​The capacity and pathogenic potential of bacteria that internalise into plant tissue

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Fruit and vegetables are an important part of a healthy diet and should make up around a third of the food we eat. Food Standards Scotland (FSS) recommend eating at least five portions of a variety of fruit and vegetables every day. Unfortunately, there are occasions when fruit and vegetables can become contaminated with bacteria that can cause foodborne illness, and certain types of fresh produce have previously been implicated in outbreaks of food poisoning. One route by which consumers can become ill is via internalised bacteria; this is when bacteria, such as E. coli, become incorporated into the plant tissues of some fruits and salads.

FSS and Food Standards Agency (FSA) co-funded this study to investigate the capacity and pathogenic potential of bacteria that can internalise into plant tissues. The study revealed some key factors surrounding internalised bacteria that have identified areas for potential improvement of current practices and opportunities for further research.

The study concluded that current washing practices used in post-harvest production do not remove or inactivate any internalised bacteria and are ineffective at removing all external bacteria from plant surfaces. The study also revealed that internalised E. coli were not compromised in their ability to interact with and bind to human gut epithelial cells and hence are still likely to be able to cause disease.

These conclusions reinforce the importance of Good Agricultural Practices, such as use of clean irrigation water. Growers can get further information from our fresh produce tool which helps manage microbiological contamination risks and provide guidance on industry best practice.

Consumer advice regarding fresh produce remains unchanged; it is important to wash all fruit and vegetables before you eat them to ensure they are clean and safe to eat because soil can sometimes carry harmful bacteria. Washing will help remove these bacteria, including E. coli, from the surface of fruit and vegetables. Wash fresh produce under a running tap and rub them under water, for example in a bowl of fresh water. Start with the least soiled items first and give each of them a final rinse. Washing loose produce is particularly important as it tends to have more soil attached to it than pre-packaged fruit and vegetables. Peeling or cooking fruit and vegetables can also remove bacteria but it is still recommended that you give them a rinse first.