Culture-Negative Prosthetic Valve Endocarditis with Concomitant Septicemia Due to a Nontoxigenic Corynebacterium diphtheriae Biotype Gravis Isolate in a Patient with Multiple Risk Factors

Abstract

A 54-year-old female with a prosthetic mitral valve presented with a 3-day history of dizziness, subjective fever, and chills. Blood cultures were positive for a pleomorphic Gram-positive rod. Initial phenotypic testing could only support the identification of a Corynebacterium species. Nucleic acid sequencing (16S rRNA) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) were conclusive for Corynebacterium diphtheriae. Definitive phenotypic testing classified the strain as nontoxigenic C. diphtheriae biotype Gravis.