Tannin-rich pomegranate rind extracts reduce adhesion to and invasion of Caco-2 cells by Listeria monocytogenes and decrease its expression of virulence genes

Abstract

Pomegranate rind is rich in tannins that have remarkable antimicrobial activities. This study aimed to evaluate the effects of a tannin-rich fraction from pomegranate rind (TFPR) on Listeria monocytogenes virulence gene expression and on the pathogen's interaction with human epithelial cells. Growth curves were monitored to determine the effect of TFPR on L. monocytogenes growth. The 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide and fluorescence staining assays were used to examine the cytotoxicity of TFPR. The effects of TFPR on L. monocytogenes adhesion to and invasion of epithelial cells were investigated using Caco-2 cells. Real-time quantitative PCR analysis was conducted to quantify mRNA levels of three virulence genes in L. monocytogenes. Results showed that a MIC of TFPR against L. monocytogenes was 5 mg/ml in this study. TFPR exhibited cytotoxicity against Caco-2 cells when the concentration was 2.5 mg/ml. Subinhibitory concentrations of TFPR significantly reduced, in a dose-dependent manner, adhesion to and invasion of Caco-2 cells by L. monocytogenes. When L. monocytogenes was grown in the presence of 2.5 mg/ml TFPR, the transcriptional levels of prfA, inlA, and hly decreased by 17-, 34-, and 28-fold, respectively.