Acinetobacter
baumannii is a multidrug resistant pathogen associated with hospital outbreaks
across the globe, particularly in the intensive care unit. The ability of A. baumannii to form biofilms allows it
to survive in the hospital environment for long periods, causing
ventilator-associated pneumonia, hospital-acquired bloodstream infection and urinary
tract infection (UTI). Fimbriae play an important role in bacterial adhesion to
host cells or inert surfaces as this is a vital step in the process of
bacterial colonisation and biofilm formation. Many fimbrial adhesins bind to
specific host receptors and thus represent essential virulence factors that
define tissue tropism. We identified three chaperone-usher (CU) gene clusters (csu, fim1
and fim2) and the biofilm-associated
protein (bap) from whole genome
sequencing of two index case isolates within a collection of A. baumannii strains. Both Csu and Bap
have been characterised previously. Here we studied the expression and function
of an uncharacterised A. baumannii
fimbrial cluster (referred to as fim2) in a collection of A. baumannii strains. A Fim2 major subunit-specific antibody was
generated to demonstrate the expression of Fim2 in two A. baumannii UTI strains (M14 and M960), and this correlated with
the ability of these two strains to adhere strongly to human uroepithelial
cells. Immunofluorescence analysis showed that Fim2 is located at the cell
surface of strains M14 and M960. Sequencing of the fim2 cluster of strains M14 and M960 revealed identical sequences,
comprising of an ~5 kb operon encoding a major subunit, chaperone, usher and adhesin.
The fim2 CU gene cluster was cloned
and expression in a recombinant E. coli
strain resulted in increased biofilm formation and adhesion to human
uroepithelial cells. Finally, biofilm formation by the recombinant E. coli strain was abrogated by
affinity-purified Fim2 major subunit-specific antibodies, demonstrating the
direct contribution of Fim2 to biofilm formation in vitro.