Adhesion of Leptospira at a solid-liquid interface: a model.

Two strains of the saprophytic Leptospira biflexa serovar patoc display reversible and irreversible adhesion at a solid-liquid interface. Both forms of adhesion are enhanced in the presence of 20 microM carbonyl cyanide meta-chlorophenyl hydrazone (CCCP), an uncoupler which inhibits motility of the bacteria. Microscopic observations also indicated that motility may have a role in adhesion as only actively motile organisms were seen to detach from the substratum. A dynamic model is proposed for adhesion of these organisms at a solid-liquid interface. It is suggested that the level of reversible adhesion is determined by the comparative rates of attachment (ON phase) and detachment (OFF phase). As reversible adhesion is mediated by weak forces of attraction, bacterial motility or gentle washing could promote the OFF phase. When motility is inhibited, the OFF phase is reduced and the ON phase continues (as motility is not required for the ON phase) causing the level of reversible adhesion to increase. Since reversible adhesion is a prerequisite for irreversible adhesion, then increased reversible adhesion leads directly to increased irreversible adhesion. Reversible adhesion appears to be mediated by the weak attractive forces of the "secondary minimum" whereas the mechanism facilitating irreversible adhesion of leptospires is not known.