FIG. 4.

(A) Microtiter assay of the hemolysin activity of various clones in E. coli XL1-Blue MR. Twofold serial dilutions of supernatants (except for row B) were added sequentially to columns 1 to 8 (1:2 to 1:256) in microtiter plates to a final volume of 100 μl with 1% (vol/vol) washed sheep erythrocytes in KRT. Row A contains supernatant of L. monocytogenes. Row B contains sheep erythrocytes with no added bacterial supernatant; row C contains supernatant of E. coli containing SuperCos1; row D contains supernatant of pCML77; row E contains supernatant of pCML75; row F contains supernatant of pCML76. (B) Microtiter assay of the cohemolysin activity of various clones in E. coli XL1-Blue MR. Same experiment as that for panel A, except that sheep erythrocytes were pretreated with 0.025 U/ml of sphingomyelinase for 30 min at 37°C prior to the addition of the bacterial supernatants. A and B are representative of at least three independent experiments.