Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2005
Publication Date: 10/1/2005
Citation: Solomon, E.B., Cooke, P.H., Burke, A.M., Ukuku, D.O., Annous, B.A. 2005. Biofilm formation by salmonella spp. on cantaloupe surfaces. Journal of Food Safety. 25:276:287.
Interpretive Summary: From 2000-2002, three successive outbreaks of Salmonella were linked to the consumption of contaminated cantaloupes. Traceback studies indicated that the cantaloupes involved originated from farms in Mexico. As a result, the Food and Drug Administration issued an alert banning the import of all melons from Mexico. Previous research in our laboratory has demonstrated the lack of effectiveness of aqueous sanitizers in eliminating Salmonella from cantaloupe melons. In addition, the efficacy of aqueous sanitizers is greatly reduced when the target bacteria are allowed to reside on the melon for more than 24 hours. The nature of the interactions between cells of Salmonella and cantaloupe surfaces is unknown. The research presented here demonstrates that cells of Salmonella do not exist as single, solitary organisms, but instead organize together into biofilms (communities of microorganisms covered in layers of polymer). These biofilms form quickly on melon surfaces and are difficult to inactivate or remove. The formation of biofilms by cells of Salmonella is likely responsible for the limited efficacy of sanitizers. The research described here enhances our knowledge of the behavior of Salmonella on produce surfaces and will aid in the design of more effective intervention treatments.
Technical Abstract: The ability of two strains of Salmonella to form biofilms on cantaloupe surfaces was investigated. Ten µl of bacteria were spot-inoculated onto melon rinds in pre-marked areas and melons were held at either 10 or 22 degree C. Biofilm formation was monitored using scanning electron microscopy (SEM) on excised portions of the melon rind at 2, 24, 48, and 144 hours post-inoculation. Micrographs indicated that biofilm formation occurred rapidly following introduction of cells onto the melon surface. Fibrillar material was visible after just two hours and cells were embedded in extracellular polymeric material after 24 hours at either temperature. These results indicate that a human pathogen is capable of forming a biofilm on plant tissue and that biofilm formation may be responsible for the increased recalcitrance of attached bacteria to aqueous sanitizers.