A Rare Case of Native Aortic Valve Infective Endocarditis Caused by Citrobacter koseri

Background Infective endocarditis (IE) is a life‐threatening condition usually caused by Gram‐positive cocci. The Gram‐negative rod Citrobacter koseri is an opportunistic pathogen that only rarely has been described to cause IE. Case Summary We present a case of native aortic valve IE caused by C. koseri in an 84‐year‐old male. The patient was admitted three times before the diagnosis of IE was confirmed by transoesophageal echocardiography. He was initially treated with IV ceftriaxone and ciprofloxacin before undergoing open‐heart surgery with a biologic valve replacement. He was discharged 125 days after initial admission. Discussion Presumably, the primary focus of the infection was the genitourinary tract. Despite appropriate antimicrobial therapy, infection source control was not obtained until aortic valve replacement. Take‐Home Message The possibility of infective endocarditis should be evaluated in the case of prolonged bacteraemia with microbiological pathogens considered atypical for infective endocarditis.