THE HYDROPHOBIC SURFACE PROTEIN LAYER OF ENTEROAGGREGATIVE ESCHERICHIA-COLI STRAINS

The surface of three strains of enteroaggregative Escherichia coli (EA ggEC) and three strains of enteropathogenic E. coli (EPEC) were examin ed using the freeze-substitution technique of electron microscopy and as a result an electron dense surface layer was found only on EAggEC s trains but not on EPEC strains. The analysis of the outer membrane pro teins by polyacrylamide gel electrophoresis revealed the existence of a unique 38 kDa protein in EAggEC strains. The protein could be easily extracted from the bacterial surface with 5 M LiCl treatment at room temperature. The antiserum raised in mice with 38 kDa protein extracte d from the electrophoresed gel was immunoreacted with the surface of t he bacteria of EAEgEC by immunoelectron microscopy. The hydrophobic su rface character of the EAggEC strains was lost after the extraction of the protein layer by LiCl. We thus conclude that the surface protein layer therefore plays an important role in the expression of the aggre gative phenotype in EAggEC strains.