THE TYPE-3 FIMBRIAL ADHESIN GENE (MRKD) OF KLEBSIELLA SPECIES IS NOT CONSERVED AMONG ALL FIMBRIATE STRAINS

The type 3 fimbriae of enteric bacteria mediate agglutination, in vitr o, of erythrocytes treated with tannic acid. The gene encoding the pol ypeptide, MrkD, that mediates this agglutination reaction was placed d ownstream of an inducible promoter, and the ability of MrkD alone to f acilitate hemagglutination was determined. Although Escherichia coli t ransformants could be shown to produce the MrkD protein, hemagglutinat ion did not occur in the absence of other mrk gene products. In additi on, the MrkD polypeptide did not cross the bacterial outer membrane un less a fimbrial chaperone protein was also present. Analysis of the fr equency of the mrkD gene within the genus Klebsiella indicated that th is gene is conserved in strains of Klebsiella oxytoca but not in other fimbriate Klebsiella species. In the small number of strains of Klebs iella pneumoniae that do possess a related mrkD gene, this determinant could be found on a plasmid in one strain. The ability of type 3 fimb riate bacteria to adhere to type V collagen was found to be a function of a specific MrkD polypeptide. This adhesin is frequently found in s trains of K. oxytoca but is rarely associated with the type 3 fimbriae of K. pneumoniae.