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Fourteen strains of Clostridium difficile, previously characterized by SDS-PAGE, were examined for the presence of surface structures. None of the strains were fimbriated but, when grown in the presence of glucose, all exhibited a thin ruthenium red-positive layer. Two strains, belonging to different electrophoretic groups, were also observed after treatment with homologous and heterologous antisera. The strain belonging to the electrophoretic group 2, usually associated with the disease, showed a 30-80nm thick capsule in ultrathin sections. The strains belonging to group 5, mainly observed in isolates from healthy children, exhibited a thinner polysaccharide layer (10-20 nm). No stabilization was observed when these strains were treated with heterologous antisera. This capsule-like material did not seem to be associated with adhesive properties of C. difficile strains.

The penetration process of an enteroinvasive strain of Escherichia coli 0124 into HEp-2 cells has been studied by electron microscopy. Bacteria penetrated into cultured cells by a phagocytosis-like mechanism, and multiplied within the vacuoles as well as in the cytoplasmic matrix. On the whole, the infection cycle of EIEC appeared to be similar to that described for Shigella. The stain examined has also been found to elaborate a 40 nm-thick glyocalix, which is probably involved in the recognition of host surface receptors and therefore in the attachment of microorganisms to the cell membrane.