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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Water Quality and Contamination".

Deadline for manuscript submissions: closed (31 August 2018) | Viewed by 100855

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Dr. Karina Yew-Hoong Gin

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Guest Editor

Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, E1A 07-03, Singapore 117576, Singapore
Interests: water quality; pathogens and indicators; antimicrobial resistance; harmful algal blooms; emerging contaminants; environmental modelling; fate and transport processes
Special Issues, Collections and Topics in MDPI journals

Dr. Charmaine Ng

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Guest Editor

NUS Environmental Institute, E2S2, National University of Singapore, Singapore City, Singapore
Interests: antimicrobial resistance; microbial water quality; pathogens; microbiomes; resistomes; wastewater; urban water cycle
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent years, the emergence of antimicrobial resistance has drawn heightened global concern because of the severe ramifications on the treatment of microbial infections. In particular, the issue of antibiotic resistance arises due to the overuse and misuse of antibiotics in both developed and developing countries. Bacteria develop antibiotic resistance in the presence of residual levels of antibiotics and these antibiotic resistant bacteria in turn, are able to spread their resistance to other bacteria through mechanisms such as horizontal gene transfer, mediated by mobile genetic elements (e.g. plasmids, integrons) or co-selecting agents such as biocides and toxic metals. There is a worrying trend that pathogens are developing antibiotic resistance to a degree where last resort antibiotics are no longer effective. This, in turn, has severe implications on public health and healthcare costs.

In an effort to better understand the rising levels of antimicrobial resistance, surveillance studies have been undertaken across countries in a common effort to explore the occurrence of antimicrobial resistance in both clinical and natural environments. Implementating such initiatives through assessing the types of antibiotics used, antibiotic resistant bacteria (ARB) present and associated antibiotic resistant genes (ARG) in microbiomes enables better understanding of the impact of antibiotics in the medical, agriculture and aquaculture industries. Aquatic environments harbor diverse freshwater bacterial communities which may be subjected to anthropogenic pressures, while domestic wastewaters receive direct loads of antibiotics and pathogenic bacteria from human excretion. The nature of these environments allows them to function as hotspots for resistance through the selection of ARB and circulation of ARG through stimulation of horizontal gene transfer between members of the microbiome.

The aims of this Special Issue are to present current trends in antimicrobial/antibiotic resistance in diverse environmental waters, ranging from the detection and occurrence of antimicrobial factors (e.g. antimicrobials, antibiotics, ARB, ARG) to their fate and transformations in different environments such as surface waters, groundwaters, biofilms and water and wastewater treatment processes. Such knowledge would be needed to assist in the management and control of antimicrobial/antibiotic resistance and ultimately, the protection of public health.

Prof. Dr. Karina Yew-Hoong Gin
Guest Editor

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Keywords

Antimicrobial resistance
Antibiotic resistance
Antibiotics
Antimicrobials
Antibiotic resistant bacteria
Antibiotic resistant genes
Resistome

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Published Papers (12 papers)

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Editorial

Jump to: Research

7 pages, 183 KiB

Open AccessEditorial

Monitoring Antimicrobial Resistance Dissemination in Aquatic Systems

by Charmaine Ng and Karina Yew-Hoong Gin

Water 2019, 11(1), 71; https://doi.org/10.3390/w11010071 - 3 Jan 2019

Cited by 21 | Viewed by 6914

Abstract

This special issue on Antimicrobial Resistance in Environmental Waters features 11 articles on monitoring and surveillance of antimicrobial resistance (AMR) in natural aquatic systems (reservoirs, rivers), and effluent discharge from water treatment plants to assess the effectiveness of AMR removal and resulting loads in treated waters. The occurrence and distribution of antimicrobials, antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) was determined by utilizing a variety of techniques including liquid chromatography—mass spectrometry in tandem (LC-MS/MS), traditional culturing, antibiotic susceptibility testing (AST), molecular and OMIC approaches. Some of the key elements of AMR studies presented in this special issue highlight the underlying drivers of AMR contamination in the environment and evaluation of the hazard imposed on aquatic organisms in receiving environments through ecological risk assessments. As described in this issue, screening antimicrobial peptide (AMP) libraries for biofilm disruption and antimicrobial candidates are promising avenues for the development of new treatment options to eradicate resistance. This editorial puts into perspective the current AMR problem in the environment and potential new methods which could be applied to surveillance and monitoring efforts. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

