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Answer shortly in reference to apurba sastry microbiology
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Now let me find Apurba Sastry microbiology specifically and pull the S. pneumoniae section:
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Apurba Sastry's textbook is not in the library, but I'll use the available microbiology textbooks (Medical Microbiology 9e, Jawetz, Sherris) which cover the same content as Apurba Sastry. Let me pull the relevant S. pneumoniae details:
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I have all the information needed. Here are concise answers to all 5 questions, based on standard medical microbiology content aligned with Apurba Sastry's Microbiology:
Clinical Vignette 39 - Pneumococcal Pneumonia
Organism: Streptococcus pneumoniae
1. Clinical Diagnosis
Pneumococcal pneumonia (community-acquired lobar pneumonia caused by Streptococcus pneumoniae). The clues are: elderly alcoholic male (predisposed to aspiration), high-grade fever, productive cough, right lower lobe infiltrates on X-ray, and Gram-positive cocci in pairs (lancet-shaped diplococci) in sputum.
2. Virulence Factors
| Factor | Role |
|---|---|
| Polysaccharide capsule | Most important - antiphagocytic, basis of 90+ serotypes |
| Pneumolysin | Cytotoxin - lyses RBCs/leukocytes, activates complement, causes local inflammation |
| IgA protease | Cleaves secretory IgA, facilitates colonization of mucosal surfaces |
| Surface adhesins (PspA, PspC) | Aid colonization of nasopharynx/oropharynx |
| Teichoic acid / C polysaccharide | Triggers inflammatory response; contains phosphorylcholine |
| Autolysin (amidase) | Releases cell wall fragments that amplify inflammation |
3. Laboratory Diagnosis
Specimen: Sputum (lower respiratory), blood (bacteremia), CSF (meningitis)
- Gram stain of sputum: Gram-positive, lancet-shaped diplococci surrounded by a capsule; numerous neutrophils
- Culture: Blood agar (5% sheep blood) - alpha-hemolytic (green/partial hemolysis), small mucoid colonies with draughtsman/coin appearance; incubated in 5-10% CO2
- Identification tests:
- Optochin (ethylhydrocupreine) sensitivity - zone of inhibition ≥14 mm (distinguishes from viridans streptococci which are resistant)
- Bile solubility test - positive (colonies dissolve in 10% sodium deoxycholate)
- Catalase negative
- Quellung (capsular swelling) reaction: Capsule swells visibly when mixed with type-specific antisera - used for serotyping
- Urine antigen test: Detects C polysaccharide (useful in adults with pneumonia)
- Blood culture: Positive in 20-30% cases in early illness
4. Prophylaxis
- PCV13 (Pneumococcal Conjugate Vaccine - 13 valent): Recommended for all children <2 years and immunocompromised adults; polysaccharide conjugated to carrier protein - produces T-cell dependent response
- PPSV23 (Pneumococcal Polysaccharide Vaccine - 23 valent): Recommended for adults >65 years, asplenic patients, alcoholics, COPD, diabetes, and other high-risk groups; T-cell independent response
- Alcoholics like this patient are specifically at high risk due to impaired splenic function and ciliary clearance - they should receive PPSV23
5. Other Organisms Causing Pneumonia
Community-acquired pneumonia (other causes):
- Haemophilus influenzae (elderly, COPD)
- Staphylococcus aureus (post-influenza)
- Klebsiella pneumoniae (alcoholics, diabetics - currant jelly sputum)
- Mycoplasma pneumoniae (atypical/walking pneumonia - young adults)
- Legionella pneumophila (atypical - water-borne, AC systems)
- Chlamydophila pneumoniae (atypical)
- Viruses: Influenza, RSV, SARS-CoV-2
Note on this case: Alcoholics are also prone to Klebsiella pneumoniae (upper lobe, thick sputum) and aspiration pneumonia (anaerobes). The Gram-positive diplococci here confirm pneumococcus.
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