Vancomycin-resistant enterococci from Portuguese wastewater treatment plants

Antibiotic resistance and virulence potentials of E. faecalis and E. faecium in hospital wastewater: a case study in Ardabil, Iran

Hospital wastewater can contaminate the environment with antibiotic-resistant and virulent bacteria. We analyzed wastewater samples from four hospitals in Ardabil province, Iran for Enterococcus faecium and Enterococcus faecalis using culture and molecular methods. We also performed antimicrobial susceptibility testing and polymerase chain reaction testing for resistance and virulence genes. Out of 141 enterococci isolates, 68.8% were E. faecium and 23.4% were E. faecalis. Ciprofloxacin and rifampicin showed the highest level of resistance against E. faecalis and E. faecium isolates at 65%. High-level gentamicin resistance (HLGR), high-level streptomycin resistance (HLSR), ampicillin, and vancomycin resistance were observed in 25, 5, 10, and 5.15% of E. faecium, and 15, 6, 15, and 3.03% of E. faecalis isolates, respectively. The ant(6')-Ia and ant(3')-Ia genes that were responsible for streptomycin resistance were observed in HLSR isolates and aph(3')-IIIa and aac(6') Ie-aph(2″)-Ia genes accounting for gentamicin resistance were detected in HLGR isolates. vanA was the predominant gene detected in vancomycin-resistant isolates. The majority of isolates were positive for gelE, asa1, esp, cylA, and hyl virulence genes. We found that drug-resistant and virulent E. faecalis and E. faecium isolates were prevalent in hospital wastewater. Proper treatment strategies are required to prevent their dissemination into the environment.

Risk control of antibiotics, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) during sewage sludge treatment and disposal: A review

Sewage sludge is an important reservoir of antibiotics, antibiotic resistance genes (ARGs), and antibiotic resistant bacteria (ARB) in wastewater treatment plants (WWTPs), and the reclamation of sewage sludge potentially threats human health and environmental safety. Sludge treatment and disposal are expected to control these risks, and this review summarizes the fate and controlling efficiency of antibiotics, ARGs, and ARB in sludge involved in different processes, i.e., disintegration, anaerobic digestion, aerobic composting, drying, pyrolysis, constructed wetland, and land application. Additionally, the analysis and characterization methods of antibiotics, ARGs, and ARB in complicate sludge are reviewed, and the quantitative risk assessment approaches involved in land application are comprehensively discussed. This review benefits process optimization of sludge treatment and disposal, with regard to environmental risks control of antibiotics, ARGs, and ARB in sludge. Furthermore, current research limitations and gaps, e.g., the antibiotic resistance risk assessment in sludge-amended soil, are proposed to advance the future studies.

Temporal disturbance of a model stream ecosystem by high microbial diversity from treated wastewater

Microbial communities in freshwater streams play an essential role in ecosystem functioning via biogeochemical cycling. Yet, the impacts of treated wastewater influx into stream ecosystems on microbial strain diversity remain mostly unexplored. Here, we coupled full‐length 16S ribosomal RNA gene Nanopore sequencing and strain‐resolved metagenomics to investigate the impact of treated wastewater on a mesocosm system (AquaFlow) run with restored river water. Over 10 days, community Bray–Curtis dissimilarities between treated and control mesocosm decreased (0.57 ± 0.058 to 0.26 ± 0.046) based on ribosomal protein S3 gene clustering, finally converging to nearly identical communities. Similarly, strain‐resolved metagenomics revealed a high diversity of bacteria and viruses after the introduction of treated wastewater; these microbes also decreased over time resulting in the same strain clusters in control and treatment at the end of the experiment. Specifically, 39.2% of viral strains detected in all samples were present after the introduction of treated wastewater only. Although bacteria present at low abundance in the treated wastewater introduced additional antibiotic resistance genes, signals of naturally occurring ARG‐encoding organisms resembled the resistome at the endpoint. Our results suggest that the previously stressed freshwater stream and its microbial community are resilient to a substantial introduction of treated wastewater.

Microbiome profiling and characterization of virulent and vancomycin-resistant Enterococcus faecium from treated and untreated wastewater, beach water and clinical sources

Vancomycin-resistant Enterococcus faecium (VREfm) is an opportunistic pathogen among the highest global priorities regarding public and environmental health. Following One Health approach, we determined for the first time the antibiotic resistance and virulence genes, and sequence types (STs) affiliation of VREfm recovered simultaneously from marine beach waters, submarine outfall of a wastewater treatment plant and an offshore discharge of untreated sewage, and compared them with the surveillance VREfm from regional university hospital in Croatia to assess the hazard of their transmission and routes of introduction into the natural environment. Importantly, VREfm recovered from wastewater, coastal bathing waters and hospital shared similar virulence, multidrug resistance, and ST profiles, posing a major public health threat. All isolates carried the vanA gene, while one clinical isolate also possessed the vanC2/C3 gene. The hospital strains largely carried the aminoglycoside-resistance genes aac(6')-Ie-aph(2″)-Ia, and aph(2″)-Ib and aph(2″)-Id, which were also predominant in the environmental isolates. The hyl gene was the most prevalent virulence gene. The isolates belonged to 10 STs of the clonal complex CC17, a major epidemic lineage associated with hospital infections and outbreaks, with ST117 and ST889 common to waterborne and hospital isolates, pointing to their sewage-driven dissemination. To gain better insight into the diversity of accompanying taxons in the surveyed water matrices, microbiome taxonomic profiling was carried out using Illumina-based 16S rDNA sequencing and their resistome features predicted using the PICRUSt2 bioinformatics tool. An additional 60 pathogenic bacterial genera were identified, among which Arcobacter, Acinetobacter, Escherichia-Shigella, Bacteroides and Pseudomonas were the most abundant and associated with a plethora of antibiotic resistance genes and modules, providing further evidence of the hazardous effects of wastewater discharges, including the treated ones, on the natural aquatic environment that should be adequately addressed from a sanitary and technological perspective.

Prevalence and distribution of antimicrobial resistance in effluent wastewater from animal slaughter facilities: A systematic review

The extensive use of antibiotics in food animal production and disposal of untreated wastewater from food animal slaughter facilities may create a shift in microbiomes of different ecosystems by generating reservoirs of antimicrobial resistance along the human-animal-environmental interface. This epidemiological problem has been studied, but its magnitude and impact on a global scale is poorly characterised. A systematic review was done to determine global prevalence and distribution patterns of antimicrobial resistance in effluent wastewater from animal slaughter facilities. Extracted data were stratified into rational groups for secondary analyses and presented as percentages. Culture and sensitivity testing was the predominant method; Escherichia spp., Enterococcus spp., and Staphylococcus aureus were the most targeted isolates. Variable incidences of resistance were detected against all major antimicrobial classes including reserved drugs such as ceftazidime, piperacillin, gentamicin, ciprofloxacin, and chloramphenicol; the median frequency and range in resistant Gram-negative isolates were: 11 (0-100), 62 (0-100), 8 (0-100), 14 (0-93) and 12 (0-62) respectively. Ciprofloxacin was the most tested drug with the highest incidences of resistance in livestock slaughterhouses in Iran (93%), Nigeria (50%) and China (20%), and poultry slaughterhouses in Germany (21-81%) and Spain (56%). Spatial global distribution patterns for antimicrobial resistance were associated with previously reported magnitude of antibiotic use in livestock or poultry farming and, the implicit existence of jurisdictional policies to regulate antibiotic use. These data indicate that anthropogenic activities in farming systems are a major contributor to the cause and dissemination of antimicrobial resistance into the environment via slaughterhouse effluents.

