The aim of this study was to assess the efficacy of four natural antimicrobial compounds (cinnamaldehyde, eugenol, resveratrol and thymoquinone) plus a control chemical disinfectant (sodium hypochlorite) in inhibiting biofilm formation by Listeria monocytogenes CMCC54004 (Lm 54004) at a minimum inhibitory concentration (MIC) and sub-MICs. Crystal violet staining assay and microscopic examination were employed to investigate anti-biofilm effects of the evaluated compounds, and a real-time PCR assay was used to investigate the expression of critical genes by Lm 54004 biofilm. The results showed that five antimicrobial compounds inhibited Lm 54004 biofilm formation in a dose dependent way. Specifically, cinnamaldehyde and resveratrol showed better anti-biofilm effects at 1/4 × MIC, while sodium hypochlorite exhibited the lowest inhibitory rates. A swimming assay confirmed that natural compounds at sub-MICs suppressed Lm 54004 motility to a low degree. Supporting these findings, expression analysis showed that all four natural compounds at 1/4 × MIC significantly down-regulated quorum sensing genes (agrA, agrC, and agrD) rather than suppressing the motility- and flagella-associated genes (degU, motB, and flaA). This study revealed that sub-MICs of natural antimicrobial compounds reduced biofilm formation by suppressing the quorum sensing system rather than by inhibiting flagella formation.

The antioxidant activity of resveratrol in cholesterol-fed rats, along with its hypolipidemic effects was determined. Thirty two male Sprague-Dawley (SD) rats were randomly divided into three groups (Control, Res30 and Res70) and fed a hyperlipidemic diet for 4 weeks. Resveratrol was suspended in 0.3% carboxymethyl cellulose (CMC) solution and given to rats of the Res30 and Res70 groups once a day for 4 weeks by oral intubation at a dose of 30 and 70 mg/kg body weight, respectively. The control group received 0.3% CMC solution alone. Resveratrol significantly lowered serum lipid, hepatic cholesterol (TC) and triglyceride (TG) levels compared to the control. Excretion of bile acids was significantly enhanced by resveratrol. The overall potential of the antioxidant system was significantly enhanced by the resveratrol as plasma and hepatic thiobarbituric acid reactive substances (TBARS) levels were lowered while serum superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) activities were increased in the cholesterol-fed rats. These findings suggest that resveratrol maintains an antioxidant efficacy as well as its anti-hyperlipidemic effect.