Research

Jump to: Editorial

21 pages, 17434 KiB

Open AccessArticle

Microbial Community Composition and Antibiotic Resistance Genes within a North Carolina Urban Water System

by Kevin Lambirth, Matthew Tsilimigras, Anju Lulla, James Johnson, Abrar Al-Shaer, Orion Wynblatt, Shannon Sypolt, Cory Brouwer, Sandra Clinton, Olya Keen, Molly Redmond, Anthony Fodor and Cynthia Gibas

Water 2018, 10(11), 1539; https://doi.org/10.3390/w10111539 - 29 Oct 2018

Cited by 15 | Viewed by 6343

Abstract

Wastewater treatment plants (WWTPs) are thought to be potential incubators of antibiotic resistance. Persistence of commonly used antibiotics in wastewater may increase the potential for selection of resistance genes transferred between bacterial populations, some of which might pose a threat to human health. In this study, we measured the concentrations of ten antibiotics in wastewater plant influents and effluents, and in surface waters up- and downstream from two Charlotte area treatment facilities. We performed Illumina shotgun sequencing to assay the microbial community and resistome compositions at each site across four time points from late winter to mid-summer of 2016. Antibiotics are present throughout wastewater treatment, and elevated concentrations of multiple antibiotics are maintained in moving stream water downstream of effluent release. While some human gut and activated sludge associated taxa are detectable downstream, these seem to attenuate with distance while the core microbial community of the stream remains fairly consistent. We observe the slight suppression of functional pathways in the downstream microbial communities, including amino acid, carbohydrate, and nucleic acid metabolism, as well as nucleotide and amino acid scavenging. Nearly all antibiotic resistance genes (ARGs) and potentially pathogenic taxa are removed in the treatment process, though a few ARG markers are elevated downstream of effluent release. Taken together, these results represent baseline measurements that future studies can utilize to help to determine which factors control the movement of antibiotics and resistance genes through aquatic urban ecosystems before, during, and after wastewater treatment. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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12 pages, 1938 KiB

Open AccessArticle

Distribution and Genotyping of Aquatic Acinetobacter baumannii Strains Isolated from the Puzi River and Its Tributaries Near Areas of Livestock Farming

by Hsin-Chi Tsai, Ming-Yuan Chou, Yi-Jia Shih, Tung-Yi Huang, Pei-Yu Yang, Yi-Chou Chiu, Jung-Sheng Chen and Bing-Mu Hsu

Water 2018, 10(10), 1374; https://doi.org/10.3390/w10101374 - 1 Oct 2018

Cited by 13 | Viewed by 5159

Abstract

Acinetobacter baumannii is an important health care-associated bacterium and a common multidrug-resistant pathogen. The use of antibiotics in the husbandry industry has raised concerns about drug-resistant A. baumannii strains, which may affect humans. This study aimed to investigate the seasonal distribution of A. baumannii in aquatic environments near areas of livestock farming. The geographic distribution, antibiotic resistance characteristic, and DNA fingerprinting genotype of A. baumannii were also studied. The results showed that environmental A. baumannii was prevalent during the summer and autumn. The hotspots for A. baumannii were found at the sampling sites of livestock wastewater channels (21.4%; 3/14) and the tributaries adjacent to livestock farms (15.4%; 2/13). The prevalence of A. baumannii at these locations was significantly higher than those adjacent to the Puzi River. Multidrug-resistant strain of A. baumannii was not found in this study, with only one strain (5%; 1/20) being resistant to tetracycline. Of the isolates that were obtained, 10% (2/20) and 20% (4/20) were found to be intermediately resistant to tetracycline and sulphamethoxazole/trimethoprim, respectively. The genotyping patterns and clustering analysis indicated that enterobacterial repetitive intergenic consensus sequence polymerase chain reaction (ERIC-PCR) differentiated A. baumannii strains effectively. There were two major clusters that could then be subtyped into 20 A. baumannii strains with 15 profiles. The A. baumannii strains that were isolated from upstream of the Puzi River and livestock wastewater channels were composed of Cluster I. Cluster II only contained isolates from downstream of the Puzi River area. Furthermore, isolates from adjacent sites were shown to have identical profiles (100%). These results suggest that A. baumannii may have spread through free-flowing water in this study. Therefore, we propose that livestock wastewater is one of the sources that contribute to A. baumannii pollution in water bodies. In summary, continuous monitoring of antibiotic pollution in livestock wastewater is required. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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11 pages, 1162 KiB

