Understanding the Difference between Wet & Dry Surface Biofilms

Effective cleaning and disinfection is not only in relation to the removal of visible soils but also microorganisms that may be responsible for illness and disease that are not visible to the naked eye.

When we think of microorganisms, we often visualise individual cells but in reality microorganisms often are living in a structured, organised community known as a biofilm.

Biofilms can be thought of as microbial cities. A biofilm is where microorganisms are attached to surfaces and each other by an extracellular matrix they produce. This biofilm matrix consists of various carbohydrates, proteins, lipids and extracellular DNA. The species of organism present, the surrounding environment and the availability of nutrients all influence the composition of this matrix. These biofilms can contain multiple species of microorganisms and even contain antibiotic resistance ‘superbugs’.

Living in a biofilm can be advantageous and provide protection to the microorganisms in several ways. One such mechanism is that the extracellular matrix provides protection to the organisms encased within by inhibiting the penetration of antimicrobial agents.

Not all biofilms are bad biofilms. Specific organisms within biofilms can be used for the removal of waste and contaminants from water and soil. Our gut also contains beneficial biofilms assisting with the maintenance of overall health. However, biofilms can also cause illness and disease. One well known biofilm that causes disease is dental plaque. Biofilms can also be implicated in other diseases such as cystic fibrosis, urinary tract infections and chronic wounds. Additionally, biofilms can lead to infection through formation on indwelling catheters and implanted devices in healthcare.

The examples listed above are all biofilms formed in moist or aqueous conditions. However, biofilms can also form on inanimate, dry surfaces. These dry surface biofilms can lead to reservoirs of microorganisms that when touched can spread and colonise other surfaces or people. Sampling dry surface biofilms can be difficult as they are often well established on these surfaces and protected within the matrix.

Extensive research into the existence, persistence and transfer of these dry surface biofilms has been conducted by microbiologists at Macquarie University. Associate Professor Karen Vickery and her team have demonstrated the presence of viable multi-drug resistant, pathogenic or disease causing microorganisms on high touch hospital surfaces following terminal cleaning with 500ppm chlorine1. This research published in the Journal of Hospital Infection highlights the difficult nature of successfully disinfecting surfaces and removing these biofilms. The team has also successfully replicated this dry surface biofilm formation in the laboratory for study. Using these models, the Macquarie University team have demonstrated transfer of viable organisms 19 times from a single contact with a dry surface biofilm2.

The Whiteley dry surface biofilm remover, Surfex, has been independently tested by this team at Macquarie University3. Dry surface biofilm was challenged with Surfex, other surface disinfectants, generic chlorine and hydrogen peroxide. Surfex resulted in a complete kill of the dry surface biofilm.

So what does this information mean in terms of cleaning? It is important to take this biofilm formation into consideration when developing cleaning and disinfection strategies, targeting their removal. The selection of appropriate products for cleaning and disinfection is important to minimise biofilm presence on surfaces. Education on surface contamination, dry surface biofilm and the correct use of the chosen products is equally as crucial as the product itself.

Written by: Dr Jessica Farrell


1 Vickery, K., et al. (2012). “Presence of biofilm containing viable multiresistant organisms despite terminal cleaning on clinical surfaces in an intensive care unit.” Journal of Hospital Infection 80(1): 52-55.  https://doi.org/10.1016/j.jhin.2011.07.007

2 Chowdhury, D., et al. (2018). “Transfer of dry surface biofilm in the healthcare environment: the role of healthcare workers’ hands as vehicles.” Journal of Hospital Infection 100(3): e85-e90   https://doi.org/10.1016/j.jhin.2018.06.021

3 Chowdhury, D., et al. (2019). “Effect of disinfectant formulation and organic soil on the efficacy of oxidizing disinfectants against biofilms.” Journal of Hospital Infection 103(1): e33-e41.   https://doi.org/10.1016/j.jhin.2018.10.019