Cut pieces of melons, particularly cantaloupe, are a common sight in fruit salads and fresh snack trays. Unfortunately, Salmonella can cling to the surface of the melon, and be brought onto the fleshy edible pieces during peeling and cutting. New research is shedding light on how the bacteria stick so tenaciously, and how they can be removed without damaging the melon.
Melon pieces are increasingly recognized as a source of disease, due to contamination with Salmonella. Food technologist Gerry Sapers of the ARS Eastern Regional Research Center in Wyndmoor, PA leads a team of scientists in developing ways to make this popular component safer. The research approach is a broad-based assault on the pathogen's ability to associate with the melon surface initially, its ability to survive and grow, and ultimately contaminate the edible fleshy pieces.
Sapers is working with microbiologists Bassam Annous and Dike Ukuku on several key aspects of the contamination problem. The surface features of cantaloupe make use of chemical sanitizers a challenge. "Honeydew has a very smooth surface," says Ukuku, "but the rind of a cantaloupe is covered with what's called netting. On the microscopic scale, it gives the Salmonella a lot of nooks and crannies to hide and grow. Chemical sanitizers don't go into those very small spaces as well as we could wish." New methods of treating the surface of the melon, including the use of flash pasteurization and other interventions, are areas of active research.
Ukuku and Annous are also working to understand how the Salmonella form biofilms, a very thin layer of sugary polymer, which can protect the bacteria from sanitizers such a chlorine or ozone. Most of the harmless bacteria which live on the surfaces of fruits and vegetables live in these biofilm communities. The danger arises when the Salmonella takes part in the community, forming a complex ecology that can be difficult to remove. New research by Annous has shown that Salmonella can begin forming this protective structure more rapidly after initial exposure than previously believed. Postdoctoral research associate Ethan Solomon is cataloguing the ability of dozens of isolates of Salmonella to form biofilms under different growth conditions. This research will further explain how the bacteria resist attempts to remove them.