Citrus flavonoid represses Salmonella pathogenicity island 1 and motility in S. Typhimurium LT2

Salmonellosis is one of the leading health problems worldwide. With the rise of drug resistance strains, it has become imperative to identify alternative strategies to counter bacterial infection. Natural products were used historically to identify novel compounds with various bioactivities. Citrus species is a rich source of flavonoids. Naringenin, a flavonone, is present predominantly in grapefruit. Previously we have demonstrated that naringenin is potent inhibitor of cell–cell signaling. The current study was undertaken to understand the effect of naringenin on Salmonella Typhimurium LT2. The cDNA microarrays were employed to study the response of S. Typhimurium to naringenin treatment. Naringenin specifically repressed 24 genes in the Salmonella pathogenicity island 1 and down-regulated 17 genes involved in flagellar and motility. Furthermore, phenotypic assays support the result of microarray analysis. In addition, naringenin seems to repress SPI-1 in pstS/hilD-dependent manner. Altogether the data suggest that naringenin attenuated S. Typhimurium virulence and cell motility. This is the first molecular evidence to demonstrate effect of naringenin on bacterial virulence and cell motility.

Research Highlights
► Naringenin, a citrus flavonoid inhibited the motility of Salmonella Typhimurium LT2.
► Naringenin reduces the adherence and internalization of S. Typhimurium cells to epithelial cells.
► The microarray analysis demonstrated that naringenin selectively repressed SPI1 and flagella.
► Furthermore, naringenin seems to repress SPI1 in PstS and HilD dependent fashion.
► This is the first evidence of attenuation of Salmonella virulence and motility by naringenin.