β-lactam resistance genes in bacteriophage and bacterial DNA from wastewater, river water, and irrigation water in Washington State

Antibiotic resistance profiles and mutations that might affect drug susceptibility in metagenome-assembled genomes of Legionella pneumophila and Aeromonas species from municipal wastewater

Antibiotic resistance (AR) has emerged as a significant global health issue. Wastewater treatment plants (WWTPs) contain diverse bacterial communities, including pathogens, and have been identified as crucial reservoirs for the emergence and dissemination of AR. The present study aimed to identify antibiotic resistance genes (ARGs) and screen for the presence of mutations associated with AR in Legionella pneumophila and Aeromonas spp. from municipal wastewater. Metagenome-assembled genomes (MAGs) of L. pneumophila and Aeromonas spp. were reconstructed to investigate the molecular mechanisms of AR in these organisms. A total of 138 nonsynonymous single nucleotide variants (SNVs) in seven genes associated with AR and one deletion mutation in the lpeB gene were identified in L. pneumophila. In Aeromonas spp., two (aph(6)-Id and aph(3'')-Ib) and five (blaMOX-4, blaOXA-1143, blaOXA-724, cepH, and imiH) ARGs conferring resistance to aminoglycosides and β-lactams were identified, respectively. Moreover, this study presents β-lactam resistance genes, blaOXA-1143 and blaOXA-724, for the first time in Aeromonas spp. from a municipal WWTP. In conclusion, these findings shed light on the molecular mechanisms through which clinically relevant pathogenic bacteria such as L. pneumophila and Aeromonas spp. found in natural environments like municipal wastewater acquire AR.

Rethinking the words hostspot reservoir and pristine in the environmental dimensions of antimicrobial resistance

We assess three words commonly used to represent the environmental dimensions of antimicrobial resistance (AMR) - 'hotspot', 'reservoir' and 'pristine' - through two questions: how are these terms used in published research; and how do these terms shape research being conducted? We advocate for the community to reflect on and improve its use of language, and suggest four potentially more productive and precise terms for AMR hazard: presence; transmission; evolution and connectivity.

The Impact of Wastewater on Antimicrobial Resistance: A Scoping Review of Transmission Pathways and Contributing Factors

BACKGROUND/OBJECTIVES

Antimicrobial resistance (AMR) is a global issue driven by the overuse of antibiotics in healthcare, agriculture, and veterinary settings. Wastewater and treatment plants (WWTPs) act as reservoirs for antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). The One Health approach emphasizes the interconnectedness of human, animal, and environmental health in addressing AMR. This scoping review analyzes wastewater's role in the AMR spread, identifies influencing factors, and highlights research gaps to guide interventions.

METHODS

This scoping review followed the PRISMA-ScR guidelines. A comprehensive literature search was conducted across the PubMed and Web of Science databases for articles published up to June 2024, supplemented by manual reference checks. The review focused on wastewater as a source of AMR, including hospital effluents, industrial and urban sewage, and agricultural runoff. Screening and selection were independently performed by two reviewers, with conflicts resolved by a third.

RESULTS

Of 3367 studies identified, 70 met the inclusion criteria. The findings indicated that antibiotic residues, heavy metals, and microbial interactions in wastewater are key drivers of AMR development. Although WWTPs aim to reduce contaminants, they often create conditions conducive to horizontal gene transfer, amplifying resistance. Promising interventions, such as advanced treatment methods and regulatory measures, exist but require further research and implementation.

CONCLUSIONS

Wastewater plays a pivotal role in AMR dissemination. Targeted interventions in wastewater management are essential to mitigate AMR risks. Future studies should prioritize understanding AMR dynamics in wastewater ecosystems and evaluating scalable mitigation strategies to support global health efforts.

Metagenomic insights into plasmid-mediated antimicrobial resistance in poultry slaughterhouse wastewater: antibiotics occurrence and genetic markers

Slaughterhouse wastewater represents important convergence and concentration points for antimicrobial residues, bacteria, and antibiotic resistance genes (ARG), which can promote antimicrobial resistance propagation in different environmental compartments. This study reports the assessment of the metaplasmidome-associated resistome in poultry slaughterhouse wastewater treated by biological processes, employing metagenomic sequencing. Antimicrobial residues from a wastewater treatment plant (WWTP) that treats poultry slaughterhouse influents and effluents were investigated through high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS). Residues from the macrolide, sulfonamide, and fluoroquinolone classes were detected, the latter two persisting after the wastewater treatment. The genetic markers 16S rRNA rrs (bacterial community) and uidA (Escherichia coli) were investigated by RT-qPCR and the sul1 and int1 genes by qPCR. After treatment, the 16S rRNA rrs, uidA, sul1, and int1 markers exhibited reductions of 0.67, 1.07, 1.28, and 0.79 genes copies, respectively, with no statistical significance (p > 0.05). The plasmidome-focused metagenomics sequences (MiSeq platform (Illumina®)) revealed more than 100 ARG in the WWTP influent, which can potentially confer resistance to 14 pharmacological classes relevant in the human and veterinary clinical contexts, in which the qnr gene (resistance to fluoroquinolones) was the most prevalent. Only 7.8% of ARG were reduced after wastewater treatment, and the remaining 92.2% were associated with an increase in the prevalence of ARG linked to multidrug efflux pumps, substrate-specific for certain classes of antibiotics, or broad resistance to multiple medications. These data demonstrate that wastewater from poultry slaughterhouses plays a crucial role as an ARG reservoir and in the spread of AMR into the environment.

