Normal microbiota of respiratory system

• Suppress pathogens by competitive inhibition in upper respiratory system
• Lower respiratory system is sterile

Streptococcal Pharyngitis

• Also called strep throat
• Streptococcus pyogenes
• Resistant to phagocytosis

Scarlet Fever

• Streptococcus pyogenes
• Pharyngitis
• Erythrogenic toxin produced
• Rash- fine, rough, blanches with pressure; worse in skin folds; spares face
• Followed by peeling

Diphtheria

• Corynebacterium diphtheriae: Gram-positive rod
• Diphtheria toxin
• Diphtheria membrane: Fibrin, tissue, bacterial cells
• Prevented by DTaP vaccine
• Diphtheria toxoid

Otitis Media

• S. pneumoniae (35%)
• H. influenzae (20–30%)
• M. catarrhalis (10–15%)
• S. pyogenes (8–10%)
• S. aureus (1–2%)
• Incidence of S. pneumoniae reduced  by vaccine

Common Cold

• Rhinoviruses (50%)
• Coronaviruses (15–20%)
• Over 200 agents cause
• Sneezing, nasal secretions, congestion
• Fever suggests complications
• Ear infection
• Sinus infection

Pertussis (whooping cough)

•  Bordetella pertussis
• Gram-negative coccobacillus
• Capsule
• Tracheal cytotoxin of cell wall damages ciliated cells
• Pertussis toxin
• Prevented by DTaP vaccine (acellular Pertussis cell fragments)
• Increase in cases in last 20 years because of waning immunity from vaccine

Turberculosis

• Mycobacterium tuberculosis
• Acid-fast rod; transmitted from human to human; aerosol
• M. bovis: <1% U.S. cases; not transmitted from human to human
• M. avium-intracellulare complex infects people with late-stage HIV infection

Treatment of tuberculosis

• Treatment: Prolonged treatment with multiple antibiotics
• Rifampin, Isoniazid
• MDR- multidrug resistance rising concern
• Vaccines: BCG, live, avirulent M. bovis; not widely used in United States
• ineffective in adolescents and adults
• Gives positive PPD
• Deadly in HIV positive individuals

Tuberculin skin test

• Tuberculin skin test screening
• PPD- purified protein derivative of M. tuberculosis injected subcutaneously
• Cell-mediated immune response against organisms occurs within 48 hours
• Indurated and red
• Positive reaction means current or previous infection
• Followed by X-ray or CT exam, acid-fast staining of sputum, culturing of bacteria

Pneumococcal pneumonia

• Streptococcus pneumoniae
• Gram-positive encapsulated diplococci
• Most common cause of bacterial pneumonia; 2/3 of cases; “typical pneumonia”
• Symptoms: Infected alveoli of lung fill with fluids; interferes with oxygen uptake
• Treatment: antibiotics
• Prevention: Pneumococcal vaccine

Mycoplasmal pneumonia

• Primary atypical pneumonia; “walking pneumonia”
• Mycoplasma pneumoniae
• wall-less bacteria
• Fried-egg colonies
• Common in children and young adults
• low fever, cough, headache
• Treatment: antibiotics

Legionellosis

• Legionella pneumophila
• Gram-negative rod
• Found in water
• Cooling tanks; air conditioning
• Transmitted by inhaling aerosols; not transmitted from human to human
• Potentially fatal pneumonia that tends to affect older men who drink or smoke heavily
• Treatment: antibiotics

Psittacosis (Ornithosis)

• Chlamydophila psittaci
• Gram-negative intracellular bacterium
• Transmitted to humans from bird droppings
• Reorganizes into reticulate body after being phagocytized
• fever, headache, chills
• Treatment: antibiotics

Chlamydial pneumonia

• Chlamydophila pneumoniae
• Transmitted from human to human
• Mild respiratory illness common in young people; resembles mycoplasmal pneumonia
• Treatment: antibiotics

Viral pneumonia

• occurs as a complication of influenza, measles, or chickenpox
• Viral etiology suspected if no other cause is determined

Respiratory Syncytial Virus (RSV)

• Common in infants; 4500 deaths annually
• Causes cell fusion (syncytium) in cell culture
• Epidemics in winter and spring
• Life-threatening pneumonia in infants (2-6 months)
• Treatment: antivirals

Influenza (flu)

• Symptoms: Chills, fever, headache, and muscle aches
• No intestinal symptoms
• 1% mortality, very young and very old
• Treatment: Zanamivir (Relenza) and oseltamivir (Tamiflu) inhibit neuraminidase
• Prophylaxis: vaccine

Influenza Virus

• Hemagglutinin (HA) spikes used for attachment to host cells
• Neuraminidase (NA) spikes used to release virus from cell

Antigenic shift

• Changes in HA and NA spikes
• Probably due to genetic recombination between different strains infecting the same cell

Antigenic drift

• Point mutations in genes encoding HA or NA spikes
• May involve only 1 amino aci
• Allows virus to avoid immune response

Pneumocystis pneumonia

• Causative agent: Pneumocystis jirovecii; formerly Pneumocystis carinii 
• Unknown; possibly humans or soil
• Mild disease in healthy; severe, deadly pneumonia in immunocompromised (HIV)