Evidence for a one-hit theory in the immune bactericidal reaction and demonstration of a multi-hit response for hemolysis by streptolysin O and Clostridium perfringens theta-toxin.

An analytical method was developed for estimating the number of hits necessary to lyse or kill cells in which various concentrations of the cells are treated with a constant amount of the lytic or killing agent in a constant reaction volume. The reaction may be due to a single-component agent or occur by a sequential chain of reactions due to a multi-component agent, even including side, abortive, or counter-reactions. It was clearly shown by this method that immune bactericidal reactions followed a one-hit theory. It was shown by this method that streptolysin O required four or five hits for hemolysis and Clostridium perfringens theta-toxin required two hits. These results were confirmed by both logarithmic dose-response and survival analyses. It was also shown that streptolysin O and theta-toxin can act complementarily on accumulation of the hits for hemolysis.