Mechanism Of Synergistic Effect On Cell Death Induced By Colistin And Catalase In Paenibacillus Polymyxa

Colistin,a potent Gram-negative bacteria bactericidal antibiotic,can induce cell death in its producing strain Paenibacillus polymyxa.The bactericidal mechanisms of colistin including induced drug-target interaction cell membrane damage and reactive oxygen species(ROS)generation have been demonstrated.The synergistic phenomenon that colistin together with catalase enhanced the killing on P.polymyxa,a 3-log decrease of CFU compared with the one treated by colistin alone.In order to reveal the mechanisms underly synergistic effect of colistin and catalase on P.polymyxa,the bacterial growth,intergrity of cell membrane and change of ROS level were detected.It was confirmed that colistin also had a destructive effect on Gram-positive bacteria cell membrane.Meanwhile,the synergistic treatment of colistin and catalase increased cellular ROS level.Synergistic mechanism was mainly dependent on cell membrane damage induced by colistin;the oxidative stress of ROS was accessary for accelerating the cell death.Under the synergistic effect,high concentration hydrogen peroxide accumulation due to the inhibition of intracellular catalase activity caused more hazardous hydroxyl radical formation(HPF fluorescence intensity higher than the control)converted from hydrogen peroxide via Fenton reaction.Hydroxyl radical played a significant role in rapid cell death of P.polymyxa,a 4-log decrease of CFU.The addition of thiourea promoted the cell survival,a 1-log increase of CFU.High hydrogen peroxide level activated and inhibited transcription level of hydrogen peroxide sensing regulator OxyR gene and PerR gene,respectively,which increased the catalase genes(CotJC,ydhU and katA)transcription.However,the inhibition of intracellular catalase activity would not influence the hydrogen peroxide concentration.