Open AccessArticle

Presence of Antibiotic-Resistant Escherichia coli in Wastewater Treatment Plant Effluents Utilized as Water Reuse for Irrigation

by Asli Aslan, Zachariah Cole, Anunay Bhattacharya and Oghenekpaobor Oyibo

Water 2018, 10(6), 805; https://doi.org/10.3390/w10060805 - 18 Jun 2018

Cited by 30 | Viewed by 11729

Abstract

Providing safe water through water reuse is becoming a global necessity. One concern with water reuse is the introduction of unregulated contaminants to the environment that cannot be easily removed by conventional wastewater treatment plants (WWTP). The occurrence of ampicillin, sulfamethoxazole, ciprofloxacin, and tetracycline-resistant Escherichia coli through the treatment stages of a WWTP (raw sewage, post-secondary, post-UV and post-chlorination) was investigated from January to May 2016. The highest concentrations of antibiotic resistant E. coli in the effluent were detected in April after rainfall. Ampicillin-resistant E. coli was the most common at the post UV and chlorination stages comprising 63% of the total E. coli population. The minimum inhibitory concentration (MIC) analysis showed that one in five isolates was resistant to three or more antibiotics, and the majority of these E. coli were resistant to ampicillin, followed by sulfamethoxazole and ciprofloxacin. The highest MIC was detected at the finished water after application of multiple disinfection methods. Tetracycline resistance was the least observed among others, indicating that certain drug families may respond to wastewater treatment differently. Currently, there are no policies to enforce the monitoring of antibiotic-resistant pathogen removal in WWTP. Better guidelines are needed to better regulate reuse water and prevent health risk upon exposure to antibiotic-resistant bacteria. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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11 pages, 5680 KiB

Open AccessArticle

Antibiotic Resistance and Extended-Spectrum Beta-Lactamase Production of Escherichia coli Isolated from Irrigation Waters in Selected Urban Farms in Metro Manila, Philippines

by Pierangeli G. Vital, Enrico S. Zara, Cielo Emar M. Paraoan, Ma. Angela Z. Dimasupil, Joseth Jermaine M. Abello, Iñigo Teodoro G. Santos and Windell L. Rivera

Water 2018, 10(5), 548; https://doi.org/10.3390/w10050548 - 25 Apr 2018

Cited by 35 | Viewed by 14838

Abstract

Highly-polluted surface waters are increasingly used for irrigation in different agricultural settings because they have high nutrient content and are readily available. However, studies showed that they are reservoirs for the emergence and dissemination of antibiotic-resistant bacteria in the environment. In this study, the resistance of 212 Escherichia coli isolates from irrigation water, soil, and vegetables in selected urban farms in Metro Manila, Philippines was evaluated. Results showed that antibiotic resistance was more prevalent in water (67.3%) compared to soil (56.4%) and vegetable (61.5%) isolates. Resistance to tetracycline was the highest among water (45.6%) and vegetable (42.3%) isolates while ampicillin resistance was the highest among soil isolates (33.3%). Multidrug-resistant (MDR) isolates were also observed and they were more prevalent in water (25.3%) compared to soil (2.8%) and vegetable (8.4%) isolates. Interestingly, there are patterns of antibiotic resistance that were common to isolates from different samples. Extended-spectrum beta-lactamase production (ESBL) was also investigated and genes were observed to be present in 13 isolates. This provides circumstantial evidence that highly-polluted surface waters harbor antibiotic-resistant and MDR E. coli that may be potentially transferred to primary production environments during their application for irrigation purposes. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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24 pages, 27690 KiB

