Leicester Microbial Sciences and Infectious Diseases Centre (LeMID)

Foodborne disease

According to the World Health Organisation, foodborne disease is highly prevalent worldwide: 420,000 people die each year due to foodborne infection.

Foodborne infections are not only a direct cause of mortality, but contracting a foodborne pathogen increases susceptibility to other communicable and non-communicable disease. In developing countries, diarrhoea and malabsorption of nutrients is more likely to occur alongside a number of diseases, including foodborne infections by bacterial species such as Campylobacter jejuni.

Food poisoning is different from foodborne disease, the symptoms of food-poisoning often occur rapidly after consumption of infected food or drink with symptoms including diarrhoea and vomiting.

Foodborne disease is due to contamination of water and food products by micro-organisms. These bacterial organisms then colonise the intestine, or other parts of the gastrointestinal tract, and intestinal function undergoes changes leading to symptoms; this is because these bacteria replicate at a high rate and produce toxins or inflammation within the body.

What causes foodborne infection?

The common microorganisms that cause food-borne infection include bacteria such as Salmonella and Campylobacter jejuni and parasites such as Cryptosporidium parvum and Giardia intestinalisa.

At the University of Leicester, we work extensively with Campylobacter jejuni.

Campylobacter jejuni

Campylobacter jejuni and the closely related species Campylobacter coli are the main bacterial species responsible for incidents of foodborne disease in the UK, and the rest of the developed world

A common location for these organisms is the gastrointestinal tract of chickens including those that are reared for human consumption. As a results these bacteria are readily transferred to consumers. LeMID researchers are interested in the molecular genetics underpinning the ability of C. jejuni to colonise to the avian gut, evade stringent immune responses, and cause disease in humans.

Features of Campylobacter jejuni

  • Campylobacter jejuni is microaerophillic, meaning that its optimal environment is one of low oxygen
  • Flagella at cell poles provides an ability to swim through the thick mucus layer towards the surfaces of intestinal cells 
  • Corkscrew cell shape contributes to movement through the mucus 
  • Campylobacter jejuni can disrupt the epithelial layer and invade intestinal cells
  • Campylobacter jejuni produce multiple virulence factors including a Cytolethal distending toxin (CTD)
  • Complex polysaccharides on the surfaces of the Campylobacter jejuni bacterial cells are often similar to polysaccharides found in intestinal cells. A Phenomenon referred to as molecular mimicry
  • Some Campylobacter jejuni strains have polysaccharide that are thought to stimulate an autoimmune host response and cause the serious complication of GBS following a bout for diarrhoeal disease


Rod-shaped, gram-negative bacteria that are non-spore forming, motile enterobacteria. Salmonella is group of bacteria that are a major cause of foodborne illness throughout the world according to the World Health Organisation. The bacteria can survive for weeks in a dry environment and months in water.

Non-typhoid Serotypes

Transfer of Salmonella infection can be from animal-to-human and human-to-human. Invasion of the human gastrointestinal tract is the primary cause for Salmonellosis (food-poisoning). Infection often occurs after ingestion of food or drink containing a high concentration of bacteria. The World Health Organisation tells us that Salmonella is 1 of the 4 key global causes of diarrhoeal diseases.

Green leafy salads with lettuce and spinach can be colonised by foodborne pathogens such as Salmonella, E. coli and Listeria.  Salads such as these are ranked as the second most common source of foodborne illness in the EU as the source for outbreaks of food poisoning.

Dr Primrose Freestone and colleagues found that the juice produced due to cut-ends of salad leaves allowed Salmonella to grow in water, even when refrigerated.

The work done by Dr Primrose Freestone and colleagues indicates the necessity for vigilance in salad production and preparation, however, it does not indicate that the consumer will become ill from eating salads.

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