<P> Microbes form a biofilm in response to various different factors, which may include cellular recognition of specific or non-specific attachment sites on a surface, nutritional cues, or in some cases, by exposure of planktonic cells to sub-inhibitory concentrations of antibiotics . When a cell switches to the biofilm mode of growth, it undergoes a phenotypic shift in behavior in which large suites of genes are differentially regulated . </P> <P> A biofilm may also be considered a hydrogel, which is a complex polymer containing many times its dry weight in water . Biofilms are not just bacterial slime layers but biological systems; the bacteria organize themselves into a coordinated functional community . Biofilms can attach to a surface such as a tooth, rock, or surface which may include a single species or of a diverse group of microorganisms . The biofilm bacteria are able to share nutrients and are sheltered from harmful factors in the environment, such as desiccation, antibiotics, and a host body's immune system . A biofilm usually begins to form when a free - swimming bacterium attaches to a surface . </P> <P> The formation of a biofilm begins with the attachment of free - floating microorganisms to a surface . It is thought that the first colonist bacteria of a biofilm adhere to the surface initially through weak, reversible adhesion via van der Waals forces and hydrophobic effects . If the colonists are not immediately separated from the surface, they can anchor themselves more permanently using cell adhesion structures such as pili . </P> <P> Hydrophobicity can also affect the ability of bacteria to form biofilms . Bacteria with increased hydrophobicity have reduced repulsion between the extracellular matrix and the bacterium . Some bacteria species are not able to attach to a surface on their own successfully due to their limited motility but are instead able to anchor themselves to the matrix or directly to other, earlier bacteria colonists . Non-motile bacteria cannot recognize surfaces or aggregate together as easily as motile bacteria . </P>

Which surfaces tend to have the least amount of biofilm