Insights into the relationship between antimicrobial residues and bacterial populations in a hospital-urban wastewater treatment plant system

Antibiotics in hospital effluents: occurrence, contribution to urban wastewater, removal in a wastewater treatment plant, and environmental risk assessment

The study presented the occurrence of antibiotics in 16 different hospital effluents, the removal of antibiotics in urban wastewater treatment plant (WWTP), and the potential ecotoxicological risks of the effluent discharge on the aquatic ecosystem. The total concentration of antibiotics in hospital effluents was ranged from 21.2 ± 0.13 to 4886 ± 3.80 ng/L in summer and from 497 ± 3.66 to 322,735 ± 4.58 ng/L in winter. Azithromycin, clarithromycin, and ciprofloxacin were detected the highest concentrations among the investigated antibiotics. The total antibiotic load to the influent of the WWTP from hospitals was 3.46 g/day in summer and 303.2 g/day in winter. The total antibiotic contribution of hospitals to the influent of the WWTP was determined as 13% in summer and 28% in winter. The remaining 87% in summer and 72% in winter stems from the households. The total antibiotic removal by conventional physical and biological treatment processes was determined as 79% in summer, whereas it decreased to 36% in winter. When the environmental risk assessment was performed, azithromycin and clarithromycin in the effluent from the treatment plant in winter posed a high risk (RQ > 10) for the aquatic organisms (algae and fish) in the receiving environment. According to these results, the removal efficiency of antibiotics at the WWTP is inadequate and plant should be improved to remove antibiotics by advanced treatment processes.

Impact of industrial wastewater on the dynamics of antibiotic resistance genes in a full-scale urban wastewater treatment plant

Urban Wastewater Treatment Plants (UWTPs) treating mixed urban sewage and industrial wastewater are among the major hotspots for the spread of Antibiotic Resistance Genes (ARGs) into the environment. This study addresses the impact of the wastewater origin on ARG dynamics in a full-scale UWTP (15,000 Population Equivalent, PE) by operating the plant with and without industrial wastewater. Composite samples (4 L) from different treatment points were characterized for their chemical composition, bacterial abundance and for the abundance of four resistance genes against tetracycline, sulfonamides, erythromycin, and quinolones (tetA, sul2, ermB, and qnrS), and of the class 1 integrons (intI1). Although the chemical composition of the outflow significantly differed when the plant operated with or without industrial wastewater, the system efficiency in the removal of bacterial cells, ARGs, and intI1 was constant. The final disinfection by peracetic acid (PAA) did not affect the removal of ARGs, independently of the wastewater origin and the chemical characteristics of the inflows. Our results demonstrated that a well-functioning small size UWTP could treat a significant amount of industrial wastewater mixed in the urban sewage without affecting the overall ARGs and class 1 integrons released into the environment.

Evaluation of antibiotic resistant lactose fermentative opportunistic pathogenic Enterobacteriaceae bacteria and blaTEM-2 gene in cephalosporin wastewater and its discharge receiving river

This study investigated the concentration of cephalosporin, the resistant levels of lactose fermentative opportunistic pathogenic Enterobacteriaceae bacteria (LFOPEB) against seven antibiotics and one cephalosporin-resistant gene in cephalosporin wastewater (CPWW) treatment plant and its discharge receiving river. Although large numbers of bacteria have been removed during the CPWW treatment process, the antibiotic resistant rates of the isolates to β-lactam antibiotics significantly increased (p = 0.032) after treatment, while the percentage of resistant LFOPEB to non-β-lactam antibiotics did not change dramatically. Furthermore, the discharge of the effluent of CPWW treatment plant (CPWW_eff) led to an obvious increase in the percentages of β-lactam antibiotic-resistant LFOPEB and relative abundance of the blaTEM-2 gene in the downstream receiving river (RW_down) in comparison with those in the upstream receiving river (RW_up). The antibiotic resistant phenotypes of isolates in the influent of CPWW treatment plant (CPWW_in), CPWW_eff and RW_down appeared to be seriously affected by the cephalosporin residues, which suggested that main antibiotic resistance phenotypes in antibiotic contaminated water were closely associated with its antibiotic composition. Therefore, CPWW treatment process has been proved to result in selective growth of ARB and proliferation of ARG. Besides, CPWW_eff was also proved to be an important supplier of ARB and ARG to the receiving river.

Variation of bacterioplankton community along an urban river impacted by touristic city: With a focus on pathogen

Bacterioplankton communities play a critical role in ecological processes in river systems, and shifts of their composition may impact microbial levels and raise public health concerns. The aim of this study was to comprehensively analyze the essential factors influencing bacterioplankton community, along with pathogen, and to estimate the health risk caused by the pathogens downstream of the Liushahe River, which is located in the famous touristic city Xishuangbanna. Results showed that wastewater treatment plants (WWTPs) and a subtropical recreational park impacted the bacterioplankton community and pathogen population, and potential pathogen identification demonstrated that 76 of 145 reference genera were present in the river. Moreover, the bacterioplankton community and pathogen were differently impacted by environmental gradients, and SRP, NO₂ and pH were main factors influencing bacterioplankton community while pathogen population was highly correlated with temperature and turbidity. In addition, it is noted that the pathogen population was dominated by bacterioplankton community and this might because the capacity of resistance invasion pathogen was determined by of bacterioplankton community diversity. Therefore, bacterioplankton community diversity can be used to control and predict the amount of pathogens. Quantitative microbial risk assessment (QMRA) also revealed that the infection risks of Escherichia coli (E. coli), Mycobacterium avium (M. avium), and Pseudomonas aeruginosa (P. aeruginosa) during five recreational activities, especially water-based activities in the touristic city, were greater than that in natural areas and mostly exceeded the U.S. EPA risk limit for recreational activities. Our study offered the first insight into the potential relationship between the bacterioplankton community and bacterial pathogens within a touristic river.