Wastewater surveillance for antibiotic resistance genes during the late 2020 SARS-CoV-2 peak in two different populations

The United States Centers for Disease Control and Prevention reported a rise in resistant infections after the coronavirus disease 2019 (COVID-19) pandemic started. How and if the pandemic contributed to antibiotic resistance in the larger population is not well understood. Wastewater treatment plants are good locations for environmental surveillance because they can sample entire populations. This study aimed to validate methods used for COVID-19 wastewater surveillance for bacterial targets and to understand how rising COVID-19 cases from October 2020 to February 2021 in Portugal (PT) and King County, Washington contributed to antibiotic resistance genes in wastewater. Primary influent wastewater was collected from two treatment plants in King County and five treatment plants in PT, and hospital effluent was collected from three hospitals in PT. Genomic extracts were tested with the quantitative polymerase chain reaction for antibiotic resistance genes conferring resistance against antibiotics under threat. Random-effect models were fit for log-transformed gene abundances to assess temporal trends. All samples collected tested positive for multiple resistance genes. During the sampling period, mecA statistically significantly increased in King County and PT. No statistical evidence exists of correlation between samples collected in the same Portuguese metro area.

Carbapenemase gene blaOXA-48 detected at six freshwater sites in Northern Ireland discharging onto identified bathing locations

Faecal contamination of surface waters has the potential to spread not only pathogenic organisms but also antimicrobial resistant organisms. During the bathing season of 2021, weekly water samples, from six selected coastal bathing locations (n = 93) and their freshwater tributaries (n = 93), in Northern Ireland (UK), were examined for concentrations of faecal indicator bacteria Escherichia coli and intestinal enterococci. Microbial source tracking involved detection of genetic markers from the genus Bacteroides using PCR assays for the general AllBac marker, the human HF8 marker and the ruminant BacR marker for the detection of human, and ruminant sources of faecal contamination. The presence of beta-lactamase genes blaOXA-48, blaKPC, and blaNDM-1 was determined using PCR assays for the investigation of antimicrobial resistance genes that are responsible for lack of efficacy in major broad-spectrum antibiotics. The beta-lactamase gene blaOXA-48 was found in freshwater tributary samples at all six locations. blaOXA-48 was detected in 83% of samples that tested positive for the human marker and 69% of samples that tested positive for the ruminant marker over all six locations. This study suggests a risk of human exposure to antimicrobial resistant bacteria where bathing waters receive at least episodically substantial transfers from such tributaries.

Landscape of plasmids encoding β-lactamases in disinfection residual Enterobacteriaceae from wastewater treatment plants

Conventional disinfection processes, such as chlorination and UV radiation, are ineffective in controling antibiotic-resistant bacteria, especially disinfection residual Enterobacteriaceae (DRE) encoding β-lactamases, some of which have been classified as "critical priority pathogens" by the World Health Organization. However, few studies have focused on the transferability, phenotype, and genetic characteristics of DRE-derived plasmids encoding β-lactamases, especially extended-spectrum β-lactamases and carbapenemases. In this study, we isolated 10 typical DRE harboring plasmid-mediated blaNDM, blaCTX-M, or blaTEM in post-disinfection effluent from two wastewater treatment plants (WWTPs), with transfer frequency ranging from 1.69 × 10-6 to 3.02 × 10-5. According to genomic maps of plasmids, all blaNDM and blaTEM were cascaded with IS26, and blaCTX-M was adjacent to ISEcp1 or IS26, indicating the important role of these elements in the movement of β-lactamase-encoding genes. The presence of intact class 1 integrons on pWTPN-01 and pWTPC-03 suggested the ability of these DRE-derived plasmids to integrate other exogenous antibiotic resistance genes (ARGs). The coexistence of antibiotic, disinfectant, and heavy metal resistance genes on the same plasmid (e.g., pWTPT-03) implied the facilitating role of disinfectants and heavy metals in the transmission of DRE-derived ARGs. Notably, two plasmid transconjugants exhibited no discernible competitive fitness cost, suggesting a heightened environmental persistence. Furthermore, enhanced virulence induced by β-lactamase-encoding plasmids in their hosts was confirmed using Galleria mellonella infection models, which might be attributed to plasmid-mediated virulence genes. Overall, this study describes the landscape of β-lactamase-encoding plasmids in DRE, and highlights the urgent need for advanced control of DRE to keep environmental and ecological security.

Phages in different habitats and their ability to carry antibiotic resistance genes

As the most abundant organisms on Earth, phages play a key role in the evolution of bacterial antibiotic resistance. Although previous studies have demonstrated the molecular mechanisms of horizontal gene transfer mediated by mobile genetic elements, our understanding of the intertwined relationships between antibiotic resistance genes (ARGs) and phages is limited. In this study, we analysed 2781 metagenomic samples to reveal the composition and species interactions of phage communities in different habitats as well as their capacity to carry ARGs with health risks. The composition of phage communities varies in different habitats and mainly depends on environmental conditions. Terrestrial habitats display more complex and robust interactions between phages than aquatic and human-associated habitats, resulting in the highest biodiversity of phages. Several types of phages in certain taxa (4.95-7.67%, mainly belonging to Caudoviricetes) have the capacity to carry specific ARGs and display a high potential risk to human health, especially in human-associated habitats. Overall, our results provide insights into the assembly mechanisms of phage communities and their effects on the dissemination of antibiotic resistance.