Open AccessArticle

An Increase of Abundance and Transcriptional Activity for Acinetobacter junii Post Wastewater Treatment

by Muhammad Raihan Jumat, Muhammad Fauzi Haroon, Nada Al-Jassim, Hong Cheng and Pei-Ying Hong

Water 2018, 10(4), 436; https://doi.org/10.3390/w10040436 - 6 Apr 2018

Cited by 14 | Viewed by 6544

Abstract

A membrane bioreactor (MBR)-based wastewater treatment plant (WWTP) in Saudi Arabia is assessed over a five-month period in 2015 and once in 2017 for bacterial diversity and transcriptional activity using metagenomics, metatranscriptomics and real time quantitative polymerase chain reaction (RT-qPCR). Acinetobacter spp. are shown to be enriched in the chlorinated effluent. Members of the Acinetobacter genus are the most abundant in the effluent and chlorinated effluent. At the species level, Acinetobacter junii have higher relative abundances post MBR and chlorination. RNA-seq analysis show that, in A. junii, 288 genes and 378 genes are significantly upregulated in the effluent and chlorinated effluent, respectively, with 98 genes being upregulated in both. RT-qPCR of samples in 2015 and 2017 confirm the upregulation observed in RNA-seq. Analysis of the 98 genes show that majority of the upregulated genes are involved in cellular repair and metabolism followed by resistance, virulence, and signaling. Additionally, two different subpopulations of A. junii are observed in the effluent and chlorinated effluent. The upregulation of cellular repair and metabolism genes, and the formation of different subpopulations of A. junii in both effluents provide insights into the mechanisms employed by A. junii to persist in the conditions of a WWTP. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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12 pages, 2645 KiB

Open AccessArticle

Distribution and Abundance of Antibiotic Resistance Genes in Sand Settling Reservoirs and Drinking Water Treatment Plants across the Yellow River, China

by Junying Lu, Zhe Tian, Jianwei Yu, Min Yang and Yu Zhang

Water 2018, 10(3), 246; https://doi.org/10.3390/w10030246 - 28 Feb 2018

Cited by 49 | Viewed by 7026

Abstract

Understanding how antibiotic resistance genes (ARGs) are distributed in drinking water treatment processes is important due to their potential public health risk. Little is known about the occurrence and distribution of ARGs in typical drinking water treatment processes, such as sand settling reservoirs (SSRs) and drinking water treatment plants (DWTPs), in the Yellow River, especially at the catchment scale. In this study, ARG profiling was investigated from water samples of influent (river water) and effluent (source water) of SSRs and finished water of DWTPs in six cities along the Yellow River catchment using real-time quantitative polymerase chain reaction (qPCR) and 16S rRNA gene sequencing. Seventeen ARGs and two mobile genetic elements (MGEs) were detected, among which aadE, strA, strB, tetA, sulII, intl1, and Tn916 had high detection rates (over 80%). The absolute abundances (gene copies/mL of water) of ARGs were reduced by the SSRs and DWTPs generally, but no reductions were observed for the relative abundances (gene copies/16S rRNA gene) of ARGs. Spatial distributions of ARGs and bacteria were not observed. The distribution of bacterial genera was clustered into four dominant patterns in different water type samples. The bacterial genera Pseudomonas, Massilia, Acinetobacter, Sphingomonas, Methylobacterium, and Brevundimonas dominated the finished water, with Brevundimonas and Methylobacterium being speculated to be potential hosts for two ARGs (strA and strB) through network analysis. The enrichment of these two genera, likely caused by selection of disinfection process, may contribute to the higher relative abundance of ARGs in finished water. This study provides insight and effective assessment of the potential risk of ARGs in drinking water treatment processes at the catchment scale. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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19 pages, 4085 KiB

