A microplate spectrofluorometric assay for bacterial biofilms.

A spectrofluorometric assay was developed for quantification of bacterial biofilms grown on a microtiter plate. The method involved staining biofilms formed by gram-negative and gram-positive bacteria with wheat germ agglutinin-Alexa Fluor 488 conjugate, which selectively binds to N-acetylglucosamine residues in biofilms. The fluorescence of stained biofilms was measured with a fluorescent plate reader. This method was compared with a widely used microplate colorimetric assay involving crystal violet staining of biofilms formed by both gram-negative and gram-positive bacteria. A strong linear association existed between the two methods (r (2)=0.99/0.94). Being more sensitive and specific as compared to colorimetric method, the spectrofluorometric assay provides a better alternative for quantification and characterization of bacterial biofilms.