Antimicrobial resistance due to the content of potentially toxic metals in soil and fertilizing products

Potentially toxic metals (PTM), along with PTM-resistant bacteria and PTM-resistance genes, may be introduced into soil and water through sewage systems, direct excretion, land application of biosolids (organic matter recycled from sewage, especially for use in agriculture) or animal manures as fertilizers, and irrigation with wastewater or treated effluents. In this review article, we have evaluated whether the content of arsenic (As), cadmium (Cd), chromium (CrIII + CrVI), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), and zinc (Zn) in soil and fertilizing products play a role in the development, spreading, and persistence of bacterial resistance to these elements, as well as cross- or co-resistance to antimicrobial agents. Several of the articles included in this review reported the development of resistance against PTM in both sewage and manure. Although PTM like As, Hg, Co, Cd, Pb, and Ni may be present in the fertilizing products, the concentration may be low since they occur due to pollution. In contrast, trace metals like Cu and Zn are actively added to animal feed in many countries. In several studies, several different bacterial species were shown to have a reduced susceptibility towards several PTM, simultaneously. However, neither the source of resistant bacteria nor the minimum co-selective concentration (MCC) for resistance induction are known. Co- or cross-resistance against highly important antimicrobials and critically important antimicrobials were identified in some of the bacterial isolates. This suggest that there is a genetic linkage or direct genetic causality between genetic determinants to these widely divergent antimicrobials, and metal resistance. Data regarding the routes and frequencies of transmission of AMR from bacteria of environmental origin to bacteria of animal and human origin were sparse. Due to the lack of such data, it is difficult to estimate the probability of development, transmission, and persistence of PTM resistance. Abbreviations: PTM: potentially toxic metals; AMR: antimicrobial resistance; ARG: antimicrobial resistance gene; MCC: minimum co-selective concentration; MDR: multidrug resistance; ARB: antimicrobial resistant bacteria; HGT: horizontal gene transfer; MIC: minimum inhibitory concentration.

Pharmaceutically active compounds in the Xiangjiang River, China: Distribution pattern, source apportionment, and risk assessment

The occurrence of 36 pharmaceutically active compounds in surface water of the Xiangjiang River was investigated in two seasons (n = 38). Twenty-five of these compounds were detected, with cefotaxime (maximum concentration 830 ng L^-1) the most abundant compound followed by amoxicillin (maximum concentration 710 ng L^-1). The spatiotemporal distribution was observed; indicating that pollution hotspots were mostly located in economically developed and densely populated regions such as Changsha City. Lower concentrations were found in summer than winter, which may be attributed to the dilution effect of a flood event and higher water temperatures. The distribution of pharmaceuticals was significantly correlated with temperature and ammonia nitrogen content. A principal component analysis-multiple linear regression model estimated that domestic sewage was the main source of pharmaceuticals, although the source composition varied among different sampling sites. Risk assessment was conducted using both individual and mixture models for preliminary identification of potential hazards. Sulfamethoxazole, clarithromycin, and azithromycin posed a high risk to algae, while sulfamethoxazole, trimethoprim, and erythromycin-H₂O showed a medium risk to invertebrates. Moreover, the mixture risk quotients calculated using a concentration addition model ranged from 0.31 to 9.60 in winter, and from 0.06 to 0.61 in summer, indicating a potential risk to the aquatic environment. This study provides scientific support to policy-makers to establish contaminant management priorities and enriches the global data on emerging contaminants.

Bacterial lineages putatively associated with the dissemination of antibiotic resistance genes in a full-scale urban wastewater treatment plant

Urban wastewater treatment plants (UWTPs) are reservoirs of antibiotic resistance. Wastewater treatment changes the bacterial community and inevitably impacts the fate of antibiotic resistant bacteria and antibiotic resistance genes (ARGs). Some bacterial groups are major carriers of ARGs and hence, their elimination during wastewater treatment may contribute to increasing resistance removal efficiency. This study, conducted at a full-scale UWTP, evaluated variations in the bacterial community and ARGs loads and explored possible associations among them. With that aim, the bacterial community composition (16S rRNA gene Illumina sequencing) and ARGs abundance (real-time PCR) were characterized in samples of raw wastewater (RWW), secondary effluent (sTWW), after UV disinfection (tTWW), and after a period of 3 days storage to monitoring possible bacterial regrowth (tTWW-RE). Culturable enterobacteria were also enumerated. Secondary treatment was associated with the most dramatic bacterial community variations and coincided with reductions of ~2 log-units in the ARGs abundance. In contrast, no significant changes in the bacterial community composition and ARGs abundance were observed after UV disinfection of sTWW. Nevertheless, after UV treatment, viability losses were indicated ~2 log-units reductions of culturable enterobacteria. The analysed ARGs (qnrS, bla_CTX-M, bla_OXA-A, bla_TEM, bla_SHV, sul1, sul2, and intI1) were strongly correlated with taxa more abundant in RWW than in the other types of water, and which associated with humans and animals, such as members of the families Campylobacteraceae, Comamonadaceae, Aeromonadaceae, Moraxellaceae, and Bacteroidaceae. Further knowledge of the dynamics of the bacterial community during wastewater treatment and its relationship with ARGs variations may contribute with information useful for wastewater treatment optimization, aiming at a more effective resistance control.

Enantioselective fractionation of fluoroquinolones in the aqueous environment using chiral liquid chromatography coupled with tandem mass spectrometry

This paper aims to examine the multiresidue enantiomeric profiling of (fluoro)quinolones and their metabolites in solid and liquid environmental matrices using chiral HPLC-MS/MS method and a CHIRALCEL^® OZ-RH column. Simultaneous chiral separation was obtained for chiral ofloxacin and its main metabolites ofloxacin-N-oxide and desmethyl-ofloxacin; moxifloxacin; the prodrug prulifloxacin and its active compound ulifloxacin; flumequine; nadifloxacin and R-(+)-besifloxacin. Achiral antibiotics (ciprofloxacin, norfloxacin and nalidixic acid) were also included in the method to enable the analysis of all targeted quinolones within one analytical run. Satisfactory enantiomeric resolution (Rs ≥ 1) was obtained for five out of eight chiral drugs enabling quantitative analysis. The overall performance of the method was satisfactory with a method precision <20%, relative recoveries >70% for most of the analytes and method detection limits (MDL) at low ng L^-1 levels (0.1 < MDL (ng L^-1)< 6.4, 0.1 < MDL (ng L^-1)< 6.6 and 0.1 < MDL (ng L^-1)< 7.0 in influent, effluent and river waters for 83% compounds, 0.01 < MDL (ng g^-1)< 4.9 in solids for 91% compounds). Enantiomeric profiling from a week-long monitoring campaign in the UK showed that (±)-ofloxacin was found to be racemic in upstream waters but it was enriched with S-(-)-enantiomer in wastewater and in receiving waters. This could be due to the fact that ofloxacin can be used both as a racemate and as a S-(-)-enantiomer. Its consumption was further confirmed by the chiral signature of the investigated ofloxacin metabolites. As a result, alterations in the enantiomeric composition of antibiotics could influence not only their activity and toxicity in the environment, but also could induce changes in the microbial communities constantly exposed to them.

