Scientists from the Quadram Institute and the UK Health Security Agency have found that bacteria populations remain stable on factory floors despite cleaning efforts in ready-to-eat food production facilities.
In 2019, six people died from a listeria outbreak caused by contaminated ready-to-eat foods served in several hospitals across the UK. In light of this, scientists are conducting vital research that helps understand how these pathogens can persist in ready-to-eat food preparation environments.
Listeria monocytogenes is a foodborne bacteria that causes a disease called listeriosis. Symptoms for healthy people include high temperature, aches and pains, feeling unwell or unwell; but infection in pregnant, elderly or immunocompromised women can cause death.
Therefore, food safety is paramount within the food industry. However, even in the face of well-implemented strategies to disinfect facilities and control microbial risks, microbes such as listeria can occasionally breach food safety barriers and contaminate food products. This is particularly dangerous in ready-to-eat foods, where consumers do not kill contaminating bacteria by heating the food before eating it. Despite this danger, very little research has been done to understand bacteria in ready-to-eat food production environments.
The researchers wanted to understand possible sources of cross-contamination and factors that contribute to the survival of L. monocytogenes in these environments, particularly the communities of other microbes that sustain and protect it.
They began by taking soil samples from a ready-to-eat food factory that they had periodically detected. L. monocytogenes in specific areas of the factory that are not in contact with food. They took samples from different locations: a preparation area, where ingredients were kept at 4°C, and a production area where food was assembled and packaged, kept at 10°C. Their goal was to measure changes in bacterial communities over time, so they sampled the sites for ten weeks, before and after cleaning. They then cultured and performed genetic analysis on the samples to identify which bacteria were present and in what proportions.
The results showed that the populations of bacteria that coexist with L. monocytogenes They remained stable over time and have been adapted to factory conditions, including food safety controls. María Díaz of the Quadram Institute and leader of the study explains, “as L. monocytogenes is supported by a stable community of other bacteria, we may now need to develop new strategies to disrupt the entire bacterial population and effectively eliminate the pathogen.”
While overall bacterial populations and bacteria ratios remained stable before and after cleaning, Maria explains that we cannot assume that cleaning efforts are not working. “The populations are very stable and cleaning does not change the composition, it does not allow one bacteria to grow on another. After cleaning, bacteria are reduced in number and the bacterial load is lower, which makes cross contamination less likely”.
However, there was a marked difference between different areas of the factory at different temperatures; suggesting that bacterial populations are highly adapted to the different environments within the factory. It also suggests that the bacteria present in the factory are established populations rather than bacteria introduced from external sources, as despite the movement of personnel between them, the populations remained stable.
While the factory had listeria under control at the time of sampling, this new research is important for understanding different microbial communities in different environments in ready-to-eat food facilities. Researchers hope that understanding how listeria survives in these environments can lead to more precise laboratory testing of cleanup methods. María adds that “thanks to this research we can better understand the lifestyle of this pathogen and begin to develop laboratory models that allow us to investigate new ways to kill listeria.”
María Díaz will present her data at this year’s Society for Microbiology Annual Conference taking place at the Edinburgh International Convention Centre. Her talk “Deciphering Microbial Dynamics in a Ready-to-Eat Food Production Facility: Insights into the Persistence of Listeria monocytogenes” will take place on April 11.