The characteristics of the capsule of the enterotoxemic Escherichia coli (ETEEC) O139:K12 strains that strongly adhere to Hep-2 cells were examined. Electron microscopic studies using the freeze-substitution technique revealed that ETEEC strains had a capsule of approximately 25 nm. These strains show hydrophobic surface properties and strong adherence to human polymorphonuclear leukocytes (PMNs). In contrast, ETEEC strains RK-O139 and ED-1 show weak adherence to HEp-2 cells and fail to express the capsule layer on the cell surface. These ETEEC strains possess hydrophilic surface properties and also adhere to PMNs. The lipopolysaccharide (LPS) analysis by means of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that ETEEC strains had the same LPS profile and long O-side chains of LPS. Furthermore, all strains were resistant to serum killing activity. These results suggest that the capsule of ETEEC strains does not contribute as an antiphagocytic factor, but as an adherence factor to host cells.
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