Antibiotic resistance in wastewater treatment plants: Tackling the black box

Wastewater is among the most important reservoirs of antibiotic resistance in urban environments. The abundance of carbon sources and other nutrients, a variety of possible electron acceptors such as oxygen or nitrate, the presence of particles onto which bacteria can adsorb, or a fairly stable pH and temperature are examples of conditions favouring the remarkable diversity of microorganisms in this peculiar habitat. The wastewater microbiome brings together bacteria of environmental, human and animal origins, many harbouring antibiotic resistance genes (ARGs). Although numerous factors contribute, mostly in a complex interplay, for shaping this microbiome, the effect of specific potential selective pressures such as antimicrobial residues or metals, is supposedly determinant to dictate the fate of antibiotic resistant bacteria (ARB) and ARGs during wastewater treatment. This paper aims to enrich the discussion on the ecology of ARB&ARGs in urban wastewater treatment plants (UWTPs), intending to serve as a guide for wastewater engineers or other professionals, who may be interested in studying or optimizing the wastewater treatment for the removal of ARB&ARGs. Fitting this aim, the paper overviews and discusses: i) aspects of the complexity of the wastewater system and/or treatment that may affect the fate of ARB&ARGs; ii) methods that can be used to explore the resistome, meaning the whole ARB&ARGs, in wastewater habitats; and iii) some frequently asked questions for which are proposed addressing modes. The paper aims at contributing to explore how ARB&ARGs behave in UWTPs having in mind that each plant is a unique system that will probably need a specific procedure to maximize ARB&ARGs removal.

Occurrence and diversity of antibiotic resistance in untreated hospital wastewater

Antibiotics, antibiotic-resistant bacteria (ARB), antibiotic-resistance genes (ARGs), and mobile genetic elements (MGEs) have been reported in many environments. However, the investigation of their occurrence and diversity in untreated hospital wastewater is still insufficient. High concentrations of antibiotic residues were found in hospital wastewater using solid-phase extraction and UPLC-MS/MS analysis. The concentrations of six of 14 antibiotics reached μg/L levels in the hospital wastewater, which is higher than reported in other aquatic environments. Results of high-throughput sequencing analysis indicated that sequences affiliated to genera Escherichia and Acinetobacter were the predominant in the cultivable multiple-antibiotic-resistant bacteria (CMARB) recovered from the wastewater of three hospitals in China, with compositions of 34%-74%. Notably, several genera containing clinically pathogenic or opportunistic CMARB (e.g., Escherichia, Acinetobacter, Aeromonas, Myroides, Enterococcus, Proteus, Pseudomonas, and Streptococcus) were detected at high relative abundances in the wastewaters of the three hospitals. High-capacity quantitative PCR showed that 131-139 unique ARGs of the 178 targeted genes were detected in the hospital wastewaters. The high prevalence of five MGEs and 12 ARGs was confirmed with qPCR, and some positive correlations between ARGs and MGEs were identified, such as between intI1 and qnrD, intI2 and sul3, intI3 and tetX, Tn916/Tn1545 and sul2, and ISCR1 and sul3. These results suggest that highly abundant antibiotic-resistant pathogens and highly mobile ARGs already exist in the human body, and that their release from hospitals without effective treatment poses high risks to environments and human health.

Bacteria That Make a Meal of Sulfonamide Antibiotics: Blind Spots and Emerging Opportunities

The release of sulfonamide antibiotics into the environment is alarming because the existence of these antibiotics in the environment may promote resistance in clinically relevant microorganisms, which is a potential threat to the effectiveness of antibiotic therapies. Controllable biodegradation processes are of particular significance for the inexpensive yet effective restoration of sulfonamide-contaminated environments. Cultivation-based techniques have already made great strides in successfully isolating bacteria with promising sulfonamide degradation abilities, but the implementation of these isolates in bioremediation has been limited by unknown microbial diversity, vast population responsiveness, and the impact of perturbations from open and complex environments. Advances in DNA sequencing technologies and metagenomic analyses are being used to complement the information derived from cultivation-based procedures. In this Review, we provide an overview of the growing understanding of isolated sulfonamide degraders and identify shortcomings of the prevalent literature in this field. In addition, we propose a technical paradigm that integrates experimental testing with metagenomic analysis to pave the way for improved understanding and exploitation of these ecologically important isolates. Overall, this Review aims to outline how metagenomic studies of isolated sulfonamide degraders are being applied for the advancement of bioremediation strategies for sulfonamide contamination.

Insight into effects of antibiotics on reactor performance and evolutions of antibiotic resistance genes and microbial community in a membrane reactor

A lab-scale anoxic/oxic-membrane bioreactor was designed to treat antibiotics containing wastewater at different antibiotics concentrations (0.5 mg/L, 1 mg/L and 3 mg/L of each antibiotic). Overall COD and NH₄⁺N removal (more than 90%) were not affected during the exposure to antibiotics and good TN removal was also achieved, while TP removal was significantly affected. The maximum removal efficiency of penicillin and chlorotetracycline reached 97.15% and 96.10% respectively due to strong hydrolysis, and sulfamethoxazole reached 90.07% by biodegradation. However, 63.87% of norfloxacin maximum removal efficiency was achieved mainly by sorption. The system had good ability to reduce ARGs, peaking to more than 4 orders of magnitude, which mainly depended on the biomass retaining of the membrane module. Antibiotics concentration influenced the evolution of ARGs and bacterial communities in the reactor. This research provides great implication to reduce ARGs and antibiotics in antibiotics containing wastewater using A/O-MBR.

UPLC-MS/MS analysis of antibiotics in pharmaceutical effluent in Tunisia: ecotoxicological impact and multi-resistant bacteria dissemination

The UPLC MS/MS analysis showed the presence of the two antibiotics in the pharmaceutical industry discharges during 3 months; norfloxacin and spiramycin which were quantified with the mean concentrations of 226.7 and 84.2 ng mL^-1, respectively. Sixteen resistant isolates were obtained from the pharmaceutical effluent and identified by sequencing. These isolates belong to different genera, namely Citrobacter, Acinetobacter, Pseudomonas, Delftia, Shewanella, and Rheinheimera. The antibiotic resistance phenotypes of these isolates were determined (27 tested antibiotics-discs). All the studied isolates were found resistant to amoxicillin and gentamicin, and 83.33% of isolates were resistant to ciprofloxacin. Multiple antibiotic resistances were revealed against β-lactams, quinolones, and aminoglycosides families. Our overall results suggest that the obtained bacterial isolates may constitute potential candidates for bioremediation and can be useful for biotechnological applications. Genotoxic effects were assessed by a battery of biotests; the pharmaceutical wastewater was genotoxic according to the bacterial Vitotox test and micronuclei test. Genotoxicity was also evaluated by the comet test; the tail DNA damages reached 38 and 22% for concentrated sample (10×) and non-concentrated sample (1×), respectively. However, the histological sections of kidney and liver's mice treated by pharmaceutical effluent showed normal histology and no visible structural effects or alterations as cytolysis, edema, or ulcerative necrosis were observed. Residual antibiotics can reach water environment through wastewater and provoke dissemination of the antibiotics resistance and induce genotoxic effects.

