Pathogen studies could result in safer produce.

Bacteria can quickly attach to the surfaces of produce and form biofilms that likely improve their ability to colonize and survive. A biofilm is a mass of microbes attached to a surface and to each other by bacterial polymers (complex sugars). This polymer coating may protect bacterial cells from exposure to antimicrobial compounds, such as chlorine, used to sanitize produce.

Conventional washing methods for removing microbial contaminants from the surfaces of fresh fruit and vegetable produce surfaces have been found to be only marginally effective, so Agricultural Research Service (ARS) scientists in Wyndmoor, Pennsylvania, want to give the produce-packing and -processing industries better techniques.

Bassam A. Annous, a microbiologist at the Food Safety Intervention Technologies Research Unit of the ARS Eastern Regional Research Center, and his colleagues are working on new technologies to remove or inactivate pathogens on both fresh and minimally processed produce.

The human pathogen Salmonella is often responsible for produce-related outbreaks of foodborne illness. For example, it is difficult to remove Salmonella from cantaloupe surfaces; the pathogen can attach to inaccessible sites and form a biofilm on the cantaloupe rind. In this way it may avoid contact with sanitizing solutions. Surviving Salmonella cells can then be transferred from the surface of the melon into the internal tissues during cutting.

Annous and his colleagues recently gained new insight into biofilm formation by Salmonella on various surfaces. The ability of Salmonella cells to form biofilm on plastic or stainless-steel surfaces was dependent on the production of fimbriae (hairlike structures) and cellulose that help the cells attach to and colonize surfaces.

Biofilm formation by Salmonella cells starts by attaching to the rind of cantaloupe following contamination. Once attached to the rind, Salmonella cells rapidly develop biofilm by growing and excreting polymers. This new knowledge helps explain how Salmonella survives harsh sanitizing environments.