Diagnostic and management challenges in dual-pathogen culture-negative endocarditis: a case report of Brucella Canis native valve infective endocarditis and subsequent saccharomyces cerevisiae prosthetic valve infective endocarditis.

BACKGROUND

Infective endocarditis caused by fastidious organisms, such as rough Brucella canis, can evade standard serology, risking unrecognised native-valve destruction and secondary prosthetic valve endocarditis.

CASE PRESENTATION: A woman in her 40 s developed native aortic IE requiring composite mechanical root replacement; cultures were sterile. Nine months post-operatively, she presented with mechanical prosthetic valve endocarditis and paravalvular regurgitation, undergoing redo homograft replacement. Retrospective rough-lipopolysaccharide ELISA of archived serum confirmed persistent B. canis seropositivity. Multi-target PCR across two independent reference laboratories identified superimposed Saccharomyces cerevisiae prosthetic valve endocarditis, corroborated by histology.

MANAGEMENT & OUTCOME: Doxycycline-induced gastritis and drug interactions necessitated modifying antibacterial therapy to amikacin, co-trimoxazole, and rifampicin; fungal endocarditis was treated with liposomal amphotericin B and subsequent posaconazole suppression. At six months, transoesophageal echocardiography and [¹⁸F]-FDG PET-CT confirmed complete infection resolution.

CONCLUSION

This case highlights suspecting rough Brucella in culture-negative infective endocarditis, evaluating unexpected molecular fungal detections alongside histology, and tailoring regimens around severe antimicrobial toxicities.