Monitoring viruses and beta-lactam resistance genes through wastewater surveillance during a COVID-19 surge in Suwon, South Korea

The present study reports data on a long-term campaign for monitoring SARS-CoV-2, norovirus, hepatitis A virus, and beta-lactam resistance genes in wastewater samples from a wastewater treatment plant during COVID-19 surge in Suwon, South Korea. Real-time digital PCR (RT-dPCR) assays indicated 100 % occurrence of all but hepatitis A virus and blaNDM gene in influent wastewater samples. CDC-N1 assay detected SARS-CoV-2 in all influent samples with an average log-transformed concentration of 5.1 ± 0.39 and the highest level at 6.02 gene copies/L. All samples were also positive for norovirus throughout the study with a mean concentration 5.67 ± 0.65 log10 gene copies/L. On the contrary, all treated wastewater (effluent) tested negative for both viruses' genetic materials. Furthermore, plasmid-mediated AmpC β-lactamases (PABLs) genes blaDHA, blaACC, and blaFOX, extended-spectrum β-lactamases (ESBLs) genes blaTEM and blaCTX, and Klebsiella pneumoniae carbapenemase (blaKPC) gene were measured at average concentrations of 7.05 ± 0.26, 5.60 ± 0.35, 7.82 ± 0.43, 8.38 ± 0.20, 7.64 ± 0.29, and 7.62 ± 0.41 log10 gene copies/L wastewater, respectively. Beta-lactam resistance genes showed strong correlations (r), the highest being 0.86 for blaKPC - blaFOX, followed by 0.82 for blaTEM - blaCTX and 0.79 for blaTEM - blaDHA. SARS-CoV-2 RNA occurrence in the wastewater was strongly associated (r = 0.796) with COVID-19 cases in the catchment during the initial study period of six months. A positive association of the SARS-CoV-2 RNA with the prevalence of COVID-19 cases showed a promising role of community-scale monitoring of pathogens to provide considerable early signals of infection dynamics. High concentrations of beta-lactam resistance genes in wastewater indicated a high concern for one of the biggest global health threats in South Korea and the need to find control measures. Moreover, antibiotic-resistance genes in treated wastewater flowing through water bodies and agricultural environments indicate further dissemination of antibiotic resistance traits and increasing microbial antibiotic resistance.

Linking antibiotic resistance gene patterns with advanced faecal pollution assessment and environmental key parameters along 2300 km of the Danube River

The global spread of antimicrobial resistance (AMR) in the environment is a growing health threat. Large rivers are of particular concern as they are highly impacted by wastewater discharge while being vital lifelines serving various human needs. A comprehensive understanding of occurrence, spread and key drivers of AMR along whole river courses is largely lacking. We provide a holistic approach by studying spatiotemporal patterns and hotspots of antibiotic resistance genes (ARGs) along 2311 km of the navigable Danube River, combining a longitudinal and temporal monitoring campaign. The integration of advanced faecal pollution diagnostics and environmental and chemical key parameters allowed linking ARG concentrations to the major pollution sources and explaining the observed patterns. Nine AMR markers, including genes conferring resistance to five different antibiotic classes of clinical and environmental relevance, and one integrase gene were determined by probe-based qPCR. All AMR targets could be quantified in Danube River water, with intI1 and sul1 being ubiquitously abundant, qnrS, tetM, blaTEM with intermediate abundance and blaOXA-48like, blaCTX-M-1 group, blaCTX-M-9 group and blaKPC genes with rare occurrence. Human faecal pollution from municipal wastewater discharges was the dominant factor shaping ARG patterns along the Danube River. Other significant correlations of specific ARGs were observed with discharge, certain metals and pesticides. In contrast, intI1 was not associated with wastewater but was already established in the water microbiome. Animal contamination was detected only sporadically and was correlated with ARGs only in the temporal sampling set. During temporal monitoring, an extraordinary hotspot was identified emphasizing the variability within natural waters. This study provides the first comprehensive baseline concentrations of ARGs in the Danube River and lays the foundation for monitoring future trends and evaluating potential reduction measures. The applided holistic approach proved to be a valuable methodological contribution towards a better understanding of the environmental occurrence of AMR.

Field-realistic dose of cefotaxime enhances potential mobility of β-lactam resistance genes in the gut microbiota of zebrafish (Danio rerio)

