Screening Of Phages In Sewage Treament System And The Experimental Study On Prevention And Control Of Salmonella Typhimurium

Salmonella Typhimurium as a kind of widespread pathogenic bacteria that infects both domestic animals and human has become a danger to human health and one of the major problems that affect environmental and public health.Sewage,aquaculture wastewater and medical wastewater are the primary reservoirs of Salmonella Typhimurium.Using appropriate method to prevent and control Salmonella Typhimurium in sewage,accordingly eliminating these pathogens at source to reduce the risk of human and livestock,has important practical significance for protecting human health,reducing economic loss and maintaining social stability.As the population increased dramatically and the accelerating of urbanization construction,water resource is more and more poor day by day.Urban sewage reuse is an effective means to solve the shortage of water resources.However,there are lots of problems in the process of wastewater recycling,especially the pathogenic microorganisms will lead to huge risks for the use of reclaimed water.At present,the majority of sewage plants use the method of chlorine disinfection to prevent pathogenic bacterium.However,chlorine disinfection will produce secondary pollutants that have toxic side effects on humans and animals.So there is still a public health risk in reclaimed water which issterilized by chlorine disinfection and discharged into the environment.As a result,making the green,safe,and pollution-free bacteriophage into bactericidal agent used for preventing pathogens has obvious advantages compared to chlorine disinfection,and a favorable application prospect in the field of wastewater treatment.This study investigated the number of distribution of phages with Salmonella Typhimurium as host in a sewage treatment plant(A~2O process)in Taiyuan.The phage Pst87170 and Pst65110 are screened in this sewage treatment plant and their biological characteristics and cracking capability are investigated.Then build the hybrid phage preparations used for the water prevention and control of salmonella typhimurium,and its prevention effect was studied.The main results are as follows:(1)In the sewage treatment system(A~2O process),the number of Salmonella Typhimurium phages in raw sewage and grit chamber is higher than that in anaerobic tank,anoxic tank,aerobic tank and secondary settling tank.Also,the number of phage distribution has obvious seasonal variation that the content of phages in summer is significantly higher than that in winter.(2)The phage Pst87170 belonging to Siphoviridae had a regular icosohedron cubic symmetry head with 87 nm in diameter and a long tail(about 170 nm in length and about 9 nm in width).The phage belongs to temperate phages with double-stranded DNA.The optimal MOI(multiplicity of infection)was 0.1.One-step growth kinetics of the phage Pst87170 showed that the latent period and the burst period were about 100 and 130 min,respectively,and the average burst size was about 103 phage particles per infected cell.The phage has strong adsorption ability,superior thermal stability and tolerance of pH.(3)The phage Pst65110 belonging to Siphoviridae had a regular icosohedron cubic symmetry head with 65 nm in diameter,a short neck with 6nm in length,a tail sheath(about 38 nm in length and about 21 nm in width),and a tail fiber(about 65 nm in length and about 5 nm in width).The phage belongs to temperate phages with double-stranded DNA.The optimal MOI(multiplicity of infection)was 0.01.One-step growth kinetics of the phage Pst65110 showed that the latent period and the burst period were about 80 and70 min,respectively,and the average burst size was about 194 phage particles per infected cell.The phage has strong adsorption ability,superior thermal stability and tolerance of p H.(4)On the condition of high concentration of host bacterium and abundant nutrition,single phage and hybrid phage can effectively inhibit the proliferation of the host bacterium and accordingly reach a good effect of prevention.But using single phage for processing,insensitive bacteria appear fastly,while the hybrid phage can effectively reduce the probability of insensitive bacteria appear.(5)The prevention and control of Salmonella Typhimurium test showed that under the condition of 25 degrees the initial concentration of 105 cfu/mL of pathogenic bacteria in secondary effluent have fallen to below 100 cfu/mL after 8 hours when it was processed by hybrid phage(Pst87170 and Pst65110).Compared to single phage,using hybrid phage can limit the number of bacteria in lower level and keep for a long time,proved that the phage Pst87170 and Pst65110 equal proportional mixture can prevent Salmonella Typhimurium in sewage effectively.Phage Pst87170 and Pst65110 had the potential to be developed into phage mixtures applying to removal of corresponding pathogens in wastewater treatment system.