Biofilms are naturally occurring complex communities of micro-organisms. They start by free-floating individual 'planktonic' bacteria cells attaching to a surface in a wet environment. 'Bacterial Biofilm' is the first step in a microbial colony. Only certain bacteria have the ability to attach and form initial biofilms.  Where favourable conditions exist  planktonic bacteria will attach and quickly proliferate.

The first cells attach to surfaces using their adhesion features - Fimbrea, Pili and a Polysaccharide (slime) layer. Once anchored the growing multicellular community communicate between cells by Quorum Sensing. Together they begin to exude a hydrogel, a sticky slime known as  “Extracellular Polymeric Substances” (EPS). The slimy layer is often felt on the surfaces of containers of static water after just a few days.  The hydrophobic EPS gel provides increasing levels of protection for the growing biofilm community and improves adhesion to the surface. Within the colony millions of single cell bacteria take up different roles. Together they act much like a multi-cellular organism, including the exchange of DNA. Enabling adaptions to develop rapidly, such as antibiotic resistance. Some cells eventually break away from the colony. Once detached those now mobile cells float downstream to quickly spread infections to new locations. 

As a core biofilm develops, members of the increasingly complex community gain protection from turbulence, heat, cleaning chemicals, biocides, anti-microbial agents and antibiotics. Biofilms can be extremely difficult to kill or remove once they become established in a system.  Eventually a hard protective outer plaque layer can even form. Coating and blocking membranes, tanks, pipework and machinery. On a smaller scale it is seen as dental plaque on teeth. Inside the biofilm plaque corrosive excreta from the organisms accumulates. Damaging equipment such as heat exchangers by 'MIC' - Microbiologically Induced Corrosion. These acids causes dental cavities. 

The effects of Biofilms are wide reaching. If allowed to develop biofilm matrices become havens for other unicellular and multicellular micro-organisms. Allowing numerous other species of bacteria, yeasts, fungi, amoeba, protozoa, etc. to proliferate; even harbouring viruses. Each colony is unique. Unless controlled, biofilms facilitate the spread and persistence of pathogens, waterborne diseases and toxins in any water rich environment.