Bacterial Pneumonia

Epidemiology and Etiology:

•  Community-Acquired Pneumonia:
• Streptococcus pneumoniae
• Haemophilus influenzae
• Maraxella catarrhalis
• Staphylococcus aureus
• Legionella pneumophila
• Enterobacteriaceae (Klebsiella pneumoniae) and Pseudomonas spp.
• Community-Acquired Atypical Pneumonia
• Mycoplasma pneumoniae
• Chlamydia spp. (C. pneumoniae, C. psittaci, C. trachomatis)
• Coxiella burnetti (Q fever)
• Viruses:
1. RSV (children)
2. parainfluenza virus (children)
3. influenza A and B (adults)
4. adenovirus (military)
5. SARS virus
• Nosocomial pneumonia:
• Gram-negative rods – Enterobacteriaceae (Klebsiella spp, Serratia marcescens, Escherichia coli), Pseudomonas spp.
• Staphylococcus aureus (usually penicillin-resistant)
• Aspiration pneumonia
• Admixture of:
1. Anaerobic oral flora:
1. Bacteroides
2. Prevotella
3. Fusobacterium
4. Peptostreptococcus
2. Aerobic bacteria
1. Streptococcus pneumoniae
2. Staphylococcus aureus
3. Haemophilus influenzae
4. Pseudomonas aeruginosa
• Chronic pneumonia
• Nocardia
• Actinomyces
• Granulomatous:
1. Mycobacterium tuberculosis
2. atypical mycobacteria
3. Histoplasma capsulatum
4. Coccidioides immitis
5. Blastomyces dermatitidis
• Necrotizing pneumonia and Lung abscess
• Anaerobic bacteria (extremely common), with or without mixed aerobic infection
• Staphylococcus aureus
• Klebsiella pneumoniae
• Streptococcus pyogenes
• Type 3 pneumococcus
• Pneumonia in the Immunocompromised:
• CMV
• Pneumocystis carinii
• Mycobacterium avium-intracellulare
• Invasive aspergillosis
• Invasive candidiasis
• “usual” bacterial, viral, and fungal organisms

Common sites:

Gross features:

• 2 patterns (overlap):
• lobular bronchopneumonia
• patchy consolidation of the lung
• usually multilobar, bilateral, basal > apical
• slightly elevated lesions
• dry
• granular
• gray-red to yellow
• poorly delimited margins
• lobar pneumonia:
• consolidation of a large portion of a lobe or entire lobe
• 4 stages classically (natural coarse):
• congestion
• heavy
• boggy
• red
• red hepatization
• red
• firm
• airless
• liver-like consistency
• grey hepatization
• grayish brown
• dry appearance to cut surface
• resolution
• abscess in some (type 3 pneumococci, Klebsiella

Histologic features:

• lobar pneumonia:
• four stages classically (natural coarse):
• congestion
• vascular engorgement
• intra-alveolar fluid with few neutrophils
• numerous bacteria
• red hepatization
• massive confluent exudation
• red cells, neutrophils, and fibrin filling alveolar spaces
• gray hepatization
• disintegration of red cells
• persistent fibrinopurulent exudate
• resolution
• exudate is digested to form a granular, semifluid debris
• or organization with fibroblasts
• bronchopulmonary
• suppurative, neutrophil-rich exudate filling bronchi, bronchioles, and adjacent alveolar spaces

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

Other features:

References:

• Robbins 2005