A new study has investigated the impact of Yersinia enterocolitica bacteria as a potential underreported cause of foodborne disease in humans.

The study from the Quadram Institute and University of East Anglia, working with the UK Health Security Agency (UKHSA) found that diverse populations of these bacteria are more commonly found on foods than we previously thought.

Whole genome sequencing revealed similarities between the types of Yersinia found on foods and those isolated from humans.

This calls for a much-improved surveillance strategy to monitor Yersinia so we can properly understand how it is impacting human health.

Yersinia enterocolita. Image: Samuel Bloomfield, Quadram institute

Yersinia enterocolitica bacteria inhabit animal guts, and when certain types infect the human gut, they can cause yersiniosis. This is a type of gastroenteritis, causing diarrhoea, fever, stomach cramps and vomiting. It will usually clear up without treatment but can occasionally lead to more complicated conditions.

The number of cases of yersiniosis is low, but it is likely that the numbers are under-reported. Not everyone with gastroenteritis reports it unless the symptoms are severe or don’t clear up. Patients with gastroenteritis aren’t routinely screened for Yersinia; when Hampshire introduced a screening method to all diarrhoeic stool samples the number of yersiniosis cases diagnosed went from two over a 30 month period to 199.

Pigs have traditionally been thought of as the main sources for Yersinia infection, either through eating undercooked pork or direct contact with the animals or their environment. But a number of outbreaks have been traced to other foods including chicken, milk and leafy greens.

To better understand the burden of yersiniosis and to get a picture of the potential sources of infection, researchers from the Quadram Institute, with expertise from the UKHSA, undertook a genomic survey of Yersinia enterocolitica on different foods on sale to consumers in supermarkets.

They investigated varied retail samples of chicken, pork, salmon and leafy greens for the presence of Yersinia enterocolitica. They used multiple methods of culturing the bacteria, to ensure they captured as big a snapshot as possible of what was present.

The study was supported by the Biotechnology and Biological Sciences Research Council, part of UKRI, and the Food Standards Agency.

Almost three quarters of chicken samples harboured the bacteria, as well as four fifths of the salmon tested. The bacteria were also found on one of ten leafy greens sampled, which is concerning as these foods are often eaten uncooked, and so could lead to a significant risk of exposure to the bacteria.

Yersinia identified in the samples then underwent whole genome sequencing, to identify the specific strains present and so fully capture what diversity of Yersinia enterocolitica are on our foods. Up to five subtypes of Yersinia enterocolitica were identified from a single source.

Almost all the Yersinia enterocolitica identified belonged to a group of Yersinia enterocolitica called biotype 1A. This biotype is not thought to be a major cause of disease in humans. However, when the researchers compared the genome sequences of the Yersinia found on food with previous samples obtained from humans, they found that many of the food-derived samples were closely related to the human-derived ones.

The findings of this study pose questions about the threat that Yersinia enterocolitica in the food chain poses to human health.

These bacteria appear to be more prevalent on supermarket foods than other more high-profile bacteria, like Campylobacter and Salmonella. And yet the number of cases of yersiniosis reported is much lower than for these causes of foodborne disease, even though the pervasive biotype 1A has also been found in human samples.

What is now needed is surveillance of Yersinia enterocolitica from both food and human sources to better understand biotype 1A’s role in infection and to make sure our food is as safe as possible.

Reference:

Yersinia enterocolitica biovar 1A: An underappreciated potential pathogen in the food chain, Raphaёlle Palau, Samuel Bloomfield, Claire Jenkins, David R. Greig, Frieda Jorgensen, Alison Mather,
International Journal of Food Microbiology DOI: 10.1016/j.ijfoodmicro.2023.110554