According to new findings from University College Cork, bacteria that cause food poisoning are adept at utilising key food ingredients to neutralise acid in the stomach, thereby allowing them to pass into the intestine unscathed.
The new research, presented by UCC’s Professor Colin Hill at the Society for General Microbiology's autumn meeting in Nottingham, has important implications for understanding and reducing the incidence of Listeria infections.
L. monocytogenes as a food-borne pathogen has significant public health and economic impacts with manufacturers of ready-to-eat foods required, under EU regulation, to examine the processing environment for microbe as part of their hazard analysis critical control point (HACCP) approach and sampling schemes.
Using ingredients as a shield
The new data indicates that certain food ingredients may also play a role in the incidence of food poisoning linked to Listeria.
"People who consume foods that are contaminated with Listeria and are also high in glutamate, such as soft cheese or meat products, have a higher chance of developing serious infection than someone eating the same quantity of bacteria in a low-glutamate food," said Prof Hill.
"Of course this is further complicated by the fact that a contaminated, low-glutamate food could be eaten in combination with a high-glutamate food such as tomato juice, which could also increase the risk of infection,” he added.
The Cork-based researchers also noted that the bacterium can take advantage of food processing and storage conditions to help them survive.
"Bacteria that are exposed to low pH before entering the body may adapt to become more acid-tolerant and therefore better equipped to deal with acidic conditions in the body,” explained Prof Hill. “For example, Listeria contaminating naturally acidic foods such as cheese may be more likely to cause infection than Listeria carried at a more neutral pH in water.”
Such observations may go some way to explaining the headlines earlier this year, when seven people died from listerioisis in Austria and Germany after consuming contaminated cheese.
"The number of cases of listeriosis has nearly doubled in the last decade in Europe. This is because the bacterium is so good at overcoming the challenges it faces in food and in the body," said Prof Hill. "Our studies show that consuming Listeria in one food may be quite safe, while eating the same amount in another food might be lethal. By understanding the role of the food matrix we may be able to identify and eliminate high-risk foods from the diet of susceptible people."