FIG. 2.

Adhesion and invasion of Y. pestis derivatives or E. coli expressing ail to HEp-2 or THP-1 cells. HEp-2 (A, C, and E) and THP-1 (B and D) cells were infected with Y. pestis derivatives (A and B) or E. coli AAEC185 derivatives (C and D). Percent adhesion was calculated by dividing cell-associated CFU by the number of all bacteria in the well (bound plus unbound) and multiplying by 100. Data are from three independent experiments performed in duplicate (n = 6). *, P < 0.0005; **, P < 0.00005. HEp-2 cell invasion (E) was assessed after the addition of gentamicin to kill extracellular bacteria for 1 h (P = 0.1; n = 6).