With large amounts of cephalosporin end up in natural ecosystems, water has been acknowledged as the large reservoir of β-lactam resistance over the past decades. However, there is still insufficient knowledge available on the function of the living organisms to the transmission of antibiotic resistance. For this reason, in this study, using adult zebrafish (Danio rerio) as animal model, exposing them to environmentally relevant dose of cefotaxime for 150 days, we asked whether cefotaxime contamination accelerated β-lactam resistance in gut microbiota as well as its potential transmission. Results showed that some of β-lactam resistance genes (βRGs) were intrinsic embedded in intestinal microbiome of zebrafish even without antibiotic stressor. Across cefotaxime treatment, the abundance of most βRGs in fish gut microbiome decreased apparently in the short term firstly, and then increased with the prolonged exposure, forming distinctly divergent βRG profiles with antibiotic-untreated zebrafish. Meanwhile, with the rising concentration of cefotaxime, the range of βRGs' host-taxa expanded and the co-occurrence relationships of mobile genetics elements (MGEs) with βRGs intensified, indicating the enhancement of βRGs' mobility in gut microbiome when the fish suffered from cefotaxime contamination. Furthermore, the path of partial least squares path modeling (PLS-PM) gave an integral assessment on the specific causality of cefotaxime treatment to βRG profiles, showing that cefotaxime-mediated βRGs variation was most ascribed to the alteration of MGEs under cefotaxime stress, followed by bacterial community, functioning both direct influence as βRG-hosts and indirect effects via affecting MGEs. Finally, pathogenic bacteria Aeromonas was identified as the critical host for multiple βRGs in fish guts, and its β-lactam resistance increased over the duration time of cefotaxime exposure, suggesting the potential spreading risks for the antibiotic-resistant pathogens from environmental ecosystems to clinic. Overall, our finding emphasized cefotaxime contamination in aquatic surroundings could enhance the β-lactam resistance and its transmission mobility in fish bodies.

Application of Nucleotide-Based Kinetic Modeling Approaches to Predict Antibiotic Resistance Gene Degradation during UV- and Chlorine-Based Wastewater Disinfection Processes: From Bench- to Full-Scale

This study investigated antibiotic resistance gene (ARG) degradation kinetics in wastewaters during bench- and full-scale treatment with UV light and chlorine─with the latter maintained as free available chlorine (FAC) in low-ammonia wastewater and converted into monochloramine (NH₂Cl) in high-ammonia wastewater. Twenty-three 142-1509 bp segments (i.e., amplicons) of seven ARGs (blt, mecA, vanA, tet(A), ampC, bla_NDM, bla_KPC) and the 16S rRNA gene from antibiotic resistant bacteria (ARB) strains Bacillus subtilis, Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae were monitored as disinfection targets by qPCR. Rate constants for ARG and 16S rRNA gene amplicon degradation by UV, FAC, and NH₂Cl were measured in phosphate buffer and used to expand and validate several recently developed approaches to predict DNA segment degradation rate constants based solely on their nucleotide contents, which were then applied to model ARG degradation during bench-scale treatment in buffer and wastewater matrixes. Kinetics of extracellular and intracellular ARG degradation by UV and FAC were well predicted up to ∼1-2-log₁₀ elimination, although with decreasing accuracy at higher levels for intracellular genes, while NH₂Cl yielded minimal degradation under all conditions (agreeing with predictions). ARB inactivation kinetics varied substantially across strains, with intracellular gene degradation lagging cell inactivation in each case. ARG degradation levels observed during full-scale disinfection at two wastewater treatment facilities were consistent with bench-scale measurements and predictions, where UV provided ∼1-log₁₀ ARG degradation, and chlorination of high-ammonia wastewater (dominated by NH₂Cl) yielded minimal ARG degradation.

Similarities of P1-Like Phage Plasmids and Their Role in the Dissemination of blaCTX-M-55

The P1-like phage plasmid (PP) has been widely used as a molecular biology tool, but its role as an active accessory cargo element is not fully understood. In this study, we provide insights into the structural features and gene content similarities of 77 P1-like PPs in the RefSeq database. We also describe a P1-like PP carrying a blaCTX-M-55 gene, JL22, which was isolated from a clinical strain of Escherichia coli from a duck farm. P1-like PPs were very similar and conserved based on gene content similarities, with only eight highly variable regions. Importantly, two kinds of replicon types, namely, IncY and p0111, were identified and can be used to specifically identify the P1-like phage. JL22 is similar to P1, acquiring an important foreign DNA fragment with two obvious features, namely, the plasmid replication gene repA' (p0111) replacing the gene repA (IncY) and a 4,200-bp fragment mobilized by IS1380 and IS5 and containing a blaCTX-M-55 gene and a trpB gene encoding tryptophan synthase (indole salvaging). The JL22 phage could be induced but had no lytic capacities. However, a lysogenic recipient and intact structure of JL22 virions were observed, showing that the extended-spectrum β-lactamase blaCTX-M-55 gene was successfully transferred. Overall, conserved genes can be a good complement to improve the identification efficiency and accuracy in future screening for P1-like PPs. Moreover, the highly conserved structures may be important for their prevalence and dissemination. IMPORTANCE As a PP, P1 DNA exists as a low-copy-number plasmid and replicates autonomously with a lysogenization style. This unique mode of P1-like elements probably indicates a stable contribution to antibiotic resistance. After analyzing these elements, we show that P1-like PPs are very similar and conserved, with only eight highly variable regions. Moreover, we observed the occurrence of replicon IncY and p0111 only in the P1-like PP community, implying that these conserved regions, coupled with IncY and p0111, can be an important complement in future screening of P1-like PPs. Identification and characterization of JL22 confirmed our findings that major changes were located in variable regions, including the first detection of blaCTX-M-55 in such a mobile genetic element. This suggests that these variable regions may facilitate foreign DNA mobilization. This study features a comprehensive genetic analysis of P1-like PPs, providing new insights into the dissemination mechanisms of antibiotic resistance through P1 PPs.

