The MdrL Efflux Pump Mediates The Tolerance Mechanism Of Listeria Monocytogenes To Benzalkonium Chloride

Efflux pump Mdr L which is negatively regulated by regulator Lad R may play roles in tolerance to benzalkonium chloride(BC)in Listeria monocytogenes.But the mechanism of regulation has not been studied.To investigate the roles of efflux pump Mdr L in tolerance to BC,the mdr L deleted strain ?mdr L was constructed,and the physiologist of the mutant strain ?mdr L and the wild-type strain EGD-e obtained by sub-lethal or lethal levels BC were compared in this study.In addition,to study the interaction of the regulator Lad R with the efflux pump Mdr L,the lad R deleted strain named ?lad R was constructed.Transcriptional level analysis was tested by quantitative real-time PCR to reflect the difference of the mutant strain ?lad R and the wild-type strain EGD-e,the binding reaction of Lad R and the mdr L promotor was studied by electrophoretic mobility shift assay(EMSA)experiments.The conclusions are as follows:(1)Efflux pumps mediated the tolerance to BC of L.monocytogenes.Growth curves of EGD-e showed that the lag-phase duration was prolonged,and the maximum growth rate and the maximum optical density were little changed opon exposure to sub-lethal levels of BC.However,the growth of EGD-e was totally inhibited,when it was exposed to sub-lethal levels of BC and reserpine at the same time.(2)Efflux pump Mdr L plays a role in the tolerance to BC in L.monocytogenes.A significantly difference was observed in the serial diluted culture between ?mdr L and EGD-e on the plates in the presence of BC(4 ?g/m L).Compared with the wild-type strain EGD-e,two log decreases was observed in ?mdr L in the presence of the lethal concentration of BC.(3)Efflux pump Mdr L plays no significant role in the efflux of ethidium bromide(EB).No difference was observed in the accumulation and efflux to EB between ?mdr L and EGD-e.(4)Efflux pump Mdr L is negatively regulated by the regulator Lad R.Transcriptional level analysis revealed the mutant strain ?lad R was strongly increased by 51 times compared with the wild type strain EGD-e.(5)The regulator Lad R can specificly bind with the mdr L promotor.EMSA experiments demonstrated that Lad R can specific binding with the mdr L promotor,and the binding activity raised with the increase of the concentration of Lad R.In conclusion,efflux pump Mdr L plays a role in tolerance to BC in L.monocytogenes.Efflux pump Mdr L is negatively regulated by the regulator Lad R,which is achieved by the binding of Lad R with the mdr L promotor.