Quantification of Cultivable Biofilm Cells

The enumeration of colony-forming units (CFUs) is one of the most used analytical methods to evaluate the microbial load of a biofilm sample. This method consists of seeding a biofilm sample on an agar culture medium, contained in a Petri dish, and counting the colonies that grow in this environment. CFU quantification may be applied to understand some factors that affect the composition and formation of biofilms, to identify and quantify the number of cultivable cells adhered to a surface, to diagnose infections, and to compare the anti-biofilm efficacy of conventional or alternative antimicrobial agents. Therefore, this chapter presents the relevant aspects of CFU quantification, the main types of agar culture media used in this assay, the methodological sequence for quantifying CFUs, and the main techniques and software used for colony counting. Proper assay planning, including the correct selection of the culture medium and incubation conditions (time, temperature, and oxygen tension), in conjunction with the quality rigor established at each stage of the method, positively impacts the growth of target colonies and the CFU signal.