The Production of F41 Fimbriae by Piglet Strains of Enterotoxigenic Escherichia coli that Lack K88, K99 and 987P Fimbriae

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Abstract
The enterotoxigenic E. coli strains 1676, 1706, 1751 and KEC96a, which do not produce fimbrial adhesive antigens of the K88, K99 or 987P antigen type, reacted in vitro and in vivo 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) hemagglutinating properties of E. coli strains 1676, 1706 and 1751, reacted in vitro with an F41+ strain. The antiserum also inhibited the MR hemagglutinating activity of F41 antigen and gave an anionic precipitation line in immunoelectrophoresis experiments with an extract containing F41 antigen. The MR hemagglutinating properties of an antigen extract containing material B from E. coli strain 1706 were neutralized by antiserum to F41 fimbriae and by OK antisera to E. coli strains that produce F41 and K99 fimbriae. These sera also gave an anionic precipitation line with the MR hemagglutinin from E. coli strain 1706; the MR hemagglutinin 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 hemagglutinin. Transmission electron microscopy on the ileum of newborn gnotobiotic piglets infected with E. coli 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 ultrathin sections from a piglet infected with an E. coli strain that produces both F41 and K99. Staining with ruthenium red suggested that this material was associated with polysaccharide.