What best describes a biofilm?

• A. A free-floating cluster of viruses
• B. A community of bacteria attached to a surface, cemented by sugars
• C. A layer of fungi on skin
• D. A collection of protozoa in water

Answer: (B)

Biofilms are communities of microorganisms that attach to a surface and live within a self-produced matrix. This matrix, made largely of extracellular polymeric substances, is rich in polysaccharides (sugars) along with proteins and extracellular DNA, which cement the cells together and to the surface. That sticky, protective matrix helps the community resist drying, disinfectants, and antibiotics, and it enables coordination and nutrient sharing among the cells. While biofilms can include fungi as part of the community, the defining idea is a surface-attached, matrix-embedded microbial community, most commonly bacteria. A free-floating cluster of viruses isn’t a biofilm because they don’t form such surface-attached, matrix-embedded communities of living cells.