Clinically Relevant β-Lactam Resistance Genes in Wastewater Treatment Plants

Antimicrobial resistance (AMR) is one of the largest global concerns due to its influence in multiple areas, which is consistent with One Health's concept of close interconnections between people, animals, plants, and their shared environments. Antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) circulate constantly in various niches, sediments, water sources, soil, and wastes of the animal and plant sectors, and is linked to human activities. Sewage of different origins gets to the wastewater treatment plants (WWTPs), where ARB and ARG removal efficiency is still insufficient, leading to their transmission to discharge points and further dissemination. Thus, WWTPs are believed to be reservoirs of ARGs and the source of spreading AMR. According to a World Health Organization report, the most critical pathogens for public health include Gram-negative bacteria resistant to third-generation cephalosporins and carbapenems (last-choice drugs), which represent β-lactams, the most widely used antibiotics. Therefore, this paper aimed to present the available research data for ARGs in WWTPs that confer resistance to β-lactam antibiotics, with a particular emphasis on clinically important life-threatening mechanisms of resistance, including extended-spectrum β-lactamases (ESBLs) and carbapenemases (KPC, NDM).

Biogeographical variation in antimicrobial resistance in rivers is influenced by agriculture and is spread through bacteriophages

Antibiotic resistance is currently an extensive medical challenge worldwide, with global numbers increasing steadily. Recent data have highlighted wastewater treatment plants as a reservoir of resistance genes. The impact of these findings for human health can best be summarized using a One Health concept. However, the molecular mechanisms impacting resistance spread have not been carefully evaluated. Bacterial viruses, that is bacteriophages, have recently been shown to be important mediators of bacterial resistance genes in environmental milieus and are transferrable to human pathogens. Herein, we investigated the biogeographical impact on resistance spread through river-borne bacteriophages using amplicon deep sequencing of the microbiota, absolute quantification of resistance genes using ddPCR, and phage induction capacity within wastewater. Microbial biodiversity of the rivers is significantly affected by river site, surrounding milieu and time of sampling. Furthermore, areas of land associated with agriculture had a significantly higher ability to induce bacteriophages carrying antibiotic resistance genes, indicating their impact on resistance spread. It is imperative that we continue to analyse global antibiotic resistance problem from a One Health perspective to gain novel insights into mechanisms of resistance spread.

OXA-48-Like β-Lactamases: Global Epidemiology, Treatment Options, and Development Pipeline

Modern medicine is threatened by the rising tide of antimicrobial resistance, especially among Gram-negative bacteria, where resistance to β-lactams is most often mediated by β-lactamases. The penicillin and cephalosporin ascendancies were, in their turn, ended by the proliferation of TEM penicillinases and CTX-M extended-spectrum β-lactamases. These class A β-lactamases have long been considered the most important. For carbapenems, however, the threat is increasingly from the insidious rise of a class D carbapenemase, OXA-48, and its close relatives. Over the past 20 years, OXA-48 and "OXA-48-like" enzymes have proliferated to become the most prevalent enterobacterial carbapenemases across much of Europe, Northern Africa, and the Middle East. OXA-48-like enzymes are notoriously difficult to detect because they often cause only low-level in vitro resistance to carbapenems, meaning that the true burden is likely underestimated. Despite this, they are associated with carbapenem treatment failures. A highly conserved incompatibility complex IncL plasmid scaffold often carries bla_OXA-48 and may carry other antimicrobial resistance genes, leaving limited treatment options. High conjugation efficiency means that this plasmid is sometimes carried by multiple Enterobacterales in a single patient. Producers evade most β-lactam-β-lactamase inhibitor combinations, though promising agents have recently been licensed, notably ceftazidime-avibactam and cefiderocol. The molecular machinery enabling global spread, current treatment options, and the development pipeline of potential new therapies for Enterobacterales that produce OXA-48-like β-lactamases form the focus of this review.

Vertical and horizontal distributions of clinical antibiotic resistance genes and bacterial communities in Danjiangkou Reservoir, China

The Danjiangkou Reservoir is an important water source for the middle route of the South-to-North Water Diversion Project in China. The current anthropogenic pollution of this reservoir is a great public health concern. Therefore, the horizontal and vertical distributions of seven clinical antibiotic resistance genes (ARGs) and bacterial communities in the Danjiangkou Reservoir were investigated using qPCR and next-generation sequencing, respectively. The average relative abundance of ARGs was 3.01 × 10^-4 to 1.90 × 10^-3 and 4.66 × 10^-4 to 1.85 × 10^-3 in horizontal and vertical profiles, respectively. There was a significant difference in the vertical composition of ARGs, which was caused by different media (i.e. water column vs. sediment). No significant differences in the composition of ARGs were found in the horizontal profile. Proteobacteria was the most abundant phylum, followed by Actinobacteria in the Danjiangkou Reservoir. The beta diversity pattern of the microbial communities in the vertical profile was consistent with that of the ARGs. Moreover, a significant difference in the horizontal composition of the bacterial communities among these water columns was found. All of these factors have resulted in noticeably different co-occurrence patterns of ARGs and bacterial communities between water columns and surface sediment samples. ARGs were closely associated with Proteobacteria and Chloroflexi in the sediment samples, indicating potential anthropogenic pollution in the Danjiangkou Reservoir. Although there was no significant correlation between the occurrence of ARGs and 11 opportunistic pathogens, our results point to potential risks for the development of multi-resistant pathogens due to the simultaneous presence of ARGs and pathogens in the study area. These results provide a good basis for thorough ecological evaluation and remediation of the Danjiangkou Reservoir.

