Case reportA case of culture-negative endocarditis due to Streptococcus tigurinus
Introduction
Culture-negative endocarditis remains a diagnostic and therapeutic challenge despite recent medical advances [1]. Blood cultures are negative in 2.5–31% of patients with endocarditis [2], [3], and the epidemiology varies between countries. In Japan, blood cultures were negative in approximately 20% of 513 endocarditis patients [4]. In 2012, Zbinden et al. first reported a novel member of the Streptococcus mitis group, Streptococcus tigurinus, which was named after Tigurum, Zurich where it was first isolated from blood cultures of patients with endocarditis, meningitis and spondylodiscitis [5]. S. tigurinus can cause invasive infections in both immunocompromised and immunocompetent patients [6]. Here we report a case of culture-negative endocarditis in Japan caused by S. tigurinus, which was identified by 16S ribosomal RNA (16S rRNA) analysis.
Section snippets
Case report
A man in his 40s with endocarditis was referred to our tertiary care hospital for work-up and treatment in February 2013. This patient noted recurrent low-grade fever from the autumn of 2012, and developed cough and dyspnea in early February 2013. His past history included dental treatments over several months in 2012 and aortic insufficiency, but there was no immunodeficiency. Echocardiography revealed a vegetation on the aortic valve, as well as severe aortic and mitral insufficiency with
Discussion
S. tigurinus has been described as causing invasive infections, including infective endocarditis, bacteremia, meningitis, spondylodiscitis, and prosthetic joint infection [6]. A study of S. tigurinus endocarditis in rats showed enhancement of resistance to phagocytosis by macrophages and an increased ability to enter endothelial cells [9]. In the same study, the infective dose 90% (ID90) of S. tigurinus strains was as low as 104 CFU/ml and was similar to that of Staphylococcus aureus and
Conflict of interest statement
None.
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