Biofilm Facts
Frequently asked questions on biofilm
How is biofilm different from suspended (planktonic) bacteria?
Being attached rather than suspended makes a world of difference. Biofilm organisms have an enhanced survival mechanism. Bacteria change as soon as they are attached to a surface. The most obvious change is that they excrete a slimy material. Biofilm bacteria turn on a whole different set of genes, which makes it a significantly different organism to deal with. Biofilm behavior is much more complex because they live in organized communities. They are resistant to biocides and antimicrobial agents. Disinfectants are effective for killing single cells, but not clumps it only kills those on the outside. These outside cells sacrifice themselves for the rest of the colony.
The biofilms are permeated at all levels by a network of channels through which water, bacterial garbage, nutrients, enzymes, metabolites and oxygen travel to and fro. Gradients of chemicals and ions between microzones provide the power to shunt the substances around the biofilm." (Coghlan 1996)
The association of bacteria with a surface and the development of a biofilm can be viewed as a survival mechanism. Bacteria benefit by acquiring nutrients and protection from biocides.
What is denser biofilm According to Mittelman (1985)?
At higher flow rates, a denser, somewhat more tenacious biofilm is formed. As a result, these surfaces often appear to be free from foulants, since they are not slimy to the touch.
What is the limited biofilm thickness?
The maximum thickness of the biofilm can be considered to be the thickness of the laminar flow layer. In a constant flow system, an equilibrium thickness is reached which is dependent on water velocity and nutrients. Growth of the biofilm beyond the laminar layer will result in the release of planktonic `pioneer' cells that will, conditions permitting, establish the biofilm in another section of pipe.(Patterson 1991) In systems that have fluctuating water flow, such as automated watering systems with periodic flushing, bacteria will be sloughed off during the flush. This results in random particle showers of bacteria which can explain day-to-day fluctuations seen in total bacteria count results.
Extract taken from Richard Bentham on the Legionella web site.
Further links on Biofilm
http://microbiologybytes.wordpress.com/2008/07/25/biofilms-use-chemical-weapons/