Under The Scope - A Closer Look at Bio-film


Q. What is Bio-Film?

Bio-film is any group of microorganisms in which cells stick to each other and these cells often adhere to a surface.

Q. What are the physical characteristics of Bio-film?

Bio-films are characterized by generic diversity and complex structural character of content and complex community interactions. Their extracellular matrix, which is a collection of extracellular molecules secreted by cells, provides structural and biochemical support to the surrounding cells.

Q. How does Bio-film grow or multiply?

The formation of a bio-film begins with the attachment of free-floating microorganisms to a surface. These first colonists adhere to the surface initially through weak, reversible van der Waals forces(1). If the colonists are not immediately separated or removed from the surface, they can anchor themselves more permanently using cell adhesion molecules such as pili(2). The first colonists facilitate the arrival of the other cells by providing more diverse adhesion sites as they begin to build the matrix that holds the bio-film together. Some species are able to attach to a surface on their own while others anchor themselves to the matrix or directly to the earlier colonists. Once colonization has begun, the bio-film will grow through a combination of cell division and recruitment.

Q. Where is Bio-film found?

Bio-film is usually found on solid surfaces, submerged in or exposed to some aqueous solution. (The slimy feeling on our teeth when we first wake in the morning is an example.) Bio-films may consist of many species of bacteria and archaea(3) living within the matrix of excreted polymeric compounds.  This matrix protects the cells within it and facilitates communication among them through chemical and physical signals. Some bio-films have been found to contain water channels that help distribute nutrients and signaling molecules. In cases like these, the matrix is so strong that the bio-film can actually become fossilized.

Q. Is Bio-film harmful?

Bio-film can be responsible for aesthetically unpleasant tastes and odors and can cause corrosion in a water supply. But there remains the larger question - Can bio-film bacteria cause disease in humans? The answer to this question has been debated for many years when evaluating health risks related to drinking water contamination and bacterial contamination in general. It is commonly believed that in the absence of fecal contamination water is ‘safe’ to drink – that in the general population there is no established relationship between general bacteria ingested in water and human health. However, although most bio-film bacteria are considered harmless to a healthy population there are exceptions.

Information available from the CDC (Center for Disease Control) details increasing evidence of potentially harmful bacteria associated with bio-film growth in water distribution systems. Examples of this include the occurrences of Legionella outbreaks that have been linked to drinking water.

Other examples are in reported cases of Pseudomonas aeruginosa (a well-known bio-film organism) causing infections in people with compromised immune systems.

It has also been discovered that both human viruses and pathogenic Cryptosporidium can be trapped within bio-film after contamination events, making this type of contamination potentially hazardous.

Q. How is Bio-film eliminated?

The methods generally used to remove bio-film in water treatment and distribution systems may involve high pressure forces, heat shock(4), or the use of chemical disinfectants such as chlorine dioxide. Unfortunately some of these methods are temporary fixes and can result in a major sloughing off of the bio-film which potentially can create a greater adverse effect. And, in the end, the bio-film will most likely reoccur. A better approach is a preventative one - treating susceptible areas with consistent doses of UV light, ozone or a low dose of chemical or chlorine dioxide.



(1) In physical chemistry, the van der Waals forces or van der Waals interaction (named after Dutch scientist Johannes Diderik van der Waals) are the residual attractive or repulsive forces between molecules or atomic groups that do not arise from covalent bonds, or ionic bonds.

(2) The typical structure of a bacterial adhesion is that of a fimbria or pili.

(3) Any of a group of microorganisms that resemble bacteria but are different from them in certain aspects of their chemical structure, such as the composition of their cell walls.

(4) In biochemistry, heat shock is the effect of subjecting a cell to a higher temperature than that of the ideal body temperature of the organism from which the cell line was derived.