FIG 2.

Hemolytic activity at different pH levels. The indicated strains were grown at 37°C to an OD₆₀₀ of 0.9 in BHI of pH 7.6 (A) or pH 5.5 (B) before the supernatant was removed. Filtered supernatants were added to a 10% suspension of red blood cells at a 1:1 ratio and incubated for 3 h at 37°C. The absorbance was measured at 541 nm. The figure shows the hemolytic activity of the indicated strains relative to the wild type (100%) with the standard deviations. All samples were compared to the wild type using a two-tailed Student t test (***, P < 0.001).