The microbial quality of urban recreational water is of great concern to public health.The monitoring of indicator organisms and several pathogens alone is not sufficient to accurately and comprehensively identify microbial risks.To assess the levels of bacterial pathogens and health risks in urban recreational water,we analyzed pathogen diversity and quantified four pathogens in 46 water samples collected from waterbodies in Beijing Olympic Forest Park in one year.The pathogen diversity revealed by 16 S r RNA gene targeted next-generation sequencing（NGS） showed that 16 of 40 genera and 13 of 76 reference species were present.The most abundant species were Acinetobacter johnsonii,Mycobacterium avium and Aeromonas spp.Quantitative polymerase chain reaction（q PCR） of Escherichia coli（uid A）,Aeromonas（aer A）,M.avium（16S r RNA）,Pseudomonas aeruginosa（oaa） and Salmonella（inv A） showed that the aer A genes were the most abundant,occurring in all samples with concentrations of 10^（4–6） genome copies/100 m L,followed by oaa,inv A and M.avium.In total,34.8% of the samples harbored all genes,indicating the prevalence of these pathogens in this recreational waterbody.Based on the q PCR results,a quantitative microbial risk assessment（QMRA） showed that the annual infection risks of Salmonella,M.avium and P.aeruginosa in five activities were mostly greater than the U.S.EPA risk limit for recreational contacts,and children playing with water may be exposed to the greatest infection risk.Our findings provide a comprehensive understanding of bacterial pathogen diversity and pathogen abundance in urban recreational water by applying both NGS and q PCR.
Qijia CuiTingting FangYong HuangPeiyan DongHui Wang
Antibiotic resistance is a serious public health risk that may spread via potable and reclaimed water. Effective disinfection is important for inactivation of antibiotic-resistant bacteria and disruption of antibiotic resistance genes. Ampicillin is a widely prescribed antibiotic but its effectiveness is increasingly undermined by resistance. In this study, changes in ampicillin resistance for Escherichia coli （E. coli） CGMCC 1.1595 were analyzed after exposure to different doses of ultraviolet （UV） or chlorine, and damage incurred by the plasmid encoding ampicillin resistance gene blaTEM-1 was assessed. We reported a greater stability in ampicillinresistant E. coli CGMCC 1.1595 after UV irradiation or chlorination when compared with previously published data for other E. coli strains. UV irradiation and chlorination led to a shift in the mortality frequency distributions of ampicillin-resistant E. coli when subse-quently exposed to ampicillin. The ampicillin hemiinhibitory concentration （IC5o） without disinfection was 3800mg·L^-1, and an increment was observed after UV irradiation or chlorination. The IC50 of ampicillin-resistant E. coli was 1.5-fold higher at a UV dose of 40 mJ·cm^-2, and was 1.4-fold higher when exposed to 2.0 mg·L^-1 chlorine. These results indicate that UV irradiation and chlorination can potentially increase the risk of selection for E. coli strains with high ampicillin resistance. There was no evident damage to blaTEM-1 after 1-10 mg Cl2· L^-1 chlorination, while a UV dose of 80 mJ·cm^-2 yielded a damage ratio for blaTEM-1 of approximately 1.2-log.Therefore, high UV doses are required for effective disruption of antibiotic resistance genes in bacteria.
Tetracycline-resistant bacteria（TRB） are of concern as emerging microbial contaminants in reclaimed water.To understand the effects of UV disinfection on TRB,both inactivation and reactivation profiles of TRB,as well as 16 tetracycline-resistant isolates from secondary effluent,were characterized in this study.The inactivation ratio of TRB was significantly lower（3.0-log） than that of heterotrophic bacteria（〉4.0-log） in the secondary effluent.Additionally,the proportion of TRB significantly increased from 1.65%to 15.51%under20 mJ/cm^2 ultraviolet（UV） exposure.The inactivation rates of tetracycline-resistant isolates ranged from 0.57/s to 1.04/s,of which tetracycline-resistant Enterobacter-1 was the most tolerant to UV light.The reactivation of TRB,tetracycline-resistant isolated strains,as well as heterotrophic bacteria commonly occurred in the secondary effluent even after20 mJ/cm^2 UV exposure.The colony forming ability of TRB and heterotrophic bacteria reached 3.2-log and 3.0-log under 20 mJ/cm^2 UV exposure after 22 hr incubation.The final inactivation ratio of tetracycline-resistant Enterobacter-1 was 1.18-log under 20 mJ/cm^2 UV exposure after 22 hr incubation,which is similar to those of TRB（1.18-log） and heterotrophic bacteria（1.19-log）.The increased proportion of TRB and the reactivation of tetracycline-resistant enterobacteria in reclaimed water could induce a microbial health risk during wastewater reuse.
Jing-Jing HuangJinying XiHong-Ying HuYi LiSun-Qin LuFang TangYu-Chen Pang
