Salad is good for you, generally speaking, so growing fresh greens in orbit seems like a winning way for space farers to stay healthy. New research suggests that as nutritious as space salad might be, it could pose something of a risk to astronauts.

The problem is growing leafy plants like lettuce and spinach in space can come with a side dish of bacteria, according to a new study from a team at the University of Delaware. In tests on plants grown in simulated microgravity, they were shown to actually be more susceptible than normal to the Salmonella enterica pathogen.

We know that the International Space Station (ISS) is home to a lot of aggressive bacteria and fungi, and if these space microbes were to cause widespread sickness in an astronaut crew, it would mean lives were at risk.

"You don't want the whole mission to fail just because of a food safety outbreak," says plant biologist Harsh Bais from the University of Delaware. Bais and his colleagues used a device called a clinostat to perform some clever rotation tricks in the lab, putting lettuce plants into a similar state as they would be in microgravity. They then added S. enterica bacteria to the leaves.