Salmonella outbreaks are relatively rare from fresh produce, but the bacteria remains a health risk. New research suggest the risk is greater among precut salad.

In lab tests, scientists found Salmonella enterica bacteria multiplied more quickly when exposed to solitary salad leaves. Juices released by damaged salad leaves further enhanced the bacteria's motility.

When released into a dish with water and a damaged salad leaf, 100 individual Salmonella bacteria multiplied to more than 100,000 bacteria in the span of five days. Individual leaves were also more prone to Salmonella biofilms.

Leaf juices failed to encourage an abundance of other microorganisms typically found on the surface of salad leaves.

"We wanted to investigate what happens to Salmonella in a bag of salad to better understand the potential risks to consumers and inform future research on reducing attachment of this pathogen to salad leaves," Primrose Freestone, a microbiologist at the University of Leicester, said in a press release. "This study is part of our ongoing research into ways to reduce the risk of Salmonella persisting and growing when it is present in bagged salad."

There are a variety of best practices to mitigate the risk of outbreak during farming, harvest and production of edible greens, but nothing is foolproof in thwarting Salmonella.

The pathogen especially likes spinach, and can infect root juices, allowing it to infiltrate the plant's insides via the vascular system.

"Consumers seem to be more preoccupied with nutritional facts, but they should not forget that foodborne pathogens can be deadly," Andreas Karatzas, assistant professor in food microbiology at the University of Reading, told the Guardian.

Researchers say bagged salads are generally safe to eat. Precut lettuces are washed in chlorinated water.

"Don't be alarmed, we still eat bagged salad, but don't keep bagged salad any longer than you need to, we normally buy it on the day we eat it," Freestone told BBC. "Buy the bag with the best sell-by date, avoid lots of mushed leaves and if it's inflated then don't use it."