Proteus mirabilis – a rare cause of non-HACEK Gram-negative infective endocarditis

Infective endocarditis caused by Proteus mirabilis is strikingly rare. Here, we describe the case of an 86-year old man with five recurrent septic episodes over a period of three months associated with Proteus mirabilis bacteraemia secondary to underlying Proteus endocarditis. The final diagnosis was made based on clinical findings, blood culture results and transoesophageal echocardiogram. The patient was treated medically with 6 weeks of ceftriaxone and long-term oral ciprofloxacin. On completion of intravenous therapy the patient remained well. We performed a literature review and found this to be only the fourth confirmed case of Proteus mirabilis endocarditis successfully treated with antibiotic therapy alone. This case highlights an important but rare cause of endocarditis, reinforcing the need to consider this diagnosis in recurrent Gram-negative bacteraemia even if by an atypical organism.