Towards the standardization of Enterococcus culture methods for waterborne antibiotic resistance monitoring: A critical review of trends across studies

Antibiotic resistance is a major 21^st century One Health (humans, animals, environment) challenge whose spread limits options to treat bacterial infections. There is growing interest in monitoring water environments, including surface water and wastewater, which have been identified as key recipients, pathways, and sources of antibiotic resistant bacteria (ARB). Aquatic environments also facilitate the transmission and amplification of ARB. Enterococcus spp. often carry clinically-important antibiotic resistance genes and are of interest as environmental monitoring targets. Enterococcus spp. are Gram-positive bacteria that are typically of fecal origin; however, they are also found in relevant environmental niches, with various species and strains that are opportunistic human pathogens. Although the value of environmental monitoring of antibiotic-resistant Enterococcus has been recognized by both national and international organizations, lack of procedural standardization has hindered generation of comparable data needed to implement integrated surveillance programs. Here we provide a comprehensive methodological review to assess the techniques used for the culturing and characterization of antibiotic-resistant Enterococcus across water matrices for the purpose of environmental monitoring. We analyzed 117 peer-reviewed articles from 33 countries across six continents. The goal of this review is to provide a critical analysis of (i) the various methods applied globally for isolation, confirmation, and speciation of Enterococcus isolates, (ii) the different methods for profiling antibiotic resistance among enterococci, and (iii) the current prevalence of resistance to clinically-relevant antibiotics among Enterococcus spp. isolated from various environments. Finally, we provide advice regarding a path forward for standardizing culturing of Enterococcus spp. for the purpose of antibiotic resistance monitoring in wastewater and wastewater-influenced waters within a global surveillance framework.

Occurrence of antibiotics and bacterial resistance genes in wastewater: resistance mechanisms and antimicrobial resistance control approaches

Antimicrobial pharmaceuticals are classified as emergent micropollutants of concern, implying that even at low concentrations, long-term exposure to the environment can have significant eco-toxicological effects. There is a lack of a standardized regulatory framework governing the permissible antibiotic content for monitoring environmental water quality standards. Therefore, indiscriminate discharge of antimicrobials at potentially active concentrations into urban wastewater treatment facilities is rampant. Antimicrobials may exert selective pressure on bacteria, leading to resistance development and eventual health consequences. The emergence of clinically important multiple antibiotic-resistant bacteria in untreated hospital effluents and wastewater treatment plants (WWTPs) has been linked to the continuous exposure of bacteria to antimicrobials. The levels of environmental exposure to antibiotics and their correlation to the evolution and spread of resistant bacteria need to be elucidated to help in the formulation of mitigation measures. This review explores frequently detected antimicrobials in wastewater and gives a comprehensive coverage of bacterial resistance mechanisms to different antibiotic classes through the expression of a wide variety of antibiotic resistance genes either inherent and/or exchanged among bacteria or acquired from the reservoir of antibiotic resistance genes (ARGs) in wastewater systems. To complement the removal of antibiotics and ARGs from WWTPs, upscaling the implementation of prospective interventions such as vaccines, phage therapy, and natural compounds as alternatives to widespread antibiotic use provides a multifaceted approach to minimize the spread of antimicrobial resistance.

Prevalence of Vancomycin-Resistant Enterococci and Antimicrobial Residues in Wastewater and Surface Water

Due to the extensive use of antimicrobial agents in human and veterinary medicine, residues of various antimicrobials get into wastewater and, subsequently, surface water. On the one hand, a combination of processes in wastewater treatment plants aims to eliminate chemical and biological pollutants; on the other hand, this environment may create conditions suitable for the horizontal transfer of resistance genes and potential selection of antibiotic-resistant bacteria. Wastewater and surface water samples (Morava River) were analyzed to determine the concentrations of 10 antibiotics and identify those exceeding so-called predicted no-effect environmental concentrations (PNECs). This study revealed that residues of five of the tested antimicrobials, namely ampicillin, clindamycin, tetracycline, tigecycline and vancomycin, in wastewater samples exceeded the PNEC. Vancomycin concentrations were analyzed with respect to the detected strains of vancomycin-resistant enterococci (VRE), in which the presence of resistance genes, virulence factors and potential relationship were analyzed. VRE were detected in 16 wastewater samples (11%) and two surface water samples (6%). The PNEC of vancomycin was exceed in 16% of the samples. Since the detected VRE did not correlate with the vancomycin concentrations, no direct relationship was confirmed between the residues of this antimicrobials and the presence of the resistant strains.

Role played by the environment in the emergence and spread of antimicrobial resistance (AMR) through the food chain

The role of food-producing environments in the emergence and spread of antimicrobial resistance (AMR) in EU plant-based food production, terrestrial animals (poultry, cattle and pigs) and aquaculture was assessed. Among the various sources and transmission routes identified, fertilisers of faecal origin, irrigation and surface water for plant-based food and water for aquaculture were considered of major importance. For terrestrial animal production, potential sources consist of feed, humans, water, air/dust, soil, wildlife, rodents, arthropods and equipment. Among those, evidence was found for introduction with feed and humans, for the other sources, the importance could not be assessed. Several ARB of highest priority for public health, such as carbapenem or extended-spectrum cephalosporin and/or fluoroquinolone-resistant Enterobacterales (including Salmonella enterica), fluoroquinolone-resistant Campylobacter spp., methicillin-resistant Staphylococcus aureus and glycopeptide-resistant Enterococcus faecium and E. faecalis were identified. Among highest priority ARGs bla CTX -M, bla VIM, bla NDM, bla OXA -48-like, bla OXA -23, mcr, armA, vanA, cfr and optrA were reported. These highest priority bacteria and genes were identified in different sources, at primary and post-harvest level, particularly faeces/manure, soil and water. For all sectors, reducing the occurrence of faecal microbial contamination of fertilisers, water, feed and the production environment and minimising persistence/recycling of ARB within animal production facilities is a priority. Proper implementation of good hygiene practices, biosecurity and food safety management systems is very important. Potential AMR-specific interventions are in the early stages of development. Many data gaps relating to sources and relevance of transmission routes, diversity of ARB and ARGs, effectiveness of mitigation measures were identified. Representative epidemiological and attribution studies on AMR and its effective control in food production environments at EU level, linked to One Health and environmental initiatives, are urgently required.

