Guide to Biofilm and Biofilm Removal

What is Biofilm?

The term Biofilm refers to the formation of an encased or protected community of micro-organisms that stick to each other and surfaces via a self-produced protective slime referred to as an extracellular matrix (ECM). A biofilm is referred to as sessile meaning they are attached in place.

The slime is made up of an extracellular polymeric substance (EPS), bacterial cells, other proteins, organic materials, and water. The ability to produce the adherent slimy EPS is a universal attribute of bacteria. Once formed the slime/matrix can provide a protective environment for one or more species of bacteria offering more resistance to anti-microbial agents than in a free swimming, planktonic state.

The protection provided by the biofilm can allow for booming colonies of bacteria and micro-organisms to flourish. [1][2]
 

Where do Biofilms form?

From as early as  16,000 scientists like Antonie van Leeuwenhoek observed a microbiological phenomenon that micro-organisms attach to and grow universally on surfaces.

As understanding grew it became clear that micro-organisms were not always freely suspended planktonic cells and bacteria grew faster and more actively in a community when on a surface. The study of industrial water systems further confirmed the tenacity of surface-based biofilms that were also resistant to disinfectants such as chlorine.

Studies show rougher surfaces increase microbial colonisation, likely due to increased surface area and diminished shear forces. However, biofilms will form on any surface with only the adherence varying dependent on surface composition and its environmental conditions.  [4][5]
 

How do Biofilms form?

The lifecycle of a biofilm can vary depending on the species however the following lifecycle marks the process of biofilm formation:

1. Attachment and adhesion Attachment is the first step of biofilm formation in which the planktonic or freely suspended cell attaches and adheres to a surface becoming sessile.
   
2. Accumulation and proliferation Following attachment, the extracellular matrix protective slime begins to form which allows for attachment of further bacteria cells and begins the binding and stabilization of a bacteria colony structure accumulating and forming multiple layers.
   
3. Maturation The structure forming allows for water and nutrients to pass through the biofilm in channels making the biofilm a flourishing community of maturing, protected bacteria.
   
4. Dispersion Dispersion can depend on the species of biofilm or environmental conditions. There can be several reasons that portions of a biofilm can detach leading to dispersal.
   

In some species like E. coli or P. aeruginosa enzymes in the protective matrix rupture it resulting in dispersal of mature bacterial cells. In other occasions ineffective disinfection, physical disruption or water flow can result in surface damage allowing for dispersal or sloughing of the biofilm. Dispersal allows bacteria to become planktonic (freely suspended) again and enables colonisation of new surfaces starting the lifecycle over again. [5]
 

What threat do biofilms pose in water distribution systems?

The protection biofilms offer to waterborne pathogens (some which responsible for outbreaks of disease due to the consumption of contaminated water) make their existence in a water distribution system a health risk.

Biofilms formed in potable water systems may contain bacterial pathogens such as legionella pneumophila and coliforms. Legionella pneumophila inhaled via small droplets of water (aerosols) causes Legionellosis, in its most severe form, Legionaires’ disease.

The risk of Legionaires’ disease, a potentially fatal pneumonia that everyone is susceptible to, can be reduced by following measures set out in HSE Legionnaires’ disease – The Control of Legionella bacteria in water systems (L8)

Protozoa are commonly found in water distribution system-based biofilms, and pathogens like Mycobacterium spp., P. aeruginosa, Klebsiella spp., Burkholderia spp., Giardia and Cryptosporidium transmit via contaminated water. Biofilms are present in contaminated water and offer protection to the microbiological threat. [6][7]
 

How can biofilms and associated microbiological risks be removed?

Due to low costs and established routines chlorine disinfection is currently the main chemical strategy used to control microbiological threat in water systems.

Unfortunately, high chlorine disinfection concentrations lead to an increase in the production of potentially carcinogenic by products such as haloacetic acids and trihalomethanes hazardous to health.

Regulations in place to protect water system users against dangerous disinfection by products requires chlorine based disinfectants to be used at dose rates that are ineffective at removing established biofilms. Penetration of some layers is possible but likely results in a wider issue as the damaged biofilm will disperse and spread to other surfaces.

Biofilms increased resistance to conventional disinfection processes and the potentially hazardous by products of chlorine disinfection means new approaches to biofilm removal are required.[6]
 

What is a new approach to Biofilm removal?

Research has shown that hydrogen peroxide is highly effective at biofilm removal. Substantial biofilm removal with hydrogen peroxide is achieved through the degradation of the extracellular matrix.

Hydrogen peroxide has depolymerising properties and the production of hydroxl radicals from hydrogen peroxide has been seen to be among some of the most effective agents at degrading biofilm. [8]

As covered in our recent blog post Stabilised Hydrogen Peroxide Disinfection and Cleaning, SureClear Stabilised Hydrogen Peroxide is formulated to sustain the effectiveness of hydrogen peroxide’s strong oxidising disinfection power.

Unlike chlorine-based disinfectants, SureClear stabilised hydrogen peroxide creates no carcinogenic by products. Once disinfection has completed only water and oxygen are formed as by products.

HSE Legionella ACOP HSG274 Pt 2 approves use of Silver Stabilised Hydrogen Peroxide as a disinfectant to control legionella in a water systems. [9]

[1] Branda SS, Vik S, Friedman L, Kolter R. Biofilms: the matrix revisited. Trends Microbiol. 2005 Jan;13(1):20-6. doi: 10.1016/j.tim.2004.11.006. PMID: 15639628.

[2] Mah TF, O’Toole GA. Mechanisms of biofilm resistance to antimicrobial agents. Trends Microbiol. 2001 Jan;9(1):34-9. doi: 10.1016/s0966-842x(00)01913-2. PMID: 11166241.

[3] Donlan RM. Biofilms: microbial life on surfaces. Emerg Infect Dis. 2002 Sep;8(9):881-90. doi: 10.3201/eid0809.020063. PMID: 12194761; PMCID: PMC2732559.

[4] Characklis WG Attached microbial growths-II. Frictional resistance due to microbial slimes. Water Res. 1973;7:1249–58 10.1016/0043-1354(73)90002-X

[5] Ranganathan, Vasudevan. (2014). Biofilms: Microbial Cities of Scientific Significance. Journal of Microbiology & Experimentation. 1. 10.15406/jmen.2014.01.00014.

[6] Simões, Lúcia & Simões, Manuel. (2013). Biofilms in drinking water: Problems and solutions. RSC Advances. 3. 2520-2533. 10.1039/C2RA22243D.

[7] https://www.hse.gov.uk/legionnaires/what-is.htm – Health and Safety Executive – What is Legionnaires’ disease?