Biofilm forming ability of Salmonella enterica serovar Tennessee isolates originating from feed

Abstract

Salmonella enterica subspecies enterica serovar Tennessee was the most frequent Salmonella serovar isolated from plant-based animal feed throughout a two-year period (2012-2013) of research conducted in the region of the Autonomous Province of Vojvodina. In this study, the ability of biofilm formation was investigated on 20 isolates of S. Tennessee. The starting point for this research was the established biofilm-forming ability of serovar Tennessee strains, which significantly contributes to their wide distribution in the environment (plant materials), and hence in animal feed. In this study, biofilm formation was investigated on polystyrene (microplate biofilm assay) and stainless steel (scanning electron microscopy) surfaces by culturing in Luria Bertani broth (LB) and Triptone Soya Broth (TSB). The expression of major matrix components of Salmonella biofilm (curli fimbriae and cellulose) was examined by cultivation on Congo Red agar. All isolates of S. Tennessee produced a biofilm on a polystyrene surface in a microtiter plate test, by cultivation in LB at an incubation temperature of 20 °C. Scanning electron microscopy revealed biofilm formation of S. Tennessee on a stainless steel surface by cultivation in LB, but not in TSB. The expression of curli fimbriae and cellulose, as well as the formation of characteristic “rdar” colonies on Congo Red agar has been observed in all isolates of S. Tennessee. This serovar is not specifically adapted to humans and animals, so the available epidemiological data do not indicate its major implication in food-borne infection outbreaks. However, this serovar manifests a pronounced ability for adherence to plant surfaces, biofilm formation and increased resistance to long-term desiccation, which is the most likely explanation for its frequent identification in low water activity feed.