Background Differentiation of Streptococcus pneumoniae from other viridans group streptococci is well known to be challenging in clinical laboratories. Matrix assisted laser desorption ionisation–time of flight mass spectrometry (MALDI-TOF MS) had been reported to be a good alternative for Streptococcus species level identification. However, differentiation of S. pneumoniae from other Streptococcus mitis group organisms was found to be problematic using the Bruker MALDI Biotyper system.
Methods This study used the Bruker MALDI Biotyper system in addition to a mass spectra model analysis generated by 10 reference strains of S. pneumoniae, 8 strains of S. mitis and 2 strains of S. oralis in the ClinProTools to identify 28 clinical isolates of S. pneumoniae and 47 isolates of S. mitis/oralis. The results were compared with those generated by the MALDI Biotyper system alone.
Results The percentages of correct species level identification using the MALDI Biotyper system alone and the direct transfer and extraction method were 66.7% (50/75) and 70.7% (53/75), respectively. With the additional ClinProTools mass spectra analysis, the percentages of correct identification by the direct transfer and extraction method increased to 85.3% (64/75) and 100% (75/75), respectively. This new workflow significantly improved the accuracy of S. pneumoniae and S. mitis/oralis identification.
Conclusions The additional ClinProTools mass spectra analysis with extraction method after MALDI Biotyper identification significantly improved the accuracy of identification among S. pneumoniae, S. oralis and S. mitis. The extra 15 min processing time of spectra analysis should be affordable in most clinical laboratories. We suggest that the same approach could be further explored in handling other bacterial species with high similarities.