Analysis of viromes and microbiomes from pig fecal samples reveals that phages and prophages rarely carry antibiotic resistance genes

Understanding the transmission of antibiotic resistance genes (ARGs) is critical for human health. For this, it is necessary to identify which type of mobile genetic elements is able to spread them from animal reservoirs into human pathogens. Previous research suggests that in pig feces, ARGs may be encoded by bacteriophages. However, convincing proof for phage-encoded ARGs in pig viromes is still lacking, because of bacterial DNA contaminating issues. We collected 14 pig fecal samples and performed deep sequencing on both highly purified viral fractions and total microbiota, in order to investigate phage and prophage-encoded ARGs. We show that ARGs are absent from the genomes of active, virion-forming phages (below 0.02% of viral contigs from viromes), but present in three prophages, representing 0.02% of the viral contigs identified in the microbial dataset. However, the corresponding phages were not detected in the viromes, and their genetic maps suggest they might be defective. We conclude that among pig fecal samples, phages and prophages rarely carry ARG. Furthermore, our dataset allows for the first time a comprehensive view of the interplay between prophages and viral particles, and uncovers two large clades, inoviruses and Oengus-like phages.

Antibiotic resistance genes in bacteria: Occurrence, spread, and control

The production and use of antibiotics are becoming increasingly common worldwide, and the problem of antibiotic resistance is increasing alarmingly. Drug-resistant infections threaten human life and health and impose a heavy burden on the global economy. The origin and molecular basis of bacterial resistance is the presence of antibiotic resistance genes (ARGs). Investigations on ARGs mostly focus on the environments in which antibiotics are frequently used, such as hospitals and farms. This literature review summarizes the current knowledge of the occurrence of antibiotic-resistant bacteria in nonclinical environments, such as air, aircraft wastewater, migratory bird feces, and sea areas in-depth, which have rarely been involved in previous studies. Furthermore, the mechanism of action of plasmid and phage during horizontal gene transfer was analyzed, and the transmission mechanism of ARGs was summarized. This review highlights the new mechanisms that enhance antibiotic resistance and the evolutionary background of multidrug resistance; in addition, some promising points for controlling or reducing the occurrence and spread of antimicrobial resistance are also proposed.

Monitoring antibiotic resistance genes in wastewater treatment: Current strategies and future challenges

Antimicrobial resistance (AMR) is a growing threat to human and animal health. Progress in molecular biology has revealed new and significant challenges for AMR mitigation given the immense diversity of antibiotic resistance genes (ARGs), the complexity of ARG transfer, and the broad range of omnipresent factors contributing to AMR. Municipal, hospital and abattoir wastewater are collected and treated in wastewater treatment plants (WWTPs), where the presence of diverse selection pressures together with a highly concentrated consortium of pathogenic/commensal microbes create favourable conditions for the transfer of ARGs and proliferation of antibiotic resistant bacteria (ARB). The rapid emergence of antibiotic resistant pathogens of clinical and veterinary significance over the past 80 years has re-defined the role of WWTPs as a focal point in the fight against AMR. By reviewing the occurrence of ARGs in wastewater and sludge and the current technologies used to quantify ARGs and identify ARB, this paper provides a research roadmap to address existing challenges in AMR control via wastewater treatment. Wastewater treatment is a double-edged sword that can act as either a pathway for AMR spread or as a barrier to reduce the environmental release of anthropogenic AMR. State of the art ARB identification technologies, such as metagenomic sequencing and fluorescence-activated cell sorting, have enriched ARG/ARB databases, unveiled keystone species in AMR networks, and improved the resolution of AMR dissemination models. Data and information provided in this review highlight significant knowledge gaps. These include inconsistencies in ARG reporting units, lack of ARG/ARB monitoring surrogates, lack of a standardised protocol for determining ARG removal via wastewater treatments, and the inability to support appropriate risk assessment. This is due to a lack of standard monitoring targets and agreed threshold values, and paucity of information on the ARG-pathogen host relationship and risk management. These research gaps need to be addressed and research findings need to be transformed into practical guidance for WWTP operators to enable effective progress towards mitigating the evolution and spread of AMR.

β-Lactam Resistance Gene NDM-1 in the Aquatic Environment: A Review

New Delhi Metallo-β-lactamase-1 (NDM-1) offers carbapenem antibiotics resistance that creates an evolving challenge in treating bacterial infections. NDM-1-bearing strains were observed in surface waters around New Delhi in 2010 and after then identified globally. The usage of antibiotics may hasten the growth of the NDM-1-producing bacteria, which pose severe hazards to human and animal health. The emergence of the NDM-1 in the aquatic environment is turning out to be a growing concern worldwide. NDM-1 gene conferring resistance to a widespread class of antibiotics has been observed in bacteria disseminated in animal production wastewaters, hospital sewage, domestic sewage, industrial effluents, wastewater treatment plants, drinking water, surface water, and even in groundwater. This review recapitulates the currently published research studies on the prevalence and geographical distribution of the NDM-1 gene in the aquatic environment, its habitats, and healthcare risk associated with NDM-1-producing bacteria, in addition to molecular techniques employed to reveal the occurrence of the NDM-1 in the aquatic environment, including conventional polymerase chain reaction, real-time qPCR, DNA hybridization, and microarray-based methods.

