Corynebacterium macclintockiae: a potential pathogen of cardiac implantable electronic device-related endocarditis: Case report.

Accurate diagnosis of cardiac implantable electronic device infections is important for preventing severe complications. While non-diphtherial Corynebacterium species such as C. striatum and C. jeikeium are well recognized pathogens, C. macclintockiae remains poorly characterized. Recent genomic studies suggest that some isolates identified as C. jeikeium may in fact be C. macclintockiae, thereby posing diagnostic challenges. An 82-year-old man with a cardiac resynchronization therapy defibrillator presented with weight loss, hypotension, and inflammation. Blood cultures yielded Gram-positive bacilli initially identified as C. jeikeium, later confirmed as C. macclintockiae through 16S rRNA and rpoB sequencing supported by whole-genome sequencing (97.7% average nucleotide identity to reference strain). Transesophageal echocardiography revealed tricuspid vegetation and lead echogenicity, which was consistent with infective endocarditis. The patient received six weeks of intravenous vancomycin followed by lifelong oral minocycline, achieving clinical stability and reduction in vegetation. This case represents one of the first reports of C. macclintockiae causing cardiac implantable electronic device-associated endocarditis. Its identification highlights the limitations of standard biochemical and MALDI-TOF MS systems and the value of genomic confirmation in distinguishing between closely related species. C. macclintockiae may become pathogenic in susceptible hosts, such as those with cardiac devices, and it should be considered when patients present with unexplained device-related symptoms. Integrating molecular diagnostics into clinical practice was helpful in this case for accurate identification and improved management of a rare bacterial infection.