FIG. 1.

Inactivation of the speB gene in NZ131 enhanced internalization by CHO-K1 cells. S. pyogenes NZ131 was grown to the mid-exponential (exp) and stationary (stat) phases in THY broth. Aliquots were centrifuged, and the bacteria were resuspended in DMEM prior to the addition of 10⁷ CFU to preconfluent CHO-K1 cell monolayers with (+) or without (−) 5% FCS. The infection proceeded for 2 h prior to the assessment of internalization by differential immunogold-silver staining. (A) Internalization of M49 strain NZ131 (open bars) and NZ131 speB (solid bars). (B) Internalization of M12 strain 86-858. The data represent the mean number of streptococci per cell ± standard error from at least three separate experiments.