The role of filamentous hemagglutinin adhesin in adherence and biofilm formation in Acinetobacter baumannii ATCC19606T

• FhaB1 and FhaC1 autotransporter genes of Acinetobacter baumannii were identified.
• Exoprotein (FhaB1) and transporter (FhaC1) were produced within the same cell.
• FhaB1C1 enhanced the adherence of recombinant bacteria to A546 cell line.
• Combined immunization with FhaB1 and FhaC1 proved protective against A. baumannii.

Filamentous hemagglutinin adhesins (FHA) are key factors for bacterial attachment and subsequent cell accumulation on substrates. Here an FHA-like Outer membrane (OM) adhesin of Acinetobacter baumannii ATCC19606T was displayed on Escherichia coli. The candidate autotransporter (AT) genes were identified in A. baumannii ATCC19606T genome. The exoprotein (FhaB1) and transporter (FhaC1) were produced independently within the same cell (FhaB1C1). The fhaC1 was mutated. In vitro adherence to epithelial cells of the recombinant FhaB1C1 and the mutant strains were compared with A. baumanni ATCC19606T. A bivalent chimeric protein (K) composed of immunologically important portions of fhaB1 (B) and fhaC1 (C) was constructed. The mice vaccinated with chimeric protein were challenged with A. baumannii ATCC19606T and FhaB1C1 producing recombinant E. coli. Mutations in the fhaC1 resulted in the absence of FhaB1 in the OM. Expression of FhaB1C1 enhanced the adherence of recombinant bacteria to A546 bronchial cell line. The results revealed association of FhaB1 with bacterial adhesion and biofilm formation. Immunization with a combination of recombinant B and K proteins proved protective against A. baumanni ATCC19606T. The findings may be applied in active and passive immunization strategies against A. baumannii.