A 56-year-old male presented with fever, weight loss, and dyspnea, diagnosed with infective endocarditis on a prosthetic aortic valve. Initial blood cultures were negative, but valve cultures after surgery grew mixed Cutibacterium species. Further investigation using 16S rRNA gene sequencing on the valve tissue and serology revealed Bartonella henselae as the true underlying pathogen, despite the initial Cutibacterium isolation. This case highlights the diagnostic challenges in culture-negative endocarditis and the importance of advanced molecular techniques. The patient was successfully treated with doxycycline and gentamicin.
Key note: Mixed or unexpected culture results, especially with commensals, should prompt further investigation for fastidious or atypical pathogens in infective endocarditis.