Rare case of Proteus mirabilis native mitral valve endocarditis in an immunocompromised patient

Background Bacterial infective endocarditis caused by Proteus mirabilis is rare and there are few cases in the literature. The natural history and treatment of this disease is not as clear but presumed to be associated with complicated urinary tract infection (cUTI). Case presentation A 65-year-old female with a history of rheumatoid arthritis, factor V Leiden hypercoagulability, and prior saddle pulmonary embolism presented to the emergency department following a mechanical fall. Computed Tomography showed evidence of acute/subacute splenic emboli. Complicated UTI was likely secondary to a ureteral stone. Blood and urine cultures also grew out P. mirabilis. Transthoracic echocardiography revealed a mobile echogenic density on the anterior mitral valve (MV) leaflet consistent with a vegetation. The patient underwent MV replacement, and P. mirabilis was isolated from the surgically removed valve. Conclusions We hypothesize that the patient's immunocompromised status following steroid and Janus Kinase inhibitor usage for rheumatoid arthritis contributed to Gram-negative bacteremia following P. mirabilis UTI, ultimately seeding the native MV. Additional studies with larger numbers of Proteus endocarditis cases are needed to investigate an association between immunosuppression and Proteus species endocarditis.