The long-term impact of cefalexin on organic substrate degradation and microbial community structure in EGSB system

In order to investigate long-term effect of cefalexin (CFX) on the performance of expanded granular sludge bed (EGSB) system and microbial community structure, two 1.47 L EGSB reactors E1 and E2 were designed and run for 224 days treating with synthetic antibiotic wastewater. For the purpose of comparison, E1 was fed with synthetic antibiotic industry wastewater with CFX added as the test reactor, while, E2 was fed without any CFX added as the control reactor (E2). The addition of CFX resulted in the continual increasing of soluble COD (sCOD) and accumulation of VFAs in the effluent of E1 system. Besides, it was found that the accumulation of CFX by-products D-1, D-2 and D-3 was negative correlation with sCOD removal efficiency. Furthermore, the microbial community structures were also investigated. For the bacterial community, Gelria and Syntrophorhabdus which can ferment propionate and other organic pollutants as their substrate were obviously enriched in E1 system. For the archaea, there was more functional diversity in E1 system than in E2 system. Furthermore, fungi also played an important role on the removal of complex organics in E1 system.

Effects of subchronic oral toxic metal exposure on the intestinal microbiota of mice

Oral exposure to toxic metals such as cadmium (Cd), lead (Pb), copper (Cu) and aluminum (Al) can induce various adverse health effects in humans and animals. However, the effects of these metals on the gut microbiota have received limited attention. The present study demonstrated that long-term toxic metal exposure altered the intestinal microbiota of mice in a metal-specific and time-dependent manner. Subchronic oral Cu exposure for eight weeks caused a profound decline in gut microbial diversity in mice, whereas no significant changes were observed in groups treated with other metals. Cd exposure significantly increased the relative abundances of organisms from the genera Alistipes and Odoribacter and caused marked decreases in Mollicutes and unclassified Ruminococcaceae. Pb exposure significantly decreased the abundances of eight genera: unclassified and uncultured Ruminococcaceae, unclassified Lachnospiraceae, Ruminiclostridium_9, Rikenellaceae_RC9_gut_group, Oscillibacter, Anaerotruncus and Lachnoclostridium. Cu exposure affected abundances of the genera Alistipes, Bacteroides, Ruminococcaceae_UCG-014, Allobaculum, Mollicutes_RF9_norank, Rikenellaceae_RC9_gut_group, Ruminococcaceae_unclassified and Turicibacter. Al exposure increased the abundance of Odoribacter and decreased that of Anaerotruncus. Exposure to any metal for eight weeks significantly decreased the abundance of Akkermansia. These results provide a new understanding regarding the role of toxic metals in the pathogenesis of intestinal and systemic disorders in the host within the gut microbiota framework.

Abundance of antibiotics, antibiotic resistance genes and bacterial community composition in wastewater effluents from different Romanian hospitals

Antimicrobial resistance represents a growing and significant public health threat, which requires a global response to develop effective strategies and mitigate the emergence and spread of this phenomenon in clinical and environmental settings. We investigated, therefore, the occurrence and abundance of several antibiotics and antibiotic resistance genes (ARGs), as well as bacterial community composition in wastewater effluents from different hospitals located in the Cluj County, Romania. Antibiotic concentrations ranged between 3.67 and 53.05 μg L^-1, and the most abundant antibiotic classes were β-lactams, glycopeptides, and trimethoprim. Among the ARGs detected, 14 genes confer resistance to β-lactams, aminoglycosides, chloramphenicol, macrolide-lincosamide-streptogramin B (MLSB) antibiotics, sulfonamides, and tetracyclines. Genes encoding quaternary ammonium resistance and a transposon-related element were also detected. The sulI and qacEΔ1 genes, which confer resistance to sulfonamides and quaternary ammonium, had the highest relative abundance with values ranging from 5.33 × 10^-2 to 1.94 × 10^-1 and 1.94 × 10^-2 to 4.89 × 10^-2 copies/16 rRNA gene copies, respectively. The dominant phyla detected in the hospital wastewater samples were Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. Among selected hospitals, one of them applied an activated sludge and chlorine disinfection process before releasing the effluent to the municipal collector. This conventional wastewater treatment showed moderate removal efficiency of the studied pollutants, with a 55-81% decrease in antibiotic concentrations, 1-3 order of magnitude lower relative abundance of ARGs, but with a slight increase of some potentially pathogenic bacteria. Given this, hospital wastewaters (raw or treated) may contribute to the spread of these emerging pollutants in the receiving environments. To the best of our knowledge, this study quantified for the first time the abundance of antibiotics and ARGs in wastewater effluents from different Romanian hospitals.

The influence of the autochthonous wastewater microbiota and gene host on the fate of invasive antibiotic resistance genes

The aim of this study was to assess the fate of invasive antibiotic resistance genes (ARG) discharged in wastewater. With this objective, antibiotic resistant bacteria (ARB) known to harbor specific ARG were inoculated in wastewater (hospital effluent, or municipal raw and treated wastewater) and in ultra-pure sterile water microcosms. Two sets of wastewater ARB isolates were used - set 1, Enterococcus faecalis, Acinetobacter johnsonii, Klebsiella pneumoniae and set 2, Enterococcus faecium, Acinetobacter johnsonii, Escherichia coli. Non-inoculated controls were run in parallel. Samples were collected at the beginning and at the end (15days) of the incubation period and the abundance of the genes 16S rRNA, intI1, bla_TEM and vanA and the bacterial community composition were analyzed. In general, the genes bla_TEM and vanA had lower persistence in wastewater and in ultra-pure water than the genes 16S rRNA or the class 1 integron integrase intI1. This effect was more pronounced in wastewater than in ultra-pure water, evidencing the importance of the autochthonous microbiota on the elimination of invasive ARG. Wastewater autochthonous bacterial groups most correlated with variations of the genes intI1, bla_TEM and vanA were members of the classes Gammaproteobacteria, Bacilli or Bacteroidia. For bla_TEM, but not for vanA, the species of the ARB host was important to determine its fate. These are novel findings on the ecology of ARB in wastewater environments.

Assessing the Risk of Antibiotic Resistance Transmission from the Environment to Humans: Non-Direct Proportionality between Abundance and Risk

The past decade has witnessed a burst of study regarding antibiotic resistance in the environment, mainly in areas under anthropogenic influence. Therefore, impacts of the contaminant resistome, that is, those related to human activities, are now recognized. However, a key issue refers to the risk of transmission of resistance to humans, for which a quantitative model is urgently needed. This opinion paper makes an overview of some risk-determinant variables and raises questions regarding research needs. A major conclusion is that the risks of transmission of antibiotic resistance from the environment to humans must be managed under the precautionary principle, because it may be too late to act if we wait until we have concrete risk values.

