Inhibitory Effect And Mechanism Of Octyl Gallate(OG) Against Quorum Sensing Of Pseudomonas Aeruginosa

Octyl gallate(OG)is an important alkyl ester derivative of Gallic acid(GA).It is a fatsoluble antioxidant with excellent antioxidant,antibacterial,anti-inflammatory,anti-mutation,anti-tumor,and anti-virus activities.The hydrophobic alkyl long chain in its molecule enhances the ability to penetrate the phospholipid bilayer in the biofilm,which makes its biological activity stronger,and broadens its application range in food system.As a food additive for fatty food,OG has been approved by the Food and Drug Administration of the United States(FDA),the Food and Agriculture Organization of the United Nations(FAO)and the World Health Organization(WHO).At present,a small number of literatures have reported that OG has bacteriostatic effect on common foodborne bacteria,but there are few reports on its antibacterial mechanism and inhibition of bacterial quorum sensing.Therefore,the study on its antibacterial mechanism and inhibition of quorum sensing is of great significance.Firstly,the antibacterial activity and mechanism of OG against Pseudomonas aeruginosa were investigated.The results showed that the minimum inhibitory concentration(MIC)of OG to P.aeruginosa was 0.8 mmol / L,and the minimum bactericidal concentration(MBC)was6.4mmol/L.The analysis of time-killing kinetics curve of P.aeruginosa by OG showed that the inhibition of OG on P.aeruginosa was concentration-dependent.The proportion of saturated fatty acids in bacteria membrane fatty acids treated with OG was significantly increased,with the highest increase of 99.3%.Secondly,the inhibitory effect and mechanism of OG on quorum sensing of P.aeruginosa were studied.After treatment with OG,the highest inhibition rates of P.aeruginosa pyocyanin,rhamnolipid and elastase were 49.1%,53.3% and 65.1%,respectively.At the same time,OG could significantly inhibit the movement ability of bacteria.In the experiment of swarming and swimming,the maximum inhibition distance of movement radius of bacteria was 14.5mm and12 mm,respectively.The maximum inhibitory rate of OG on the expression of major genes in the three circuits of Las,Rhl,Pqs in P.aeruginosa quorum sensing system was 95%.The quorum-sensing-related signal molecule HHQ of P.aeruginosa under the action of OG can not be transformed into PQS,a signal factor with stronger regulatory ability,which leads to the accumulation of HHQ in the system.Through molecular docking,OG can compete with quorum sensing related signal molecules 3-oxo-C12-HS,C14-HS and PQS to bind to the corresponding target protein,which plays the role of blocking signal transmission.Through the influence of OG on the expression of quorum sensing related genes,the synthesis of signal factors and the competition to combine targets can effectively inhibit the quorum sensing of P.aeruginosa.Finally,the effects of OG on the P.aeruginosa biofilm formation,preformed biofilm,and bacterial membrane fatty acids in biofilm were studied.The biofilm formed under the action of OG was observed by scanning electron microscope(SEM)and confocal microscope.The surface of biofilm was obviously damaged,the number of bacteria decreased,and the cell morphology was destroyed.Besides,the lowest survival rate of bacteria in the biofilm was20.3%,and the thickness of biofilm was reduced by up to 60 ?m.When the biofilm was preformed under the action of OG,the surface of the biofilm was also obviously damaged.The lowest survival rate of bacteria in the biofilm was 10.1%,and the biofilm was reduced by up to75 ?m.In the biofilm formed under the action of OG,the content of saturated fatty acids in the bacterial membrane decreased,while that in the preformed biofilm under the action of OG increased.The negative influences of OG on the formation of biofilm and the preformed biofilm have two different mechanisms.