A case of infective endocarditis following urinary tract infection by Proteus mirabilis

Infective endocarditis (IE) is most commonly caused by gram-positive cocci, whereas that caused by gram-negative rods, particularly Enterobacteriaceae, is uncommon. In particular, only a few dozen cases of IE caused by Proteus mirabilis have been reported globally. This report describes a 93-year-old woman who developed calculous pyelonephritis, renal impairment, and P. mirabilis bacteremia. She presented with multiple cerebral infarcts on cranial imaging after her consciousness was impaired. Transthoracic echocardiography revealed mobile vegetation on the mitral valve, leading to a diagnosis of possible IE according to the modified Duke criteria. P. mirabilis was detected in blood and urine cultures. Based on the antimicrobial susceptibility testing and the clinical course, the antibiotics were changed stepwise, including switching to oral agents when intravenous therapy became difficult. Owing to the patient's advanced age and overall condition, surgery was not performed. However, vegetation enlargement and a new cerebral infarction occurred, indicating treatment failure. This rare case of IE developed following a urinary tract infection and P. mirabilis bacteremia and was incidentally diagnosed by echocardiography. The case underscores the importance of considering echocardiographic evaluation in patients with P. mirabilis bacteremia accompanied by cerebrovascular events, as IE might be an underlying complication.