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Bacteriology-46 Bacterial infections of the lower respiratory tract*


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What aerobic bacteria are commonly found in the nose and nasopharynx
Staphylococcus aureus, Staphylococcus epidermidis
Corynebacteria spp. (diphtheroids)
Haemophilus influenzae
Moraxella catarrhalis

Sometimes Streptococcus pneumoniae, Streptococcus pyogenes
What aerobic bacteria are commonly found in the oropharynx
Staphylococcus aureus, Staphylococcus epidermidis
alpha hemolytic streptococci
Corynebacteria sp. (diphtheroids)
Moraxella catarrhalis
Also Streptococcus pneumoniae, Streptococcus pyogenes, Neisseria meningitidis, Haemophilus sp
What anaerobic bacteria are in the nose, nasopharynx and oropharynx
What are the pulmonary defense mechanisms
Barriers to aspiration
Tracheobronchial mucociliary action
Oropharyngeal colonization with avirulent commensals
Alveolar and circulating phagocytic cells
Immunoglobulins and complement components
How do microbes reach the lungs and pleural spaces
Aspiration of oropharyngeal contents
Lymphohematogenous spread
Penetration of the thoracic wall or diaphragm
What particle can reach the alveoli
Those less than 3 microns in diameter. Larger particles are trapped in mucus at higher levels or excluded from airways
What are some microbes than can reach the alveoli by inhalation of small particles
Mycobacterium tuberculosis
Mycoplasma pneumoniae
Legionella pneumophila
Name two systemic infections that spread to the lungs via the blood
Pneumonic plague and typhoid pneumonia
Intravenous drug users are at high risk of developing intravascular infection that may be complicated by what
Hematogenous pneumonia
What are some risk factors for aspiration
Impaired consciousness
Esophageal dysfunction
Disruption of normal protective barriers
When culturing a sputum specimen, what should it have
Mucus and inflammatory cells, not just saliva
What is the 5th cause of death in the US
Pneumonia plus influenza.
What causes 60% of community acquired pneumonia requiring hospitalization
What typically causes acute onset of illness, often with a single episode of shaking chills; cough rapidly becomes productive, and sputum may be rust colored or blood tinged; shortness of breath and pleuritic chest pain are common
Pneumococcal pneumonia
What is the pathology of pneumococcal pneumonia
Alveoli initially become filled with fluid and later are filled with acute inflammatory exudate.
In pneumococcal pneumonia, what does sputum smear reveal
Abundant polymorphonuclear leukocytes and gram positive diplococci
CXR will show patchy, lobular or lobar consolidation
What are some factors that suggest a poor prognosis for pneumococcal pneumonia
Type 3 pneumococci
Old age
B cell immunodeficiency
Splenectomy or functional asplenia
Underlying diseases (Diabetes, CHF, COPD)
Multilobe involvement
Why are pneumonias caused by Gram-negative bacteria often more severe with higher fatalities
Most of the Gram-negative bacteria that cause pneumonia have capsules that resist phagocytosis and killing by neutrophils
How does atypical pneumonia syndrome differ from typical pneumonia
Illness typically is less severe and less acute in onset. Cough is nonproductive or less purulent, with no predominant organism visible on gram stain or sputum. CXR variable, but lobar consolidation is uncommon
Anaerobic pleuropulmonary infections may lead to what
Aspiration syndromes; lung abscess, empyema

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