Characterization of surface layer proteins from different Clostridium difficile clinical isolates

In a previous study we suggested that two surface proteins of a Clostridium difficile strain were involved in the formation of a regularly assembled s urface layer (S-layer) external to the cell wall. In the present paper six C. difficile strains isolated from cases and healthy carriers were studied. By using freeze-etching and negative staining techniques two superimposed structurally different lattices were detected on the cell surface of the di fferent C. difficile strains. In each strain, the outer S-layer lattice was arranged in a square symmetry and the inner S-layer lattice in hexagonal s ymmetry. The S-layer proteins from the different strains were isolated and characterized. Each strain showed two distinct S-layer glycoproteins rangin g in molecular mass 36-56 kDa. Antigenic cross-reactivity among the S-layer proteins of higher molecular masses extracted from each strain was demonst rated whereas no antigenic relationship was observed among the different S- layer proteins of lower molecular masses. N-terminal sequence analysis show ed the presence of common structural motifs conserved among the high S-laye r proteins as well as among the low S-layer proteins. These data indicate t hat the presence of S-layer on C. difficile strains is common and that its glycoprotein subunits show a certain degree of heterogeneity. (C) 2000 Acad emic Press.