Immunogenicity of some common thermolabile surface antigens of Escherichia coli

The development in rabbits of antibodies against common thermolabile Escherichia coli surface antigens - and against O and K antigens - was investigated. Three strains, E3b (O75:K95:H5), E56b (O8:K27:H-), and H61 (O45:K1:H10), and five rabbits per strain were used. Immunization was carried out by routine procedures using non-heated whole cell vaccines. Homologous and heterologous reactions were recorded. Bacterial agglutination showed no great differences between homologous antisera. Maximum agglutination titers were reached after three immunizations, i.e., 12 dyas after the first immunization. The development of antibodies to the many single common and specific antigens was followed by examination in crossed immunoelectrophoresis (CIE). Indication of immune tolerance of polysaccharide K27 antigen was found. The finding of pre-immune antibody and the rapid response to immunization indicate that many of the reactions recorded should be regarded as secondary responses. Several antigens in the three strains were identical or serologically related. The common cross-reacting thermolabile surface antigens showed similar electrophoretic mobility in the three stains. Some rabbits were found to be overall good producers of antibodies and some were poor. The occurrence or absence of pre-immune antibody to common antigens could not be sued to select the good antibody producers. It is suggested that the immune response to the common surface antigens that could be reckoned as outer membrane proteins may influence the relationship between host and bacterium.