Abstract
There are challenges in viridans group streptococci (VGS) identification especially for the mitis group. Few studies have investigated the performance of MALDI-TOF MS system in VGS identification. Using 16S rRNA gene and gyrB gene sequencing as a gold standard, the performance of two MALDI-TOF MS instruments in the identification of 181 VGS clinical isolates was studied. The Bruker Biotyper and Vitek MS IVD systems correctly identified 88.4% and 98.9% of the 181 isolates, respectively. The Vitek MS RUO system was the least reliable, only correctly identifying 38.7% of the isolates to species level with several misidentifications and invalid results. The Bruker Biotyper system was very unreliable in the identification of species within the mitis group. Among 22 non-pneumococci isolates (S. mitis/S. oralis/S. pseudopneumoniae), Biotyper misidentified 21 of them as S. pneumoniae leading to a low sensitivity and low positive predictive value in these species. In contrast, the Vitek MS IVD demonstrated a better resolution for pneumococci and non-pneumococci despite the inability to distinguish between S. mitis/S. oralis. For more accurate species-level identification, further improvements in the VGS spectra databases are needed. Based on MALDI-TOF analysis and selected 16S rRNA gene plus gyrB genes sequencing, we designed a practical VGS identification algorithm.
Highlights
The viridans group streptococci (VGS) are a heterogeneous group of gram positive cocci, which form part of the normal human flora of the oral cavity, respiratory, urogenital, and gastrointestinal tracts (Spellberg and Brandt, 2011)
The proposed integrated algorithm is a practical approach in VGS identification at this stage
This database covers rare viridans group streptococci (VGS) species not included in the Vitek MS In Vitro Diagnosis (IVD) system (Karpanoja et al, 2014)
Summary
The viridans group streptococci (VGS) are a heterogeneous group of gram positive cocci, which form part of the normal human flora of the oral cavity, respiratory, urogenital, and gastrointestinal tracts (Spellberg and Brandt, 2011). Accurate identification of species within the VGS group is important for assessing the clinical significance of the organism and to facilitate appropriate antimicrobial therapy (Sinner and Tunkel, 2009; Doern and Burnham, 2010). Sequence analysis targeting different single genes such as 16S rRNA gene, rpoA, rpoB, rnpB, rodA, soda, and gdh, have been used in the identification of VGS species with various degrees of success (Poyart et al, 1998; Ip et al, 2006; Westling et al, 2008; Konishi et al, 2009; Nielsen et al, 2009; Park et al, 2010). Only multilocus sequence analysis (MLSA) can accurately and reliably identify species within the VGS group. Galloway-Peña et al reported that the gyrB amino acid sequence may offer a more practical and accurate method for speciating invasive VGS strains than MLSA (Galloway-Pena et al, 2014)
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