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Published on: August 15, 2025
Whole genome sequencing as a tool for phylogenetic analysis of clinical strains of Mitis group streptococci
L H Rasmussen1,2, R Dargis1, K Højholt1,3
1Department of Clinical Microbiology, Slagelse Hospital, Slagelse, Denmark.
Abstract:
Identification of Mitis group streptococci (MGS) to the species level is challenging for routine microbiology laboratories. Correct identification is crucial for the diagnosis of infective endocarditis, identification of treatment failure, and/or infection relapse. Eighty MGS from Danish patients with infective endocarditis were whole genome sequenced. We compared the phylogenetic analyses based on single genes (recA, sodA, gdh), multigene (MLSA), SNPs, and core-genome sequences. The six phylogenetic analyses generally showed a similar pattern of six monophyletic clusters, though a few differences were observed in single gene analyses. Species identification based on single gene analysis showed their limitations when more strains were included. In contrast, analyses incorporating more sequence data, like MLSA, SNPs and core-genome analyses, provided more distinct clustering. The core-genome tree showed the most distinct clustering.
Insights
Accurate identification of Mitis group streptococci (MGS) is vital for diagnosing infective endocarditis. Whole genome sequencing and core-genome analyses offer superior species identification compared to single-gene methods.
Area of Science:
- Microbiology
- Genomics
- Infectious Diseases
Background:
- Accurate species-level identification of Mitis group streptococci (MGS) is difficult in routine microbiology laboratories.
- Correct MGS identification is critical for diagnosing infective endocarditis, treatment failure, and infection relapse.
Purpose of the Study:
- To compare the effectiveness of different phylogenetic analyses for MGS species identification.
- To evaluate the utility of whole genome sequencing for MGS identification in clinical isolates.
Main Methods:
- Whole genome sequencing of 80 MGS isolates from Danish patients with infective endocarditis.
- Phylogenetic analysis using single genes (recA, sodA, gdh), multilocus sequence analysis (MLSA), single nucleotide polymorphisms (SNPs), and core-genome sequences.
Main Results:
- Six phylogenetic analyses generally revealed similar patterns with six monophyletic clusters.
- Single-gene analyses demonstrated limitations in species identification with increased strain numbers.
- MLSA, SNP, and core-genome analyses provided more distinct clustering.
- Core-genome tree analysis exhibited the most distinct clustering for MGS species.
Conclusions:
- Whole genome sequencing provides robust data for MGS phylogenetic analysis.
- Core-genome analysis is the most effective method for accurate MGS species identification, surpassing single-gene approaches.
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