Astronauts seeking a healthy diet of leafy green vegetables while in space may be in for a bit of bad news. Researchers have found that lettuce and other plants grown in space are more susceptible to bacterial infections, such as salmonella.

NASA and other space agencies have been attempting to grow different types of food on the International Space Station (ISS) over the last several years. The hope is that astronauts will be able to one day sustain a healthy diet on long stays in space, such as a trip to Mars. However, it seems that even when things like lettuce are grown in controlled environments with ideal temperature, light, and water, these leafy green vegetables are still subject to many pathogenic bacteria and fungi found on ISS.

This has raised a high level of concern for long-term missions, which could be “derailed” if a foodborne illness outbreak occurs. Researchers say that a lot of these disease-causing microbes onboard ISS are “very aggressive” and can “easily colonize the tissue of lettuce and other plants.” This ultimately means that if a person eats lettuce that has been contaminated with E. coli or salmonella, they can get very ill, along with others onboard.

The US Department of Health and Human Services describes salmonella as the most common cause of foodborne illness. It often occurs in raw poultry, eggs, beef, and sometimes on unwashed fruit and vegetables. Symptoms include fever, diarrhea, abdominal cramps, and a headache, and typically lasts 4-7 days. The agency adds that if salmonella gets into the bloodstream, it can be extremely serious and even life-threatening.