Extracellular antigens from Listeria monocytogenes. II. Cytotoxicity of hemolytic and lipolytic antigens of Listeria for cultured mouse macrophages.

Purified preparations of hemolytic and lipolytic antigens were shown to be cytotoxic for tissue cultures of mouse peritoneal macrophage monolayers. The percent reduction in viability was proportional to the concentration of antigen used although, for a brief period, the hemolytic antigen stimulated the growth of cultured macrophages. Hemolytic and lipolytic antigens were synthesized by an hemolysin-producing strain (7973), but were deficient or totally lacking in nonhemolysin-producing strains (9037-7, 4219). The inoculation of strain 7973 onto macrophage monolayers at a bacterium to macrophage ratio of 10:1 resulted in a complete loss of viable phagocytic cells. The decrease in viable phagocytic cells was accompanied by an increase in viable listeria. Pronounced cytopathic activity with proliferation of listeria was also observed when 200 U of lipolytic antigen were added to macrophage monolayers that had been infected with the smooth type nonhemolysin-producing strain (4219) on the previous day. On the other hand, a high percentage of macrophages survived when exposed to nonhemolysin-producing strains only. In this case, listeria were not recovered by routine culture methods. The data presented do not establish that phagocytic cell destruction with accompanying microbial proliferation is the direct result of hemolysin elaboration; however, they suggest that there is need for further exploration of the role of the hemolysin in listeriosis.