Two Cases of Pasteurella Multocida Infection of the Lung that Required Differentiation from Mycobacterial Infections

Case 1 : A 62-year-old woman underwent pre- and post-operative chemotherapy and mastectomy for right breast cancer. After treatment, she experienced a chronic cough. Chest computed tomography (CT) showed exacerbation of bronchiectasis and centrilobular nodules in the right middle lobe and a new appearance of centrilobular nodules in the right lower lobe. As pulmonary tuberculosis was suspected, bronchoscopy was performed and Pasteurella multocida was isolated. Long-term erythromycin therapy proved effective and was maintained,whereas adding a 14-day amoxicillin course to ongoing erythromycin yielded minimal clinical impact.Case 2 : A 66-year-old man underwent Chest CT for follow-up of rheumatoid arthritis and chronic bronchitis,which showed an enlarged cavity in the right upper lobe. Pulmonary mycobacteriosis was suspected. Bronchoscopy was performed and P. multocida was isolated. Finally, amoxicillin treatment was effective.P. multocida infection is a well-known skin and soft tissue infection triggered by trauma caused by pet animals,such as dogs and cats ; however, it is also known to cause respiratory infections. P. multocida pulmonary infections present with centrilobular nodules accompanied by bronchiectasis on imaging in some cases, and may require differentiation from pulmonary mycobacteriosis, such as M. tuberculosis and non-tuberculous mycobacterial infections, although this is not well known. In recent years, the incidence of P. multocida has increased,and differentiating between pulmonary mycobacteriosis and P. multocida pulmonary infections is important.Herein, we report two cases of pulmonary infection with P. multocida that required differentiation from pulmonary mycobacteriosis. Shinshu Med J 73 : 241―244, 2025