Distribution of Beta-Lactamase Producing Gram-Negative Bacterial Isolates in Isabela River of Santo Domingo, Dominican Republic

Bacteria carrying antibiotic resistance genes (ARGs) are naturally prevalent in lotic ecosystems such as rivers. Their ability to spread in anthropogenic waters could lead to the emergence of multidrug-resistant bacteria of clinical importance. For this study, three regions of the Isabela river, an important urban river in the city of Santo Domingo, were evaluated for the presence of ARGs. The Isabela river is surrounded by communities that do not have access to proper sewage systems; furthermore, water from this river is consumed daily for many activities, including recreation and sanitation. To assess the state of antibiotic resistance dissemination in the Isabela river, nine samples were collected from these three bluedistinct sites in June 2019 and isolates obtained from these sites were selected based on resistance to beta-lactams. Physico-chemical and microbiological parameters were in accordance with the Dominican legislation. Matrix-assisted laser desorption ionization-time of flight mass spectrometry analyses of ribosomal protein composition revealed a total of 8 different genera. Most common genera were as follows: Acinetobacter (44.6%) and Escherichia (18%). Twenty clinically important bacterial isolates were identified from urban regions of the river; these belonged to genera Escherichia (n = 9), Acinetobacter (n = 8), Enterobacter (n = 2), and Klebsiella (n = 1). Clinically important multi-resistant isolates were not obtained from rural areas. Fifteen isolates were selected for genome sequencing and analysis. Most isolates were resistant to at least three different families of antibiotics. Among beta-lactamase genes encountered, we found the presence of blaTEM, blaOXA, blaSHV, and blaKPC through both deep sequencing and PCR amplification. Bacteria found from genus Klebsiella and Enterobacter demonstrated ample repertoire of antibiotic resistance genes, including resistance from a family of last resort antibiotics reserved for dire infections: carbapenems. Some of the alleles found were KPC-3, OXA-1, OXA-72, OXA-132, CTX-M-55, CTX-M-15, and TEM-1.

Revealing antimicrobial resistance in stormwater with MinION

Discharge of urban stormwater containing organic matter, heavy metals and sometime human feces, to the natural aquatic reservoirs without any treatment is not only an environmental problem. It can lead to prevalence of antibiotic resistant bacteria in stormwater systems and transmission of antibiotic resistance genes to the environment. We performed antibiotic resistome identification and virus detection in stormwater samples from Stockholm, using publicly available metagenomic sequencing MinION data. A MinION platform offers low-cost, precise environmental metagenomics analysis. 37 groups of antibiotic resistant bacteria (ARB), 11 resistance types with 26 resistance mechanisms - antibiotic resistance genes (ARGs) giving tolerance to the aminoglycoside, beta-lactams, fosmidomycin, MLS, multidrug and vancomycin were identified using ARGpore pipeline. The majority of the identified bacteria species were related to the natural environment such as soil and were not dangerous to human. Alarmingly, human pathogenic bacteria carrying resistance to antibiotics currently used against them (Bordetella resistant to macrolides and multidrug resistant Propionibacterium avidum) were also found in the samples. Most abundant viruses identified belonged to Caudovirales and Herpesvirales and they were not carrying ARGs. Unlike the virome, resistome and ARB were not unique for stormwater sampling points. This results underline the need for extensive monitoring of the microbial community structure in the urban stormwater systems to assess antimicrobial resistance spread.

Prevalence, antibiotic resistance and virulence of Enterococcus spp. from wastewater treatment plant effluent and receiving waters in South Africa

Poorly operating wastewater treatment plants (WWTPs) result in faecal pollution of receiving waters, posing a health risk to humans and animals. The aim of this study was to determine the antimicrobial resistance patterns and presence of virulent genes in Enterococcus spp. isolated from three WWTPs' final effluent and receiving waters in the North West Province, South Africa. Sixty-three Enterococcus spp. were identified and their antimicrobial susceptibility, as well as the presence of five virulence genes, determined. The antibiotic inhibition zone diameter data were subject to cluster analysis. Sixty-eight percent of the screened Enterococcus spp. were resistant to three or more antibiotics and harboured plasmids. Five virulence genes were detected and six multi-virulence profiles observed. Cluster analysis indicated groupings of isolates from all three effluent points downstream together, and between plants 1 and 2 together. The findings of this study have demonstrated that Enterococcus spp. harbouring virulence factors and plasmids that mediate multiple antibiotic resistance are present in effluent and receiving water systems that support various social needs. This is a cause for concern and it is recommended that Enterococcus be used as an additional faecal indicator when microbiological quality of water is assessed.

Antibiotic-contaminated wastewater irrigated vegetables pose resistance selection risks to the gut microbiome

Wastewater reuse in food crop irrigation has led to agroecosystem pollution concerns and human health risks. However, there is limited attention on the relationship of sub-lethal antibiotic levels in vegetables and resistance selection. Most risk assessment studies show non-significant toxicity, but overlook the link between antibiotics in crops and propagation of gut microbiome resistance selection. The review highlights the risk of antibiotics in treated water used for irrigation, uptake, and accumulation in edible vegetable parts. Moreover, it elucidates the risks to the adaptive resistance selection of the gut microbiome from sub-lethal antibiotic levels, as a result of dietary contaminated vegetables. Experiments have reported that bacterial resistance selection is possible at concentrations that are several hundred-folds lower than lethal effect levels on susceptible cells. Consequently, mutants selected at low antibiotic levels, such as those from vegetables, are fitter and more resistant compared to those selected at high concentrations. Necessary standardization, such as the development of minimum acceptable antibiotic limits allowable in food crop irrigation water, with a focus on minimum selection concentration, and not only toxicity, has been proposed. Wastewater irrigation offers environmental benefits and can contribute to food security, but it has non-addressed risks. Research gaps, future perspectives, and frameworks of mitigating the potential risks are discussed.

Tagging the vanA gene in wastewater microbial communities for cell sorting and taxonomy of vanA carrying cells

Failure to understand the microbial ecology driving the proliferation of antibiotic resistance in the environment prevents us from developing strategies to limit the spread of antibiotic resistant infectious disease. In this study, we developed for the first time a tyramide signal amplification-fluorescence in situ hybridization-fluorescence-activated cell sorting protocol (TSA-FISH-FACS) for the characterization of all vanA carrying bacteria in wastewater samples. Firstly, we validated the TSA-FISH protocol through microscopy in pure cultures and wastewater influent. Then, samples were sorted and quantified by FACS and qPCR. Significantly higher percentage tagging of cells was detected in vanA carrying pure cultures and wastewater samples spiked with vanA carrying cells as compared to vanA negative Gram positive strains and non-spiked wastewater samples respectively. qPCR analysis targeting vanZ, a regulating gene in the vanA cluster, showed its relative abundance was significantly greater in Enterococcus faecium ATCC 700221-spiked and positively sorted samples compared to the E. faecium spiked and negatively sorted samples. Phylogenetic analysis was then performed. Although further efforts are needed to overcome technical problems, we have, for the first time, demonstrated sorting bacterial-cells carrying antibiotic resistance genes from wastewater samples through a TSA-FISH-FACS protocol and provided insight into the microbial ecology of vancomycin resistant bacteria. Future potential applications using this approach will include the separation of members of an environmental microbial community (cultured and hard-to-culture) to allow for metagenomics on single cells or, in the case of clumping, targeting a smaller portion of the community with a priori knowledge that the target gene is present.

