Comparison of the reflectance and Crystal Violet assays for measurement of biofilm formation by Enterococcus

In previous work, we described a protocol for measuring biofilm formation on opaque and non-opaque surfaces using reflected light. In the present work, we used the reflectance assay to assess biofilm formation for 14 strains of Enterococcus and compared our results with those obtained using a Crystal Violet (CV) assay. In general, the results for the two assays were in agreement: both identified the same Enterococcus strain as the highest biofilm-forming strain and the same two strains as the lowest biofilm-forming strains. However, two Enterococcus strains identified as high biofilm formers by the CV assay were not identified as such by the reflectance assay. A single numerical value was obtained for each of the reflectance assay results that corresponded well with the confluence of a biofilm (and presumably its depth) using phase contrast microscopy. * Corresponding author: Dr S. L. Broschat School of Electrical Engineering and Computer Science Washington State University PO Box 642752 Pullman, WA 99164-2752 USA T 1 509 335 5693 F 1 509 335 3818 E [email protected] 1 School of Electrical Engineering and Computer Science, Center for Integrated Biotechnology, Washington State University, Pullman, WA 99164-2752, USA 2 Department of Veterinary Microbiology and Pathology, Center for Integrated Biotechnology, Washington State University, Pullman, WA 99164-7040, USA 3 Department of Civil and Environmental Engineering, University of California at Davis, Davis, CA 95616, USA