TABLE 3.

Effect of heat shock on hemolytic activity of pneumolysin^a

Strain	Hemolytic units		% increase after heat shock
	30°C	42°C
D39	9,331 ± 2,347	16,515 ± 4,592	177*
HYK304 (clpL mutant)	10,210 ± 1,429	13,477 ± 3,155	132
HYK302 (clpP mutant)	13,063 ± 2,859	15,414 ± 2,489	118

^aHemolytic activity in cultures equivalent to an A₆₀₀ of 1. Fifty microliters of cell lysate was serially diluted (1:1) into 50 μl of phosphate-buffered saline. Then 50 μl of a 1.5% suspension of human red blood cells was added to each well. The plate was incubated for 30 min at 37°C. The hemolytic units were calculated from the well in which 50% hemolysis had occurred. Values are the means ± standard deviation of three independent experiments. *, P < 0.05.