Effects of tourist flows on antibiotic resistance in wastewater of a Greek island

AIM

Antibiotic resistance in wastewaters reflects the clinical resistome. This study aimed at investigating whether changes in the population size and composition in the popular tourist destination of Zakynthos island are associated with differentiation in the antibiotic resistance of environmental micro-organisms isolated from wastewater.

METHODS AND RESULTS

The resistance profiles of four species (Escherichia coli, Staphylococcus sp., Pseudomonas sp. and Enterococcus sp.) were studied in 124 raw and treated municipal wastewaters from November 2015 to August 2016. Isolates were tested against their susceptibility to several antibiotics of different antimicrobial categories. Data concerning the alteration in the population size and composition, due to the tourist mobility, were collected and logistic regression models were used to examine the relationships between antimicrobial resistance and population changes. The decrease in resistance of E. coli to amoxicillin-clavulanate, of enterococci to norfloxacin and ampicillin, and of pseudomonads to almost all antibiotics tested was associated with population increase due to tourist flows. In contrast, the presence of tourists was linked to an increase in quinupristin-dalfopristin resistant enterococci. Resistance of staphylococci did not change during the tourist period.

CONCLUSION

Changes in population composition in touristic areas are reflected in antibiotic resistance of environmental bacteria in wastewater.

SIGNIFICANCE AND IMPACT OF THE STUDY

In touristic areas, where people carrying different resistomes are merged, medication should be adapted accordingly.

Enterococci, from Harmless Bacteria to a Pathogen

Enterococci are gastrointestinal commensals whose hardiness allowed them to colonize very diverse environments, including soils, water, food, and feed. This ability to overcome adverse conditions makes enterococci problematic once they colonize hospital niches. Together with the malleability of their genomes, the capacity to acquire and disseminate determinants of antibiotic resistance has contributed to converting what was once just another opportunistic pathogen into a first-class clinical problem. This review discusses the dimension of the emergence of enterococcal resistance to key antimicrobial agents, the dissemination of this resistance, and its significance in terms of public health, with the aim of raising awareness of the need to devise and implement surveillance programs and more effective antibiotic stewardship.

The Contribution of Wastewater to the Transmission of Antimicrobial Resistance in the Environment: Implications of Mass Gathering Settings

Antimicrobial resistance (AMR) is the major issue posing a serious global health threat. Low- and middle-income countries are likely to be the most affected, both in terms of impact on public health and economic burden. Recent studies highlighted the role of resistance networks on the transmission of AMR organisms, with this network being driven by complex interactions between clinical (e.g., human health, animal husbandry and veterinary medicine) and other components, including environmental factors (e.g., persistence of AMR in wastewater). Many studies have highlighted the role of wastewater as a significant environmental reservoir of AMR as it represents an ideal environment for AMR bacteria (ARB) and antimicrobial resistant genes (ARGs) to persist. Although the treatment process can help in removing or reducing the ARB load, it has limited impact on ARGs. ARGs are not degradable; therefore, they can be spread among microbial communities in the environment through horizontal gene transfer, which is the main resistance mechanism in most Gram-negative bacteria. Here we analysed the recent literature to highlight the contribution of wastewater to the emergence, persistence and transmission of AMR under different settings, particularly those associated with mass gathering events (e.g., Hajj and Kumbh Mela).

Introduction to wastewater microbiology: special emphasis on hospital wastewater

The important role of proper sanitation in maintaining good public health has been confirmed in the past years. Wastewater treatment plants (WWTPs) serve as efficient processes in removing pathogens, organic pollutants, nutrients, and pharmaceuticals from wastewaters. However, the advance systems of treatment that we use today are the result of a series of inventions that have been performed since 19th century. This chapter explains the evolution of the wastewater origin and the treatment processes along with the developments in microbiology and pathology that led to the present-day scenario of research and advance facilities. Pharmaceuticals can easily enter the environment due to their incomplete degradation in the treatment processes and because of their adverse effects on organisms and environment they are becoming a matter of great concern. A brief discussion on the presence of pharmaceutical compounds in different environment sectors such as wastewater, WWTPs, and the natural aquatic environment has been provided.

Quantification and Multidrug Resistance Profiles of Vancomycin-Resistant Enterococci Isolated from Two Wastewater Treatment Plants in the Same Municipality

Wastewater treatment plants (WWTPs) are points of control for the environmental dissemination of antimicrobial resistant bacteria. Vancomycin-resistant enterococci (VRE) were used as indicators of antimicrobial resistance (AMR) in two WWTPs (biologically aerated filter (BAF) and conventional activated sludge (CAS)) in the same municipality. The removal and abundance of enterococci and VRE as well as the species and antimicrobial resistance profiles of VRE were assessed. Enterococci and VRE from the primary and final effluents were enumerated. Results were assessed from an ecological context. VRE was not selected for by either WWTP but the BAF system outperformed the CAS system for the removal of enterococci/VRE. Enterococcus faecalis (n = 151), E. faecium (n = 94) and E. casseliflavus/E. gallinarum (n = 59) were the dominant VRE species isolated. A decrease in levofloxacin resistance in enterococci was observed in the BAF WWTP. An increase in nitrofurantoin resistant (p < 0.001) and a decrease in quinupristin/dalfopristin (p = 0.003) and streptomycin (p = 0.022) resistant enterococci were observed in the CAS WWTP, corresponding to a shift of VRE from E. faecalis to E. faecium. Wastewater treatment processes can be managed to limit the dissemination of antimicrobial resistance determinants into the surrounding environment.

