Background:

Brachybacterium muris is a species of Gram positive and strictly aerobic bacterium. It was first reported in 2003 after being isolated from the liver of a laboratory mouse strain. It was also found on human skin and nasal cavity. Herein, we present the first case pleural effusion infection in humans caused by Brachybacterium muris.
Case presentation:
A 65-year-old man was admitted to our hospital for a 4-week history of fever, accompanied by chills, occasional abdominal pain, occasional chest tightness and shortness of breath. On the day of hospitalization, thoracentesis was performed and 1000mL of yellow cloudy fluid was released. Result of pleural fluid culture was positive and B. muris was identified using 16S rDNA amplification and sequence comparisons.
Conclusion:
To our knowledge, this is the first report of pleural effusion infection caused by B. muris. B. muris can be pathogenic in humans.