(C) Quantification of the number of CFU/ml of CHO cells infected for 3 h with the wt strain of S. aureus, the mutant deficient for α-hemolysin (Hla−), or the Hla(−) mutant expressing an α-hemolysin plasmid in the absence or presence of cAMP. * p<0.05 (paired Student's t-test). These data are representative of two independent experiments. 