Legionellosis


  Legionella pneumophila: Gram-negative rod
• Legionnaires' disease acquired its name in July 1976 when an outbreak of pneumonia occurred among people attending a convention of the American Legion in Philadelphia.
• Transmission

  Inhaling aerosols; not transmitted from human to human
• Symptoms

  Potentially fatal pneumonia that tends to affect older men who drink or smoke heavily
• Diagnosis

  Culture on selective media, DNA probe
• Psittacosis (Ornithosis)


  Chlamydophila psittaci: Gram-negative intracellular bacterium