Abstract
Nowadays, more than 95 different Streptococcus pneumoniae serotypes are known, being less than one third responsible for the majority of severe pneumococcal infections. After the introduction of conjugate vaccines, a change in the epidemiology of the serotypes causing invasive pneumococcal disease has been observed making the surveillance of circulating serotypes especially relevant. Some recent studies have used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) technology to identify the most frequent pneumococcal serotypes that cause invasive disease. The objectives of this study were to evaluate the efficacy of previously described discriminatory peaks determined by MALDI-TOF MS for the identification of serotypes 6B, 19F, 19A and 35B using reference and clinical isolates and to try to identify other discriminatory peaks for serotypes 11A, 19F and 19A using transformed pneumococcal strains. Most of the proposed peaks defined in the literature for the identification of serotypes 6B, 19F, 19A, 35B were not found in the spectra of the 10 reference isolates nor in those of the 60 clinical isolates tested corresponding to these four serotypes. The analysis and comparison of the mass spectra of genetically modified pneumococci (transformed strains) did not allow the establishment of new discriminatory peaks for serotypes 11A, 19F, and 19A. MALDI-TOF MS in the usual range of 2,000 to 20,000 m/z did not prove to be a valid technique for direct S. pneumoniae serotyping.
Highlights
Streptococcus pneumoniae serotyping is not currently of the utmost importance for routine clinical practice unlike in the pre-antibiotic era, when it was critical for the patients treatment with monospecific antisera [1]
Serotyping is of great significance from an epidemiological and preventive perspective because it makes possible to define the distribution of serotypes causing invasive pneumococcal disease (IPD) and contributes to updating the composition of pneumococcal vaccines that include the most frequent S. pneumoniae serotypes causing IPD
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 included in the study of Nakano et al [23] together with serotypes 6B, 19F and 19A
Summary
Streptococcus pneumoniae serotyping is not currently of the utmost importance for routine clinical practice unlike in the pre-antibiotic era, when it was critical for the patients treatment with monospecific antisera [1]. Serotyping is of great significance from an epidemiological and preventive perspective because it makes possible to define the distribution of serotypes causing invasive pneumococcal disease (IPD) and contributes to updating the composition of pneumococcal vaccines that include the most frequent S. pneumoniae serotypes causing IPD.
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