Transcriptome of Streptococcus pyogenes SSI-1 inside four differenct host cells was examined. Using custom made whole genomic ORF array, monitoring of the S. pyogenes transcriptome inside host cell was carried out by extracted S.pyogenes RNA from host cells infected with S. pyogenes at 0, 1, 2, 4 hr after infection. In this study, two human cells (Hela and Kyse) and two mouse cells (Mef Atg5+/+ and Mef Atg 5-/- ) were used. Two biologically-and three technical-replicated samples were prepared. Gene expression levels were compared between bacteria infected cells and uninfected cells. In addition, differences of the gene expression between the different infection time and host cell type were examined.