FIG 4 .
The Act-associated hemolytic activity neutralization assay and the protease activity of A. hydrophila strains E1 and E2 compared to that of A. hydrophila SSU and/or ATCC 7966T. (A) The neutralization of hemolytic activity associated with Act in the culture filtrates of A. hydrophila E1 and ATCC 7966T compared to A. hydrophila SSU. The culture filtrates of the strains studied were mixed with either preimmune rabbit serum (control) or 5-fold dilutions of hyperimmune rabbit serum (laboratory stock) containing antibodies to Act before the measurement of hemolytic activity. (B) Protease activity in the culture supernatants of A. hydrophila E1 and E2 compared to that of A. hydrophila SSU and ATCC 7966T. A. hydrophila E1 demonstrated a statistically significant decrease in protease activity compared to that of E2 and the two control strains, SSU and ATCC 7966T. The data were normalized to 1 × 108 CFU to account for any minor differences in the growth rates. All of the experiments were performed in triplicate, and the data presented are arithmetic means ± standard deviations. OD595, optical density at 595 nm.