Potential of MALDI-TOF MS as an alternative approach for capsular typing Streptococcus pneumoniae isolates

Abstract

Streptococcus pneumoniae can be classified in more than 90 capsular types, as traditionally determined by serological methods and more recently by PCR-based techniques. Such methods, however, can be expensive, laborious or unable to accurately discriminate among certain serotypes. Therefore, determination of capsular types, although extremely important for epidemiological purposes and for estimating the impact of pneumococcal conjugate vaccines, is mainly restricted to research laboratories, being rarely performed in the clinical setting. In the present study, MALDI-TOF MS was evaluated as an alternative tool to characterize 416 pneumococcal isolates belonging to serotypes 6A, 6B, 6C, 9N, 9V or 14. For MALDI-TOF MS analysis, each isolate was submitted to an extraction protocol using formic acid and acetonitrile. Measurements were performed with a Bruker Microflex LT mass spectrometer using default parameters and generating spectra in the range of 2,000–20,000 m/z. Spectra were analyzed with the BioNumerics software v7.6. Isolates were mainly distributed according to the capsular type in a Neighbor Joining tree and serotypes investigated were successfully discriminated by the presence/absence of 14 selected biomarkers. The results suggest that MALDI-TOF MS is a promising alternative for typing pneumococcal strains, highlighting its usefulness for rapid and cost-effective routine application in clinical laboratories.

Utility of MALDI-TOF MS as a new tool for Streptococcus pneumoniae serotyping

“…In our study we only included clinical isolates of serotypes 11A, 19F and 19A, because they were the isolates corresponding to the serotype of the available transformed strains, and of serotype 6B that was included in the analysis of Pinto et al . [24] and serotype 35B that was also included in the study of Nakano et al . [23] together with serotypes 6B, 19F and 19A.…”

“…However, typing applications are extremely new and their use is currently restricted to specialized laboratories [22]. Among these new typing applications, some authors have used MALDI-TOF MS to identify pneumococcal serotypes [23–24].…”

“…The main aim of this work was to assess if the discriminatory peaks previously described in the literature for serotypes 6B, 19A, 19F, and 35B [23–24] were present in the spectra of pneumococcal clinical isolates of the same serotypes, regardless of the origin of the sample or the genotype. Another aim was to analyze if the mass spectra obtained by MALDI-TOF MS showed specific discriminatory peaks using three different transformed pneumococci of serotypes 11A, 19F, 19A, and if those peaks were also present in the spectra of clinical isolates of the same serotypes.…”

Characterization of Clostridium tyrobutyricum Strains Using Three Different Typing Techniques

“…In a study performed by Illikoud et al on 161 Brochothrix thermospacta isolates, one major cluster encompassed more than 70% of the analyzed strains [ 28 ]. MALDI-TOF MS typing is a fast and cost-effective alternative to other typing methods [ 39 , 40 ]. To the best of our knowledge, this is the first study that investigated intra-species diversity among cheese spoiling clostrida using this technique.…”

MALDI-TOF Mass Spectrometry and Specific Biomarkers: Potential New Key for Swift Identification of Antimicrobial Resistance in Foodborne Pathogens

“…Spectrum processing parameters should not be neglected and indeed enhance screening performance. Several other MALDI-TOF MS studies used BioNumerics™ as their main tool for analysis [73][74][75]. However, even if previously mentioned software suggests a high capacity to customize and optimize spectra, it is also important to highlight the fact that it is also possible to carry it out during the acquisition step by modifying MALDI-TOF parameters.…”