Phenotypic and genetic characterization of multidrug-resistant Staphylococcus aureus in the tropics of Southeast Asia

Antibiotic resistance has become a major public health problem throughout the world. The presence of antibiotic-resistant bacteria such as Staphylococcus aureus and antibiotic resistance genes (ARGs) in hospital wastewater is a cause for great concern today. In this study, 276 Staph. aureus isolates were recovered from hospital wastewater samples in Malaysia. All of the isolates were screened for susceptibility to nine different classes of antibiotics: ampicillin, ciprofloxacin, gentamicin, kanamycin, erythromycin, vancomycin, trimethoprim and sulfamethoxazole, chloramphenicol, tetracycline and nalidixic acid. Screening tests showed that 100 % of Staph.aureus isolates exhibited resistance against kanamycin, vancomycin, trimethoprim and sulfamethoxazole and nalidixic acid. Additionally, 91, 87, 50, 43, 11 and 8.7 % of isolates showed resistance against erythromycin, gentamicin, ciprofloxacin, ampicillin, chloramphenicol and tetracycline, respectively. Based on these results, 100 % of isolates demonstrated multidrug-resistant (MDR) characteristics, displaying resistance against more than three classes of antibiotics. Of 276 isolates, nine exhibited resistance to more than nine classes of tested antibiotics; these were selected for antibiotic susceptibility testing and examined for the presence of conserved ARGs. Interestingly, a high percentage of the selected MDR Staph.aureus isolates did not contain conserved ARGs. These results indicate that non-conserved MDR gene elements may have already spread into the environment in the tropics of Southeast Asia, and unique resistance mechanisms against several antibiotics may have evolved due to stable, moderate temperatures that support growth of bacteria throughout the year.

Presence and distribution of Macrolides-Lincosamide-Streptogramin resistance genes and potential indicator ARGs in the university ponds in Guangzhou, China

This study aimed to determine the occurrence, abundance, and variation of seven Macrolides-Lincosamide-Streptogramin (MLS) resistance genes (ereB, ermA, ermB, ermF, mefA, vatB, mphA) and six potential indicator ARGs (tet (B), sul1, qnrS, fexA, IntI1, ermB) from three ponds at university by quantitative PCR and assess the impacts on the surroundings. Solid samples (fish feces, soil and sediment) and water samples were tested. All the genes were found at low levels in soil samples. For the MLS resistance genes, only two MLS genes (ermB, ermF) were detected in all samples and significant correlations between ermB and Σ MLS (R = 0.91 in solid samples; R = 0.86 in water samples, p < 0.01) were found. For the potential indicators, intl1 and sul1 were present at high levels in the three different ponds while the other genes showed varying levels. These findings show that the ermB gene can probably be served as an indicator to evaluate the overall level of MLS resistance genes. The fairly low abundance of all the tested resistance genes in soil samples and the moderate levels in other samples suggests that the university ponds kept a good state and did not have a significant impact on their surroundings.

Low-Concentration Ciprofloxacin Selects Plasmid-Mediated Quinolone Resistance Encoding Genes and Affects Bacterial Taxa in Soil Containing Manure

The spread of antimicrobial resistance in environment is promoted at least in part by the inappropriate use of antibiotics in animals and humans. The present study was designed to investigate the impact of different concentrations of ciprofloxacin in soil containing manure on the development of plasmid-mediated quinolone resistance (PMQR) – encoding genes and the abundance of soil bacterial communities. For these studies, high-throughput next-generation sequencing of 16S rRNA, real-time polymerase chain reaction and standard microbiologic culture methods were utilized. We demonstrated that the dissipate rate of relative abundances of some of PMQR-encoding genes, such as qnrS, oqxA and aac(6^′)-Ib-cr, were significantly lower with ciprofloxacin 0.04 and 0.4 mg/kg exposure as compared to no-ciprofloxacin control and ciprofloxacin 4 mg/kg exposure during 2 month. Also, the number of ciprofloxacin resistant bacteria was significantly greater in ciprofloxacin 0.04 and 0.4 mg/kg exposure as compared with no-ciprofloxacin control and the ciprofloxacin 4 mg/kg exposure. In addition, lower ciprofloxacin concentration provided a selective advantage for the populations of Xanthomonadales and Bacillales in orders while Agrobacterium, Bacillus, Enterococcus, and Burkholderia in genera. These findings suggest that lower concentration of ciprofloxacin resulted in a slower rate of PMQR-encoding genes dissipation and selected development of ciprofloxacin-resistant bacteria in soil amended with manure.

Antibiotics in Wastewater of a Rural and an Urban Hospital before and after Wastewater Treatment, and the Relationship with Antibiotic Use-A One Year Study from Vietnam

Hospital effluents represent an important source for the release of antibiotics and antibiotic resistant bacteria into the environment. This study aims to determine concentrations of various antibiotics in wastewater before and after wastewater treatment in a rural hospital (60 km from the center of Hanoi) and in an urban hospital (in the center of Hanoi) in Vietnam, and it aims to explore the relationship between antibiotic concentrations in wastewater before wastewater treatment and quantities of antibiotics used in the rural hospital, over a period of one year in 2013. Water samples were collected using continuous sampling for 24 h in the last week of every month. The data on quantities of antibiotics delivered to all inpatient wards were collected from the Pharmacy department in the rural hospital. Solid-phase extraction and high performance liquid chromatography-tandem mass spectrometry were used for chemical analysis. Significant concentrations of antibiotics were present in the wastewater both before and after wastewater treatment of both the rural and the urban hospital. Ciprofloxacin was detected at the highest concentrations in the rural hospital's wastewater (before treatment: mean = 42.8 µg/L; after treatment: mean = 21.5 µg/L). Metronidazole was detected at the highest concentrations in the urban hospital's wastewater (before treatment: mean = 36.5 µg/L; after treatment: mean = 14.8 µg/L). A significant correlation between antibiotic concentrations in wastewater before treatment and quantities of antibiotics used in the rural hospital was found for ciprofloxacin (r = 0.78; p = 0.01) and metronidazole (r = 0.99; p < 0.001).

