Identification of Streptococcus viridans group Isolated from the Blood of Patients

Yi, Jongyoun; Song, Byoung Wook; Lee, Kyu; Han, Kyu Sub; Park, Myoung Hee; Kim, Eui Chong

Abstract

BACKGROUND: Streptococcus viridans group (SVG) is the normal flora of the upper respiratory tract, skin and genitourinary tract, and is the major causative agent isolated in 30-40% of bacterial endocarditis patients. However, SVG has not been properly identified to the species level for lack of diagnostic system which enables the accurate identification of SVG. Poyart et al. have recently described the identification of SVG to the species level by DNA sequencing of superoxide dismutase gene (sodAint). Using this method, we report here the identification of SVG isolated from the patients in Seoul National University Hospital within recent 2 years.
METHODS
According to the method by Poyart et al., a set of two oligonucleotides, D1 (5 '-CCI TAY ICI TAY GAY GCI YTI GAR CC-3 ') and D2 (5 '-ARR TAR TAI GCR TGY TCC CAI ACR TC-3 ') were used as PCR primers, and PCR products of 480-bp size were obtained. The PCR products purified by MicroSpin S-400 HR Column were sequenced using ABI-PRISM 3700 Sequence Analyzer. D1 and D2 were used as sequencing primers. The clinical isolates were respectively identified as the species showing the greatest sequence homology which was demonstrated by the BLAST program provided by NCBI(USA).
RESULTS
Clinical strains isolated from 26 patients who had shown two or more positive blood cultures were analyzed by DNA sequencing of superoxide dismutase gene, which showed 6 strains of S. salivarius, five S. oralis, four S. sanguis, three S. pasteuri, three S. equisimilis, two S. gordonii, one S. constellatus, one S. luteciae, and one S. mitis. S. salivarius and S. sanguis were clearly discriminated, while S. equisimilis and S. pyogenes were not. Species identification results by conventional method seldom corresponded to those by DNA sequencing. Among 7 patients suspected to have bacterial endocarditis, S. sanguis were isolated in 4 patients, and S. gordonii, S. oralis, S. pasteuri in one, respectively. Among 17 patients with liver cirrhosis or cancer, S. salivarius were isolated in 6 patients, and S. oralis in four.
CONCLUSIONS
In this study, we could identify the species of SVG isolated from the patients with bacteremia; S. sanguis were frequently isolated from patients with bacterial endocarditis, while S. salivarius from ones with malignancy. These results imply that a different group of underlying diseases could show correspondingly different group of SVG species which cause bacteremia, and we suggest that further pathophysiological study on the correlations between underlying disease and the species of SVG be performed.