Bacterial and Bacteriophage Antibiotic Resistance in Marine Bathing Waters in Relation to Rivers and Urban Streams

Fecal pollution of surface water may introduce bacteria and bacteriophages harboring antibiotic resistance genes (ARGs) into the aquatic environment. Watercourses discharging into the marine environment, especially close to designated bathing waters, may expose recreational users to fecal pollution and therefore may increase the likelihood that they will be exposed to ARGs. This study compares the bacterial and bacteriophage ARG profiles of two rivers (River Tolka and Liffey) and two small urban streams (Elm Park and Trimleston Streams) that discharge close to two marine bathing waters in Dublin Bay. Despite the potential differences in pollution pressures experienced by these waterways, microbial source tracking analysis showed that the main source of pollution in both rivers and streams in the urban environment is human contamination. All ARGs included in this study, bla_TEM, bla_SHV, qnrS, and sul1, were present in all four waterways in both the bacterial and bacteriophage fractions, displaying a similar ARG profile. We show that nearshore marine bathing waters are strongly influenced by urban rivers and streams discharging into these, since they shared a similar ARG profile. In comparison to rivers and streams, the levels of bacterial ARGs were significantly reduced in the marine environment. In contrast, the bacteriophage ARG levels in freshwater and the marine were not significantly different. Nearshore marine bathing waters could therefore be a potential reservoir of bacteriophages carrying ARGs. In addition to being considered potential additional fecal indicators organism, bacteriophages may also be viewed as indicators of the spread of antimicrobial resistance.

Impact of flooding on urban soils: Changes in antibiotic resistance and bacterial community after Hurricane Harvey

Major perturbations in soil and water quality are factors that can negatively impact human health. In soil environments of urban areas, changes in antibiotic-resistance profiles may represent an increased risk of exposure to antibiotic-resistant bacteria via oral, dermal, or inhalation routes. We studied the perturbation of antibiotic-resistance profiles and microbial communities in soils following a major flooding event in Houston, Texas, caused by Hurricane Harvey. The main objective of this study was to examine the presence of targeted antibiotic-resistance genes and changes in the diversity of microbial communities in soils a short time (3-5 months) and a long time (18 months) after the catastrophic flooding event. Using polymerase chain reaction, we surveyed fourteen antibiotic-resistance elements: intI1, intI2, sul1, sul2, tet(A) to (E), tet(M), tet(O), tet(W), tet(X), and bla_CMY-2. The number of antibiotic-resistance genes detected were higher in short-time samples compared to samples taken a long time after flooding. From all the genes surveyed, only tet(E), bla_CMY-2, and intI1 were prevalent in short-time samples but not observed in long-time samples; thus, we propose these genes as indicators of exogenous antibiotic resistance in the soils. Sequencing of the V3-V4 region of the bacterial 16S rRNA gene was used to find that flooding may have affected bacterial community diversity, enhanced differences among bacterial lineages profiles, and affected the relative abundance of Actinobacteria, Verrucomicrobia, and Gemmatimonadetes. A major conclusion of this study is that antibiotic resistance profiles of soil bacteria are impacted by urban flooding events such that they may pose an enhanced risk of exposure for up to three to five months following the hurricane. The occurrence of targeted antibiotic-resistance elements decreased eighteen months after the hurricane indicating a reduction of the risk of exposure long time after Harvey.

Poultry and Wild Birds as a Reservoir of CMY-2 Producing Escherichia coli: The First Large-Scale Study in Greece

Resistance mediated by β-lactamases is a globally spread menace. The aim of the present study was to determine the occurrence of Escherichia coli producing plasmid-encoded AmpC β-lactamases (pAmpC) in animals. Fecal samples from chickens (n = 159), cattle (n = 104), pigs (n = 214), and various wild bird species (n = 168), collected from different Greek regions during 2018-2020, were screened for the presence of pAmpC-encoding genes. Thirteen E. coli displaying resistance to third-generation cephalosporins and a positive AmpC confirmation test were detected. bla_CMY-2 was the sole pAmpC gene identified in 12 chickens' and 1 wild bird (Eurasian magpie) isolates and was in all cases linked to an upstream ISEcp1-like element. The isolates were classified into five different sequence types: ST131, ST117, ST155, ST429, and ST1415. Four chickens' stains were assigned to ST131, while five chickens' strains and the one from the Eurasian magpie belonged to ST117. Seven pAmpC isolates co-harbored genes conferring resistance to tetracyclines (tetM, tetB, tetC, tetD), 3 carried sulfonamide resistance genes (sulI and sulII), and 10 displayed mutations in the quinolone resistance-determining regions of gyrA (S83L+D87N) and parC (S80I+E84V). This report provides evidence of pAmpC dissemination, describing for the first time the presence of CMY-2 in chickens and wild birds from Greece.

