Preliminary study on total protein extraction methods from Enterococcus faecalis biofilm

Enterococcus faecalis is the major pathogen of post-endodontic disease and refractory periapical periodontitis, and recent research on this species has focused on its pathogenicity. E. faecalis most often causes disease in the form of a biofilm, and total protein expression shows a strong association with its virulence. Therefore, the purpose of our study was to explore different methods of extracting the total proteins of the E. faecalis (ATCC 33186 standard strain) biofilm. The total proteins in the biofilm were extracted using an ultrasonication method with varied parameters, including duration, amplitude setting, period, and duty cycle. After the optimal conditions of ultrasonication were determined based on the protein profile from sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, the total protein content in the biofilm was detected using the bicinchoninic acid assay, Bradford Coomassie brilliant blue assay, and Lowry assay, and the results were compared and analyzed. The parameters for the optimal conditions of ultrasonication were as follows: a processing duration of 2 min, amplitude setting of 20%, and ultrasonication period of 4 s at a 50% duty cycle. The total protein content was 2299.1 mg/dish when measured by the bicinchoninic assay, 3793.8 mg/dish when measured by the Bradford Coomassie brilliant blue assay, and 1858.0 mg/dish when measured by the Lowry assay. These results demonstrate that the Bradford Coomassie brilliant blue assay is a simple and feasible method for use in detecting the total protein content in a bacterial biofilm.