Haemophilus parainfluenzae Infective Endocarditis Diagnosed by Direct 16S rRNA Sequencing of Vegetation

ABSTRACT

The HACEK group of microorganisms is responsible for approximately 3-6% of endocarditis cases and is a major cause of culture-negative endocarditis. Here, we report a case of Haemophilus parainfluenzae infective endocarditis that was diagnosed by direct PCR sequencing of 16S rRNA from resected vegetation. A healthy 26-yr-old man was admitted to the emergency room (ER) on March 27, 2011 because of intermittent high fever. The patient was prescribed cefpodoxime for 5 days at the ER. Six and 11 sets of blood cultures were performed at the ER and in a general ward, respectively, using BACTEC Plus Aerobic/F (Becton-Dickinson, USA) and Lytic Anaerobic/F Plus (BD) together. Echocardiography revealed a large vegetation at the posterior mitral valve leaflet. After performing mitral valvoplasty on hospital day (HD) 11, the vegetation tissue was cultured in thioglycolate broth, blood agar, Brucella agar, and MacConkey agar for 7 days, but no organism was grown. Direct PCR sequencing of 16S rRNA of the tissue revealed the presence of H. parainfluenzae. In the 17 sets of blood cultures, bacterial growth was detected in only 2 aerobic bottles of 5 sets taken at HD 9 after 10-day and 14-day incubation. The organism was identified as H. parainfluenzae by using the VITEK NHI card (bioMerieux, France). Direct PCR sequencing of vegetation could be useful in diagnosing bacterial pathogens in infective endocarditis patients, especially in culture-negative cases.