Biofilms are an assemblage of bacteria which are formed when the bacteria are living in a layer of slime which they have produced. Usually biofilms are associated with surfaces, however, they can also exist as aggregates in fluids and mucus layers. In this biofilm phenotype, the bacteria are protected from antibiotics and our host immunity, even though when theyâ€re living as individual cells, they can be sensitive to antibiotics. When they get together in this group as a community in the slime matrix, then they become much more difficult to kill. Theyâ€re also protected from host immunity and cells such as macrophages which normally phagocytose (eat) infectious cells. They canâ€t do that very effectively with a biofilm because itâ€s physically too large. We really think biofilm formation is a protective mechanism that bacterial cells use to survive in the infection.