PCR-electrospray ionization mass spectrometry for direct detection of pathogens and antimicrobial resistance from heart valves in patients with infective endocarditis

Abstract

Microbiological diagnosis is pivotal to the appropriate management and treatment of infective endocarditis. We evaluated PCR-electrospray ionization mass spectrometry (PCR/ESI-MS) for bacterial and candidal detection using 83 formalin-fixed paraffin-embedded heart valves from subjects with endocarditis who had positive valve and/or blood cultures, 63 of whom had positive valvular Gram stains. PCR/ESI-MS yielded 55% positivity with concordant microbiology at the genus/species or organism group level (e.g., viridans group streptococci), 11% positivity with discordant microbiology, and 34% with no detection. PCR/ESI-MS detected all antimicrobial resistance encoded by mecA or vanA/B and identified a case of Tropheryma whipplei endocarditis not previously recognized.

Fig 1

Histological identification of T. whipplei. (A) Routine hematoxylin and eosin staining revealed a vegetation with scattered macrophages and rare neutrophils (400× original magnification). (B) The macrophages contained periodic acid-Schiff-positive diastase-resistant rods consistent with Whipple bacilli (1,000× original magnification). The bacilli stained poorly with routine stains used for valve histopathology examination, including tissue Gram stain (C) (1,000× original magnification) and Gomori methenamine silver stain (D) (1,000× original magnification).