Emergence of type I restriction modification system‐negative emm1 type Streptococcus pyogenes clinical isolates in Japan

Streptococcus pyogenes emm1 type is the dominant cause of streptococcal toxic shock syndrome (STSS) in Japan and many other developed countries. Recently, the number of STSS patients in Japan was reported to be increasing. Hence, we analyzed the S. pyogenes clinical isolates detected in Japan after 2005. We found that the regions encoding the Spy1908–1910 two-component regulatory system and the adjacent type I restriction modification system were deleted in some emm1 type isolates. The isolates with the deletion were detected only in the emm1 strains that were isolated between 2010 and 2013, but not before 2010. Twenty-six of 46 (56.5%) emm1 type isolates were isolated in 2010–2013, and among these isolates, five of seven (71.4%) emm1 type STSS isolates were shown to have that deletion. PFGE and PCR analysis for the presence of several pyrogenic exotoxin-related genes suggested that the emm1 isolates with and without the deletion shared the same genetic background. The emm1 isolates with the deletion could incorporate exogenous plasmids by experimental electroporation transformation far more efficiently. These results suggested that the novel emm1 isolates have occupied a fairly large part of total emm1 isolates.