Streptococcus sinensis sp. nov., a novel species isolated from a patient with infective endocarditis

Abstract

A bacterium was isolated from the blood culture of a patient with infective endocarditis. The cells were facultative anaerobic, nonsporulating, gram-positive cocci arranged in chains. The bacterium grows on sheep blood agar as alpha-hemolytic, gray colonies of 0.5 to 1 mm in diameter after 24 h of incubation at 37 degrees C in ambient air. Growth also occurs in 10 or 40% bile and on bile esculin agar but not in 6% NaCl. No enhancement of growth is observed in 5% CO(2). It is nongroupable with Lancefield groups A, B, C, D, F, or G antisera and is resistant to optochin and bacitracin. The organism is aflagellated and is nonmotile at both 25 and 37 degrees C. It is Voges-Proskauer test positive. It produces leucine arylamidase and beta-glucosidase but not catalase, urease, lysine decarboxylase, or ornithine decarboxylase. It hydrolyzes esculin and arginine. It utilizes glucose, lactose, salicin, sucrose, pullulan, trehalose, cellobiose, hemicellulase, mannose, maltose, and starch. 16S rRNA gene sequencing showed that there were 3.6, 3.7, 4.3, 4.7, and 5.9% differences between the 16S rRNA gene sequence of the bacterium and those of Streptococcus gordonii, Streptococcus intermedius, Streptococcus constellatus, Streptococcus sanguis, and Streptococcus anginosus, respectively. The G+C content of it (mean plus minus standard deviation) was 53.0% plus minus 2.9%. Based on phylogenetic affiliation, it belongs to the mitis or anginosus group of Streptococcus. For these reasons a new species, Streptococcus sinensis sp. nov., is proposed, for which HKU4 is the type strain. Further studies should be performed to ascertain the potential of this bacterium to become an emerging cause of infective endocarditis.

FIG. 1.

Scanning electron micrograph of S. sinensis. The bacterium is arranged in chains and is aflagellated. Cells vary in diameter from 0.82 to 0.98 μm. Bar, 1 μm.

FIG. 2.

Phylogenetic tree showing the relationship of S. sinensis sp. nov. to the related Streptococcus species. A total of 1,373 nucleotide positions in each 16S rRNA gene were included in the analysis. The scale bar indicates the estimated number of substitutions per 100 bases using the Jukes-Cantor correction. Names and accession numbers are given as cited in the GenBank database.

FIG. 3.

Phylogenetic tree showing the relationship of S. sinensis sp. nov. to the five closely related Streptococcus species using the sequence of the hypervariable region in the 16S rRNA genes. One hundred seventy-seven nucleotide positions in each 16S rRNA gene were included in the analysis. The scale bar indicates the estimated number of substitutions per 100 bases using the Jukes-Cantor correction. Names and accession numbers are given as cited in the GenBank database.