Which organism is a likely causative agent in aspiration pneumonia?

• A. Lactobacillus sp.
• B. Mobiluncus sp.
• C. Porphyromonas sp.
• D. Clostridium sp.

Answer: (C)

Aspiration pneumonia is usually caused by anaerobic bacteria from the mouth that colonize the oropharynx and are inhaled into the lungs. Porphyromonas species are anaerobic Gram-negative rods that are integral members of oral flora and are commonly recovered from infections following aspiration. Their ability to thrive in low-oxygen environments and their presence in the oropharynx make them well-suited to cause pneumonia after aspiration, especially in individuals with impaired swallowing or dental disease.

Lactobacillus species are typically harmless or only opportunistic in the gut and vagina and are not common culprits in lung infections. Mobiluncus is associated mainly with bacterial vaginosis and not with respiratory disease. Clostridium species can cause a variety of anaerobic infections, including some lung abscesses, but they are less characteristically linked to aspiration pneumonia compared with oral anaerobes like Porphyromonas.