Strain Selection

A total of 88 Salmonella isolates, maintained at the Istituto Zooprofilattico Sperimentale delle Venezie, were selected to study their ability to form biofilm. The strains belonged to 15 different serotypes, namely, Salmonella Derby, Salmonella Dublin, Salmonella Enteritidis, Salmonella Hadar, Salmonella Infantis, Salmonella Kentucky, Salmonella Livingstone, Salmonella Mbandaka, Salmonella Montevideo, monophasic variant of S. Typhimurium (MVST), S. Newport, Salmonella Rissen, Salmonella Senftenberg, Salmonella Thompson, and S. Typhimurium. For each serotype, two strains were included from each of the sources animals, food, and humans, with the exception of S. Dublin and S. Mbandaka, for which only one human isolate was retrieved. Therefore, six strains were tested for each serotype, except S. Dublin and S. Mbandaka. A detailed description of isolates is reported in Supplementary Table S1. The strains were stored at −80°C in cryobank tubes with preservative medium (Copan Diagnostics, CA, United States) and were tested for purity before use. For inoculation, each strain was transferred from the stock cultures into tryptic soy broth (TSB) and incubated overnight at 37°C. The grown cultures were used for inoculation into different media for subsequent quantification of biofilm production.