Adhesion of acinetobacter baumannii to extracellular proteins detected by a live cell-protein binding assay.

INTRODUCTION Acinetobacter baumannii is involved in various infectious diseases ranging from nosocomial community-acquired infections to those acquired following war or natural disasters. The treatment has become exceedingly difficult partly because the bacterium can form biofilms. Therefore, it is imperative to elucidate mechanisms of the biofilm formation that may be exploited to develop therapeutic strategies. OBJECTIVE To develop an assay by which the role of the bacterial extracellular proteins can be studied in mediating cell adhesion and biofilm formation. METHODS Biofilm mutants of A. baumannii were generated. Proteins from the cell-free spent cultures and outer membrane fractions of the mutants and the wild type strain were characterized by SDS-PAGE based proteomic analysis. The PAGE-based membrane binding assays were developed to examine bacterial adhesion to the released proteins immobilized on the blotting membranes. RESULTS The mutants exhibited deficiencies in formation of biofilms and in production of the biofilm-related proteins, such as OmpA. A novel PAGE-based membrane binding assay was established, and the results show attachment of the wild type cells to the released proteins in contrast to that of the mutant cells deficient in the outer membrane proteins. The results imply that these mutants have lost the cell surface-associated proteins that mediate cell adhesion to the released proteins. CONCLUSION This novel assay can be used to study the live bacterial adhesion to extracellular proteins. The results suggest that the outer membrane proteins may mediate cell attachment through binding to the released proteins for biofilm formation.