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Updated: Mar 15, 2026
Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43
Published on: September 11, 2020
Description and characterization of a penicillin-resistant Streptococcus dysgalactiae subsp. equisimilis clone
Kurt Fuursted1, Marc Stegger2, Steen Hoffmann2
1Department of Microbiology & Infection Control, Statens Serum Institut, DK-2300 Copenhagen S, Denmark kfu@ssi.dk.
Background:
During a 27 month period, we detected four incidents of penicillin-resistant (PR) Streptococcus dysgalactiae subsp. equisimilis (SDSE) isolated from blood cultures of three patients.
Methods:
The 4 PR-SDSE were compared phenotypically and molecularly (using WGS) with 36 penicillin-susceptible SDSE from blood cultures obtained in the same catchment area and time period.
Results:
Phylogenetic analysis showed that the four PR-SDSE belonged to a single clone and a possible epidemiological link between the three patients was identified to be a dermatology department. MICs of penicillin were determined to be 0.5-2 mg/L using Etest and 0.5 mg/L when tested by a broth microdilution method. The four PR-SDSE were unrelated to the 36 penicillin-susceptible isolates, which could suggest that they did not evolve locally from a susceptible clone, but have been introduced into the region. In silico genome-based resistome analysis revealed identical PBP mutations in all four isolates. We detected mutations in multiple PBPs, including two amino acid substitutions within the active sites of the transpeptidase domain of PBP2x (T341P and Q555E), which have also been detected in other PR streptococci. The remaining mutations were, however, all located outside the active-site motifs of the transpeptidase domain.
Conclusions:
To the best of our knowledge, this is the first description and characterization of invasive PR-SDSE. The resistant isolates had several amino acid changes in various PBPs compared with penicillin-susceptible SDSE. The observation that SDSE also can become PR emphasizes the importance of performing antimicrobial susceptibility testing.
Insights
Four cases of penicillin-resistant Streptococcus dysgalactiae subsp. equisimilis (SDSE) were identified. These resistant strains, linked to a dermatology department, exhibited specific PBP mutations, highlighting the need for antimicrobial susceptibility testing.
Area of Science:
- Microbiology
- Genomics
- Infectious Diseases
Background:
- This study investigated the emergence of penicillin-resistant Streptococcus dysgalactiae subsp. equisimilis (PR-SDSE) in clinical blood cultures.
- Four incidents of PR-SDSE were detected over a 27-month period, affecting three patients.
Observation:
- Phenotypic and whole-genome sequencing (WGS) analyses compared PR-SDSE with susceptible strains.
- Phylogenetic analysis revealed the four PR-SDSE isolates belonged to a single clone with a potential link to a dermatology department.
Findings:
- In silico resistome analysis identified identical mutations in penicillin-binding proteins (PBPs) in all four PR-SDSE isolates.
- Specific PBP2x mutations (T341P and Q555E) were noted, alongside other mutations outside active-site motifs.
- PR-SDSE isolates appeared introduced into the region rather than evolving locally from susceptible strains.
Implications:
- This is the first documented description and characterization of invasive penicillin-resistant Streptococcus dysgalactiae subsp. equisimilis.
- The emergence of resistance in SDSE underscores the critical importance of routine antimicrobial susceptibility testing.
- Understanding the genetic basis of resistance in SDSE can inform clinical management and public health strategies.
