Ripeness Plays Role in Vulnerability of Produce to Salmonella

Foodborne pathogens attach to fruits in different ways depending on their ripeness, according to researchers from Imperial College London, who presented their work at the Society for General Microbiology’s Spring Conference in Dublin, Ireland, in late March.

Salmonella bacteria that attach to ripe tomatoes produce an extensive network of filaments, which is not seen when they attach to the surface of unripe tomatoes. This could affect how they are maintained on the surface,” says Gad Frankel, PhD, professor of molecular pathogenesis. “We are not completely sure yet why this happens; it might be due to the surface properties of the tomatoes or alternatively the expression of ripening hormones.”

What these two different types of attachment could mean for food safety is still unclear. Dr. Frankel says that his findings do not necessarily imply that the riper the fruit, the more vulnerable it is to pathogenic contamination. “Salmonella strains appear to bind ripe and unripe fruit at equal efficiency,” Dr. Frankel says. “And the composition of the filamentous network is not yet known.”

And the filaments don’t appear in all produce, or with all pathogens. “We did not see similar structures when Salmonella are bound to salad leaves. Moreover, pathogenic E. coli strains do not produce these filaments on tomatoes, so for now this seems to be specific to Salmonella.”

Still, understanding the filamentous network further could prove helpful for food safety. Dr. Frankel’s lab next plans to determine what the filaments are made of, what triggers Salmonella to make them, and what are the implications of the filaments for the long-term survival of Salmonella on tomatoes.

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