Q.66 Which one of the following bacterial species can cause atypical pneumonia?
(A) Chlamydia pneumoniae
(B) Streptococcus pneumoniae
(C) Klebsiella pneumoniae
(D) Haemophilus influenzae
Chlamydia pneumoniae is the bacterial species that causes atypical pneumonia among the given options. Atypical pneumonia refers to lung infections caused by pathogens like Chlamydia pneumoniae, which differ from typical bacterial pneumonias in presentation and detection methods.
Option Analysis
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(A) Chlamydia pneumoniae: This obligate intracellular bacterium causes mild, community-acquired atypical pneumonia with symptoms like persistent cough and low-grade fever. It spreads person-to-person and is harder to detect via Gram stain or routine cultures.
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(B) Streptococcus pneumoniae: A Gram-positive diplococcus, it causes typical lobar pneumonia with acute onset, high fever, rusty sputum, and consolidation on imaging. It responds to standard antibiotics and is a leading cause of community-acquired pneumonia.
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(C) Klebsiella pneumoniae: This Gram-negative rod leads to severe, necrotizing typical pneumonia, often in alcoholics or hospitalized patients, producing currant jelly sputum and cavitary lesions.
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(D) Haemophilus influenzae: A Gram-negative coccobacillus, it causes typical bronchopneumonia, especially in children or those with COPD, presenting with abrupt fever and purulent sputum.
The correct answer is (A), as confirmed by medical sources distinguishing atypical pathogens.
A typical pneumonia, often called “walking pneumonia,” arises from specific bacterial species like Chlamydia pneumoniae that produce milder symptoms than typical pneumonias. This condition affects young adults and accounts for up to 40% of community-acquired cases, making it a key topic for CSIR NET Life Sciences students studying microbiology and infectious diseases.
What Defines Atypical Pneumonia?
Atypical pneumonia involves interstitial lung patterns on X-rays, dry cough, and minimal sputum, unlike the lobar consolidation in typical cases. Bacterial species causing atypical pneumonia evade Gram staining and require special diagnostics like PCR or serology. Common culprits include Mycoplasma pneumoniae, Legionella, and Chlamydia pneumoniae.
Key Bacterial Species: Chlamydia pneumoniae
Chlamydia pneumoniae triggers year-round respiratory infections, starting with pharyngitis and progressing to pneumonia. It infects epithelial cells and macrophages, with an incubation of 3-4 weeks. Unlike viruses, antibiotics like macrolides treat it effectively.
Comparison of Pneumonia Pathogens
| Pathogen | Type | Key Features | Common in |
|---|---|---|---|
| Chlamydia pneumoniae | Atypical | Mild cough, intracellular, hard to culture | Young adults |
| Streptococcus pneumoniae | Typical | Lobar, rusty sputum, Gram+ | All ages, esp. elderly |
| Klebsiella pneumoniae | Typical | Currant jelly sputum, cavitary | Alcoholics, nosocomial |
| Haemophilus influenzae | Typical | Bronchopneumonia, purulent | Children, COPD patients |
This table highlights why only Chlamydia pneumoniae fits atypical criteria.
Clinical Relevance for CSIR NET
For exams like CSIR NET, recognize atypical pathogens by their “extrapulmonary” hints like headache or myalgia. Treatment differs: atypicals need macrolides, while typicals use beta-lactams. Vaccination targets typical bacteria like Streptococcus pneumoniae.
