The most common bacteria causing bacterial lobar pneumonia is - - UPPSC 2023

UPPSC 2023

Applied Microbiology & Infection control

Easy

Appeared in: UPPSC 2023

Explanation

Streptococcus pneumoniae (pneumococcus) is the most frequent cause of community-acquired acute pneumonia (CAP).
It classically causes lobar pneumonia, which involves the consolidation of an entire lung lobe.
Diagnosis is supported by finding gram-positive, lancet-shaped diplococci in a sputum Gram stain.
While it's part of the normal flora in about 20% of adults, its invasion of the lung parenchyma leads to the characteristic inflammatory exudate seen in pneumonia.

Option B: Staphylococcus aureus is a significant cause of pneumonia, but it typically causes bronchopneumonia (patchy consolidation) rather than lobar pneumonia. It is also more commonly associated with hospital-acquired pneumonia or as a secondary infection after a viral illness like influenza.
Option C: Pseudomonas aeruginosa is a major pathogen in hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP). It is not a common cause of community-acquired lobar pneumonia in otherwise healthy individuals.
Option D: E. coli, a gram-negative bacillus, is an uncommon cause of pneumonia. When it does occur, it is typically in the context of hospital-acquired infections, or in specific vulnerable populations like neonates and the severely immunocompromised.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Etiology of Bacterial Lobar Pneumonia as background academic context rather than a clinical decision trigger.
Identifying S. pneumoniae as the likely cause of community-acquired lobar pneumonia guides initial empirical antibiotic therapy, often with penicillins or macrolides.
A classic sign of pneumococcal pneumonia is the production of rust-colored sputum, which is a key assessment finding for nurses.
Vaccination with the pneumococcal vaccine is a critical preventive measure for at-risk populations, including the very young, the elderly (above 65), and individuals with chronic illnesses or compromised immune systems.

How to Approach the Question

First, identify the key terms in the question: "bacterial lobar pneumonia" and "most common".
This is a factual recall question that requires knowledge of microbiology and respiratory pathology.
Recall the classic textbook cause of lobar pneumonia. Streptococcus pneumoniae is the prototype organism for this condition.
Evaluate the other options. Consider the typical clinical settings for each bacterium. S. aureus, Pseudomonas, and E. coli are more strongly associated with hospital-acquired or specific patient populations, not typical community-acquired lobar pneumonia.

Concept Tested & Keywords

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E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 709-711

E6 Pathology-Textbook of PATHOLOGYHarsh Mohan Part 2 (215-514) p. 43-45

E6 PATHOLOGY QUICK REVIEWBased on Harsh Mohan Textbook of PATHOLOGY p. 164-166