Biofilm:

  The formation of a biofilm begins when free-floating micro-organisms are attached to a surface. Initially, the weak van der Waals forces and hydrophobic effects that bind to the surface of a biofilm's first colonist bacteria. When the colonists are not instantly removed from the surface, they will more firmly attach themselves using cell adhesion mechanisms such as pili. Hydrophobicity can also affect the bacteria's ability to form biofilms. The repulsion between substratum and bacterium has been reduced by bacteria with increased hydrophobicity. Microbes form a biofilm in reaction to different stimuli, including the cellular identification of particular or non-specific attachment sites on a surface, dietary signals, or in certain instances, sensitivity of planktonic cells to sub-inhibitory antibiotic concentrations. A cell that transitions to the growth mode of biofilm undergoes a phenotypic behavioural change in which broad sets of genes are differentially regulated. A biofilm can therefore be called a hydrogel, a dynamic material that retains its dry weight in water many times. Biofilms are not just forms of bacterial slime but also biological structures. Biofilms, though, aren't necessarily less susceptible to antibiotics. For example, Pseudomonas aeruginosa's biofilm type has no greater resistance to antimicrobials than stationary-phase planktonic cells do, whereas the biofilm has greater resistance to antimicrobials when contrasted with logarithmic-phase planktonic cells. Such antibiotic tolerance may be attributed to the presence of recurrent cells in both stationary-phase cells and biofilms.