A biofilm is defined as a group of microorganisms that stick to each other on a surface. These organisms produce a substance called extracellular polymeric substance (EPS). EPS is primarily composed of polysaccharides and proteins, but other molecules such as DNA and lipids are also contained within these structures. What makes attacking biofilms particularly difficult is the fact that there may be a variety of bacteria and fungi living and thriving within the biofilm. What also must be noted is that bacteria living within a biofilm are functionally different from the same bacteria in planktonic form—that is free floating bacteria outside of the biofilm. The bacteria within the biofilm are able to communicate with each other and from this communication they can express genes that will aid in the growth and survival of the biofilm. Furthermore, once the biofilm is of an adequate size, pieces of it may fragment, or detach from the structure, and travel elsewhere to attach to another surface, thereby making the resistance greater.