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Relationships among streptococci from the mitis group, misidentified as Streptococcus pneumoniae

Ewa Sadowy1, Agnieszka Bojarska2, Alicja Kuch3

  • 1Department of Molecular Microbiology, National Medicines Institute, Chełmska 30/34, 00-725, Warsaw, Poland. e.sadowy@nil.gov.pl.

European Journal of Clinical Microbiology & Infectious Diseases : Official Publication of the European Society of Clinical Microbiology
|May 16, 2020
PubMed

Insights

Misidentified Streptococcus pneumoniae strains were analyzed using genetic and phenotypic methods. These bacteria, often mistaken for pneumococci, belong to the Streptococcus mitis group, highlighting complex species relationships.

Area of Science:

  • Microbiology
  • Genomics
  • Taxonomy

Background:

  • Streptococcus pneumoniae is a significant human pathogen, but misidentification of similar streptococci can occur.
  • Accurate identification is crucial for effective treatment and epidemiological surveillance.

Purpose of the Study:

  • To investigate the phenotypic and genotypic characteristics of streptococci misidentified as Streptococcus pneumoniae.
  • To clarify the taxonomic and phylogenetic relationships of these misidentified isolates.

Main Methods:

  • Phenotypic testing (optochin susceptibility, bile solubility).
  • Molecular identification using lytA and 16S rRNA gene sequencing.
  • Whole-genome sequencing (WGS) for comprehensive genomic analysis.
  • Phylogenetic analyses including MLSA, rMLST, and core-genome analysis.

Main Results:

  • Sixty-three misidentified isolates were analyzed over 20 years.
  • All isolates possessed a 6-bp deletion in the lytA 3' terminus, characteristic of Mitis streptococci.
  • Most isolates lacked the pneumococcal signature at position 203 in 16S rRNA genes.
  • Phylogenetic analyses clearly separated these isolates from S. pneumoniae, associating them with Streptococcus pseudopneumoniae and Streptococcus mitis groups.
  • Core-genome analysis identified a distinct cluster within the Mitis group, suggesting a potential novel species.

Conclusions:

  • Misidentified streptococci are phylogenetically distinct from Streptococcus pneumoniae and belong to the Mitis group.
  • The study reveals complex phylogenetic and taxonomic relationships within S. mitis-like bacteria.
  • Evidence suggests the Mitis group may comprise several distinct species, necessitating refined diagnostic approaches.

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