Study On Screening Of Bacterial Quorum Sensing From Plant Extraction And Their Inhibitions On Biofilm Formation

For a long time, bacteria was considered to be isolated and had no connection with each other. However, in recent years, studies have found that the world of bacteria was like the human world. They also have their own "language". This language was called signal molecular. Bacterial cells can produce signal molecules and release it into the environment. When the signal molecular reached a certain concentration in the environment, it made some specific genes which depended on the bacterial density express. This phenomenon was called "quorum sensing, QS"). Quorum sensing was known as a physiological behavior which can regulate gene expression according to the changes of cell density. The studies had found that bacterial quorum-sensing system can control the important steps in the pathogenic process, such as the production of pathogenic factors, biofilm formation and so on.Microbacteria was a major factor in the area of food spoilage and infection. Only the bacterial density reached a certain number can lead to the occurrence of food spoilage and pathogenicity. With antibiotics and preservatives widely used, bacterial resistance had become more and more serious. It had become a global problem, a major hazard to human health. In recent years, researches were on how AHLs-mediated quorum sensing affects food spoilage and pathogenicity of pathogenic bacteria. It was a new research focus in the field of the preservation of food and pathogen control. This kind of research can give us a promising approach in the field of food preservation and pathogen control.In this study, we used the N-acylhomoserine lactone-mediated quorum-sensing system of gram-negative bacteria as a target to screen quorum sensing inhibitor from the plant materials and to study the influence on biofilm formation of Escherichia coli ATCC 8099. From this reaearch, we wanted to provide theoretical basis and technical support in the development of new antimicrobial agents. Specific studies are as follows:1 Screeing for materials which can interrupt quorum sensing systemIn this study, we use the bacteria, Chromobacterium violaceum 026 (CV026), which can pruduce purple pigment regulated by the signal molecule acylated lactone (AHL). We used the method of plate detection to study the capacity of inhibiting the production of purple pigment and the growth of CV026 by the extract of the 34 kinds of spices and tea. We screed extracts of lavender and roses had the capacity of QSI that can interrupt the quorum sensing system but can't interfer with the growth of CV026.2 Research of the capacity of QSI of extracts of lavender and roseIn this part, we used different kinds of extraction methods to get the extraction. In order to check the capacity of inhibiting the quorum sensing system of Chromobacterium violaceum 026(CV026), we applied the quatitative and qualitative methods. We used organic solvents and water as extraction solvent. In order to get the best results, we used ethyl acetate ester as the extraction solvent of lavender and extracted for 24h quietly. Rose was different from lavender. We used water as the extraction solvent and extracted for 1h by ultrasonic treatment. Further, we studied the inhibition of production of purple pigment of CV026 by different concentrations of the extracts and found that inhibition with the concentration of the extracts showed significant dose-effect relationship.3 Influence on biofilm formation of E.coli 8099 by lavender and rose extractionIn this part, we checked the influence on biofilm formation of E.coli ATCC 8099 by lavender ethyl acetate extraction and rose water extraction by ultrasonic treated for 1h. The studied qualitative and quantitative methods were applied in this part. The results showed that the two extracts can inhibit biofilm formation of E.coli ATCC 8099. From the qualitative results, we can see the biofilm was thinner and less brightter in the study group than in the control group. Also, we can see obvious holes in the study group. Furthermore, we studied the inhibition of biofilm formation of E. coli ATCC8099 by lavender extraction at different concentrations and found that inhibition with the concentration of the extracts showed significant dose-effect relationship.