Reduction of erythromycin resistance gene erm(F) and class 1 integron-integrase genes in wastewater by Bardenpho treatment

Viral community in landfill leachate: Occurrence, bacterial hosts, mediation antibiotic resistance gene dissemination, and function in municipal solid waste decomposition

A municipal solid waste (MSW) landfill is a significant source of antibiotic resistance, pathogens and viruses and also a habitat for microbial consortia that perform MSW decomposition. Viruses are of great significance in ecological interactions such as MSW decomposition and antibiotic resistance gene (ARG) transmission. In this study, the viral community structure and the associated driver, the linkage of viruses and their bacterial hosts, the virus-associated ARG dissemination and virtual community function on MSW decomposition were investigated in landfill leachate from seven cities, China. The seven cities include four megacities, two large-scale cities and one small-scale city, representing the leachate characters of China. The results showed that the leachates were dominated by the phage families Siphoviridae, Myoviridae and Podoviridae (91.7 ± 3.6) %. Their putative hosts were the important MSW decomposers Lactobacillus, Pseudomonas, Clostridium, Proteiniphilum, and Bacteroides. The structure of the viral community was significantly affected by pH (P = 0.007, analyzed by RDA) and the bacterial community (R = 0.83, P < 0.001, analyzed by Mantel test). The relative abundance of ARGs showed a strong correlation (R > 0.8, P < 0.01) with viral family, suggesting that viruses play an important role in ARGs dissemination. Phage regulate bacterial population abundance through top-down effects, thus participating in MSW decomposition. These results demonstrate that viral community are involve in ARGs transmission and dissemination and mediate MSW decomposition in landfill.

The responses of marine anammox bacteria-based microbiome to multi-antibiotic stress in mariculture wastewater treatment

Saline mariculture wastewater containing multi-antibiotics poses a challenge to anaerobic ammonia oxidation (anammox) process. Herein, the halophilic marine anammox bacteria (MAB)-based microbiome was used for treating mariculture wastewater (35‰ salinity) under multi-antibiotics (enrofloxacin + oxytetracycline + sulfamethoxazole, EOS) stress. And the main focus of this study lies in the response of MAB-based microbiome against multi-antibiotics stress. It is found that MAB-based microbiome shows stable community structure and contributes high nitrogen removal efficiency (>90%) even under high stress of EOS (up to 4 mg·L^-1). The relative abundance of main functional genus Candidatus Scalindua, responsible for anammox, had little change while controlling the influent EOS concentration within 4 mg·L^-1, whereas, significantly decreased to 2.23% at EOS concentration of as high as 24 mg·L^-1. As an alternative, antibiotic resistance bacteria (ARB) species Rheinheimera dominated the microbial community of MAB-based biological reactor under extremely high EOS stress (e.g. 24 mg·L^-1 in influent). The response mechanism of MAB-based microbiome consists of extracellular and intracellular defenses with dependence of EOS concentration. For example, while EOS within 4 mg·L^-1 in this study, most of the antibiotics were retained by extracellular polymeric substances (EPS) via adsorption; If increasing the EOS concentration to 8 and even 24 mg·L^-1, part of antibiotics could intrude into the cells and cause the intracellular accumulation of antibiotic resistance genes (ARGs) (total abundance up to 2.44 × 10^-1 copies/16S rRNA) for EOS response. These new understandings will facilitate the practical implementation of MAB-based bioprocess for saline nitrogen- and antibiotics-laden wastewater treatment.

Occurrence of antibiotics and antibiotic resistance genes in WWTP effluent-receiving water bodies and reclaimed wastewater treatment plants

There is a growing concern on the fate and the consequent ecological or health risks of antibiotics and antibiotic resistance genes (ARGs) in natural or artificial water environment. The effluent of wastewater treatment plants (WWTPs) has been reported to be an important source of antibiotics and ARGs in the environment. WWTP effluent could be discharged into surface water bodies or recycled, either of which could lead to different exposure risks. The impact of WWTP effluents on the levels of antibiotics and ARGs in effluent-receiving water bodies and the removal efficiency of antibiotics and ARGs in reclaimed wastewater treatment plants (RWTPs) were seldom simultaneously investigated. Thus, in this study, we investigated the occurrence of antibiotics and ARGs in four WWTP effluents, and their downstream effluent-receiving water bodies and RWTPs in seasons of low-water-level. The total concentrations of ofloxacin, norfloxacin, ciprofloxacin, roxithromycin, azithromycin, erythromycin, tetracycline, oxytetracycline, chlortetracycline, and sulfamethoxazole in the secondary effluents were 1441.6-4917.6 ng L^-1. Ofloxacin had the highest concentration. The absolute and relative abundances of total ARGs (qnrD, qnrS, ermA, ermB, tetA, tetQ, sul1, and sul2) in the secondary effluents were 10³-10⁴ copies mL^-1 and 10^-4-10^-2 ARG/16S rRNA. Sul1 and sul2 were the major species with the highest detection frequencies and levels. In most cases, WWTP effluents were not the major contributors to the levels and species of antibiotics and ARGs in the surface water bodies. Four RWTPs removed 43.5-98.9% of antibiotics and - 0.19-2.91 log of ARGs. Antibiotics and ARGs increased in chlorination, ozonation and filtration units. Antibiotics had significantly positive correlations with ARGs, biological oxygen demands, total phosphorus, total nitrogen, and ammonia nitrogen in the four effluent-receiving water bodies. In RWTPs, the total concentrations of antibiotics showed a significant positive correlation with the total abundance of ARGs.

