The biofilm-forming ability of Salmonella enterica subsp. enterica isolated from swine-feed mills

Animal feed has been considered an important vehicle for introducing Salmonella enterica subsp. enterica in pig farms. Salmonella survival and persistence in feed mill environments have been associated with biofilm-forming ability. This study evaluated 54 Salmonella isolates from swine-feed mills for: i. phenotypic expression of curli fimbriae and cellulose; ii. pellicle formation at the air-liquid interface; iii. adhesion on polystyrene microtiter plates; and iv. the presence of the main genes associated with biofilm formation. Regarding phenotypic cell morphology assays, all Salmonella isolates presented morphotype RDAR at 28 degrees C and SAW at 37 degrees C. Rigid pellicle formation at the air-liquid interface was observed in 51.85% (28/54), while fragile pellicle was seen in 18.52% (10/54), and 29.62% (16/54) were not able to produce pellicle. Biofilm quantification on polystyrene microtiter plates showed that 98.15% (53/54) of Salmonella isolates were able to form biofilms at 28 degrees C, while 83.33% (45/54) of the isolates were classified as non-adherent at 37 degrees C. The genes csgD, fimA, adrA, and bapA were found in all isolates evaluated. These results indicated that Salmonella serovars from swine-feed mills have the biofilm-forming ability.