High Levels of Antibiotic Resistance Genes and Their Correlations with Bacterial Community and Mobile Genetic Elements in Pharmaceutical Wastewater Treatment Bioreactors

To understand the diversity and abundance of antibiotic resistance genes (ARGs) in pharmaceutical wastewater treatment bioreactors, the ARGs in sludge from two full-scale pharmaceutical wastewater treatment plants (PWWTPs) were investigated and compared with sludge samples from three sewage treatment plants (STPs) using metagenomic approach. The results showed that the ARG abundances in PWWTP sludge ranged from 54.7 to 585.0 ppm, which were higher than those in STP sludge (27.2 to 86.4 ppm). Moreover, the diversity of ARGs in PWWTP aerobic sludge (153 subtypes) was higher than that in STP aerobic sludge (118 subtypes). In addition, it was found that the profiles of ARGs in PWWTP aerobic sludge were similar to those in STP aerobic sludge but different from those in PWWTP anaerobic sludge, suggesting that dissolve oxygen (DO) could be one of the important factors affecting the profiles of ARGs. In PWWTP aerobic sludge, aminoglycoside, sulfonamide and multidrug resistance genes were frequently detected. While, tetracycline, macrolide-lincosamide-streptogramin and polypeptide resistance genes were abundantly present in PWWTP anaerobic sludge. Furthermore, we investigated the microbial community and the correlation between microbial community and ARGs in PWWTP sludge. And, significant correlations between ARG types and seven bacterial genera were found. In addition, the mobile genetic elements (MGEs) were also examined and correlations between the ARGs and MGEs in PWWTP sludge were observed. Collectively, our results suggested that the microbial community and MGEs, which could be affected by DO, might be the main factors shaping the profiles of ARGs in PWWTP sludge.

Hospital effluents management: Chemical, physical, microbiological risks and legislation in different countries

Hospital wastewater (HWW) can contain hazardous substances, such as pharmaceutical residues, chemical hazardous substances, pathogens and radioisotopes. Due to these substances, hospital wastewater can represent a chemical, biological and physical risk for public and environmental health. In particular, several studies demonstrate that the main effects of these substances can't be neutralised by wastewater treatment plants (WWTPs). These substances can be found in a wide range of concentrations due to the size of a hospital, the bed density, number of inpatients and outpatients, the number and the type of wards, the number and types of services, the country and the season. Some hazardous substances produced in hospital facilities have a regulatory status and are treated like waste and are disposed of accordingly (i.e., dental amalgam and medications). Legislation is quite homogeneous for these substances in all industrial countries. Problems that have emerged in the last decade concern substances and microorganisms that don't have a regulatory status, such as antibiotic residues, drugs and specific pathogens. At a global level, guidelines exist for treatment methods for these effluents, but legislation in all major industrial countries don't contain limitations on these parameters. Therefore, a monitoring system is necessary for these effluents as well as for substances and pathogens, as these elements can represent a risk to the environment and public health.

Quinolone resistant Aeromonas spp. as carriers and potential tracers of acquired antibiotic resistance in hospital and municipal wastewater

Members of the genus Aeromonas are recognized carriers of antibiotic resistance in aquatic environments. However, their importance on the spread of resistance from hospital effluents to the environment is poorly understood. Quinolone resistant Aeromonas spp. (n = 112) isolated from hospital effluent (HE) and from raw (RWW) and treated wastewater (TWW) of the receiving urban wastewater treatment plant (UWTP) were characterized. Species identification and genetic intraspecies diversity were assessed based on the 16S rRNA, cpn60 and gyrB genes sequence analysis. The antibiotic resistance phenotypes and genotypes (qnrA, qnrB, qnrC, qnrD, qnrS, qnrVC; qepA; oqxAB; aac(6′)-Ib-cr; blaOXA; incU) were analyzed in function of the origin and taxonomic group. Most isolates belonged to the species Aeromonas caviae and Aeromonas hydrophila (50% and 41%, respectively). The quinolone and the beta-lactamase resistance genes aac(6′)-Ib-cr and blaOXA, including gene blaOXA-101, identified for the first time in Aeromonas spp., were detected in 58% and 56% of the isolates, respectively, with identical prevalence in HE and UWTP wastewater. In contrast, the gene qnrS2 was observed mainly in isolates from the UWTP (51%) and rarely in HE isolates (3%), suggesting that its origin is not the clinical setting. Bacterial groups and genes that allow the identification of major routes of antibiotic resistance dissemination are valuable tools to control this problem. In this study, it was concluded that members of the genus Aeromonas harboring the genes aac(6′)-Ib-cr and blaOXA are relevant tracers of antibiotic resistance dissemination in wastewater habitats, while those yielding the gene qnrS2 allow the traceability from non-clinical sources.

Antibiotic resistance in urban aquatic environments: can it be controlled?

Over the last decade, numerous evidences have contributed to establish a link between the natural and human-impacted environments and the growing public health threat that is the antimicrobial resistance. In the environment, in particular in areas subjected to strong anthropogenic pressures, water plays a major role on the transformation and transport of contaminants including antibiotic residues, antibiotic-resistant bacteria, and antibiotic resistance genes. Therefore, the urban water cycle, comprising water abstraction, disinfection, and distribution for human consumption, and the collection, treatment, and delivery of wastewater to the environment, is a particularly interesting loop to track the fate of antibiotic resistance in the environment and to assess the risks of its transmission back to humans. In this article, the relevance of different transepts of the urban water cycle on the potential enrichment and spread of antibiotic resistance is reviewed. According to this analysis, some gaps of knowledge, research needs, and control measures are suggested. The critical rationale behind the measures suggested and the desirable involvement of some key action players is also discussed.

Multidrug Resistance in Quinolone-Resistant Gram-Negative Bacteria Isolated from Hospital Effluent and the Municipal Wastewater Treatment Plant

This study is aimed to assess if hospital effluents represent an important supplier of multidrug-resistant (MDR) Gram-negative bacteria that, being discharged in the municipal collector, may be disseminated in the environment and bypassed in water quality control systems. From a set of 101 non-Escherichia coli Gram-negative bacteria with reduced susceptibility to quinolones, was selected a group of isolates comprised by those with the highest indices of MDR (defined as nonsusceptibility to at least one agent in six or more antimicrobial categories, MDR ≥6) or resistance to meropenem or ceftazidime (n = 25). The isolates were identified and characterized for antibiotic resistance phenotype, plasmid-mediated quinolone resistance (PMQR) genes, and other genetic elements and conjugative capacity. The isolates with highest MDR indices were mainly from hospital effluent and comprised ubiquitous bacterial groups of the class Gammaproteobacteria, of the genera Aeromonas, Acinetobacter, Citrobacter, Enterobacter, Klebsiella, and Pseudomonas, and of the class Flavobacteriia, of the genera Chryseobacterium and Myroides. In this group of 25 strains, 19 identified as Gammaproteobacteria harbored at least one PMQR gene (aac(6')-Ib-cr, qnrB, qnrS, or oqxAB) or a class 1 integron gene cassette encoding aminoglycoside, sulfonamide, or carbapenem resistance. Most of the E. coli J53 transconjugants with acquired antibiotic resistance resulted from conjugation with Enterobacteriaceae. These transconjugants demonstrated acquired resistance to a maximum of five classes of antibiotics, one or more PMQR genes and/or a class 1 integron gene cassette. This study shows that ubiquitous bacteria, other than those monitored in water quality controls, are important vectors of antibiotic resistance and can be disseminated from hospital effluent to aquatic environments. This information is relevant to support management options aiming at the control of this public health problem.