Antibiotic Resistance and Sewage-Associated Marker Genes in Untreated Sewage and a River Characterized During Baseflow and Stormflow

Since sewage is a hotspot for antibiotic resistance genes (ARGs), the identification of ARGs in environmental waters impacted by sewage, and their correlation to fecal indicators, is necessary to implement management strategies. In this study, sewage treatment plant (STP) influent samples were collected and analyzed using quantitative polymerase chain reaction (qPCR) to investigate the abundance and correlations between sewage-associated markers (i.e., Bacteroides HF183, Lachnospiraceae Lachno3, crAssphage) and ARGs indicating resistance to nine antibiotics (belonging to aminoglycosides, beta-lactams, sulfonamides, macrolides, and tetracyclines). All ARGs, except bla_VIM, and sewage-associated marker genes were always detected in untreated sewage, and ermF and sul1 were detected in the greatest abundances. intl1 was also highly abundant in untreated sewage samples. Significant correlations were identified between sewage-associated marker genes, ARGs and the intl1 in untreated sewage (τ = 0.488, p = 0.0125). Of the three sewage-associated marker genes, the BIO-ENV procedure identified that HF183 alone best maximized correlations to ARGs and intl1 (τ = 0.590). Additionally, grab samples were collected from peri-urban and urban sites along the Brisbane River system during base and stormflow conditions, and analyzed for Escherichia coli, ARGs, the intl1, and sewage-associated marker genes using quantitative polymerase chain reaction (qPCR). Significant correlations were identified between E. coli, ARGs, and intl1 (τ = 0.0893, p = 0.0032), as well as with sewage-associated marker genes in water samples from the Brisbane River system (τ = 0.3229, p = 0.0001). Of the sewage-associated marker genes and E. coli, the BIO-ENV procedure identified that crAssphage alone maximized correlations with ARGs and intl1 in river samples (τ = 0.4148). Significant differences in E. coli, ARGs, intl1, and sewage-associated marker genes, and by flow condition (i.e., base vs. storm), and site types (peri-urban vs. urban) combined were identified (R = 0.3668, p = 0.0001), where percent dissimilarities between the multi-factorial groups ranged between 20.8 and 11.2%. Results from this study suggest increased levels of certain ARGs and sewage-associated marker genes in stormflow river water samples compared to base flow conditions. E. coli, HF183 and crAssphage may serve as potential indicators of sewage-derived ARGs under stormflow conditions, and this merits further investigation. Data presented in this study will be valuable to water quality managers to understand the links between sewage pollution and ARGs in urban environments.

Removal of Antibiotic Resistance Genes at Two Conventional Wastewater Treatment Plants of Louisiana, USA

Wastewater treatment plants (WWTPs) represent all known types of antibiotic resistance mechanisms and are considered as the critical points for the spread of antibiotic resistance genes (ARGs). The purpose of this study is to investigate the removal of a Class 1 integrase gene (intI1) and a selected set of ARGs (blaTEM, ermF, mecA, and tetA) at two conventional WWTPs by using chlorination in Louisiana, USA. We collected 69 wastewater samples (23 each from influent, secondary effluent, and final effluent) and determined the concentrations of ARGs by using quantitative polymerase chain reaction. All tested ARGs, except for mecA, were detected in 83–96% and 30–65% of influent and final effluent samples, respectively. Although the ARGs underwent approximately 3-log10 reduction, two WWTPs on an average still released 3.3 ± 1.7 log10 copies/mL of total ARGs studied in the effluents. Chlorination was found to be critical in the significant reduction of total ARGs (p < 0.05). Correlation analysis and the ability of intI1 to persist through the treatment processes recommend the use of intI1 as a marker of ARGs in effluents to monitor the spread of antibiotic resistance in effluents. Our study suggests that conventional WWTPs using chlorination do not favor the proliferation of antibiotic resistance bacteria and ARGs during wastewater treatment.