Characterization of a mouse-passaged, highly encapsulated variant of groupA streptococcus in in vitro and in vivo studies

JRS4(HE), a highly encapsulated, mouse-passaged variant of group A streptoc occal strain JRS4, was characterized. The mucoid phenotype of JRS4(HE) was preserved after extensive passage in vitro. The level and size of csi RS tr anscript in JRS4(HE) was similar to that of JRS4, yet JRS4(HE) expressed hi gh levels of has and sagA and exhibited an increased activity of streptolys in S. These findings indicate that the CsrRS repressor system was inactive in JRS4(HE). JRS4(HE) adhered to HEp-2 cells at the stationary phase but di d not internalize these cells. At midlogarithmic phase, JRS4(HE) neither ad hered to nor internalized cells, because of an increased amount of hyaluron ic acid. Mice injected subcutaneously with JRS4(HE) developed large, deep n ecrotic lesions. In contrast, mice challenged with JRS4 developed small, su perficial lesions. Despite the use of a high inoculum, mice challenged with JRS4(HE) did not develop a lethal bacteremic infection. It is concluded th at inactivation of CsrRS in vivo is insufficient to cause a spreading necro tic disease.