Listeria can remain threat in factories despite cleaning efforts

A new study by scientists from the two groups found that populations of bacteria that coexist with Listeria monocytogenes ​were stable over time and have adapted to the conditions of the factory floor, including food safety controls.

Researchers wanted to understand the potential sources of cross contamination and the factors that contribute to the survival of Listeria ​in these environments, particularly the communities of other microbes that support and protect it.

Tests were conducted at a ready-to-eat food factory that had recently detected Listeria ​in specific non-food contact areas.

Changes in bacterial communities

Samples were taken from different sites – a preparation area where ingredients were kept a 4°C and a production area where food was assembled and packaged kept at 10°C – in a bid to measure the changes of bacterial communities over a 10-week period, before and after cleaning.

It is from this study that researchers discovered the adaptability of bacterial populations on the factory floor. It also suggested that the bacteria present in the factory are established populations rather than bacteria introduced from outside sources, as despite movement of personnel between them, the populations remained stable.

Maria Diaz from the Quadram Institute and lead of the study explains said: “As L. monocytogenes is supported by a stable community of other bacteria, we may now need to develop new strategies to alter the whole bacterial population to effectively eliminate the pathogen.​

Despite the stability of these bacterial populations before and after cleaning, Diaz explained that we cannot assume cleaning efforts do not work.

Cleaning can work

“The populations are very stable, and cleaning is not shifting the composition – it’s not letting one bacterium grow over another,”​ she added. “After cleaning, the bacteria reduce in numbers and the bacterial load is lower, making cross contamination less likely.”​

While the factory had listeria under control at the time of sampling, this new research is important for understanding the different communities of microbes in different environments across ready-to eat-food facilities.

Researchers hope that understanding how listeria survives in these environments could inform more accurate laboratory testing of cleaning methods.

“Thanks to this research, we can better understand the lifestyle of this pathogen and start to develop laboratory models that allow us to investigate new ways of killing listeria,”​ Diaz concluded.