FIG 3.

Protease secretion and epithelial cell damage were both increased only in the Δsap8 and SAP6 OE strains. (A and B) Total proteinase activity after 12 h in either planktonic (A) or biofilm (B) growth was quantified using FTC solution as the substrate. Under both culture conditions, the total proteinase activity was 2-fold higher in the Δsap8, SAP5 OE, and SAP6 OE strains (**, P < 0.01; ***, P < 0.001) than in the CAI4 strain. (C) An epithelial cell line, SCC-15, was infected with the CAI4, Δsap4/5/6, Δsap6, Δsap8, SAP5 OE, and SAP6 OE strains for 12 h, and the cell damage was measured by LDH release. There was no significant change in LDH release in SCC-15 cells infected with the Δsap4/5/6 and SAP5 OE strains compared to cells infected with the CAI4 strain. Both the Δsap8 and SAP6 OE strains induced significant cell damage (*, P < 0.05; **, P < 0.01). The results represent the averages from triplicate samples from two independent experiments. The error bars indicate standard deviations.