| Summary: | 碩士 === 國立臺灣大學 === 醫學檢驗暨生物技術學研究所 === 105 === Viridans group streptococci (VGS) are important flora in human. Most species reside as normal flora in the human respiratory, urogenital, and gastrointestinal tracts. Despite the low virulence, several studies have shown that many species in this group are associated with infections like endocarditis, meningitis, abscesses, and septicemia, especially in patients with different underlying conditions can cause serious infection. The nomenclature and classification have been under constant renewal, mainly due to new molecular typing methods. At present, the species of VGS can be divided into following five major groups according to their 16S rRNA sequences, Streptococcus bovis group, Streptococcus anginosus group, Streptococcus mitis group, Streptococcus mutans group and Streptococcus salivarius group. The API tests (bioMerieux, API 20S, API Rapid ID 32 Strep) or the automated commercial kits (Vitek GPI card, MicroScan GP and Phoenix SMIC) are usually used in the clinical microbiology laboratories to identify VGS. In National Taiwan University Hospital, the Phoenix 100 panel (BD) is used as an identification method for VGS when the blood culture was positive or the sterile site was positive. Recently, matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) fingerprinting has been introduced as a routine microbial identification tool and found widespread acceptance thanks to its broad species coverage and superior turn around time.
In this study, the commercial biochemical panels and MALDI-TOF MS systems were evaluated for identification of VGS. The 27 ATCC strains were selected to check MALDI-TOF MS database and 110 clinical blood culture positive isolates from Jan 2015 to Jun 2015 in the NTUH were collected to evaluate the two identification systems. Among the 31 S. anginosus group isolates, 3 isolates were misidentified in Phoenix system and 5 isolates were misidentified in VITEK 2 system but all the isolates were identified correctly in MALDI-TOF MS system. In the 7 S. salivarius group isolates, 1 isolate was misidentified in VITEK 2 system and another isolate needed more tests to confirm. In the 22 S. bovis group isolates, 2 isolates were misidentified in Phoenix system and 2 isolates needed more tests to confirm. Among the 46 S. mitis group isolates, 4 isolates had no result and 6 isolates were misidentified in Phoenix system and 2 isolates had no result in VITEK 2 system; 24 isolates were misidentified in MALDI Biotyper and 2 isolates had no result in VITEK MS system. These results suggested that the MALDI-TOF systems at present can offer a good alternative for the identification of VGS and perform as well as or better than the commercial biochemical methods. However, there are still some challenges in the identification of Streptococcus oralis and Streptococcus mitis.
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