Aspiration of vomitus can lead to pneumonia. Which organism would NOT be a likely causative agent?

• A. Bacteroides gracilis
• B. Mobiluncus sp.
• C. Porphyromonas sp.
• D. Prevotella melaninogenica

Answer: (B)

Aspiration pneumonia usually involves anaerobic bacteria that originate from the oropharynx being inhaled into the lungs. The organisms commonly implicated are oral anaerobes such as Bacteroides species (including Prevotella and Porphyromonas) and related anaerobes. Mobiluncus species, however, are primarily associated with the vaginal flora and bacterial vaginosis, not with the oropharyngeal flora or pulmonary infections. Because Mobiluncus is not typically present in the oropharynx or aspirated lung material, it would not be a likely causative agent in aspiration pneumonia. The other organisms listed are well-established constituents of the oral anaerobic toolkit that can be involved in such infections.