Antibiofilm effects of quercetin against Salmonella enterica biofilm formation and virulence, stress response, and quorum-sensing gene expression

Salmonellosis is a prevalent food poisoning disease caused by Salmonella spp. that affects millions of people throughout the world. Contamination of chicken meat and processing equipment with Salmonella is a major issue in the food industry. Therefore, it is necessary to study not only food but also food contact surfaces [plastic (PLA) and rubber gloves (RG)] that can cause cross-contamination during processing. The inhibitory activities of quercetin, an antioxidant and antibacterial compound, were tested against S. Typhimurium and S. Enteritidis on PLA, RG, and chicken skin during biofilm. When quercetin (0-125 mu g/mL) was supplemented, the inhibitory effect was 1.50-2.61 log CFU/cm2 (125; 1/2, 62.5; 1/4, and 31.25 mu g/mL; 1/8 MIC). Furthermore, the initial biofilm formation rate of both bacteria was greater on the chicken skin surface than on the food contact surfaces. The inhibitory impact was visually observed using field-emission scanning electron microscopy and confocal laser scanning microscopy. The swimming and swarming motility was also found to be inhibited from 1/8 MIC. As determined by qRT-PCR, quercetin downregulated the expression levels of virulence (avrA, and hilA), stress response (rpoS), and quorum-sensing (luxS) genes. Our findings suggest that plant-derived quercetin is a possible antibiofilm agent against Salmonella spp. biofilm formation, as well as biofilm caused by other bacteria.