Levels of Listeria monocytogenes hemolysin are not directly proportional to virulence in experimental infections of mice.

The sulfhydryl-activated hemolysin of Listeria monocytogenes has been implicated in the virulence of the bacteria. Although loss of hemolytic activity by means of transposon mutagenesis is accompanied by loss of virulence in the mouse infection model, a direct relationship between in vitro production of hemolysin and virulence was not observed. Noticeable deviations in the extent of hemolysin production appeared to leave virulence unaffected.