Which of the following is true about Chlamydophila pneumoniae?

• A. Common agent of lower gastrointestinal tract infection
• B. Humans become infected from animal reservoirs
• C. Penicillin is an effective treatment
• D. Serology is commonly used to diagnose infections

Answer: (D)

Chlamydophila pneumoniae is an obligate intracellular bacterium that causes atypical pneumonia. Because it grows inside host cells, routine culture is difficult and slow, so direct detection isn’t as practical in many settings. Serology—detecting antibodies against C. pneumoniae, using methods like microimmunofluorescence or ELISA and looking for rising titers or specific IgM/IgG—offers a feasible way to support diagnosis and has historically been used commonly for this infection. While newer tests like PCR on respiratory specimens are also used, serology remains a common diagnostic approach in many laboratories. The other statements don’t fit: it’s not typically a lower GI tract pathogen, transmission is mainly human-to-human, and penicillin is not effective against this intracellular organism.