Abstract: Objective:To investigate the correlation between bacterial group behavior and expressions of quorum-sensing system(QS) genes in pan drug resistance Pseudomonas aeruginosa(PA).Methods:The bacterial group behaviors(including elastase,pyocyanin and biofilm) and expression of QS genes were measured.The correlation between PA group behavior and QS gene expression in pan drug resistant PA group and fully sensitive PA group was analyzed.Results:Five cases of pan drug resistance PA and 5 cases of all sensitive PA were collected.In pan drug resistance PA group,the elastase and pyocyanin were positive correlation with expression of LasI(P<0.05),and the biofilm was positively associated with RhlR(P<0.05).There was not correlation between bacterial group behavior and QS gene in all sensitive PA group(P>0.05).The differences of the Rhll level on the first day and LasI and LasR levels on the fourteenth day between two groups were statistically significant(P<0.05).The differences of the elastase,biofilm,and LasI and LasR levels between before and after treatment were statistically significant(P<0.05).The amino acid mutation in 1 strain PA was found.Conclusions:The pan drug resistance PA group behavior is correlation with QS gene.The elastase and biofilm,and more expression levels of LasI and LasR hint that the QS gene plays a key role in the drug resistance mechanism of PA.