Biofilm formation by Salmonella enterica strains isolated from feed mills

Abstract

Feed supplied to pigs is considered an important vehicle for Salmonella enterica subsp. enterica introduction on farm. Salmonella can be able to form biofilm on several abiotic surfaces, which may contribute to environmental persistence. This study aimed to evaluate the biofilm formation capacity in Salmonella strains isolated from four Brazilian feed mills. The biofilm formation was assessed in 54 Salmonella isolates belonging to different serovars by phenotypic assays: i. expression of curli fimbriae and cellulose in Luria-Bertani agar supplemented with Congo red, Coomassie brilliant blue and calcofluor; ii. adhesion on 96-well polystyrene microtiter plates. The results showed that all isolates presented the rdar morphotype (read, dry and rough colonies) on agar incubated at 28° C. From the total of isolates displaying rdar-morphotype, 14.8% (8/54) showed to be weakly adherent on polystyrene microtiter plates, and were thus considered presumptively biofilm producers. These strains were originated from ingredients and equipment samples, and were distributed among the following serovars: Montevideo (n=2), Senftenberg (n=2), Tennessee (n=1), Orion (n=1), Morehead (n=1), and S. enterica O: 16 (n=1). In this sense, biofilm formation might have played a role in Salmonella colonization of equipment in feed mills, and should be further investigated.