Mechanism of biofilm formation by Salmonella typhimurium ST19 in a high-glucose environment revealed by transcriptomics

Salmonella is one of the most common foodborne pathogens in the world, and Salmonella typhimurium, the most frequently isolated serotype, can cause zoonosis. In this study, we evaluated the effect of glucose concentration on the biofilm formation of 11 strains of Salmonella typhimurium. We found that among the selected strains, low-sugar conditions were more conducive to the formation of biofilms, although strain ST19 followed another rule. As the glucose concentration increased, biofilm formation showed an increasing trend. When the concentration of glucose reached 1.5%, other strains no longer formed biofilms, while strain ST19 still had strong biofilm formation ability. Therefore, we selected a culture medium containing 1.5% glucose to collect biofilms and planktonic cells of strain ST19 and compared them with strain CDC3, which did not produce a biofilm under these conditions, for transcriptomics analysis. The results showed that the related genes in the phosphotransferase system (PTS) and the operon genes regulated by AI-2 signaling molecules were highly downregulated in the biofilm bacteria of strain ST19 with a glucose content of 1.5%. At the same time, the genes involved in the two-component system, carbon metabolism and transcription regulation were significantly upregulated, which indicated that strain ST19 could adapt to a high-glucose environment by regulating glucose transport and metabolism in bacteria under a high-glucose environment and regulate biofilm formation by upregulating the expression of related genes in the two-component system. These findings illustrated that the regulated mechanism of Salmonella typhimurium's biofilm formation, which are significant to control biofilm contamination.