Assessment of copper and zinc salts as selectors of antibiotic resistance in Gram-negative bacteria

Some metals are nowadays considered environmental pollutants. Although some, like Cu and Zn, are essential for microorganisms, at high concentrations they can be toxic or exert selective pressures on bacteria. This study aimed to assess the potential of Cu or Zn as selectors of specific bacterial populations thriving in wastewater. Populations of Escherichia coli recovered on metal-free and metal-supplemented culture medium were compared based on antibiotic resistance phenotype and other traits. In addition, the bacterial groups enriched after successive transfers in metal-supplemented culture medium were identified. At a concentration of 1mM, Zn produced a stronger inhibitory effect than Cu on the culturability of Enterobacteriaceae. It was suggested that Zn selected populations with increased resistance prevalence to sulfamethoxazole or ciprofloxacin. In non-selective culture media, Zn or Cu selected for mono-species populations of ubiquitous Betaproteobacteria and Flavobacteriia, such as Ralstonia pickettii or Elizabethkingia anophelis, yielding multidrug resistance profiles including resistance against carbapenems and third generation cephalosporins, confirming the potential of Cu or Zn as selectors of antibiotic resistant bacteria.

Insights into the amplification of bacterial resistance to erythromycin in activated sludge

Wastewater treatment plants are significant reservoirs for antimicrobial resistance. However, little is known about wastewater treatment effects on the variation of antibiotic resistance. The shifts of bacterial resistance to erythromycin, a macrolide widely used in human medicine, on a lab-scale activated sludge system fed with real wastewater was investigated from levels of bacteria, community and genes, in this study. The resistance variation of total heterotrophic bacteria was studied during the biological treatment process, based on culture dependent method. The alterations of bacterial community resistant to erythromycin and nine typical erythromycin resistance genes were explored with molecular approaches, including high-throughput sequencing and quantitative polymerase chain reaction. The results revealed that the total heterotrophs tolerance level to erythromycin concentrations (higher than 32 mg/L) was significantly amplified during the activated sludge treatment, with the prevalence increased from 9.6% to 21.8%. High-throughput sequencing results demonstrated an obvious increase of the total heterotrophic bacterial diversity resistant to erythromycin. Proteobacteria and Bacteroidetes were the two dominant phyla in the influent and effluent of the bioreactor. However, the prevalence of Proteobacteria decreased from 76% to 59% while the total phyla number increased greatly from 18 to 29 through activated sludge treatment. The gene proportions of erm(A), mef(E) and erm(D) were greatly amplified after biological treatment. It is proposed that the transfer of antibiotic resistance genes through the variable mixtures of bacteria in the activated sludge might be the reason for the antibiotic resistance amplification. The amplified risk of antibiotic resistance in wastewater treatment needs to be paid more attention.

Molecular evidence of the close relatedness of clinical, gull and wastewater isolates of quinolone-resistant Escherichia coli

Escherichia coli with reduced susceptibility to quinolones isolated from different environmental sources (urban wastewater treatment plants, n=61; hospital effluent, n=10; urban streams, n=9; gulls, n=18; birds of prey, n=17) and from hospitalised patients (n=28) were compared based on multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). The habitats with the most diversified genotypes of quinolone-resistant E. coli, corresponding to the highest genetic diversity (H'), were wastewater and gulls. In addition, genetically distinct populations were observed in clinical samples and birds of prey, suggesting the influence of the habitat or selective pressures on quinolone-resistant E. coli. The close genetic relatedness between isolates of clinical origin and from gulls and wastewater suggests the existence of potential routes of propagation between these sources. The most common sequence types were ST131 and ST10, with ST131 being highly specific to patients, although distributed in all of the other habitats except birds of prey. The prevalence of antimicrobial resistance was significantly higher in isolates from patients and gulls than from other sources (P<0.01), suggesting that the effect of selective pressures met by isolates subjected to strong human impacts. The evidence presented suggests the potential circulation of bacteria between the environmental and clinical compartments, with gulls being a relevant vector of bacteria and resistance genes.

Assessing the antibiotic susceptibility of freshwater Cyanobacteria spp

Freshwater is a vehicle for the emergence and dissemination of antibiotic resistance. Cyanobacteria are ubiquitous in freshwater, where they are exposed to antibiotics and resistant organisms, but their role on water resistome was never evaluated. Data concerning the effects of antibiotics on cyanobacteria, obtained by distinct methodologies, is often contradictory. This emphasizes the importance of developing procedures to understand the trends of antibiotic susceptibility in cyanobacteria. In this study we aimed to evaluate the susceptibility of four cyanobacterial isolates from different genera (Microcystis aeruginosa, Aphanizomenon gracile, Chrisosporum bergii, Planktothix agradhii), and among them nine isolates from the same specie (M. aeruginosa) to distinct antibiotics (amoxicillin, ceftazidime, ceftriaxone, kanamycine, gentamicine, tetracycline, trimethoprim, nalidixic acid, norfloxacin). We used a method adapted from the bacteria standard broth microdilution. Cyanobacteria were exposed to serial dilution of each antibiotic (0.0015-1.6 mg/L) in Z8 medium (20 ± 1°C; 14/10 h L/D cycle; light intensity 16 ± 4 μEm(-2)s(-1)). Cell growth was followed overtime (OD450nm /microscopic examination) and the minimum inhibitory concentrations (MICs) were calculated for each antibiotic/isolate. We found that β-lactams exhibited the lower MICs, aminoglycosides, tetracycline and norfloxacine presented intermediate MICs; none of the isolates were susceptible to trimethoprim and nalidixic acid. The reduced susceptibility of all tested cyanobacteria to some antibiotics suggests that they might be naturally non-susceptible to these compounds, or that they might became non-susceptible due to antibiotic contamination pressure, or to the transfer of genes from resistant bacteria present in the environment.

