Summary: The enterotoxigenic strains 1676, 1706, 1751 and KEC96a, which do not produce fimbrial adhesive antigens of the K88, K99 or 987P antigen type reacted both and with antiserum to F41 fimbriae in an indirect immunofluorescent antibody technique. Antiserum used to demonstrate material B, an adhesive antigen thought to mediate the adhesive and mannose-resistant (MR) haemagglutinating properties of strains 1676, 1706 and 1751, reacted with an F41 strain. The antiserum also inhibited the MR haemagglutinating activity of F41 antigen and gave an anionic precipitation line in immunoelectrophoresis experiments with an extract containing F41 antigen.

The MR haemagglutinating properties of an antigen extract containing material B from strain 1706 was neutralized by antiserum to F41 fimbriae and by OK antisera to strains that produce both F41 and K99 fimbriae. These sera also gave an anionic precipitation line with the MR haemagglutinin from strain 1706 and the MR haemagglutinin gave a line of identity with F41 in gel diffusion experiments with antiserum to F41 fimbriae. OK antisera to K99 F41 bacteria and OK antisera to K88 bacteria and 987P bacteria did not react with this haemagglutinin.

Transmission electron microscopy on the ileum of newborn gnotobiotic piglets infected with strain 1706 showed irregular, poorly defined filamentous material surrounding some, though not all, bacteria but regular fimbrial structures were not visible. Fine thread-like material was visible surrounding most of the bacteria in ultra thin sections from a piglet infected with an strain that produces both F41 and K99. Staining with ruthenium red suggested. that this material was associated with polysaccharide.


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