Dissemination of the phage-associated novel superantigen gene speL in recent invasive and noninvasive Streptococcus pyogenes M3/T3 isolates in Japan

In Japan, more than 10% of streptococcal toxic shock-like syndrome (TSLS) cases have been caused by Streptococcus pyogenes M3/T3 isolates since the first reported TSLS case in 1992. Most M3/T3 isolates from TSLS or severe invasive infection cases during 1992 to 2001 and those from noninvasive cases during this period are indistinguishable in pulsed-field gel electropherograms. The longest fragments of these recent isolates were 300 kb in size, whereas those of isolates recovered during or before 1973 were 260 kb in size. These 260- and 300-kb fragments hybridized to each other, suggesting the acquisition of an about 40-kb fragment by the recent isolates. The whole part of the acquired fragment was cloned from the first Japanese TSLS isolate, NIH1, and its nucleotide sequence was determined. The 41,796-bp fragment is temperate phage phiNIH1.1, containing a new superantigen gene speL near its right attachment site. The C-terminal part of the deduced amino acid sequence of speL has 48 and 46% similarity with well-characterized erythrogenic toxin SpeC and the most potent superantigen, SmeZ-2, respectively. None of 10 T3 isolates recovered during or before 1973 has speL, whereas all of 18 M3/T3 isolates recovered during or after 1992 and, surprisingly, Streptococcus equi subsp. equi ATCC 9527 do have this gene. Though plaques could not be obtained from phiNIH1.1, its DNA became detectable from the phage particle fraction upon mitomycin C induction, showing that this phage is not defective. A horizontal transfer of the phage carrying speL may explain the observed change in M3/T3 S. pyogenes isolates in Japan.