Freshwater environments as reservoirs of antibiotic resistant bacteria and their role in the dissemination of antibiotic resistance genes

Freshwater environments are susceptible to possible contamination by residual antibiotics that are released through different sources, such as agricultural runoffs, sewage discharges and leaching from nearby farms. Freshwater environment can thus become reservoirs where an antibiotic impact microorganisms, and is an important public health concern. Degradation and dilution processes are fundamental for predicting the actual risk of antibiotic resistance dissemination from freshwater reservoirs. This study reviews major approaches for detecting and quantifying antibiotic resistance bacteria (ARBs) and genes (ARGs) in freshwater and their prevalence in these environments. Finally, the role of dilution, degradation, transmission and the persistence and fate of ARB/ARG in these environments are also reviewed. Culture-based single strain approaches and molecular techniques that include polymerase chain reaction (PCR), quantitative polymerase chain reaction (qPCR) and metagenomics are techniques for quantifying ARB and ARGs in freshwater environments. The level of ARBs is extremely high in most of the river systems (up to 98% of the total detected bacteria), followed by lakes (up to 77% of the total detected bacteria), compared to dam, pond, and spring (<1%). Of most concern is the occurrence of extended-spectrum β-lactamase producing Enterobacteriaceae, methicillin resistant Staphylococcus aureus (MRSA) and vancomycin resistant Enterococcus (VRE), which cause highly epidemic infections. Dilution and natural degradation do not completely eradicate ARBs and ARGs in the freshwater environment. Even if the ARBs in freshwater are effectively inactivated by sunlight, their ARG-containing DNA can still be intact and capable of transferring resistance to non-resistant strains. Antibiotic resistance persists and is preserved in freshwater bodies polluted with high concentrations of antibiotics. Direct transmission of indigenous freshwater ARBs to humans as well as their transitory insertion in the microbiota can occur. These findings are disturbing especially for people that rely on freshwater resources for drinking, crop irrigation, and food in form of fish.

VanA-type vancomycin-resistant Enterococcus faecium ST1336 isolated from mussels in an anthropogenically impacted ecosystem

We report the occurrence and genomic features of multidrug-resistant vancomycin-resistant Enterococcus faecium vanA belonging to a novel sequence type (designated ST1336), carrying a Tn1546-like element, in marine brown mussels (Perna perna) from anthropogenically affected coastal waters of the Atlantic coast of Brazil, highlighting a potential source of dissemination for related ecosystems, with additional consequences for seafood safety and quality.

Multidrug-Resistant Salmonella enterica Isolated from Food Animal and Foodstuff May Also Be Less Susceptible to Heavy Metals

Salmonella enterica is a foodborne pathogen showing increasing multidrug resistance (MDR). We characterized the antimicrobial resistance (AMR) genotype using microarrays in a panel of 105 nontyphoidal S. enterica isolated from food animals and foodstuff. Nineteen isolates were chosen on the basis of their MDR and virulence for determination of heavy metal susceptibilities and screened by polymerase chain reaction for heavy metal resistance genes. Whole-genome sequencing (WGS) was performed on three isolates carrying clinically important AMR genes and the cdtB toxin gene to detect other heavy metal resistance mechanisms, and conjugation assays were performed to evaluate transfer of AMR/toxin genes with heavy metal resistance genes. AMR genotyping results showed isolates harbored between 1 and 12 mobile AMR genes, with 58% being classified as MDR. The tested subset of isolates showed reduced susceptibility to zinc (78%), copper (68%), silver (63%), arsenic (47%), and tellurite (26%); phenotypes that could be attributed to zitB (n = 32%), pcoA/pcoD (n = 32%), tcrB (n = 16%), arsB (n = 16%), silA/silE (n = 42%), and terF (n = 26%) genes. WGS confirmed the presence of other heavy metal resistance genes such as copA, cusA, and czcD. Isolates often harbored multiple heavy metal resistance genes. Two strains (Sal25 and Sal368) were able to conjugate with Escherichia coli J53 at a relatively high frequency (∼10^-4 colony-forming units per recipient). Transformants selected in the presence of copper harbored either an IncHI2 (J53/Sal25 transconjugant) or IncF (J53/Sal368 transconjugant) plasmid with decreased susceptibilities to tellurite, zinc, copper, cobalt, arsenic, lead, mercury, and silver. bla_CTX-M-1 and mcr-1 genes were also transferred to one transconjugant, and tet(M) and bla_TEM-1 genes to the other. This work shows the presence of a diversity of AMR genes in this zoonotic pathogen, and suggests that heavy metals may contribute to selection of clinically important ones through the food chain, such as the plasmid-mediated colistin resistance gene mcr-1.

Simulating the fate of indigenous antibiotic resistant bacteria in a mild slope wastewater polluted stream

The fate of indigenous surface-water and wastewater antibiotic resistant bacteria in a mild slope stream simulated through a hydraulic channel was investigated in outdoor experiments. The effect of (i) natural (dark) decay, (ii) sunlight, (iii) cloudy cover, (iv) adsorption to the sediment, (v) hydraulic conditions, (vi) discharge of urban wastewater treatment plant (UWTP) effluent and (vii) bacterial species (presumptive Escherichia coli and enterococci) was evaluated. Half-life time (T_1/2) of E. coli under sunlight was in the range 6.48-27.7min (initial bacterial concentration of 10⁵CFU/mL) depending on hydraulic and sunlight conditions. E. coli inactivation was quite similar in sunny and cloudy day experiments in the early 2hr, despite of the light intensity gradient was in the range of 15-59W/m²; but subsequently the inactivation rate decreased in the cloudy day experiment (T_1/2=23.0min) compared to sunny day (T_1/2=17.4min). The adsorption of bacterial cells to the sediment (biofilm) increased in the first hour and then was quite stable for the remaining experimental time. Finally, when the discharge of an UWTP effluent in the stream was simulated, the proportion of indigenous antibiotic resistant E. coli and enterococci was found to increase as the exposure time increased, thus showing a higher resistance to solar inactivation compared to the respective total populations.

Vancomycin-resistant enterococci with vanA gene in treated municipal wastewater and their association with human hospital strains

Vancomycin-resistant enterococci (VRE) are pathogens of increasing medical importance. In Brno, Czech Republic, we collected 37 samples from the effluent of a wastewater treatment plant (WWTP), 21 surface swabs from hospital settings, and 59 fecal samples from hospitalized patients and staff. Moreover, we collected 284 gull cloacal swabs from the colony situated 35km downstream the WWTP. Samples were cultured selectively. Enterococci were identified using MALDI-TOF MS, phenotypically tested for susceptibility to antibiotics, and by PCR for occurrence of resistance and virulence genes. Pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) were used to examine genotypic diversity. VRE carrying the vanA gene were found in 32 (86%, n=37) wastewater samples, from which we obtained 49 isolates: Enterococcus faecium (44) and Enterococcus gallinarum (2), Enterococcus casseliflavus (2), and Enterococcus raffinosus (1). From 33 (69%) of 48 inpatient stool samples, we obtained 39 vanA-carrying VRE, which belonged to E. faecium (33 isolates), Enterococcus faecalis (4), and Enterococcus raffinosus (2). Nearly one-third of the samples from hospital surfaces contained VRE with the vanA gene. VRE were not detected among gulls. Sixty-seven (84%, n=80) E. faecium isolates carried virulence genes hyl and/or esp. Virulence of E. faecalis was encoded by gelE, asa1, and cylA genes. A majority of the E. faecium isolates belonged to the clinically important sequence types ST17 (WWTP: 10 isolates; hospital: 4 isolates), ST18 (9;8), and ST78 (5;0). The remaining isolates belonged to ST555 (2;0), ST262 (1;6), ST273 (3;0), ST275 (1;0), ST549 (2;0), ST19 (0;1), ST323 (3;0), and ST884 (7;17). Clinically important enterococci carrying the vanA gene were almost continually detectable in the effluent of the WWTP, indicating insufficient removal of VRE during wastewater treatment and permanent shedding of these antibiotic resistant pathogens into the environment from this source. This represents a risk of their transmission to the environment.

