What is biofilm and how does it develop?
In water distribution systems biofilm can develop within a few days even if the water meets drinking water criteria. Biofilm can host bacteria, amoeba, algae and other microorganisms. Under low flow conditions, such as in dead legs, particularly thick biofilms can form. During water flow biofilm can shear off and biofilm particles can colonize other parts of the water distribution system. External stress in the pipework, such as disinfection measures, can result in an increased expression of the biofilm phenotype cell which is responsible for the strong attachment of cells to a surface.
Biofilm establishes in several phases over a few days. It contains microorganisms within its slimy matrix. With increasing thickness, biofilm particles containing large amounts of bacteria are released into the water stream.
Why does biofilm influence the water quality?
Biofilm protects the microorganisms within from chemical agents and thermal disinfection procedures. It is extremely difficult to completely eradicate the biofilm community once established. Irregular shedding from a biofilm can result in significant deviations of bacterial counts at sampling sites or points-of-use (POU). Bacteria within biofilm communities have been shown to exhibit greater resistance against antimicrobial treatments than corresponding planktonic cells.
When biofilm loaded with bacteria is release into the water stream, high microbial counts may be measured at the outlets. Annual testing provides only a snapshot of information, while regular testing is useful to monitor the bacterial load of a pipe network.
Which microorganisms can be found inside biofilms?
The majority of bacteria in a water pipework live within biofilm (about 95 %) and only about 5 % occur in the water (planktonic) phase. Biofilms contain a large variety of waterborne microorganisms. These may include protozoa (e.g. Acanthamoeba), fungi (e.g. Aspergillus spp., Fusarium spp.), viruses and a number of human pathogenic bacteria.
Among those bacterial species found in biofilm that are potentially harmful for immunocompromised people are Pseudomonas aeruginosa, non-tuberculous Mycobacteria, Stenotrophomonas maltophilia, Acinetobacter baumanii, Chrysobacterium spp., Sphingomonas spp., Aeromonas hydrophila, Simkania negevensis, Elizabethkingia meningoseptica and Klebsiella spp.
Legionella pneumophila is perhaps the best-known waterborne bacterium colonizing biofilms, and it can be found in both central storage areas (e.g. water tanks) as well as peripheral water outlets. Pseudomonas aeruginosa is known to be a major cause of severe infections, including pneumonia, sepsis, wound and skin infections.
Biofilm in water networks may contain a large variety of microorganisms such as fungi (e.g. Aspergillus spp., left), rod-shaped bacteria (e.g. Legionella spp., middle) and protozoa (e.g. amoeba, right).
Pall Disposable Point-of-Use Water Filters contain double layer, 0.2 micron sterilizing grade membranes which act as a barrier to, and are validated for, removal of waterborne bacteria, protozoa, fungi and particles from the drinking water supply. The filters are suitable for various uses including the provision of water for drinking, food production, personal hygiene, showering and bathing. Pall Point-of-Use Water Filters can help reduce the risk of exposure to biofilm and particulates following engineering remediation measures by flushing water outlets into the filter devices.
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