Removal effect of antibiotic resistance genes in w

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Effect of disinfection process on the removal of antibiotic resistance genes in water

antibiotics and their residues will cause antibiotic resistance gene pollution. Antibiotic resistance genes are regarded as a new type of environmental pollutants and have received extensive attention in the field of environmental research. Their distribution and transmission mechanism have become the focus of current research. By summarizing the distribution of antibiotic resistant bacteria and resistance genes in the water environment and the removal effect of disinfection process on antibiotic 9. Strong rotation and hard wrench should be avoided during use. It is considered that chlorine disinfection is more economical and feasible than other disinfection methods in removing antibiotic resistance genes, and disinfection treatment can affect the conjugation and transfer rate of resistance genes, thus inhibiting the horizontal transfer of resistance genes, And may further affect the transmission and diffusion of antibiotic resistance genes

antibiotic resistance genes (args) are genes that can produce resistance to antibiotics. They are microorganisms, including pathogenic thermoplastic composites, which simplify the subsequent recycling of parts. Microorganisms, the material basis for the formation and diffusion of drug resistance, are a new class of environmental pollutants. It can spread among microorganisms, including pathogenic microorganisms, and from bacteria, human dispersal sources and animal sources to the natural environment and drinking water system. Even args can enter the human body through movable genetic elements such as plasmids carrying resistance genes, resulting in the decline of antibiotic efficacy, and the treatment of bacterial infection is more difficult. It is reported that 500000 people are affected by anti TB bacteria in the world every year, about 25000 people in the European Union die of infection with multi resistant bacteria every year, and about 63000 people in the United States die of hospital-acquired bacterial infection every year. At present, almost all antibiotics used in clinic have their resistant bacteria (ARB), and even "superbacteria", such as "New Delhi metallo-1" (NDM-1). Therefore, args is likely to cause a public health crisis

args in the environment are mainly caused by the long-term abuse or misuse of antibiotics in medical and animal husbandry, which makes environmental media such as water, soil, activated sludge become the source and sink of ARB or args. At present, a large number of reports have detected args in the water environment, soil, sediment, and even in the air. These args can persist in the environment, and after the death of microorganisms carrying args, the exposed DNA molecules released into the environment can finally be transferred into other microorganisms through genetic recombination to make them resistant, which poses a potential threat to human and animal safety. In particular, the water environment has become an important medium for the dissemination of args and one of the important repositories of args. This paper expounds the distribution of args in the water environment, summarizes the removal effect of disinfection on args in the current water treatment process, and discusses the influence mechanism of disinfection on its transmission and diffusion

1 distribution and diffusion of args in the water environment

args and ARB have been proved to be widespread in surface water, municipal sewage, sewage treatment plant effluent and drinking water, and there are many kinds of args. So far, hundreds of args have been detected in various water bodies. For example, macrolides (such as apha1, apha2, aada1), sulfonamides (such as dfra12, dfra17, Suli) and β U as many as 50 args (Table 1) include lactams (such as blatem-1, blaoxa-1, blapse-1), tetracyclines (such as TetA, Teth, tetj, tety, tetz), penicillins (such as MECA, Pena) and macrolides (such as Erma, MPHA). It is generally believed that these args in the water environment directly enter the surface water body mainly through medical and aquaculture wastewater, and can also be fertilized by feces to make them enter the soil environment first, and then penetrate into the groundwater with surface runoff such as rainwater. Therefore, args are widely distributed in the water environment, especially in sewage treatment plants. Because the wastewater containing antibiotics and ARB is directly discharged into it, a large number of args are enriched, which has become an important medium for args to gather and spread. For example, 98.4% of the strains isolated from sewage plants such as Su are resistant to the tested antibiotics, and 90.6% of the strains are resistant to at least three antibiotics. The existence of these ARBs and args in the water environment will not only threaten the safety of drinking water, but also affect the recycling of water resources. The study found that high levels of antibiotic resistance were detected in the soil irrigated with fresh water and treated wastewater. It can be seen that args are widespread in the water environment and may have an impact on human health and environmental ecology

args spread mainly through vertical gene transfer (VGT) and horizontal gene transfer (HGT). Vertical gene transfer depends on the division and reproduction between the parents of microorganisms; Horizontal gene transfer is a process in which args are transferred through the processes of conjugation, transformation, transduction, transposition and bacterial lysogenic gene transfer, so that another strain can acquire resistance. It is an important way of args transfer and diffusion in the water environment. As early as the 1940s, microbial horizontal gene transfer was described, and it was proposed that the occurrence of HGT was a common phenomenon caused by selective pressure and biological evolution. For example, studies have found that plasmids carrying tetracycline resistance genes are transferred between Escherichia coli and Aeromonas spp. in addition, resistance gene transfer between vancomycin resistant Enterococcus (VRE) and methicillin resistant Staphylococcus aureus (MRSA) has also been observed. Among them, HGT plays an important role in the spread of args through water-borne microorganisms. It is because of the existence of horizontal gene transfer that args can not only be transmitted from parents to offspring in the water environment, but also be transmitted between microorganisms of the same genus or different species. Horizontal gene transfer has even been observed in bacterial, fungal, viral and eukaryotic genomes. Therefore, the existence of args in the water environment and its transfer and diffusion through water-borne microorganisms bring hidden dangers to human health and water biosafety

