Table 1

Requirement of SipA for efficient S. typhimurium entry into HeLa cells. Bacterial internalization was measured by fluorescence microscopy (7). Values are averages ± SE of three independent experiments and have been normalized to the internalization level of wild-type bacteria after 30 min of infection, which was considered to be 100% (in this case, 1597 ± 185 bacteria internalized per 100 cells). A minimum of 250 cells were counted for each strain per time point. The Pvalues for the difference between the entry levels of the wild type and the sipA strains are as follows: 5 min, P = 0.002; 10 min, P = 0.05; 20 min, P = 0.03. IT, infection time.

Strain Invasion (%)
IT 5 minIT 10 min IT 20 min IT 30 min
Wild type 13.47  ±  1.93 32.68  ±   8.15 72.07  ±  9.43100  ±  11.55
sipA 5.26  ±  0.99 17.91  ±   5.05 46.09  ±  10.77 92.27  ±  18.72
sipA/psipA11.29  ±  2.10 31.80  ±  10.98 71.92  ±  11.06 93.88  ±  11.10