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

We tested 21 polymorphic loci encoded by the genome of Streptococcus pyogenes (group A Streptococcus, GAS). Seven of them were chosen for the MLVA scheme. The primer pairs, designed for selected loci, detect from few to several alleles, and the method has a Simpson's Index of diversity of 0.957. To test the overall performance of the method, multiplex PCR reactions were carried out for over 700 GAS strains. Using the method we were able to detect differences between highly clonal strains that share the same emm, MLST and PFGE types. The most diverse strains were M4, M2, M3 and M28. We developed a typing method that can be employed to differentiate between GAS strains. The method has high resolution and measures diversity of the GAS core chromosome, on the contrary to methods such as PFGE.