Study On The Effect Of Sewage Disinfection On Reactivation And Antibiotic Resistance Of Enterobacteria

A large number of microorganisms included drug-resistant bacteria exist in the secondary effluent of the wastewater treatment plants.Disinfection process could reduce the number of the pathogens and drug-resistant bacteria in the effluent,and play an important role in protecting the human health and promoting the wastewater reclamation and reuse.UV disnfection and chlorination are the common wastewater disinfection techniques,but the issues about bacterial reactivation and increased antibiotic resistance are outstanding after disinfection.This study chose Escherichia coli and Salmonella as the typical Enterobacteria,and in-depth studied the effect of sewage disinfection on the reactivation and antibiotic resistance of drug-resistant Enterobacteria using the microbial culture and drug susceptibility analysis.The aim of our research was to provide the scientific evidence for sewage treatment and safe reuse.Multidrug-resistant Escherichia coli SER8 and SER2 isolated from municipal wastewater treatment plant was chosen as the test strains to study the ultraviolet disinfection and reactivation.The effect of different doses of ultraviolet radiation on the reactivation rate and reactivation speeds of Escherichia coli SER8 was investigated.And the differences in different reactivation ways and different condition of water quality were analyzed.Results showed that the photoreactivation rates of Escherichia coli SER8 decreased with the increase of ultraviolet radiation doses,when the UV doses ranged from 10 m J/cm2 to 40 m J/cm2.During exposing to sunlight lamp for 48 h after ultraviolet disinfection,the photoreactivation rate of Escherichia coli SER8 in the secondary effluent was similar to that in the phosphate buffer,but there are some differences at 48~72h.At the same time,the reactivation way and water quality has a significant effect on the reactivation rates of Escherichia coli SER8.The change of antibiotic resistance pattern to tetracycline(TET),ampicillin(AMP),norfloxacin(NOR),streptomycin(STP),gentamicin(GEN),cefotaxime(CTX),sulfamethoxazole(SMZ),ciprofloxacin(CIP)and chloramphenicol(CHL)antibiotics of Escherichia coli SER8 after UV disinfection and photoreactivation was analyzed using the Kirby-Bauer disk diffusion method.The results showed that there was no change in the antibiotic resistance phenotypes to 9 antibiotics in Escherichia coli SER8 during exposing to sunlight lamp for 48 h after 20 m J/cm2 UV dose.The drug-resistance Escherichia coli SER2 isolates was chosen as the donor strains,the Escherichia coli NK5449 was chosen as receptor strains,and the conjugation experiments were carried out.The results showed that UV disinfection could affect the ability of the transfer of plasmid between Escherichia coli SER2 and NK5449 strains.The frequencies of conjugative transfer decreased with the increased ultraviolet radiation dose.The Salmonella J1 isolated from the municipal wastewater treatment plant was chosen as the test strains to study the chlorination experiment.The inactivation rates of Salmonella after chlorination were investigated.In addition,the effect of different chlorine concentration and contact time on antibiotic resistance of the drug-resistant Salmonella was analyzed.The results showed that chlorination had an effect on antibiotic resistance of Salmonella J1.When chlorine concentrations were 0.5mg/L and 2.0mg/L,the resistance phenotype of salmonella J1 to CHL and STP are changed from susceptible to intermediary after chlorination.The increase of the CT value resulted in the decrease of the sensitivity of Salmonella J1.