The Study Of Multidrug Resistant Bacteria And Resistance Genes In Urban Sewage Treatment Systems

Urban sewage treatment system is an important repository of multidrug-resistant bacteria and resistance genes,and it is also an important medium for the multidrug-resistant bacteria（MARB）and resistance genes（ARG）.With the increasing antibiotic contaminants in recent years,a great number of multidrug-resistant bacteria and antibiotic resistance genes were detected in water environments.However,the research on multidrug-resistant bacteria and resistance genes in urban sewage treatment systems is still relatively deficiency.In this study,the abundance and diversity of MARB and ARGs were researched by the examples of three urban sewage treatment systems belonging to different treatment processes and including the influents,secondary effluents and excessive sludge.The main results are as following.1.Abundance of cultivatable multidrug-resistant bacteria in urban sewage treatment systems.Detection of MARB for the three sewage treatment systems indicated that the total number of bacteria in urban sewage treatment plant was generally at the magnitude orders of 10^9-10 L^-1.The abundance of MARB resistant to 3,5,and 8 types of antibiotics was at the magnitude orders of 10^7-8 L^-1,10^6-7 L^-1 and 10^5-6 L^-1,respectively;These data were reduced to10⁷ L^-1,10⁵ L^-1,10^4-5 L^-1 and 10^3-4 L^-1 magnitude orders respectively of total bacteria,MARB resistant to 3,5 and 8 types of antibiotics in the effluents from the secondary settling tank samples.However,in excessive sludge samples,the level of total bacteria,MARB resistant to 3,5 and 8 types antibiotics reached 10^8-9 g-1,10⁷ g-1,10⁶ g-1and 10⁶ g-1 sludge,respectively.It means that after treatment,the abundance of multidrug-resistant bacteria is largely reduced,however,there is still a large number of resistant bacteria in the effluents and excessive sludge.2.Diversity of MARB resistant to 3 types of antibiotics in urban sewage treatment systems.All the resistant bacteria to 3 antibiotics were harvested and their genomic DNA were extracted for 16 S V4 high-throughput sequencing.The results showed that MARBs were clustered into Escherichia sp.,Acinetobacter sp.and Citrobacter sp.,with the highest relative abundance of Escherichia sp.of 33.59%-77.19% followed by Acinetobacter sp.of 4.22%⁵3.70%,and Citrobacter sp of 2.82%⁸.67%.3.Isolation and identification of eight resistant bacteria in excessive sludge.Total 23 isolates resistant to 8 types of antibiotics were isolated and identified.They were clustered into Escherichia coli,Acinetobacter johnsonii,and Aeromonas hydrophila sp.The existence of multiple antibiotics resistant bacteria in the excessive sludge suggested a potential risk to human health due to most of sludge improperly treated.4.Detection of antibiotic resistance genes in urban sewage treatment systems.178 types of ARGs were detected by using high-throughput fluorescence quantitative PCR detection in the influents,effluents and excessive sludge in the three sewage treatment plants,MTG,LTW,WLK.The results indicated that total 146,141,150 types of ARGs were positively detected from MTG,LTW and WLK with a certain degree of reduction in abundance.The reduction ability is found to be related to different treatment processes used with better effects of AAO process than AO or oxidation ditch process.