args, as a new type of environmental pollutants, can be spread through water-borne microorganisms in the water environment. It is found that args carried by water-borne microorganisms in the process of water treatment will not only increase the concentration of args in the water body, but also enter the source water and water supply system. Zhang et al. Have widely detected ARB and args in drinking water systems, and it has also been reported that args of 9 species or genera have been detected in large water supply plants with high abundance. The surface water participating in the urban water cycle is one of the important carriers for the spread of pathogenic microorganisms and args. Therefore, how to effectively remove and control args in the water environment needs special attention. Disinfection is an important way to kill pathogenic microorganisms harmful to human health in water, which can prevent the transmission of diseases through drinking water. It is also the final guarantee for the safety and sanitation of drinking water with the same resolution throughout the whole process. In particular, chlorine disinfection is widely used in the disinfection of wastewater and drinking water because of its economic and efficient characteristics

2 effect of disinfection on args and/or ARB abundance

disinfection can usually reduce the total amount of bacteria in the effluent, thus playing a certain role in the reduction of args. However, the removal effect of args will also be affected by disinfection methods. At present, the disinfection methods used at home and abroad include chemical disinfection (such as halogen disinfectant, ozone and peracetic acid), physical disinfection (such as membrane filtration to intercept microorganisms), photochemical disinfection (such as ultraviolet) and electrochemical disinfection. Widely used are mainly chlorine disinfection, chlorine dioxide disinfection, ozone sterilization, ultraviolet irradiation and oxidation disinfection. Although these disinfection methods can generally remove some ARBs or args in the process of water treatment, their detection rate in the effluent of sewage treatment plants is still high, and the relative total amount and species change little in the effluent (Table 2), and even the relative abundance of args increases. For example, oxidation and UV disinfection have little effect on the removal of args. The removal rate of a few args can reach 1-2 orders of magnitude, but chlorine disinfection can reach 2-3 orders of magnitude, while digestion, constructed wetlands and other non disinfection treatments can remove args by up to 1 order of magnitude

because the removal rate of args is not only affected by disinfection methods, but also by many factors such as the type of bacterial resistance, disinfection dose and the combination of various disinfection methods, it is difficult to significantly reduce or completely remove args pollution. For example, Xu et al. Used high-throughput quantitative PCR to detect the effluent of water supply plants with different water treatment processes, and found that the relative abundance of args in the disinfected effluent of the two water treatment plants was increased. Because there is basically no process specially designed for the removal of args in the treatment process of general water supply plants or sewage plants, and the content of args in the water body may also be affected by factors such as makeup, water volume, seasonal changes, use and flow area, the removal effect of args by physical, chemical and biological methods is not obvious. At present, there are few data on the control effect of disinfection process on ARB and args, so it is difficult to put forward more effective methods and ways to curb the spread of args

Table 2 removal effect of ARB and args by different treatment methods

3 influence mechanism of disinfection on args horizontal transfer

disinfection can affect args horizontal transfer by affecting the bonding efficiency of bacteria. For example, Guo et al. Found that low UV dose (up to 8 mj/cm2) can have an impact on the frequency of conjugation transfer, but the impact is very small, while low chlorine disinfection dose (up to 40 mg Cl min/l) can significantly increase the frequency of conjugation transfer by 2 to 5 times. At the same time, they found that the frequency of args transfer under high dose of UV (10 mj/cm2) or chlorine disinfection (80 mg Cl min/l) is relatively reduced. Lin et al. Also studied the transfer rate of args by UV and chlorine treatment, and found that the size of UV and low-level chlorine disinfection place has a direct impact on the deviation of the final result, which can reduce the bonding efficiency. It shows that when the UV dose (5-20 mj/cm2) gradually increases, the transfer rate gradually decreases, while when the chlorine disinfection treatment, the transfer rate does not change (the chlorine dose is 0.05-0.2 mg/l) or the transfer rate is low or even lower than the detection limit (the chlorine dose is 0.3-0.5 mg/L). It can be seen that low UV and chlorine doses have little effect on the horizontal transfer of args. When the UV dose is 10-20 mj/cm2, the transfer rate of args can be gradually reduced with the increase of dose

the specific mechanisms of the effect of disinfection on the horizontal metastasis of args are as follows: first, by reducing the survival rate of donor bacteria, thereby reducing the rate of conjugation metastasis; The second is to change the permeability of cells. It is found that chloramine produced by chlorine disinfection can stimulate bacteria to change cell permeability, make more pili appear on the surface of conjugated cells, improve the conjugation and transfer rate of args, and promote the horizontal gene transfer of args; The third is to inhibit the expression of related transfer genes. For example, at a lower residual chlorine (0.05-0.2 mg/l), it may inhibit the expression of flagella gene (flgc), an outer membrane protein gene (OmpF) and a DNA transport related gene (tag), thereby reducing the level of gene transfer rate; Fourth, by gathering different plasmids, insertion sequences and integrons, we can improve the incidence of args horizontal gene transfer

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