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

Four novel mrkD alleles namely mrkDV1, mrkDV2, mrkDV3, and mrkDV4 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 MrkDV3. In order to determine if the sequence confers the K. pneumoniae mrkDV3 the highest level of the fimbrial activity, a type 3 fimbriae display system was constructed in Escherichia coli. The E. coli JM109[pmrkABCDV3F] 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[pmrkABCDV3F] 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 MrkDV3 is responsible for the binding of type 3 fimbriae to integrin.