Profiles of bacteria/phage-comediated ARGs in pig farm wastewater treatment plants in China: Association with mobile genetic elements, bacterial communities and environmental factors

In this study, the profiles of bacteria/phage-comediated antibiotic resistance genes (b/pARGs) were monitored in water samples collected from 45 pig farm wastewater treatment plants (WWTPs) in seven different regions of China. We found that 8 major types and 112 subtypes of b/pARGs were detected in all the water samples, and the detected number ranged from 53 to 92. The absolute abundances of bARGs and pARGs in the influent were as high as 10⁹ copies/mL and 10⁶ copies/mL, respectively. Anaerobic anoxic/oxic (AAO) and anaerobic short-cut nitrification/denitrification (ASND) treatment plants can effectively reduce the absolute abundance and amount of b/pARGs. Anaerobic treatment plants cannot reduce the absolute abundance of pARGs, and even increase the amount of pARGs. Mobile genetic elements (MGEs), bacterial communities and environmental factors were important factors impacting the b/pARG profile. Among these factors, the bacterial community was the major driver that impacted the bARG profile, while bacterial community and MGEs were the major codrivers impacting the pARG profile. This study was the first to investigate the profiles of b/pARGs in pig farm WWTPs in China on such a large scale, providing a reference for the prevention and control of ARG pollution in agricultural environments.

Antimicrobial Resistance and Bacteriophages: An Overlooked Intersection in Water Disinfection

This article focuses on how bacteriophages (phages), antibiotic-resistance genes (ARGs), and disinfection practices intersect. Phages are considered to be the most abundant biological entities on Earth and they have the potential to transfer genes (including ARGs) among their bacterial hosts. In the urban water cycle, phages are used as indicators of fecal pollution and surrogates for human viral pathogens but they are also known to withstand common disinfection treatments deployed to produce safe drinking/reclaimed water. Recent studies also suggest that phages have the potential to become an additional footprint to monitor water safety. A precautionary approach should therefore include phages in surveillance programs aimed at monitoring antimicrobial resistance (AMR) in the urban water cycle. This article argues that phages ought to be used to assess the efficiency of disinfection treatments (both classical and novel) on reducing the risk associated with antibiotic resistance. Finally, this article discusses contributions to the advancement of AMR stewardship in aquatic settings and is relevant for researchers and water industry practitioners.

Genetic characterization of coliform bacterial isolates from environmental water in Thailand

INTRODUCTION

In contrast to the study in other part of the world, information about characteristics of plasmids carrying antimicrobial resistance genes (ARGs) in Enterobacteriaceae derived from environmental water in tropical Asian countries including Thailand is limited. This study, therefore, aimed to gain insight into genetic information of antimicrobial resistance in environmental water in Thailand.

METHODS

Coliform bacteria were isolated from environmental water collected at 20 locations in Thailand and identified. Then, susceptibility profiles to ampicillin, cefazoline, cefotaxime, kanamycin, ciprofloxacin, sulfamethoxazole, tetracycline, and nalidixic acid were assessed. In addition, antimicrobial resistant genes integrons, and replicon types were analyzed. And furthermore, plasmids carrying bla_TEM and tetM were identified by S1-PFGE analysis and confirmed transmissibility by transconjugation experiments.

RESULTS

In 130 coliform bacteria isolated, 89 were resistant to cefazoline while 41 isolates were susceptible. Cefazoline-resistant coliform bacteria were found to be significantly resistant to cefotaxime and tetracycline as compared to susceptible isolates. Hence, bla_TEM and tetM correlating with β-lactam antibiotics and tetracycline, respectively, were analyzed found to co-localize on the IncFrepB plasmids in isolates from pig farms' wastewater by S1-PFGE analysis. And furthermore, transmissibility of the plasmids was confirmed.

CONCLUSIONS

Results obtained in this study suggested that ARGs in coliform bacteria may have been spreading on the farm via IncFrepB plasmids. Hence, appropriate use of antimicrobials and good hygiene management on the farm are required to prevent the emergence and spread of resistant bacteria.

Bacteriophages in water pollution control: Advantages and limitations

Wastewater is a breeding ground for many pathogens, which may pose a threat to human health through various water transmission pathways. Therefore, a simple and effective method is urgently required to monitor and treat wastewater. As bacterial viruses, bacteriophages (phages) are the most widely distributed and abundant organisms in the biosphere. Owing to their capacity to specifically infect bacterial hosts, they have recently been used as novel tools in water pollution control. The purpose of this review is to summarize and evaluate the roles of phages in monitoring pathogens, tracking pollution sources, treating pathogenic bacteria, infecting bloom-forming cyanobacteria, and controlling bulking sludge and biofilm pollution in wastewater treatment systems. We also discuss the limitations of phage usage in water pollution control, including phage-mediated horizontal gene transfer, the evolution of bacterial resistance, and phage concentration decrease. This review provides an integrated outlook on the use of phages in water pollution control.

Implications of bacteriophages on the acquisition and spread of antibiotic resistance in the environment

Although bacteriophages (or simply phages) are the most abundant biological entities and have the potential to transfer genetic material between bacterial hosts, their contribution to the acquisition and spread of antibiotic resistance genes in the environment has not been extensively studied. The environment is continually exposed to a wide variety of pollutants from anthropogenic sources, which may promote horizontal gene transfer events, including those mediated by phages. Considering the significant and growing concern of antibiotic resistance, phages should be taken into consideration during the implementation of mitigation measures. This review is focused on the emergence and spread of antibiotic resistance in the environment, with a special emphasis on the role of phages.