Antibiotic-Resistance Genes in Waste Water

Waste water and waste water treatment plants can act as reservoirs and environmental suppliers of antibiotic resistance. They have also been proposed to be hotspots for horizontal gene transfer, enabling the spread of antibiotic resistance genes between different bacterial species. Waste water contains antibiotics, disinfectants, and metals which can form a selection pressure for antibiotic resistance, even in low concentrations. Our knowledge of antibiotic resistance in waste water has increased tremendously in the past few years with advances in the molecular methods available. However, there are still some gaps in our knowledge on the subject, such as how active is horizontal gene transfer in waste water and what is the role of the waste water treatment plant in the environmental resistome? The purpose of this review is to briefly describe some of the main methods for studying antibiotic resistance in waste waters and the latest research and main knowledge gaps on the issue. In addition, some future research directions are proposed.

A Decade-Long Commitment to Antimicrobial Resistance Surveillance in Portugal

Antimicrobial resistance (AMR) is a worldwide problem with serious health and economic repercussions. Since the 1940s, underuse, overuse, and misuse of antibiotics have had a significant environmental downside. Large amounts of antibiotics not fully metabolized after use in human and veterinary medicine, and other applications, are annually released into the environment. The result has been the development and dissemination of antibiotic-resistant bacteria due to many years of selective pressure. Surveillance of AMR provides important information that helps in monitoring and understanding how resistance mechanisms develop and disseminate within different environments. Surveillance data is needed to inform clinical therapy decisions, to guide policy proposals, and to assess the impact of action plans to fight AMR. The Functional Genomics and Proteomics Unit, based at the University of Trás-os-Montes and Alto Douro in Vila Real, Portugal, has recently completed 10 years of research surveying AMR in bacteria, mainly commensal indicator bacteria such as enterococci and Escherichia coli from the microbiota of different animals. Samples from more than 75 different sources have been accessed, from humans to food-producing animals, pets, and wild animals. The typical microbiological workflow involved phenotypic studies followed by molecular approaches. Throughout the decade, 4,017 samples were collected and over 5,000 bacterial isolates obtained. High levels of AMR to several antimicrobial classes have been reported, including to β-lactams, glycopeptides, tetracyclines, aminoglycosides, sulphonamides, and quinolones. Multi-resistant strains, some relevant to human and veterinary medicine like extended-spectrum β-lactamase-producing E. coli and vancomycin-resistant enterococci, have been repeatedly isolated even in non-synanthropic animal species. Of particular relevance are reports of AMR bacteria in wildlife from natural reserves and endangered species. Future work awaits as this threatening yet unsolved problem persists. GRAPHICAL ABSTRACTSummary diagram of the antimicrobial resistance surveillance work developed by the UTAD Functional Genomics and Proteomics Unit.

Insights in Waste Management Bioprocesses Using Genomic Tools

Microbial capacities drive waste stabilization and resource recovery in environmental friendly processes. Depending on the composition of waste, a stress-mediated selection process ensures a scenario that generates a specific enrichment of microbial community. These communities dynamically change over a period of time while keeping the performance through the required utilization capacities. Depending on the environmental conditions, these communities select the appropriate partners so as to maintain the desired functional capacities. However, the complexities of these organizations are difficult to study. Individual member ratios and sharing of genetic intelligence collectively decide the enrichment and survival of these communities. The next-generation sequencing options with the depth of structure and function analysis have emerged as a tool that could provide the finer details of the underlying bioprocesses associated and shared in environmental niches. These tools can help in identification of the key biochemical events and monitoring of expression of associated phenotypes that will support the operation and maintenance of waste management systems. In this chapter, we link genomic tools with process optimization and/or management, which could be applied for decision making and/or upscaling. This review describes both, the aerobic and anaerobic, options of waste utilization process with the microbial community functioning as flocs, granules, or biofilms. There are a number of challenges involved in harnessing the microbial community intelligence with associated functional plasticity for efficient extension of microbial capacities for resource recycling and waste management. Mismanaged wastes could lead to undesired genotypes such as antibiotic/multidrug-resistant microbes.

Diversity of enterococcal species and characterization of high-level aminoglycoside resistant enterococci of samples of wastewater and surface water in Tunisia

One hundred-fourteen samples of wastewater (n=64) and surface-water (n=50) were inoculated in Slanetz-Bartley agar plates supplemented or not with gentamicin (SB-Gen and SB plates, respectively) for enterococci recovery. Enterococci were obtained from 75% of tested samples in SB media (72% in wastewater; 78% in surface-water), and 85 enterococcal isolates (one/positive-sample) were obtained. Enterococcus faecium was the most prevalent species (63.5%), followed by Enterococcus faecalis (20%), Enterococcus hirae (9.4%), Enterococcus casseliflavus (4.7%), and Enterococcus gallinarum/Enterococcus durans (2.4%). Antibiotic resistance detected among these enterococci was as follows [percentage/detected gene (number isolates)]: kanamycin [29%/aph(3')-IIIa (n=22)], streptomycin [8%/ant(6)-Ia (n=4)], erythromycin [44%/erm(B) (n=34)], tetracycline [18%/tet(M) (n=6)/tet(M)-tet(L) (n=9)], chloramphenicol [2%/cat(A) (n=1)], ciprofloxacin [7%] and trimethoprim-sulfamethoxazole [94%]. High-level-gentamicin resistant (HLR-G) enterococci were recovered from 15 samples in SB-Gen or SB plates [12/64 samples of wastewater (19%) and 3/50 samples of surface-water (6%)]; HLR-G isolates were identified as E. faecium (n=7), E. faecalis (n=6), and E. casseliflavus (n=2). These HLR-G enterococci carried the aac(6')-Ie-aph(2")-Ia and erm(B) genes, in addition to aph(3')-IIIa (n=10), ant(6)-Ia (n=9), tet(M) (n=13), tet(L) (n=8) and cat(A) genes (n=2). Three HLR-G enterococci carried the esp virulence gene. Sequence-types detected among HLR-G enterococci were as follows: E. faecalis (ST480, ST314, ST202, ST55, and the new ones ST531 and ST532) and E. faecium (ST327, ST12, ST296, and the new ones ST985 and ST986). Thirty-two different PFGE patterns were detected among 36 high-level-aminoglycoside-resistant enterococci recovered in water samples. Diverse genetic lineages of HLR-G enterococci were detected in wastewater and surface-water in Tunisia. Water can represent an important source for the dissemination of these antibiotic resistant microorganisms to other environments.

