The First Case of Concurrent Infective Endocarditis and Spondylitis Caused by Streptococcus tigurinus

Dear Editor Streptococcus tigurinus, a novel bacterial species, was first discovered by Zbinden et al. in 2012 [1]. Although S. tigurinus was reported to cause invasive infections, accurate identification of this organism requires genetic analysis [1-6]. We report a patient with concurrent bacteremia, endocarditis, and spondylitis caused by S. tigurinus. A 79-yr-old male presented with chills and back pain after treatment with acupuncture. A spinal magnetic resonance imaging and echocardiogram lead to the diagnosis of spondylitis and endocarditis. On admission, he was afebrile (36.5°C) with a blood pressure of 141/71 mm Hg. His leukocyte count was 14.7×10/L, with 88.6% segmented neutrophils. The serum Creactive protein level was 8.95 mg/dL. Empirical antibiotic therapy of intravenous ceftriaxone, at a dose of 4 g/day, was initiated. The patient underwent aortic valve replacement and a bone biopsy of the vertebral body. Whitish-gray pinpoint colonies with alpha-hemolysis were isolated from the bone culture, and Gram-staining revealed gram-positive cocci in chains (Fig. 1). The isolate was identified as Streptococcus mitis/Streptococcus oralis using Vitek II (bioMérieux, Marcy l’Étoile, France) and was sensitive to penicillin. The same microorganism was isolated from blood culture, and the valve tissue culture was negative. Therefore, the antibiotic therapy was changed to intravenous penicillin G, at a dose of 18 million IU/day. The bone and valve specimens and colonies from blood culture were analyzed by 16S rRNA gene sequencing. The 16S rRNA gene was amplified by standard methods according to CLSI guideline [7]. Primers were summarized in Table 1. The amplified sequences were compared with the NCBI Blast sequence database. The isolated 16S rRNA sequence was identical to the type strain AZ_3a of S. tigurinus (GenBank accession number, JN004270.1) with 99.8% of identity (1,463 of 1,456 bases). The most closely related species within the GenBank was S. sanguinis, with a sequence identity of 98.6%. Therefore, we identified this gram-positive coccus as S. tigurinus. The same results were obtained for bone and valve specimens, with a sequence identity of 100% (711/711 for bone and 683/683 for valve). S. tigurinus was first isolated from patients presenting with infective endocarditis, spondylodiscitis, and meningitis [1]. It belongs to the Streptococcus mitis group and is closely related to Streptococcus mitis, Streptococcus pneumoniae, Streptococcus pseudopneumoniae, Streptococcus oralis, and Streptococcus infantis [1]. Colonies on sheep blood agar are circular, smooth,