Open AccessArticle

The Effects of Antibiotics on Microbial Community Composition in an Estuary Reservoir during Spring and Summer Seasons

by Zheng Xu, Yue Jiang, Shu Harn Te, Yiliang He and Karina Yew-Hoong Gin

Water 2018, 10(2), 154; https://doi.org/10.3390/w10020154 - 6 Feb 2018

Cited by 12 | Viewed by 5453

Abstract

The increased antibiotic pollutants in aquatic environments pose severe threats on microbial ecology due to their extensive distribution and antibacterial properties. A total of 16 antibiotics including fluoroquinolones (FQs) (ofloxacin (OFX), ciprofloxacin (CFX), norfloxacin (NFX)), Sulfonamides (SAs) (sulfamonomethoxine (SMM), sulfadiazine (SDZ), sulfaquinoxaline (SQX)), Tetracyclines (TCs) (tetracycline (TC), doxycycline (DC)), β-lactams (penicillin G (PEN G), penicillin V (PEN V), cefalexin (LEX)), Macrolides (MLs) (erythromycin-H₂O (ETM), tylosin (TYL)) and other antibiotics (Polymix-B (POL), Vancomycin (VAN), Lincomycin (LIN)) were detected in the surface water of the Qingcaosha Reservoir. Multivariate statistical analysis indicated that both water quality and physicochemical indexes have less contributions on variations of these antibiotics, suggesting the concentrations of antibiotics inside the reservoir are mainly affected by upstream runoff and anthropic activity along the river. Antibiotics including TYL, PEN G and ETM showed significant correlations with variations of bacterial community composition, and closely connected with various gram-negative bacteria in co-occurrence/exclusion patterns of the network, suggesting these bacterial taxa play important roles in the course of migration and transformation of related antibiotics. In conclusion, further research is required to evaluate the potential risk of genetic transfer of resistance to related bacteria induced by long-term exposure to low levels of antibiotics in the environment. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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15 pages, 17676 KiB

Open AccessArticle

Occurrence, Seasonal Variation and Risk Assessment of Antibiotics in Qingcaosha Reservoir

by Yue Jiang, Cong Xu, Xiaoyu Wu, Yihan Chen, Wei Han, Karina Yew-Hoong Gin and Yiliang He

Water 2018, 10(2), 115; https://doi.org/10.3390/w10020115 - 29 Jan 2018

Cited by 33 | Viewed by 6151

Abstract

Qingcaosha Reservoir is an important drinking water source in Shanghai. The occurrence of five groups of antibiotics was investigated in the surface water of this reservoir over a one-year period. Seventeen antibiotics were selected in this study based on their significant usage in China. Of these antibiotics, 16 were detected, while oxytetracycline was not detected in any sampling site. The detected frequency of tylosin was only 47.92% while the other 15 antibiotics were above 81.25%. The dominant antibiotic was different in four seasons: norfloxacin was dominant in spring, and penicillinV was dominant in summer, autumn and winter, with medium concentrations of 124.10 ng/L, 89.91 ng/L, 180.28 ng/L, and 216.43 ng/L, respectively. The concentrations and detection frequencies of antibiotics were notably higher in winter than in other seasons, demonstrating that low temperature and low flow may result in the persistence of antibiotics in the aquatic environment. Risk assessment suggested that norfloxacin, ciprofloxacin, penicillinV, and doxycycline in the surface water presented high ecological risks. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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16 pages, 2277 KiB

Open AccessArticle

Occurrence, Distribution, and Risk Assessment of Antibiotics in a Subtropical River-Reservoir System

by Yihan Chen, Hongjie Chen, Li Zhang, Yue Jiang, Karina Yew-Hoong Gin and Yiliang He

