Characterization of the type 3 fimbriae with different MrkD adhesins: Possible role of the MrkD containing an RGD motif

Four novel mrkD alleles namely mrkD_V1, mrkD_V2, mrkD_V3, and mrkD_V4 were identified in seventeen Klebsiella pneumoniae meningitis strains using PCR-RFLP and sequence determination. Comparative analysis revealed a most variable region containing an RGD motif in the receptor domain of MrkD_V3. In order to determine if the sequence confers the K. pneumoniae mrkD_V3 the highest level of the fimbrial activity, a type 3 fimbriae display system was constructed in Escherichia coli. The E. coli JM109[pmrkABCD_V3F] displaying meshwork-like fimbriae also had the most fimbrial activity, supporting a possible role of the varied sequences. In a dose-dependent manner, the GRGDSP hexapeptide appeared to inhibit the adhesion of the E. coli JM109[pmrkABCD_V3F] to HCT-8, an ileocecal epithelial cell line. In addition, the adhesion activity was reduced by the addition of anti-α5β1 integrin monoclonal antibody, indicating that the RGD containing region in MrkD_V3 is responsible for the binding of type 3 fimbriae to integrin.