By Michael Arthur

Imagine a group of bacteria teaming up like a gang, creating a fortress around them. This is essentially what bacterial biofilms are – a tough, sticky barrier that makes them incredibly difficult to defeat. They form on medical devices, water pipes, kitchen surfaces, and even in our bodies, leading to persistent infections and contamination. In the food industry, bacterial biofilms formed on food and non-food contact surfaces are associated with many foodborne outbreaks.

Once attached to surfaces, biofilms can remain for long periods, ranging from days to years. A recent scientific study indicated that Listeria monocytogenes biofilms persisted for 17 years on contact surfaces in a seafood processing environment (see below for further reading). Although this formidable microbial community is resistant to chemical, physical, or biological treatments, there are proven ways to deal with them.

So, how do we battle these persistent communities?

Chemical agents, such as chlorine, hydrogen peroxide, and peracetic acid, have frequently been used to control bacterial biofilms. These agents contain powerful active ingredients that can intrude the biofilm community and attack the membranes of each cell to cause damage, eventually resulting in cell death. Although these chemical agents can effectively destroy bacterial biofilms, their application must be optimised. 

First, the chemical agent must be applied according to the manufacturer’s recommendations for the concentration and contact time. This is very important because when applied below what the manufacturer has recommended, these clever biofilms will build resistance to the agents, making them ineffective. In our laboratory experiments, we observed that when chemical agents were applied without following the manufacturer’s recommendations, biofilms were not completely destroyed. 

Second, it is recommended that up-to-date chemical agents be used instead of expired agents. The expired chemical agents have fewer active ingredients; therefore, they will not completely eradicate the bacterial biofilm. What is worrying is that, when we use out-of-date products over a long period, it will enable bacterial biofilms to develop special mechanisms to withstand the chemical agents when in-date products are used later on. This is when we say that bacteria have become resistant to a particular chemical agents. 

Finally, it is essential to rotate the chemical agents. For example, if a hydrogen peroxide agent is used for approximately one or two months, it can be changed to a chlorine-based agent and vice versa. This reduces the resistance mechanisms of the bacterial biofilms.


Fighting bacterial biofilms is like battling a well-fortified enemy or playing a strategic game of chess. It takes a combination of tactics. As research continues, we’re getting better at outsmarting these resilient bacterial communities and keeping our environments safer and cleaner.

About the author: Michael Arthur is a Ph.D. student at the Technological University Dublin (TUD) but based at Ashtown Teagasc Food Research Centre, in the Food Safety Department. His Ph.D. project focuses on “evaluating the microbial quality of harvested rainwater and sustainable treatment options for the horticultural sector”. He is supervised by Dr. Kaye Burgess (Teagasc), Prof. Jesus Frias (ESHI – TUD) and Dr. Michael T. Gaffney (Teagasc). This project was funded by the Department of Agriculture, Food, and Marine (project 2019R424) and the Teagasc Walsh Scholarship Program (Ref. 2021055).

Further reading

Daeschel, D., Pettengill, J.B., Wang, Y., Chen, Y., Allard, M., Snyder, A.B., 2022. Genomic analysis of Listeria monocytogenes from US food processing environments reveals a high prevalence of QAC efflux genes but limited evidence of their contribution to environmental persistence. BMC Genomics 23, 488.