Purpose: The purpose of this study was to compare the biofilm-forming capabilities of multiple strains of Salmonella on a whole spice (black peppercorns) and polystyrene.
Methods: Biofilm-forming capacity of 14 Salmonella strains on polystyrene was examined using a multi-well plate reader. Biofilm development after 48h of growth in TSB was determined by staining the wells with crystal violet, washing plates to remove loose cells and measuring their optical densities. Biofilms of seven strains were formed on whole black peppercorns by statically incubating a single layer of whole peppercorns in Salmonella-inoculated TSB for 48h at 37°C. Peppercorns were washed twice to remove planktonic cells, dried to a water activity of 0.42, serially diluted and enumerated by plating onto selective media.
Results: Of the 14 strains tested on polystyrene, two strains were predicted to have poor biofilm-forming capacity (OD: 0.16-0.21) and twelve strains were predicted to have medium biofilm-forming capacity (OD: 0.21-0.42). Seven strains belonging to the medium biofilm-forming category were screened for formation on whole black peppercorns. Differences in biofilm formation on the two surfaces were observed for several strains. Salmonella Orion had medium biofilm-forming capacity on polystyrene but was not recovered from washed peppercorns. Salmonella svs. Tennessee and Johannesburg had very high recovery from peppercorns (7.43 ± 0.02 and 7.42 ± 0.02 log CFU/g, respectively) but had greatly varying optical densities (0.164 and 0.266, respectively) as determined by the crystal violet assay.
Significance: Salmonella biofilm formation on peppercorns and polystyrene differs by serovar and surface.