Researchers in Norway have established and evaluated a faster method to detect Listeria monocytogenes.

Scientists at Nofima found it was possible to detect Listeria in a sample after only four hours of enrichment using a handheld sequencing device called MinION from Oxford Nanopore Technologies. This is 20 hours faster than the traditional enrichment method to look for the pathogen.

However, the analysis is not quantitative and cannot discriminate between live and dead bacteria.

Other microorganisms from the processing environment can be detected at the same time when using the sequencing approach. This is cost effective and provides information on the bigger microbiological picture in a food production plant, said researchers.

Scientists used seven different Listeria monocytogenes sequence types isolated from meat processing environments with and without background microbiota such as other Listeria species and non-Listeria strains, according to the study published in the journal ASM.

Quick result needed
Eva Wagner, from Nofima, said the team investigated and compared different sequencing technologies to get quicker results on the presence or absence of Listeria in a sample.

“We were also interested in whether the sequencing method is able to differentiate between distinct Listeria types. A result on whether or not Listeria was present in a sample should ideally be provided before the start of the next work day in order for countermeasures to be implemented. It is especially important that equipment and surfaces, on which Listeria was detected, are thoroughly cleaned and disinfected,” she said.

The traditional enrichment method to detect Listeria monocytogenes involves cultivating a sample taken from the processing environment or a food product in a selective medium that favors growth of the bacterium.

This process can take from 24 hours to several days while production continues. This means that food products can be contaminated and people could be infected with Listeria during the testing process.

Nofima researcher Birgitte Moen said the next step is to collect samples from industry and test the method with them.

Providing more detail
Food producers can receive results on whether or not Listeria was detected in the sample but the current method is not always able to distinguish between similar Listeria strains.

Use of Illumina MiSeq sequencing allowed scientists to predict the presence of co-occurring Listeria monocytogenes strains.

Routine application of the approach could lead to industry actions that prevent contamination and subsequent recalls and food destruction, economic and reputational losses, and listeriosis cases.

“New sequencing technologies are used to determine the genetic code (DNA) and thus identify microorganisms. This will make today’s extensive control operations in the food industry faster, more precise and more cost effective,” said Annette Fagerlund.

Fagerlund is a researcher at Nofima and leads PathoSeq, a three-year project which runs until March 2023. The goal is to help Norwegian food producers to establish faster, more cost effective and targeted control routines for foodborne pathogens.

Another Nofima project, called Future Food Control, is looking at food safety, reducing food waste and the use of plastic packaging.

It runs until the end of 2024 and involves source tracking of pathogens, spoilage bacteria and fungi in production facilities and effective corrective actions with a focus on raw chicken and perishable, plant-based foods.

Packaging systems and storage conditions will be evaluated using recycled or renewable packaging materials without compromising safety, shelf life or having a negative impact on food waste.

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