What is the role of emm typing for the classification of group A streptococci (GAS)?

Updated: Sep 07, 2018
  • Author: Zartash Zafar Khan, MD, FACP; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
  • Print
Answer

The traditional Lancefield classification system, which is based on serotyping, has been replaced by emm typing, which has been used to characterize and measure the genetic diversity among isolates of S pyogenes. This system is based on a sequence at the 5' end of a locus (emm) that is present in all isolates. The targeted region of emm displays the highest level of sequence polymorphism known for an S pyogenes gene; more than 150 emm types have been described to date. [4] The emm gene encodes the M protein.

There are 4 major subfamilies of emm genes, which are defined by sequence differences within the 3' end, encoding the peptidoglycan-spanning domain. The chromosomal arrangement of emm subfamily genes reveals 5 major emm patterns, designated as emm patterns A through E. An example of the usefulness of emm typing is described by McGregor et al. [5]


Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!