PORE-FORMING AND HEMOLYTIC PROPERTIES OF THE GARDNERELLA-VAGINALIS CYTOLYSIN

The pleomorphic bacterium Gardnerella vaginalis releases in the cultur e broth a haemolytic exotoxin (Gvh) which is probably a virulence dete rminant of this unique bacterium, implicated in gynaecological and uro logical disorders. This 59 kDa cytolysin was purified to homogeneity i n just one chromatographic step directly from the culture supernatant, a final specific activity up to 1.9 x 10(6) HU mg-1 being obtained. T he toxin-induced lesion on human erythrocytes results from the formati on of a pore whose radius is approximately 2.4 nm. The damage is inhib ited by osmotic protectants and shows a sigmoidal dose-response profil e suggesting an aggregation process of haemolysin molecules on the tar get membrane to create the functional lesion. The extent and the kinet ics of haemolysis are strongly dependent on temperature and an activat ion energy of 64.0 kJ mol-1 has been derived. Lipid membranes can be v ery efficient inhibitors of Gvh-haemolysis, being able to bind the tox in quite avidly. The inhibitory effect requires the presence of choles terol and it is stronger when cholesterol is mixed with negatively cha rged phospholipids rather than with zwitterionic phospholipids, sugges ting that a negative surface potential increases the affinity of the t oxin for the lipid bilayer. The functional properties of Gvh have been compared with those of Clostridium perfringens theta-toxin (PFO) and Escherichia coli haemolysin (HlyA), which are representative of widesp read haemolysins produced by Gram-positive and Gram-negative bacteria, respectively. The toxin shares several features with the family of th e so-called 'sulphydryl-activated' cytolysins produced by Gram-positiv e bacteria, although Gvh does not truly belong to this family, being d eactivated by beta-mercaptoethanol and being antigenically distinct fr om them. We report here for the first time the detection in the vagina l fluid of infected women of a specific IgA response against the toxin .