Effect of growth media on gene expression levels in Salmonella Typhimurium biofilm formed on stainless steel surface

Salmonella biofilm is recognized as a frequent source of cross-contamination and has been associated with food-borne outbreaks. It is more meaningful for evaluating biofilm formation in food-based medium than in laboratory-growth medium. In the present study, the expression of functional genes during biofilm formation of Salmonella Typhimurium grown in meat-based and standard growth substrates were determined by RT-qPCR assays. The number of viable cells and the expression of tested genes during biofilm formation displayed a specific behavior according to the growth conditions. When biofilm was grown for 7 days in a laboratory trypticase soy broth (TSB), the expression of the tested genes increased, but when grown in a meat thawing loss broth (MTLB), gene expression was inhibited as compared to corresponding planktonic cells. Relative gene expression of biofilm in MTLB was lower than that in TSB. Positive relationships were found between each gene tested in biofilm cells grown in TSB and MTLB at 3, 5 and 7 days incubation, their correlation did not changed with the variation of growth media of biofilm. A preliminary positive relationship was also observed between growth days and the expression levels of some tested genes. Our results suggested that biofilm formation was coordinately governed by a highly complex regulatory network, where the genes tested in this study (adrA, bapA, csgB, csgD, csrA, rpoS, invA, sipB-C, sdiA and luxS) played important roles.