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FSPCA - Food Safety Preventive Controls Alliance

Wednesday, October 14, 2020

Research Study - Prevalence of Listeria in Frozen Produce in England

A study out of the UK looked at the prevalence of Listeria monocytogenes in frozen fruits and vegetables sold at retail. Of the 1050 samples tested, "There were 78 samples (7%) from which L. monocytogenes was detected and 101 (10%) from which other Listeria species were detected. Neither L. monocytogenes nor other Listeria species were detected at levels of >100 cfu/g in any samples."

While these samples would be acceptable in the EU because the levels are not greater than 100 cfu/gm, these products would be not be acceptable in the US. Cooking would eliminate the pathogen, but the risk would arise if these items were used in a ready-to-eat application, and through preparation and storage, the organism was able to grow to higher levels.

This demonstrates the importance of control of Listeria in these types of operations. From a consumer perspective, there is the importance of following label instructions which normally requires cooking.

International Journal of Food Microbiology
https://www.sciencedirect.com/science/article/pii/S0168160520303433
Occurrence of Listeria and Escherichia coli in frozen fruit and vegetables collected from retail and catering premises in England 2018–2019
CarolineWillisaJimMcLauchlinbHeatherAirdcCorinneAmardClareBarkerdTimothyDallmandNicolaElvissbSandraLaibLorraineSadler-Reevesae

https://doi.org/10.1016/j.ijfoodmicro.2020.108849

Abstract

Frozen vegetables have previously been associated with outbreaks of listeriosis in both the USA and Europe. An outbreak of Listeria monocytogenes serogroup 4 caused 53 cases in five European countries between 2015 and 2018. Whole genome sequencing (WGS) indicated that frozen sweet corn from a producer in Hungary was the source of illness. However, limited data is available on the prevalence of Listeria in frozen produce. A study of frozen fruit and vegetables from catering and retail premises in England was therefore carried out to assess their microbiological quality with respect to Listeria and Escherichia coli.

Between December 2018 and April 2019, 1050 frozen fruit and vegetable samples were collected. Of these, 99% were of a satisfactory or borderline microbiological quality. Eleven samples (1%) contained ≥100 cfu/g of Escherichia coli (considered unsatisfactory in products labelled as ready-to-eat). Listeria monocytogenes or other Listeria species were detected in six samples (2%) of fruit compared to 167 samples (24%) of vegetables and six samples (26%) of fruit and vegetable mixes, but none at a level of ≥100 cfu/g. Characterisation by WGS of 74 L. monocytogenes isolates identified ten genetic clusters indicating a common source. For 8 of the 10 clusters, the isolates came from homogenous food types: four were sweet corn, and there was one cluster each for beans, peas, peppers and broccoli. There were five genetic associations between isolates from frozen vegetables and from clinical cases of listeriosis, including two cultures from frozen beans that were indistinguishable from the 2015–2018 sweet corn outbreak strain.

This study indicates that L. monocytogenes was present in 10% of frozen vegetables and even though products are generally not ready-to-eat and are intended to be cooked prior to consumption, these have the potential to cause illness. Clear cooking and handling instructions are therefore required on these products to ensure that the health of consumers is not put at risk, and appropriate Good Manufacturing Practice measures should be followed by all fruit and vegetable freezing plants in order to reduce contamination with Listeria during processing.

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