Fimbrial and non-fimbrial haemagglutinins in Enterobacter aerogenes

Ten strains of Enterobacter aerogenes were examined for their ability to produce haemagglutinins and fimbriae. Nine strains formed a mannose-sensitive (MS) haemagglutinin associated with thin (4 nm) non-channelled fimbriae. These thin fimbriae of E. aerogenes were antigenically different from the thin fimbriae of other fimbriate strains of Enterobacter and Klebsiella and probably represent a new kind of fimbria not previously described in Enterobacteriaceae. Eight of these same nine strains also formed a non-fimbrial mannose-resistant, proteus-like (MR/P) haemagglutinin. The formation of thin fimbriae associated with MS haemagglutinin and of non-fimbrial MR/P haemagglutinin are properties not associated with other strains of Enterobacter and Klebsiella. E. aerogenes strain NCIB11460 was unusual among the strains examined in this series in that it alone produced mannose-resistant, Klebsiella-like (MR/K) haemagglutinin and type-3 fimbriae which, as judged by immunoelectronmicroscopy, were antigenically like those of type-3 fimbriate Klebsiella strains. The identifying characters of this exceptional strain of E. aerogenes are discussed in detail. All ten strains also produced thick fimbriae which by immunoelectronmicroscopy behaved like the type-1 fimbriae of Klebsiella strains. However, correlation between their presence and the production of MS haemagglutinin in E. aerogenes was not established. The findings are discussed in the light of the present difficult taxonomic status of E. aerogenes within the tribe Klebsielleae.