Quantification of Microbial Biofilm Biomass

The most used assays to quantify the total biomass of microbial biofilms are based on colorimetry and the biofilm mass itself. Among the colorimetric methods, staining with crystal violet and safranin stands out. These methods consist of fixing the biofilm on a specific surface, applying the dye (crystal violet or safranin) followed by a decolorizing solution, and reading the absorbance of the solution on a spectrophotometer. In turn, the determination of the dry and wet weights of the biofilm is the main analytical tool associated with the mass. Thus, this chapter discusses the main advantages and disadvantages of the methods for quantifying the microbial biofilm biomass as well as presents the methodological sequence for implementing each technique. Colorimetric and mass-based assays are easy to use, fast, and low cost. However, they do not allow distinguishing different species residing in the same biofilm, in addition to not differentiating cells and extracellular matrix. Dead cells may also be included in the signal from these methods. Therefore, the methods covered in this chapter are important for understanding the phenomena that affect biofilm biomass production and should be used as complementary tools to other biofilm analytical techniques.