<div>Background: Streptococcus suis is a zoonotic pathogen closely related to the respiratory tract of swine. Paeonol is a traditional Chinese medicine with antibacterial effect. This study demonstrated the effect of paeonol on biofilm formation and the expression of virulence factors of Streptococcus suis.&nbsp; 
 
Methods: The minimum inhibitory concentration (MIC) of paeonol on Streptococcus suis was determined by double dilution method. Crystal violet staining method was used to determine the effect of paeonol on the biofilm formation. The effects of paeonol on the morphology and structure of Streptococcus suis biofilm were observed by field emission scanning electron microscopy (FE-SEM). Real-time quantitative PCR (qRT-PCR) was used to detect the expression levels of Streptococcus suis related virulence factors under sub-MIC (1/4 MIC, 1/8 MIC) paeonol. 
 
Result: The results showed the effect of 1/4 MIC and 1/8 MIC paeonol on biofilm formation and mature biofilm was significant (*P&lt;0.05). Under the action of paeonol, the biofilm structure becomes sparse. qRT-PCR results showed that 1/8 MIC paeonol inhibits bacterial adhesion by up-regulating the expression of mrp virulence genes, thereby inhibiting the formation of Streptococcus suis biofilm.</div>

Effects of Paeonol Sub-inhibitory Concentration on Streptococcus suis Biofilm and Expression of Virulence Genes

Background: Arsenic toxicity has become a growing concern for rice growers in South East Asian countries due to the extensive use of arsenite-contaminated groundwater in rice paddies. The presence of arsenic in soil and water from irrigation results in impaired crop growth and development. The effect of exogenous pretreatment of paeonol on hydroponically grown rice seedlings was examined by investigating the antioxidant systems under arsenic stress. 
 
Methods: In the experiment, 7-day old rice seedlings (IR-64) were exposed to 10, 50, 100 &micro;M of arsenite separately and co-treatment with 10, 50, 100 &micro;M paeonol (extracted from Paeonia suffruticosa root) in a hydroponic medium for 7 days. The activity of lipid peroxidation [malondialdehyde] antioxidants [APX, CAT, SOD, GPX] in root and shoot tissue were determined by standard protcol. 
 
Result: Arsenite treatments inhibited growth correlating with increased arsenic accumulation in rice seedlings. Oxidative stress was induced by overproduction of reactive oxygen species (ROS) and disruption of antioxidant defense systems measured in terms of increased activity of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, glutathione peroxidase, catalase&nbsp; and lipid peroxidation (malondialdehyde) in root and shoot tissues separately. Paeonol pretreated seedlings along with arsenic exposure substantially decreased the level of arsenic uptake in plants resulting in comparatively higher plant growth as well as biomass substantial reduction in ROS overproduction and MDA content was observed in paeonol pretreatment as compared to arsenic-exposed seedlings alone. These findings indicate that paeonol has an ameliorating effect on arsenite-induced oxidative stress, suggesting that paeonol enhances the activity of antioxidants and prevents oxidative stress damage by transforming ROS to a neutral and non-toxic end product. Such natural ameliorative methodology will enhance agricultural production in arsenic stressed paddy field environments.

Paeonol (Extracted from Paeonia suffruticosa Root) Pretreatment Lends Antioxidant Protection against Arsenite Stress in Rice (Oryza sativa L.) Seedlings