Environmental dissemination of antibiotic resistance genes and correlation to anthropogenic contamination with antibiotics

Antibiotic resistance is a growing problem which threatens modern healthcare globally. Resistance has traditionally been viewed as a clinical problem, but recently non-clinical environments have been highlighted as an important factor in the dissemination of antibiotic resistance genes (ARGs). Horizontal gene transfer (HGT) events are likely to be common in aquatic environments; integrons in particular are well suited for mediating environmental dissemination of ARGs. A growing body of evidence suggests that ARGs are ubiquitous in natural environments. Particularly, elevated levels of ARGs and integrons in aquatic environments are correlated to proximity to anthropogenic activities. The source of this increase is likely to be routine discharge of antibiotics and resistance genes, for example, via wastewater or run-off from livestock facilities and agriculture. While very high levels of antibiotic contamination are likely to select for resistant bacteria directly, the role of sub-inhibitory concentrations of antibiotics in environmental antibiotic resistance dissemination remains unclear. In vitro studies have shown that low levels of antibiotics can select for resistant mutants and also facilitate HGT, indicating the need for caution. Overall, it is becoming increasingly clear that the environment plays an important role in dissemination of antibiotic resistance; further studies are needed to elucidate key aspects of this process. Importantly, the levels of environmental antibiotic contamination at which resistant bacteria are selected for and HGT is facilitated at should be determined. This would enable better risk analyses and facilitate measures for preventing dissemination and development of antibiotic resistance in the environment.

Occupational exposure to Staphylococcus aureus and Enterococcus spp. among spray irrigation workers using reclaimed water

As reclaimed water use expands, it is important to evaluate potential occupational health risks from exposure to this alternative water source. We compared odds of colonization with methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible S. aureus (MSSA), vancomycin-resistant enterococci (VRE), and vancomycin-susceptible enterococci (VSE) between spray irrigation workers using reclaimed water and office worker controls. Nasal and dermal swabs from 19 spray irrigation workers and 24 office worker controls were collected and analyzed for MRSA, MSSA, VRE, and VSE. Isolates were confirmed using standard biochemical tests and polymerase chain reaction assays. Antimicrobial susceptibility testing was performed by Sensititre^® microbroth dilution. Data were analyzed by two-sample proportion, chi-square, Fisher’s exact tests, and logistic regression. No MRSA or VRE were detected in any samples. MSSA was detected in 26% and 29% of spray irrigators and controls, respectively. VSE was detected in 11% and 0% of spray irrigation workers and controls, respectively. The adjusted odds of MSSA, multidrug-resistant MSSA, and either MSSA or VSE colonization were greater among spray irrigation workers, however results were not statistically significant. Future studies with larger sample sizes are needed to further evaluate this relationship.

Bacterial diversity and antibiotic resistance in water habitats: searching the links with the human microbiome

Water is one of the most important bacterial habitats on Earth. As such, water represents also a major way of dissemination of bacteria between different environmental compartments. Human activities led to the creation of the so-called urban water cycle, comprising different sectors (waste, surface, drinking water), among which bacteria can hypothetically be exchanged. Therefore, bacteria can be mobilized between unclean water habitats (e.g. wastewater) and clean or pristine water environments (e.g. disinfected and spring drinking water) and eventually reach humans. In addition, bacteria can also transfer mobile genetic elements between different water types, other environments (e.g. soil) and humans. These processes may involve antibiotic resistant bacteria and antibiotic resistance genes. In this review, the hypothesis that some bacteria may share different water compartments and be also hosted by humans is discussed based on the comparison of the bacterial diversity in different types of water and with the human-associated microbiome. The role of such bacteria as potential disseminators of antibiotic resistance and the inference that currently only a small fraction of the clinically relevant antibiotic resistome may be known is discussed.

Detection of vancomycin-resistant enterococci (VRE) at four U.S. wastewater treatment plants that provide effluent for reuse

Vancomycin-resistant enterococci (VRE), a leading cause of hospital-acquired infections, can occur in wastewater. However, to date, no previous studies have evaluated the occurrence of VRE at wastewater treatment plants (WWTPs) that send their treated effluent to reuse sites. We evaluated the occurrence, concentration, and antimicrobial resistance patterns of VRE at U.S. WWTPs associated with reuse sites. We collected 44 wastewater samples, representing treatment steps from influent to effluent, from two Mid-Atlantic and two Midwest WWTPs between October 2009 and October 2010. Samples were analyzed for total enterococci and VRE using membrane filtration. Isolates were confirmed using biochemical tests and PCR. Antimicrobial susceptibility testing was performed by Sensititre microbroth dilution. Data were analyzed by two-sample proportion tests and analysis of variance. We detected VRE in 27% (12/44) of all wastewater samples collected and VRE represented 3% of total enterococci detected at all WWTPs. More samples were VRE-positive from the Mid-Atlantic compared to the Midwest WWTPs (p=0.008). VRE concentrations decreased as treatment progressed at all WWTPs, except at Mid-Atlantic WWTP1 where there was an increase in VRE concentrations in activated sludge reactor samples. VRE were not detected in chlorinated effluent, but were detected in one un-chlorinated effluent sample. All unique VRE isolates were multidrug resistant. Fifty-five percent (12/22) of the isolates displayed high-level aminoglycoside resistance. Our findings show that chlorination reduces the occurrence of VRE in wastewater. However, WWTP workers could be exposed to VRE during wastewater treatment. Our data also raise potential concerns about VRE exposure among individuals who come into contact with un-chlorinated reclaimed water.

Human health implications of clinically relevant bacteria in wastewater habitats

The objective of this review is to reflect on the multiple roles of bacteria in wastewater habitats with particular emphasis on their harmful potential for human health. Indigenous bacteria promote a series of biochemical and metabolic transformations indispensable to achieve wastewater treatment. Some of these bacteria may be pathogenic or harbour antibiotic resistance or virulence genes harmful for human health. Several chemical contaminants (heavy metals, disinfectants and antibiotics) may select these bacteria or their genes. Worldwide studies show that treated wastewater contain antibiotic resistant bacteria or genes encoding virulence or antimicrobial resistance, evidencing that treatment processes may fail to remove efficiently these bio-pollutants. The contamination of the surrounding environment, such as rivers or lakes receiving such effluents, is also documented in several studies. The current state of the art suggests that only some of antibiotic resistance and virulence potential in wastewater is known. Moreover, wastewater habitats may favour the evolution and dissemination of new resistance and virulence genes and the emergence of new pathogens. For these reasons, additional research is needed in order to obtain a more detailed assessment of the long-term effects of wastewater discharges. In particular, it is important to measure the human and environmental health risks associated with wastewater reuse.

