Antibiotic-resistant germs are repeatedly found on lettuce. We identify the sources from which they are transferred to the plants during cultivation.

Lay summary

Antibiotic-resistant bacteria occur in the environment, in soil, bodies of surface water and organic fertilisers used in agriculture. They are presumed to pass from these sources to humans via plant-based food. However, little is known about how these bacteria are transferred from the environment to commercially grown plants. We are studying this aspect in lettuce cultivation and determining the sources from which resistant bacteria are transferred to the plants. We are investigating soil, irrigation water and fertilisers used during growth up to the point the plants are harvested. We are analysing which bacteria are transferred from which sources and in what quantities, as well as which forms of resistance persist until harvesting. Our study looks at both field and greenhouse cultivation.

While an important source of food, plant products consumed in their raw state may also be carriers of antibiotic-resistant bacteria. Unlike cooked products, germs on products that eaten raw are not killed during preparation. This is why preventive measures to stop pathogens contaminating plants in the first place are important. Until now, however, the knowledge needed to act has not been available.

We want to obtain precise information as to which germs are transferred from which sources to lettuce plants in fields and greenhouses. We are analysing disease-causing pathogens that can affect humans and environmental bacteria that are in themselves harmless to people. These, too, play a role in the development of resistant pathogens since bacteria can exchange genetic material between themselves.

Our results can be used to develop regulatory guidelines and practical measures for agriculture with the aim of preventing the spread of resistance by plant-based foods. They also provide information that could be useful in setting up monitoring programmes.