**3. The composition of biofilm**

Biofilm is primarily composed of bacterial micro-colonies which are nonrandomly distributed in a shaped matrix or glycocalyx [6]. Mostly, these microcolonies are rod-like or mushroom-shaped or they can have one or more types of bacteria. Based on bacteria type, the composition of micro-colonies contains 10–25% (by volume) of microbial cells and 79–90% (by volume) of the matrix [2, 6]. Extensive bacterial growth assists in the rapid formation of visible layers of microbes accompanied by excretion of EPS in an abundant amount [6]. At bottom of most of the biofilms, a dense layer of microorganism is bound together in polysaccharide matrix with other organic and inorganic components. The successive layer is highly irregular and loose and may extend into surrounding medium [6].
