A facultative pathogen can cause severe lung disease if inhaled but causes no gastrointestinal illness when swallowed because it is rapidly inactivated by gastric acid. Which statement best evaluates when an ingested exposure could nevertheless lead to pulmonary disease?

• A. If the organism survives gastric acidity (for example due to buffering by a large fatty meal) and then breaches the intestinal barrier to cause bacteremia, it could seed the lungs hematogenously, so ingestion could rarely lead to pulmonary disease under these special conditions.
• B. If the organism is swallowed, it will automatically express lung-specific adhesins in response to gastric pH and thereby directly colonize respiratory epithelium without entering the bloodstream or being inhaled.
• C. Ingested organisms will never be capable of causing pulmonary disease because bacteria that survive the stomach are permanently attenuated and lack any virulence factors needed for lung infection.
• D. Ingested exposure would always immediately lead to lung colonization via retrograde movement from the small intestine to the bronchi through physiological conduits that normally carry digestive contents to the lungs.

Answer: (A)