Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 2005
Publication Date: May 1, 2005
Citation: Solomon, E.B., Niemira, B.A., Sapers, G.M., Annous, B.A. 2005. Biofilm formation, cellulose production, and curli biosynthesis by salmonella spp. originating from produce, animal, and clinical sources. Journal of Food Protection. 68(5): 906-912. Interpretive Summary: American consumer demand for fresh fruits and vegetables has increased dramatically in the past decade. From 1987-1997, per capita consumption of fresh produce increased by 35 pounds per year. Concurrently, the number of outbreaks of foodborne illness associated with produce has also increased. During 2000-2002, three successive outbreaks of salmonellosis were linked to the consumption of contaminated cantaloupes. This has resulted in a great deal of research to find intervention treatments capable of inactivating Salmonella residing on the outer surface of cantaloupes. Previous work in our laboratory has resulted in the observation 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 far more difficult to inactivate or remove than single attached cells. The work described in this manuscript attempts to understand whether biofilm formation is found predominantly in produce-associated Salmonella, or is a trait also found in Salmonella originating from other sources. Our research has shown that all Salmonella are capable of forming biofilms, regardless of their source. This furthers our understanding of the behavior of Salmonella on produce surfaces and will aid in the search for more effective intervention treatments.
Technical Abstract: The ability of 71 strains of Salmonella enterica originating from produce, meat, or clinical sources to form biofilms was investigated. A crystal violet binding assay demonstrated no significant differences in biofilm formation by isolates from any source when tested in either Luria-Bertani (LB) broth supplemented with 2% glucose, tryptic soy broth, or 1/20th-strength tryptic soy broth. Curli and cellulose production were monitored by assessing morphotypes on LB agar without salts containing Congo Red and fluorescence on LB agar containing calcofluor, respectively. One-hundred percent of clinical isolates exhibited curli biosynthesis and 73% demonstrated cellulose production. All meat-related isolates formed curli and 84% produced cellulose. Eighty percent of produce-related isolates produced curli but only 52% produced cellulose. Crystal violet binding was not statistically higher in isolates of any morphotype, but was related to the media in which the strains were tested. Results indicate that biofilm formation (as measured by crystal violet binding) is not dependent on the source of the test isolate. The prevalence of cellulose deficient isolates is highest among produce-related strains. These data indicate the difficulties in assessing biofilm formation in Salmonella using a standardized crystal violet assay.