The patient was a 64-year-old man who had close contacts with a domestic dog. He was referred to our hospital on suspicion of pneumonia. A computed tomographic (CT) scan of the chest showed a consolidation on the left lower lobe. Lung cancer was suspected, and a bronchoscopy was performed. (Findings from a cytologic examination of transbronchial brushing and bronchoalveolar lavage had shown no evidence of tumor. Pasteurella multocida was cultured from a specimen.) Because his bronchoscopic examination provided no definitive diagnosis, the patient underwent CT-guided lung biopsy, and the aspirated fluids showed no malignant cells. But P. multocida was cultured from a specimen. The patient was diagnosed with pneumonia caused by P. multocida and underwent antimicrobial therapy. A follow-up chest CT scan several months later showed only scarlike lesion. Because the same bacteria was cultured from bronchoalveolar lavage, a lung aspiration specimen, and the pharyngeal swab of the patient's dog. Pulse field gel electrophoresis (PEGE) was carried out to compare these three clones of P. multocida. The results indicate that these three clones originated from the same clone. It is unlikely that the CT-guided lung biopsy specimen was contaminated with bacterial colonization in the respiratory tract. Therefore we confirmed that the causative bacteria originated from the patient's dog.