Sammendrag
Background: For characterization of clinical isolates of Streptococcus pyogenes and S. dysgalactiae subsp. equisimilis for surveillance studies, emm typing and protein profiling are currently the best available molecular methods. This study determined the emm gene type and protein profile of Streptococcus pyogenes and S. dysgalactiae subsp. equisimilis strains isolated from children with rheumatic heart disease who were receiving on-going prophylaxis.
Methods: The emm gene typing of four strains of S. pyogenes and four strains of S. dysgalactiae subsp. equisimilis was performed by PCR followed by DNA sequencing. The protein profile of these strains was also analysed by high end mass spectrometry.
Results: Six different emm gene types were identified. These were stGrobn.1, emm 70.0, emm 68.2, emm 77.0, stG4831.0 and stC839.0. StGrobn.1 was the newly discovered subtype which is associated with an S. dysgalactiae subsp. equisimilis isolate expressing Lancefield group A. The phylogenetic tree showed that the inter-strain and intra-strain differences are relatively small. Differences between the emm types from S. dysgalactiae subsp. equisimilis are normally greater than the differences between emm types from S. dysgalactiae subsp. equisimilis and S. pyogenes. The streptococcal glycosyltransferase in strain S. pyogenes emm 68.2 exhibited N-linked glycosylation carrying a unique N-acetylhexoseamine (HexNAc)-deoxyhexose. This is a novel post-translational modification (PTM) not previously recognized.
Conclusion:The S. pyogenes and S. dysgalactiae subsp. equisimilis strains assessed here had different emm gene types, proteomic and PTM patterns, enabling distinction of subgroups of these closely related strains with pathogenic potential in rheumatic fever disease. From the current study, only emm77.0 was included in the 26 multivalent Group A streptococcal (GAS) vaccine.
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