Vancomycin resistant enterococci: from the hospital effluent to the urban wastewater treatment plant

Vancomycin is an important antibiotic to treat serious nosocomial enterococci infections. Human activities, in particular those related with clinical practices performed in hospitals, can potentiate the transfer and selection of clinically-relevant resistant bacteria such as vancomycin resistant enterococci (VRE). Indeed, previous studies demonstrated the occurrence of VRE in urban wastewater treatment plants and related environments (e.g. sewage, rivers). In this study, the occurrence of VRE in a hospital effluent and in the receiving urban wastewater treatment plant was investigated. Vancomycin and ciprofloxacin resistant bacteria occurred in the hospital effluent and in raw municipal inflow at densities of 10(3) to 10(2) CFU mL(-1), being significantly more prevalent in the hospital effluent than in the urban wastewater. Most of the VRE isolated from the hospital effluent belonged to the species Enterococcus faecalis and Enterococcus faecium and presented multidrug-resistance phenotypes to ciprofloxacin, tetracycline, erythromycin, and high-level gentamicin. The same pattern was observed in clinical isolates and in enterococci isolated from the final effluent of the urban wastewater treatment plant. These results show that hospital effluents discharged into urban wastewater treatment plants may be a relevant source of resistance spread to the environment.

Tracking Change: A Look at the Ecological Footprint of Antibiotics and Antimicrobial Resistance

Among the class of pollutants considered as 'emerging contaminants', antibiotic compounds including drugs used in medical therapy, biocides and disinfectants merit special consideration because their bioactivity in the environment is the result of their functional design. Antibiotics can alter the structure and function of microbial communities in the receiving environment and facilitate the development and spread of resistance in critical species of bacteria including pathogens. Methanogenesis, nitrogen transformation and sulphate reduction are among the key ecosystem processes performed by bacteria in nature that can also be affected by the impacts of environmental contamination by antibiotics. Together, the effects of the development of resistance in bacteria involved in maintaining overall ecosystem health and the development of resistance in human, animal and fish pathogens, make serious contributions to the risks associated with environmental pollution by antibiotics. In this brief review, we discuss the multiple impacts on human and ecosystem health of environmental contamination by antibiotic compounds.

Antimicrobial resistance in Enterococcus spp. isolated from environmental samples in an area of intensive poultry production

Enterococcus spp. from two poultry farms and proximate surface and ground water sites in an area of intensive poultry production were tested for resistance to 16 clinical antibiotics. Resistance patterns were compared to assess trends and possible correlations for specific antimicrobials and levels of resistance. Enterococci were detected at all 12 surface water sites and three of 28 ground water sites. Resistance to lincomycin, tetracycline, penicillin and ciprofloxacin in poultry litter isolates was high (80.3%, 65.3%, 61.1% and 49.6%, respectively). Resistance in the surface water to the same antibiotics was 87.1%, 24.1%, 7.6% and 12.9%, respectively. Overall, 86% of litter isolates, 58% of surface water isolates and 100% of ground water isolates were resistant to more than one antibiotic. Fifty-four different resistance patterns were recognised in isolates obtained from litter and environmental samples and several E. faecium and E. faecalis isolates from litter and environment samples shared the same resistance pattern. Multiple antibiotic resistant (MAR) indices calculated to assess health risks due to the presence of resistant enterococci suggested an increased presence of antibiotics in surface water, likely from poultry sources as no other wastewater contributions in the area were documented.

Urban wastewater treatment plants as hotspots for antibiotic resistant bacteria and genes spread into the environment: a review

Urban wastewater treatment plants (UWTPs) are among the main sources of antibiotics' release into the environment. The occurrence of antibiotics may promote the selection of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB), which shade health risks to humans and animals. In this paper the fate of ARB and ARGs in UWTPs, focusing on different processes/technologies (i.e., biological processes, advanced treatment technologies and disinfection), was critically reviewed. The mechanisms by which biological processes influence the development/selection of ARB and ARGs transfer are still poorly understood. Advanced treatment technologies and disinfection process are regarded as a major tool to control the spread of ARB into the environment. In spite of intense efforts made over the last years to bring solutions to control antibiotic resistance spread in the environment, there are still important gaps to fill in. In particular, it is important to: (i) improve risk assessment studies in order to allow accurate estimates about the maximal abundance of ARB in UWTPs effluents that would not pose risks for human and environmental health; (ii) understand the factors and mechanisms that drive antibiotic resistance maintenance and selection in wastewater habitats. The final objective is to implement wastewater treatment technologies capable of assuring the production of UWTPs effluents with an acceptable level of ARB.

Changes in enterococcal populations and related antibiotic resistance along a medical center-wastewater treatment plant-river continuum

To determine if hospital effluent input has an ecological impact on downstream aquatic environment, antibiotic resistance in Enterococcus spp. along a medical center-retirement home-wastewater treatment plant-river continuum in France was determined using a culture-based method. Data on antibiotic consumption among hospitalized and general populations and levels of water contamination by antibiotics were collected. All isolated enterococci were genotypically identified to the species level, tested for in vitro antibiotic susceptibility, and typed by multilocus sequence typing. The erm(B) and mef(A) (macrolide resistance) and tet(M) (tetracycline resistance) genes were detected by PCR. Along the continuum, from 89 to 98% of enterococci, according to the sampled site, were identified as Enterococcus faecium. All E. faecium isolates from hospital and retirement home effluents were multiply resistant to antibiotics, contained erm(B) and mef(A) genes, and belonged to hospital-adapted clonal complex 17 (CC17). Even though this species remained dominant in the downstream continuum, the relative proportion of CC17 isolates progressively decreased in favor of other subpopulations of E. faecium that were more diverse, less resistant to antibiotics, and devoid of the classical macrolide resistance genes and that belonged to various sequence types. Antibiotic concentrations in waters were far below the MICs for susceptible isolates. CC17 E. faecium was probably selected in the gastrointestinal tract of patients under the pressure of administered antibiotics and then excreted together with the resistance genes in waters to progressively decrease along the continuum.

Genotypic diversity, antibiotic resistance and bacteriocin production of enterococci isolated from rhizospheres

This study aimed to identify and to characterize rhizospheric-derived enterococci. The results showed the prevalence of Enterococcus faecium species (97%) vs. Enterococcus durans (3%). Susceptibility testing for antibiotics showed a low percentage of resistance to erythromycin (3.2%) and tetracycline (11.2%), and intermediate resistance to vancomycin (6.5%). Nevertheless, a high proportion of bacteriocin production was recorded. Furthermore, PCR detection of antibiotic resistance and bacteriocin production-encoding genes was investigated. Pulsed-field gel electrophoresis typing (PFGE) showed a great variability of enterococci in the rhizosphere. Moreover, mutilocus-sequence-typing analysis (MLST) revealed the identification of three new sequence types (STs), which were registered as ST613, ST614 and ST615.

Enterococcus faecium of the vanA genotype in rural drinking water, effluent, and the aqueous environment

Total enterococci and vancomycin-resistant enterococci (VRE) were enumerated in samples of effluent (n = 50) and water (n = 167) from a number of sources. VRE were detected in the outflow of a wastewater treatment plant and in a single rural drinking water supply, suggesting potential for transmission to humans through environmental contamination.