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Published on: May 28, 2014
Accurate Differentiation of Streptococcus pneumoniae from other Species within the Streptococcus mitis Group by Peak
Mercedes Marín1,2,3,4, Emilia Cercenado1,2,3,4, Carlos Sánchez-Carrillo1
1Clinical Microbiology and Infectious Diseases Department, Hospital General Universitario Gregorio MarañónMadrid, Spain.
Abstract:
Despite the benefits of MALDI-TOF MS technology (Matrix-Assisted Laser Desorption-Ionization Time-Of-Flight Mass Spectrometry) reported worldwide and the continuous improving of the available databases, discrimination between Streptococcus pneumoniae and closely related species within the Streptococcus mitis group (SMG) using this methodology has been suboptimal. However, the accurate identification at the species level of this group of microorganisms is important for the appropriate management of infected patients. In this study, 216 SMG isolates -101 S. pneumoniae and 115 corresponding to 7 non-pneumococcal species within this group- were analyzed. All the isolates had been previously identified by conventional methods (optochin and bile solubility tests) and non-pneumococcal isolates were confirmed by sequence analysis (sodA and plys genes) when required. The isolates were also identified with the MALDI Biotyper 3.1 (Bruker Daltonics, Bremen, Germany) using an updated library containing 6,903 Main Spectra Profiles (MSPs). All the analyzed S. pneumoniae were correctly identified with MALDI-TOF MS at species level using the most updated database and all the non-pneumococcal SMG isolates were also identified at the group level. Several peaks (4,964.32, 6,888.90, and 9,516.46 m/z) have been found to be specific of S. pneumoniae, whilst a different set of peaks have proved to be present only in S. mitis (6,839.07 m/z) and S. oralis (5,297.61, 5822.53, and 6,839.07 m/z). Peak analysis allowed correct species assignment of 101/101 S. pneumoniae isolates (100%) and 102/105 S. mitis/oralis isolates (97.1%). Thus, the implementation of MALDI-TOF MS plus peak analysis for the identification of this group of microorganisms may provide precise species-level information that will allow the early implementation of directed antibiotic therapy.
Insights
Matrix-Assisted Laser Desorption-Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) with peak analysis accurately identifies Streptococcus pneumoniae and related species. This improved identification aids in timely antibiotic therapy for patients.
Area of Science:
- Microbiology
- Mass Spectrometry
- Clinical Diagnostics
Background:
- Accurate identification of Streptococcus pneumoniae and the Streptococcus mitis group (SMG) is crucial for patient management.
- Traditional methods and standard MALDI-TOF MS have shown limitations in differentiating these closely related species.
- Suboptimal discrimination impacts appropriate and timely clinical treatment decisions.
Purpose of the Study:
- To evaluate the efficacy of MALDI-TOF MS combined with peak analysis for precise species-level identification within the SMG.
- To determine if specific MALDI-TOF MS spectral peaks can reliably distinguish S. pneumoniae from other SMG members.
- To assess the potential of this enhanced method for improving clinical diagnostics.
Main Methods:
- Analysis of 216 SMG isolates (101 S. pneumoniae, 115 non-pneumococcal) previously identified by conventional tests and gene sequencing.
- Identification using MALDI Biotyper 3.1 with an updated library of 6,903 Main Spectra Profiles (MSPs).
- Specific peak analysis (m/z values) to identify discriminatory markers for S. pneumoniae, S. mitis, and S. oralis.
Main Results:
- MALDI-TOF MS correctly identified 100% of S. pneumoniae isolates using the updated database.
- All non-pneumococcal SMG isolates were identified at the group level.
- Specific peaks at 4,964.32, 6,888.90, and 9,516.46 m/z were characteristic of S. pneumoniae.
- Peak analysis achieved 100% correct assignment for S. pneumoniae and 97.1% for S. mitis/oralis.
Conclusions:
- MALDI-TOF MS, when augmented with specific peak analysis, offers precise species-level identification for S. pneumoniae and related SMG bacteria.
- This method overcomes previous limitations in differentiating closely related streptococcal species.
- The findings support the implementation of MALDI-TOF MS with peak analysis for early, directed antibiotic therapy in clinical settings.
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