Rothia mucilaginosa is a gram-positive, catalase variable, coagulase and oxidase negative, facultative anaerobic bacterium that forms gray-white colonies without hemolysis in blood agar media. With all these features, it resembles coagulasenegative staphylolococcus colonies and can easily be overlooked. Although it is considered as a part of the microbiota of the oropharynx and upper airways, it has been reported as an infectious agent in recent years, especially in immunocompromised patients. Although antimicrobial susceptibility tests for Rothia mucilaginosa have not yet been standardized and optimal antimicrobial therapy has not been established, it has often been reported to be resistant to aminoglycosides, cotrimoxazole and quinolones.

In this article, we present a case of pneumonia caused by Rothia mucilaginosa in a patient who received chemotherapy for colon cancer and also has chronic obstructive pulmonary disease.