Detection of multi-drug resistant Escherichia coli in the urban waterways of Milwaukee, WI

Urban waterways represent a natural reservoir of antibiotic resistance which may provide a source of transferable genetic elements to human commensal bacteria and pathogens. The objective of this study was to evaluate antibiotic resistance of Escherichia coli isolated from the urban waterways of Milwaukee, WI compared to those from Milwaukee sewage and a clinical setting in Milwaukee. Antibiotics covering 10 different families were utilized to determine the phenotypic antibiotic resistance for all 259 E. coli isolates. All obtained isolates were determined to be multi-drug resistant. The E. coli isolates were also screened for the presence of the genetic determinants of resistance including ermB (macrolide resistance), tet(M) (tetracycline resistance), and β-lactamases (bla OXA, bla SHV, and bla PSE). E. coli from urban waterways showed a greater incidence of antibiotic resistance to 8 of 17 antibiotics tested compared to human derived sources. These E. coli isolates also demonstrated a greater incidence of resistance to higher numbers of antibiotics compared to the human derived isolates. The urban waterways demonstrated a greater abundance of isolates with co-occurrence of antibiotic resistance than human derived sources. When screened for five different antibiotic resistance genes conferring macrolide, tetracycline, and β-lactam resistance, clinical E. coli isolates were more likely to harbor ermB and bla OXA than isolates from urban waterway. These results indicate that Milwaukee's urban waterways may select or allow for a greater incidence of multiple antibiotic resistance organisms and likely harbor a different antibiotic resistance gene pool than clinical sources. The implications of this study are significant to understanding the presence of resistance in urban freshwater environments by supporting the idea that sediment from urban waterways serves as a reservoir of antibiotic resistance.

Selective pressure of antibiotics on ARGs and bacterial communities in manure-polluted freshwater-sediment microcosms

The aim of this study was to investigate selective pressure of antibiotics on antibiotic resistance genes (ARGs) and bacterial communities in manure-polluted aquatic environment. Three treatment groups were set up in freshwater-sediment microcosms: tetracyclines group, sulfonamides group and fluoroquinolones group. Sediment and water samples were collected on day 14 after treatment. Antibiotic concentrations, ARGs abundances and bacterial community composition were analyzed. Antibiotic concentrations were determined by ultra-performance liquid chromatography-electrospray tandem mass spectrometry. ARGs abundances were quantified by real time quantitative PCR. Bacterial community composition was analyzed based on amplicon sequencing. Of the three classes of antibiotics analyzed in the treatment groups, accumulation amounts were tetracyclines> fluoroquinolone> sulfonamides in the sediment samples, while they were sulfonamides> fluoroquinolone> tetracyclines in the water samples. In the treatment groups, the relative abundances of some tet resistance genes [tet(W) and tet(X)] and plasmid-mediated quinolone resistance (PMQR) genes [oqx(B) and aac(6′)-Ib] in sediment samples were significantly higher than those in the paired water samples. Tetracyclines significantly selected the bacterial classes including Gammaproteobacteria, Clostridia, and the genera including Salmonella, Escherichia/Shigella, Clostridium, Stenotrophomonas in sediment samples. The significant selection on bacterial communities posed by sulfonamides and fluoroquinolones was also observed. The results indicated that sediment may supply an ideal setting for maintenance and persistence of tet resistance genes [tet(W) and tet(X)] and PMQR genes [oqx(B) and aac(6′)-Ib] under antibiotic pollution. The results also highlighted that antibiotics significantly selected specific bacterial communities including the taxa associated with opportunistic pathogens.

Genetic characterization of fluoroquinolone resistant Escherichia coli from urban streams and municipal and hospital effluents

Escherichia coli with reduced susceptibility to ciprofloxacin, isolated from urban streams, wastewater treatment plants and hospital effluent between 2004 and 2012, were compared based on multilocus sequence typing (MLST), quinolone and beta-lactam resistance determinants and plasmid replicon type. Isolates from the different types of water and isolation dates clustered together, suggesting the persistence and capacity to propagate across distinct aquatic environments. The most prevalent MLST groups were ST10 complex and ST131. Almost all isolates (98%) carried mutations in the chromosomal genes gyrA and/or parC, and 10% possessed the genes qepA, aac(6('))-Ib-cr and/or qnrS1. Over 80% of the isolates were resistant to three or more classes of antibiotics (MDR ≥ 3). The most prevalent beta-lactamase encoding gene was blaTEM, followed by blaCTX-M-15, co-existing with plasmid mediated quinolone resistance. The plasmid replicon types of the group IncF were the most prevalent and distributed by different MLST groups. The genes aac(6('))-Ib-cr and/or qnrS1 could be transferred by conjugation in combination with the genes blaTEM,blaSHV-12 or blaOXA-1 and the plasmid replicon types I1-Iγ, K, HI2 and/or B/O. The potential of multidrug resistant E. coli with reduced susceptibility to ciprofloxacin, harboring mobile genetic elements and with ability to conjugate and transfer resistance genes, to spread and persist across different aquatic environments was demonstrated.

Occurrence of antibiotics and antibiotic resistance genes in hospital and urban wastewaters and their impact on the receiving river

Antibiotic resistance has become a major health concern; thus, there is a growing interest in exploring the occurrence of antibiotic resistance genes (ARGs) in the environment as well as the factors that contribute to their emergence. Aquatic ecosystems provide an ideal setting for the acquisition and spread of ARGs due to the continuous pollution by antimicrobial compounds derived from anthropogenic activities. We investigated, therefore, the pollution level of a broad range of antibiotics and ARGs released from hospital and urban wastewaters, their removal through a wastewater treatment plant (WWTP) and their presence in the receiving river. Several antimicrobial compounds were detected in all water samples collected. Among antibiotic families, fluoroquinolones were detected at the highest concentration, especially in hospital effluent samples. Although good removal efficiency by treatment processes was observed for several antimicrobial compounds, most antibiotics were still present in WWTP effluents. The results also revealed that copy numbers of ARGs, such as blaTEM (resistance to β-lactams), qnrS (reduced susceptibility to fluoroquinolones), ermB (resistance to macrolides), sulI (resistance to sulfonamides) and tetW (resistance to tetracyclines), were detected at the highest concentrations in hospital effluent and WWTP influent samples. Although there was a significant reduction in copy numbers of these ARGs in WWTP effluent samples, this reduction was not uniform across analyzed ARGs. Relative concentration of ermB and tetW genes decreased as a result of wastewater treatment, whereas increased in the case of blaTEM, sulI and qnrS genes. The incomplete removal of antibiotics and ARGs in WWTP severely affected the receiving river, where both types of emerging pollutants were found at higher concentration in downstream waters than in samples collected upstream from the discharge point. Taken together, our findings demonstrate a widespread occurrence of antibiotics and ARGs in urban and hospital wastewater and how these effluents, even after treatment, contribute to the spread of these emerging pollutants in the aquatic environment.