Grapefruit juice and its constituents augment the effect of low pH on inhibition of survival and adherence to intestinal epithelial cells of Salmonella enterica serovar Typhimurium PT193

The present study examined the survival of Salmonella Typhimurium and its adherence to intestinal epithelial cells following inoculation into grapefruit juice and apple cider. Both liquids significantly inactivated S. Typhimurium (0.8–2.2 log reduction compared to the control); surviving Salmonella in grapefruit juice was 1.0–1.4 log lower than in apple cider at 24 h incubation. Grapefruit juice contains the antimicrobial substances naringin (NAR) and naringenin (NGE); however, the effect of grapefruit juice on growth and adherence of S. Typhimurium appeared not to be related to NAR. NGE at 100–200 μg/mL reduced the adherence of Salmonella to epithelial cells by 57% and 73% compared to the control (TSB at pH 7.4) after 24 h treatment, but stimulated rather than inhibited growth of Salmonella. However, when NGE at 200 μg/mL was added to TSB at pH 3.5 Salmonella survival and adherence to intestinal epithelial cells were reduced by 2.5 log and 79%, respectively, compared to the control (TSB at pH 3.5). Addition of NGE to apple cider also caused a slight reduction in the survival of S. Typhimurium, but did not enhance the inhibitory effect on adherence due to apple cider. These data showed that low pH augmented the inhibitory effect of NGE on growth and adherence of Salmonella to intestinal epithelial cells, but the mechanism of the observed augmentative effect is not clear. Understanding the mechanism of the interaction between low pH and NGE and its inhibitory effect on growth and adherence of enteric pathogens may lead to the development of new antibacterial agents.