Evaluation And Mechanism Of Quorum Sensing Activity Of Quinolones Against Pseudomonas Aeruginosa

Pseudomonas aeruginosa is a common opportunistic pathogen in clinic.With the wide spread use of antibiotics in recent years,drug resistance also arises.Therefore,new therapeutic strategies for Pseudomonas aeruginosa infection are needed.On the other hand,quorum sensing plays a role in the production of bacterial biofilm and virulence factors,which enhances the pathogenicity of bacteria.Resistance can therefore be reduced based on the bacteria’s quorum sensing system.In this paper,quinolinones were selected as the research object to test their inhibitory activity on P.aeruginosa QS system,providing a new treatment plan for drug-resistant infection of Pseudomonas aeruginosa.The main research contents are as follows:(1)Design and synthesis of quinolones;(2)The minimum inhibitory concentration and growth curve of the compound against Pseudomonas aeruginosa PAO1 were determined to determine whether the compound was bactericidal or bacteriostatic;(3)To evaluate the effects of the compounds on PAO1 virulence factors such as elastase,rhamnoolipid and pyocyanin;(4)The inhibition effect of the compound on quorum-sensing system was evaluated by quantitative fluorescence PCR;(5)To evaluate the effects of the compounds on PAO1 motor performance,including swimming and clustering tests;(6)To evaluate the effects of compounds on the formation of bacterial biofilms.A simple and practical method for regional selective halogenation of 4quinolone halogenation using potassium halide and PIFA and PIDA was established.The results showed that the compound inhibited the quorum sensing system of bacteria.Among them,the active compound 3a can effectively inhibit the secretion of quorum sensing related virulence factors of bacteria,and significantly inhibit the production of pyocyanin,elastase and rhamnoolipin.It was found that the compound did not inhibit the growth of PAO1 cells even up to 300 μg/mL,but significantly down-regulated the expressions of pqsA,pqsR,lasI,lasR,rhlI and rhlR key genes in the QS system.Compound 3a can inhibit the pyocyanin production of PAO1 at different concentrations of 75,100 μg/mL,and the optimal compound 3a has an 18%inhibitory rate against Pseudomonas aeruginosa pyocyanin when the measured concentration is 50 μg/mL.At 75 μg/mL,the inhibition rate of pseudomonas aeruginosa pyocyanin reached 50%.At 100 μg/mL,the inhibition rate reached 62%.At 100μg/mL,the inhibition rate of biofilm was 36%.At 100 μg/mL,the inhibition rate of rhamnoolipid was 44%.At 125 μg/mL,the inhibition rate of elastase was 50%.At 62.5 μg/mL,the swimming and cluster movement of bacteria could be inhibited to a certain extent,and the inhibition rate of swimming movement was 25%.In conclusion,compound 3a has good quorum-sensing inhibitory activity,which can significantly inhibit the production of related virulence factors and down-regulate the expression levels of key genes in the QS system.It is a potentially quorum-sensing inhibitor(QSI).