why do bacteria in a biofilm have different characteristics than free-floating bacteria
Biofilm Bacteria living in a biofilm usually have significantly different properties from free-floating bacteria of the same species, as the dense and protected environment of the film allows them to cooperate and interact in various ways.[34] One benefit of this environment is increased resistance to detergents and antibiotics, as the dense extracellular matrix and the outer layer of cells protect the interior of the community. In some cases antibiotic resistance can be increased a thousandfold.[35] Lateral gene transfer is often facilitated within bacterial and archaeal biofilms[36] and leads to a more stable biofilm structure.[37] Extracellular DNA is a major structural component of many different microbial biofilms.[38] Enzymatic degradation of extracellular DNA can weaken the biofilm structure and release microbial cells from the surface.
Staining A simple staining method for bacteria that is usually successful, even when the "positive staining" methods detailed below fail, is to use a negative stain. This can be achieved by smearing the sample onto the slide and then applying nigrosin (a black synthetic dye) or India ink (an aqueous suspension of carbon particles). After drying, the microorganisms may be viewed in bright field microscopy as lighter inclusions well-contrasted against the dark environment surrounding them.[4] Note: negative staining is a mild technique that may not destroy the microorganisms, and is therefore unsuitable for studying pathogens.