Multilocus variable number tandem repeat analysis (MLVA) of Streptococcus pyogenes.

Area of Science:

• Microbiology
• Genetics
• Epidemiology

Background:

• Streptococcus pyogenes (group A Streptococcus, GAS) is a significant human pathogen.
• Accurate strain typing is crucial for tracking GAS outbreaks and understanding its epidemiology.
• Existing typing methods like PFGE have limitations in resolving highly clonal strains.

Purpose of the Study:

• To develop and validate a high-resolution genotyping method for Streptococcus pyogenes.
• To assess the discriminatory power of the new method for differentiating GAS strains.
• To evaluate the method's ability to measure genetic diversity within the GAS core chromosome.

Main Methods:

• Selection and optimization of 7 polymorphic loci from the Streptococcus pyogenes genome for MLVA.
• Design of primer pairs for multiplex PCR amplification of selected loci.
• Application of the MLVA scheme to over 700 GAS strains.

Main Results:

• The MLVA scheme demonstrated a high Simpson's Index of diversity (0.957).
• The method successfully differentiated between highly clonal GAS strains sharing identical emm, MLST, and PFGE types.
• Specific strains (M4, M2, M3, M28) exhibited the highest diversity.
• The method provides higher resolution compared to PFGE for GAS strain typing.

Conclusions:

• A novel, high-resolution MLVA typing method for Streptococcus pyogenes has been established.
• This method offers superior discriminatory power for differentiating GAS strains compared to traditional methods.
• The MLVA scheme effectively measures genetic diversity within the GAS core chromosome, aiding epidemiological surveillance.