2.1 The Role of Biofilms

In the aqueous environment bacteria grow either as planktonic organisms or as constituents of a biofilm matrix. 

• Planktonic organisms are freely dispersed within the aqueous phase whereas biofilm organisms are attached to a surface surrounded by polymeric substances (24). 

• Biofilms in nature are not homogeneous and are complex microbial eco-systems consisting of a consortium of micro-organisms. 

These microorganisms may exhibit differing physiological and metabolic properties from their planktonic counterparts in response to various physical and nutrient gradients that exist within the exopolysaccharide matrix. 

• As a result various niches occur which may permit the co-existence of biofilm micro-organisms with conflicting growth requirements. 

For example, both aerobic and anaerobic populations may be isolated from the same biofilm. 

• Metabolic interdependence may occur between species which may be a factor in the increased resistance to both physical and chemical stresses exhibited by micro-organisms in biofilms. 

Biofilms therefore play an important role in the growth and survival of micro-organisms in the environment (25) and can have both economic and public health implications when present in artificial aquatic environments (26). 

A diverse range of microorganisms has been associated with biofilms including legionellae and other bacteria, protozoa, algae and fungi. 

Biofilms are a major reservoir of Legionella in artificial and natural aquatic systems, especially on the surfaces of elastomeric materials (27, 28). 

• The biofilm/water interface attracts ciliates, flagellates and amoebae, all seeking bacteria as food. 

It has been shown that bacteria, including legionellae, associated with biofilms in water distribution systems exhibit an increased resistance to both chemical and physical microbial controls including biocides such as chlorine and copper and silver ionisation.

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Format adapted by T2 Scientific© 2005	t2.200.1.v1.0
	Source: Blue Book 200 Part 1 downloaded 27 May 2005