Behavior of Escherichia coli K antigens K88ab, K88ac, and K88ad in immunoelectrophoresis, double diffusion, and hemagglutination.

Porcine enteropathogenic Escherichia coli strains were found to possess a variant of the K88 antigen provisionally termed K88ad. We propose to include this antigen into the international E. coli typing scheme. Ultrasonic extracts of field strains of E. coli possessing the K88ab, K88ac, or K88ad antigen and their E. coli K-12 K88+ transconjugants showed a specific K88 precipitation line in immunoelectrophoresis and double diffusion only when grown at 37 degrees C, but not when grown at 18 degrees C. By using agarose gels, K88ab, K88ac, and K88ad antigens showed anodic mobility in immunoelectrophoresis. When using Difco Noble agar gels, K88ad was not mobile or anodic, K88ab was cathodic; K88ac of 17 strains was cathodic and of 24 strains was anodic. The immunoelectrophoretic behavior of a K88 antigen (K88ab, K88ac, or K88ad) did not alter after transfer of the corresponding plasmid to E. coli K-12. Anodic and cathodic K88ac antigens could not be distinguished serologically. The differences between the results obtained in Noble agar gels and agarose gels are due to electro-endosmotic flow. We describe a procedure which increases the detection level of K88+ transconjugants in a mating mixture. It is based on the specific mannose-resistant attachment of K88+ cells to guinea pig erythrocytes.