FIG. 1.

Internalization of S. aureus strains Newman and Newman mAH12 into fibroblasts or epithelial cells. (a and b) Confluent layers of fibroblasts (a) or epithelial cells (b) were inoculated with a bacterial mixture of strains Newman and Newman mAH12 (ON cultures) and incubated at 37°C for 2 h. The wells were further incubated with lysostaphin to kill the extracellular bacteria. The cells were lysed, and the ratio between the two bacterial strains was determined based on the erythromycin resistance of mAH12. The data are presented as mean CFU in nine experiments. (c) Internalization of strains mAH12 and mAH12 (pCXEap) in fibroblast cells. Bacteria were used separately here because reliable quantification of mAH12 and mAH12 (pCXEap) in a mixture could not be done. The data are presented as mean number of internalized bacteria in eight experiments. Error bars indicate standard deviation. Statistical differences were determined by Student's t test. *, P < 0.05; **, P < 0.01.