Biofilm formation of meat-borne Salmonella enterica and inhibition by the cell-free supernatant from Pseudomonas aeruginosa

Abstract

Using polystyrene surfaces for attachment, we evaluated biofilm formation and cell surface hydrophobicities of 17 Salmonella enterica strains (belonging to 9 different serovars), and further assessed the effect of cell-free culture supernatants (CFS) from Pseudomonas aeruginosa (containing acylated homoserine lactones (AHLs)), on the growth and biofilm development of S. enterica. The results indicated that most of the 17 strains readily formed biofilms on polystyrene surfaces, but the development of biofilms were significantly influenced by serovars and incubation conditions. Strains of S1 (S. London), S2 (S. London), S9 (S. Indiana) and S16 (S. Typhimurium) produced greater biofilms regardless of the tested conditions compared with other strains, with maximum biofilm production of 3.08, 2.47, 2.21 and 3.39 (crystal violet assay), respectively. Significant differences in cell hydrophobicity were observed between strains, S16 (S. Typhimurium) showed highest hydrophobicity values (>56%) compared with the other strains (<46%). A significant positive correlation was observed between cell surface hydrophobicity and the capacity of individual strains to form biofilms. The presence of 30% and 60% CFS from P. aeruginosa (containing AHLs identified by thin-layer chromatography), significantly decreased the growth rates of S. enterica (S1, S9 and S16) during the exponential phase, but not during the stationary phase, and significantly inhibited biofilm development of S. enterica strains (S1, S9 and S16) when incubated both in tryptic soytone broth (TSB) and meat thawing loss broth (MTLB), reaching maximum inhibition percentage of 70.7 and 93.3, respectively. Our findings are therefore important for developing innovative control strategies of Salmonella biofilms.