A biofilm is a structured community of microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface. Biofilms are also often characterized by surface attachment, structural heterogeneity, genetic diversity, complex community interactions, and an extracellular matrix of polymeric substances.

Single-celled organisms generally exhibit two distinct modes of behavior. The first is the familiar free floating, or planktonic, form in which single cells float or swim independently in some liquid medium. The second is an attached state in which cells are closely packed and firmly attached to each other and usually form a solid surface. A change in behavior is triggered by many factors, including quorum sensing, as well as other mechanisms that vary between species. When a cell switches modes, it undergoes a phenotypic shift in behavior in which large suites of genes are up- and down- regulated.

Formation

5 stages of biofilm development. Stage 1, initial attachment; stage 2, irreversible attachment; stage 3, maturation I; stage 4, maturation II; stage 5, dispersion. Each stage of development in the diagram is paired with a photomicrograph of a developing P. aeruginosa biofilm. All photomicrographs are shown to same scale.

Formation of a biofilm 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. If the colonists are not immediately separated from the surface, they can anchor themselves more permanently using cell adhesion structures such as pili.^[1]

The first colonists facilitate the arrival of other cells by providing more diverse adhesion sites and beginning to build the matrix that holds the biofilm together. Some species are not able to attach to a surface on their own but are often able to anchor themselves to the matrix or directly to earlier colonists. It is during this colonization that the cells are able to communicate via quorum sensing. Once colonization has begun, the biofilm grows through a combination of cell division and recruitment. The final stage of biofilm formation is known as development, and is the stage in which the biofilm is established and may only change in shape and size. This development of biofilm allows for the cells to become more antibiotic resistant.

Properties

Biofilms are usually found on solid substrates submerged in or exposed to some aqueous solution, although they can form as floating mats on liquid surfaces and also on the surface of leaves, particularly in high humidity climates. Given sufficient resources for growth, a biofilm will quickly grow to be macroscopic. Biofilms can contain many different types of microorganism, e.g. bacteria, archaea, protozoa, fungi and algae; each group performing specialized metabolic functions. However, some organisms will form monospecies films under certain conditions.

Researchers from the Helmholtz Center for Infection Research have found the strategies used by biofilms. They discovered that biofilm bacteria apply chemical weapons in order to defend themselves against disinfectants and antibiotics, phagocytes and our immune system.

The lead researcher, Dr. Carsten Matz, began a serious investigation in order to find why phagocytes cannot annihilate the biofilm bacteria. He analyzed the marine bacteria, which defend themselves against the amoebae, the behavior of which copies the behavior of phagocytes. The amoebae behave in the sea just like the immune cells in human body: they search for and feed on the bacteria. When bacteria are alone and separated in the water, they become an easy catch for the attackers. However, when they attach to a surface and join other bacteria, the amoebae cannot assault them.

The researcher stated that biofilms may be seen as a source of new bioactive agents. When bacteria are organized in biofilms, they produce effective substances which individual bacteria are unable to produce alone.^[2]

Extracellular matrix

The biofilm is held together and protected by a matrix of excreted polymeric compounds called EPS. EPS is an abbreviation for either extracellular polymeric substance or exopolysaccharide. This matrix protects the cells within it and facilitates communication among them through biochemical signals. Some biofilms have been found to contain water channels that help distribute nutrients and signalling molecules. This matrix is strong enough that under certain conditions, biofilms can become fossilized.

Bacteria living in a biofilm usually have significantly different properties from free-floating bacteria of the same species, as the dense and protected environment of the film allows them to cooperate and interact in various ways. One benefit of this environment is increased resistance to detergents and antibiotics, as the dense extracellular matrix and the outer layer of cells protect the interior of the community. In some cases antibiotic resistance can be increased 1000 fold.^[3]

The chlorine shock solution

In order for biofilms to form, you must have bacteria present. When Operating with elevated ORP it increases the rate of inactivation of  bacteria and virus. This has been proven in countless studies on a broad spectrum of organisms. A facility that has biofilms in the circulating system may obtain positive plate counts in the water sample. The facility will then shock the pool with high levels of chlorine. The plate counts will then be negative. A week or two later, if plate counts are performed again, they will appear positive. This happens because chlorine is highly ineffective at penetration of biofilms. The ‘shock’ kills those at the surface of the biofilm, but does not penetrate. After a short period, bacteria growth continues and new bacteria is released into the water. If this happens at a location, they have bio-films.

A better boilout solution

Do a boilout using Truox ‘New Beginning’. This will chemically decompose the organic matrix of the film as well as disperse it due to the obvious effervescing that occurs “thus the term boilout”. Once the system is cleaned of the bio-films, Feed 24/7 to sustain at least 800mV while operating with less than 3.0ppm free chlorine. Higher ORP is even better. This will ensureany bacteria or virus hitting the water will be effectively inactive within minutes (typically seconds).

Bob Driskell

City of Antioch – Recreation
Aquatics Facility Specialist II
Prewett Park/Antioch Water Park
925-776-3074
bdriskell@ci.antioch.ca.us.

© 2009 Professional Pool Operators of America