Effect Of UV Disinfection On Horizontal Gene Transfer Of Antibiotic Resistance Genes

It’s been reported that some disinfection treatments,however,not only cannot remove ARGs and drug-resistant bacteria(ARB)effectively,but in some degree increase ARGs and ARB pollutions in water.Unfortunately,there are no reports on why some disinfection methods could promote ARGs horizontal transfer and dissemination in water treatment system.Therefore,the purpose of our study is to firstly clarify the inactivation rules of ARGs and ARB and forming rules of the injured bacteria resulting from UV disinfection;secondly we explore the characters of UV disinfection injured bacteria,finally the forming requirements and influencing factors of transformation between the free ARGs and injured bacteria were studied through laboratory simulated experiments and actual drinking water treatment system research.which can provide a support for developing a effective disinfection method to control the horizontal transfer and dissemination of ARGs.The key contents are as follows:The effect of UV disinfection on E.coli(25922)with the plasmid of RP4 followed the decreasing order is injury of ARB >inactivation of ARB > inactivation of antibiotic resistance plasmids > injury of transposons > removal of ARGs.The sensitivity of the five bacteria to the UV followed the decreasing order is P.aeruginosa 27853(RP4)> E.coli 25922(RP4)> Salmonell 50312(RP4)> E.faecalis 33186(RP4)> S.aureus 6538(RP4).The changes of morphology,substances structures,cell membrane permeability and related functions of the injured bacteria were observed by means of several technologies such as Raman spectroscopic,transmission electron microscopy,and so on.The change of cell membrane permeability of injured bacteria can be demonstrated by the decrease of cytoplasmic material,the analyses of Raman spectral features and the increase of β-galactosidase.Moreover,activities of antioxidant enzyme system of UV-injured bacteria were increasing.Water samples containing ozone-injured Escherichia coli have been assayed by the multiple-tube fermentation(MTF)technique,the membrane filter(MF)technique,enzyme substrate test(EST).MTF methods performed excellently to detect ozone-injured E.coli,detecting 100% of them at most,the EST method detected 4.76% ozone-injured E.coli at most and the MF method even detected 0% ozone-injured E.coli.The disinfection process leaded to an increase of frequency of transformation by 1-2 orders of magnitude than the control group.Concentrations of recipient bacteria,ammonia nitrogen,CODMn and metal ions,mating time,temperature,pH of water environment have positive or negative impact on the frequency of transformation,but the frequency of transformation of injured bacteria on that condition is all higher than that of the control group.The study mentioned above has fully demonstrated that UV disinfection enhanced the release of ARGs and presence of injured bacteria of competence in a large number,leading to the increase of frequency of transformation.