FIG. 5.

TagA provides increased serum resistance to E. coli DH5α and A. hydrophila SSU by increasing the inhibitory activity of C1-INH. (A) An aliquot (8 μg) of C1-INH was treated with or without 1 μg of rTagA and incubated overnight at room temperature and, on the next day, was added to an aliquot (20 μl) of mid-log-phase grown E. coli DH5α cells, as described in Materials and Methods. After incubation for 1 h at 37°C, the bacteria were serially diluted and plated onto LB agar plates. The percentage of surviving bacteria was calculated as described in Materials and Methods (*, P = 0.001 by unpaired t test). (B) TagA also contributes to the serum resistance of A. hydrophila SSU. WT bacterium or its tagA mutant was grown to mid-log phase, washed in PBS, and resuspended in an equivalent amount of PBS. An aliquot (20 μl) of the bacterial cells was added to a mixture of PBS and 50% serum and incubated at 37°C for 3 h (34). The percentage of surviving cells was calculated as described in Materials and Methods. (*, P = 0.04 by unpaired t test).