In the pneumonia case, which organism was identified as the causative agent?

In the pneumonia case, which organism was identified as the causative agent?

• A. Klebsiella pneumoniae
• B. Streptococcus pneumoniae
• C. Pseudomonas aeruginosa
• D. Staphylococcus aureus

Answer: (A)

The key idea is linking the clinical context with microbiology clues to identify the culprit. Klebsiella pneumoniae is an encapsulated Gram-negative rod that classically causes lobar pneumonia in older adults and in individuals with risk factors such as alcohol use or aspiration. Its thick capsule makes the bacteria particularly virulent, and it often yields mucoid, glossy colonies on culture. In the lab, sputum Gram stain would typically show Gram-negative bacilli that ferment lactose, which helps distinguish Klebella from other pathogens. Clinically, this organism is also associated with thick, sometimes blood-tinged sputum, though not always. By contrast, Streptococcus pneumoniae is the most common cause of community-acquired pneumonia and is a Gram-positive diplococcus; Pseudomonas is more typical in hospital-acquired cases or those with chronic lung disease like cystic fibrosis, and Staphylococcus aureus is often linked to post-viral pneumonia and can form abscesses. The combination of the patient’s risk factors and the microbiology profile pointing to encapsulated Gram-negative rods supports Klebsiella pneumoniae as the causative agent.

The key idea is linking the clinical context with microbiology clues to identify the culprit. Klebsiella pneumoniae is an encapsulated Gram-negative rod that classically causes lobar pneumonia in older adults and in individuals with risk factors such as alcohol use or aspiration. Its thick capsule makes the bacteria particularly virulent, and it often yields mucoid, glossy colonies on culture. In the lab, sputum Gram stain would typically show Gram-negative bacilli that ferment lactose, which helps distinguish Klebella from other pathogens. Clinically, this organism is also associated with thick, sometimes blood-tinged sputum, though not always.

By contrast, Streptococcus pneumoniae is the most common cause of community-acquired pneumonia and is a Gram-positive diplococcus; Pseudomonas is more typical in hospital-acquired cases or those with chronic lung disease like cystic fibrosis, and Staphylococcus aureus is often linked to post-viral pneumonia and can form abscesses. The combination of the patient’s risk factors and the microbiology profile pointing to encapsulated Gram-negative rods supports Klebsiella pneumoniae as the causative agent.