Nucleotide sequence and functions of mrk determinants necessary for expression of type 3 fimbriae in Klebsiella pneumoniae

Abstract

The nucleotide sequence of six genes involved in the expression of type 3 fimbriae of Klebsiella pneumoniae was determined. In addition to the genes that encode the fimbrial subunit (mrkA) and adhesin (mrkD), the mrkB, mrkC, and mrkE genes appear to be involved in assembly of the fimbrial filament and regulation of type 3 fimbrial expression. The mrkF gene product is required to maintain the stability of the fimbrial ifiament on the cell surface. Type 3 fimbriae on Klebsiella strains were first described by Duguid (2); they are 2 to 4 nm wide and 0.5 to 2,um long. These fimbriae mediate agglutination of tannic acid-treated erythrocytes both with and without D-mannose and are therefore referred to as mannose-resistant Klebsiella-like hemagglutinins. Type 3 fimbriae mediate attachment to the basolateral surfaces of tracheal epithelial cells and to com-ponents of basement membranes (8, 22). The genes that encode the expression of type 3 fimbriae have been cloned from a clinical isolate of Klebsiella pneu