INTERMEDILYSIN, A NOVEL CYTOTOXIN SPECIFIC FOR HUMAN-CELLS, SECRETED BY STREPTOCOCCUS-INTERMEDIUS UNS46 ISOLATED FROM A HUMAN LIVER-ABSCESS

A novel cytotoxin (intermedilysin) specific for human cells was identi fied as a cytolytic factor of Streptococcus intermedius UNS46 isolated from a human liver abscess. Intermedilysin caused human cell death wi th membrane blebs. Intermedilysin was purified from UNS46 culture medi um by means of gel filtration and hydrophobic chromatography. The puri fied toxin was resolved into major and minor bands of 54 and 53 kDa, r espectively, by sodium dodecyl sulfate-polyacrylamide gel electrophore sis. These proteins reacted with an antibody against intermedilysin. F ive internal peptide fragments of intermedilysin were sequenced and fo und to have 42 to 71% homology with the thiol-activated cytotoxin pneu molysin. However, the action of intermedilysin differed from that of t hiol-activated cytotoxins, especially in terms of a lack of activation by dithiothreitol and resistance to treatments,vith N-ethylmaleimide and 5,5'-dithio-bis-(2-nitrobenzoic acid), although cholesterol inhibi ted the toxin activity. Intermedilysin was potently hemolytic on human erythrocytes but was 100-fold less effective on chimpanzee and cynomo lgus monkey erythrocytes. Intermedilysin was not hemolytic in nine oth er animal species tested. Since human erythrocytes treated with trypsi n were far less sensitive to intermedilysin than were the intact cells , a cell membrane protein(s) may participate in the intermedilysin act ion. These data demonstrated that intermedilysin is distinguishable fr om all known bacterial cytolysins.