Partitioning of Antibiotic Resistance Genes and Fecal Indicators Varies Intra and Inter-Storm during Combined Sewer Overflows

Abstract

Combined sewer overflows (CSOs) degrade water quality through the release of microbial contaminants in CSO effluent. Improved understanding of the partitioning of microbial contaminants onto settleable particles can provide insight into their fate in end-of-pipe treatment systems or following release during CSO events. Sampling was performed across the hydrograph for three storm events as well as during baseflow and wet weather in three surface waters impacted by CSO. qPCR was performed for select antibiotic resistance genes (ARG) and a marker gene for human fecal indicator organisms (BacHum) in samples processed the partitioning of microbial contaminants on settleable particles versus suspended in the aqueous phase. Amplicon sequencing was performed on both fractions of storm samples to further define the timing and partitioning of microbial contaminants released during CSO events. Samples collected at the CSO outfall exhibited microbial community signatures of wastewater at select time points early or late in the storm events. CSOs were found to be a source of ARG. In surrounding surface waters, sul1 was higher in samples from select locations during wet weather compared to baseflow. Otherwise, ARG concentrations were variable with no differences between baseflow and wet weather conditions. The majority of ARG at the CSO outfall were observed on the attached fraction of samples: 64–79% of sul1 and 59–88% of tet(G). However, the timing of peak ARG and human fecal indicator marker gene BacHum did not necessarily coincide with observation of the microbial signature of wastewater in CSO effluent. Therefore, unit processes that remove settleable particles (e.g., hydrodynamic separators) operated throughout a CSO event would achieve up to (0.5–0.9)-log removal of ARG and fecal indicators by removing the attached fraction of measured genes. Secondary treatment would be required if greater removal of these targets is needed.

Viability-based quantification of antibiotic resistance genes and human fecal markers in wastewater effluent and receiving waters

“…Viability qPCR methods have been used to target pathogens and fecal indicators with positive correlations observed between vPCR and cultivation methods (Li et al, 2014;Varma et al, 2009). Thus, the utility of this fecal marker gene as an indicator gene for ARGs is not clear, consistent with our previous observations during combined sewer overflows (Eramo et al, 2017a). The BacHum marker was also observed infrequently in the water column downstream from WWTPs.…”

Metabolically Active Prokaryotes and Actively Transcribed Antibiotic Resistance Genes in Sewer Systems: Implications for Public Health and Microbially Induced Corrosion

“…This suggests that abundance of an ARG at the metagenomic level (total DNA) does not necessary correlate with abundance of the actively transcribed gene (mRNA). The low abundance of transcribed ARGs may also suggest that even though genomic studies have highlighted sewer systems as hotspots of ARGs [ 2 , 4 , 5 , 7 , 9 ], the proliferation of ARGs do not scale linearly with the proliferation of antibiotic-resistant bacteria. Therefore, the use of metagenomic approaches to estimate abundance of antibiotic resistance bacteria in sewer systems will most likely result in overestimation of these cells.…”

“…Overflows that mobilize sediment in addition to wastewater would shift the active microbial hazard. Previous end-of-pipe studies of combined sewer overflow (CSO) outfalls demonstrated that attached and suspended microbes can be released at different times during storms [ 9 ]. This same research showed the presence of clinically relevant bacterial classes in CSOs including Clostridia, Bacteroidia, and Epsilonproteobacteria [ 9 ]; however, these data were obtained using DNA-based techniques.…”

“…However, most of these studies have been limited to genomic DNA-based analysis that cannot measure gene expression nor discriminate between living cells and DNA from non-living cells (unless further steps are taken such as PMA-PCR or stable isotope probing). Given the public health risk posed by sewer overflows from combined and separate sanitary systems [ 8 , 9 ], a comprehensive assessment of the metabolically active prokaryote community and the occurrence of bacteria capable of expressing antibiotic resistance is warranted. Moreover, having a quantitative measurement of ARG expression and the metabolically active microbiome may help us to understand the selection for specific mechanisms of antibiotic resistance and the loading of active human pathogens in the microbiome during sewer overflow events.…”

Linking the Effect of Antibiotics on Partial-Nitritation Biofilters: Performance, Microbial Communities and Microbial Activities

“…On the other hand, an emerging environmental and human health issue in the world today is the antibiotics resistant bacteria ( Eramo et al, 2017 ; Zhu et al, 2017 ). Infectious bacteria resistant to antibiotics increase the costs of human health and increase the mortality of humans ( Cao et al, 2016 ; Miller et al, 2016 ).…”