Abstract
Two assays were designed with which isogenic laboratory strains of Escherichia coli K-12 with and without ColV plasmids were compared for their ability to adhere in vitro to mouse intestinal epithelium. In both assays, disks of intestinal tissue were exposed to bacteria. In the first, disks were homogenized and the numbers of viable bacteria adherent to them were estimated from colony counts of plates inoculated with dilutions of the homogenates. In the second, bacteria were labeled with [(14)C]aspartic acid; the number of adherent cells per disk was estimated by liquid scintillation spectrometry. Data from each assay were compared by analysis of variance. In both assays, strains bearing the ColV plasmid adhered in two- to threefold-greater numbers than isogenic strains without the plasmid. These differences were highly significant statistically. A non-colicinogenic strain free of the ColV plasmid was selected by treatment of a ColV strain with sodium dodecyl sulfate. In the radioisotopic assay, the ColV strain associated with the epithelium in significantly greater numbers than the cured derivative. A ColV strain was created by conjugation; in the radioisotopic assay this strain bound to epithelium in significantly greater numbers than the recipient strain without the plasmid. The original ColV strain, when negatively stained and examined by electron microscopy, had pili that adsorbed male-specific bacteriophage, whereas its isogenic variant without ColV did not. Some such properties, coded by the plasmid, may increase the virulence of the bacteria.