Visualization of Surface-specific Antigens in Various Strains of Enterotoxigenic E. coli

Proteinaceous surface antigens of enterotoxigenic E. coli (ETEC) appear as pili, and are important virulence factors as they allow bacteria to attach to the small intestinal mucosa. Surface antigens are classified as colonization factor antigens (CFA) and coli surface antigens (CS). Known groups include CFA/I, CFA/II (consisting of CS1, CS2 and CS3), CA/III and CFA/IV (consisting of CS4, CS5 and CS6). The goal of the present study was to examine the morphology of pili by transmission electron microscopy (TEM) and to localize specific surface antigens by immunolabelling. Using different strains of E. coli grown under various culture conditions, pili were visualized by negative staining and corresponding surface antigens were demonstrated by immunogold-labelling using both polyclonal and monoclonal antibodies. Expression of pili was dependent on culture conditions and sample handling. In contrast to CFA/I and CS3, CS6 pili were not detectable after negative staining. Selected antibodies, however, allowed surface antigens to be demonstrated unequivocally. These results will be of value in investigating the expression of colonizing factors in genetically modified bacterial strains.