Isolation and characterization of enterotoxigenic Escherichia coli mutants that produce abnormal heat-labile enterotoxins

Abstract Bacteroides fragilis populations were separated according to the size of surface structure. Subculture of the separated populations produced cultures enriched for 3 different structures; a large capsule, a small capsule and an electron-dense layer (EDL). The ability of these subpopulations to haemagglutinate (HA) erythrocytes from a number of species was examined. Populations which produced either a large or s small capsule did not have HA activity, whereas those with an extracellular EDL did. By mixing populations with EDL and those with either the large or small capsule, the degree of HA could be altered. HA was dependent on the proportion of EDL-bearing bacteria present. Fimbriae were not observed on electron microscopy.