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Identification of macrolide-resistant clones of Streptococcus pyogenes in Portugal
C Silva-Costa1, M Ramirez, J Melo-Cristino
1Laboratório de Microbiologia, Instituto de Medicina Molecular, Faculdade de Medicina de Lisboa, Lisboa, Lisbon, Portugal.
Abstract:
Although the overall level of macrolide resistance (27%) has remained stable in Portugal, a rapid inversion in the dominant phenotypes has been noted, with a sharp decrease in the MLS(B) phenotype paralleled by an increase in the M phenotype. To gain further insight into these changes, 325 macrolide-resistant isolates were characterised using a combination of pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The use of Cfr9I, an isoschizomer of SmaI, to digest M phenotype isolates that were refractory to SmaI digestion allowed direct comparison of MLS(B) and M isolates. The results from PFGE and MLST were highly concordant and identified eight major clones, accounting for 92% of the isolates, each of which was associated exclusively with a single macrolide resistance phenotype. Two major clones were found among MLS(B) isolates, characterised by sequence types (ST) 46 (T12/emm22) and ST52 (T28/emm28), whereas clones characterised by ST39 (T4/emm4) and ST28 (T1/emm1) dominated among M isolates. The clone defined by ST52 corresponded to a bacitracin-resistant clone circulating in Europe, and a novel variant expressing other surface antigens (T12/emm22) was detected. The presence of the four major clones has been reported previously in other European countries, suggesting Europe-wide dissemination of a few macrolide-resistant lineages.
Insights
Macrolide resistance in Portugal remains stable, but dominant phenotypes are shifting. Genetic analysis revealed eight major clones, each linked to specific resistance types, with some clones circulating across Europe.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Macrolide resistance in Portugal shows a stable overall level (27%) but a significant shift in dominant phenotypes.
- A decrease in the MLS(B) phenotype and a corresponding increase in the M phenotype have been observed.
Purpose of the Study:
- To investigate the genetic basis and clonal distribution underlying the changing macrolide resistance phenotypes in Portugal.
- To characterize macrolide-resistant isolates using molecular typing techniques.
Main Methods:
- Characterization of 325 macrolide-resistant isolates using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST).
- Utilized Cfr9I digestion for M phenotype isolates refractory to SmaI digestion to enable comparative analysis.
- Concordant PFGE and MLST results identified major bacterial clones and their associated resistance phenotypes.
Main Results:
- Eight major clones were identified, accounting for 92% of isolates, each exclusively associated with either MLS(B) or M macrolide resistance phenotype.
- MLS(B) isolates were dominated by clones ST46 (T12/emm22) and ST52 (T28/emm28).
- M isolates were primarily represented by clones ST39 (T4/emm4) and ST28 (T1/emm1). A previously described bacitracin-resistant clone (ST52) was identified, along with a novel variant.
Conclusions:
- The observed shift in macrolide resistance phenotypes is driven by the emergence and dissemination of specific bacterial clones.
- Four major clones identified in Portugal have also been reported in other European countries, indicating potential Europe-wide dissemination of macrolide-resistant lineages.
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