This study examined 52 strains from seven Enterobacter species to characterize their fimbrial haemagglutinins (HA) and associated fimbriae using haemagglutination tests and electron microscopy. Most haemagglutinating strains (33 of 39) produced only one type of haemagglutinin: either mannose-sensitive HA (MS-HA) associated with thick type-1 fimbriae, or mannose-resistant Klebsiella-like HA (MR/K-HA) associated with thin type-3 fimbriae. Thirteen non-haemagglutinating strains lacked fimbriae entirely. E. aerogenes strains were unique in frequently producing multiple haemagglutinins, including a third mannose-resistant type. Immune electron microscopy revealed antigenic diversity among type-1 and type-3 fimbriae across species. E. amnigenus, E. cloacae, and E. sakazakii shared similar MS-HA phenotypes and antigenically related type-1 fimbriae, consistent with their genetic relatedness. E. intermedium displayed antigenically distinct fimbriae from other species. The findings provide insights into the adhesive properties of Enterobacter species and their taxonomic relationships within the Enterobacteriaceae family.

Key findings

• Most Enterobacter strains produced single haemagglutinin types: MS-HA with thick type-1 fimbriae or MR/K-HA with thin type-3 fimbriae
• E. aerogenes strains were multiply haemagglutinating, producing MS-HA, MR/K-HA, and a third MR/P-class haemagglutinin not found in other species
• Type-1 and type-3 fimbriae showed antigenic diversity among Enterobacter species, with E. intermedium displaying fimbriae antigenically distinct from all other species examined
• Non-haemagglutinating strains (13 of 52) were consistently non-fimbriate
• Fimbrial HA production was optimal during static broth culture conditions and at 30°C growth temperature