Water 2018, 10(2), 104; https://doi.org/10.3390/w10020104 - 26 Jan 2018

Cited by 60 | Viewed by 6727

Abstract

Antibiotic pollutions in the aquatic environment have attracted widespread attention due to their ubiquitous distribution and antibacterial properties. The occurrence, distribution, and ecological risk assessment of 17 common antibiotics in this study were preformed in a vital drinking water source represented as a river-reservoir system in South China. In general, 15 antibiotics were detected at least once in the watershed, with the total concentrations of antibiotics in the water samples ranging from 193.6 to 863.3 ng/L and 115.1 to 278.2 μg/kg in the sediment samples. For the water samples, higher rain runoff may contribute to the levels of total concentration in the river system, while perennial anthropic activity associated with the usage pattern of antibiotics may be an important factor determining similar sources and release mechanisms of antibiotics in the riparian environment. Meanwhile, the reservoir system could act as a stable reactor to influence the level and composition of antibiotics exported from the river system. For the sediment samples, hydrological factor in the reservoir may influence the antibiotic distributions along with seasonal variation. Ecological risk assessment revealed that tetracycline and ciprofloxacin could pose high risks in the aquatic environment. Taken together, further investigations should be performed to elaborate the environmental behaviors of antibiotics in the river-reservoir system, especially in drinking water sources. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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18 pages, 704 KiB

Open AccessArticle

The Effect of Primary, Secondary, and Tertiary Wastewater Treatment Processes on Antibiotic Resistance Gene (ARG) Concentrations in Solid and Dissolved Wastewater Fractions

by Jennipher Quach-Cu, Bellanira Herrera-Lynch, Christine Marciniak, Scott Adams, April Simmerman and Ryan A. Reinke

Water 2018, 10(1), 37; https://doi.org/10.3390/w10010037 - 4 Jan 2018

Cited by 78 | Viewed by 14972

Abstract

Wastewater treatment plants (WWTPs) have been identified as potential sources of antibiotic resistance genes (ARGs) but the effects of tertiary wastewater treatment processes on ARGs have not been well characterized. Therefore, the objective of this study was to determine the fate of ARGs throughout a tertiary-stage WWTP. Two ARGs, sul1 and bla, were quantified via quantitative polymerase chain reaction (qPCR) in solids and dissolved fractions of raw sewage, activated sludge, secondary effluent and tertiary effluent from a full-scale WWTP. Tertiary media filtration and chlorine disinfection were studied further with the use of a pilot-scale media filter. Results showed that both genes were reduced at each successive stage of treatment in the dissolved fraction. The solids-associated ARGs increased during activated sludge stage and were reduced in each subsequent stage. Overall reductions were approximately four log₁₀ with the tertiary media filtration and disinfection providing the largest decrease. The majority of ARGs were solids-associated except for in the tertiary effluent. There was no evidence for positive selection of ARGs during treatment. The removal of ARGs by chlorine was improved by filtration compared to unfiltered, chlorinated secondary effluent. This study demonstrates that tertiary-stage WWTPs with disinfection can provide superior removal of ARGs compared to secondary treatment alone. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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3849 KiB

Open AccessArticle

Pseudomonas aeruginosa Psl Exopolysaccharide Interacts with the Antimicrobial Peptide LG21

by Joyce Seow Fong Chin, Sheetal Sinha, Anjaiah Nalaparaju, Joey Kuok Hoong Yam, Zhiqiang Qin, Luyan Ma, Zhao-Xun Liang, Lanyuan Lu, Surajit Bhattacharjya and Liang Yang

Water 2017, 9(9), 681; https://doi.org/10.3390/w9090681 - 16 Sep 2017

Cited by 4 | Viewed by 6080

Abstract

Biofilm formation by opportunistic pathogens serves as one of the major causes of chronic and persistent infections. Bacterial cells in the biofilms are embedded in their self-generated protective extracellular polymeric substances (EPS), which include exopolysaccharides, large adhesin proteins and extracellular DNA. In this study, we identified an antimicrobial peptide (AMP) LG21 that is able to interact specifically with the Psl exopolysaccharide of Pseudomonas aeruginosa, thus it can be used as a diagnostic tool for P. aeruginosa biofilms. Molecular dynamics simulation analysis showed that residues numbered from 15 to 21 (WKRKRFG) in LG21 are involved in interacting with Psl. Our study indicates that host immune systems might detect and interact with microbial biofilms through AMPs. Engineering biofilm EPS-targeting AMPs might provide novel strategies for biofilm detection and treatment. Full article

(This article belongs to the Special Issue Antimicrobial Resistance in Environmental Waters)

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