Antibiotics and antibiotic resistance genes in natural environments

Characterization of ciprofloxacin-resistant isolates from a wastewater treatment plant and its receiving river

In this study we characterised the ciprofloxacin-resistant strains isolated in biofilm and sediments from a wastewater treatment plant (WWTP) discharge point and its receiving river. We also examined the prevalence of qnrA, qnrB, qnrS and aac(6')-Ib-cr genes in these isolates and determined whether they harbour plasmid-encoded β-lactamases such as TEM, SHV and CTX-M. Moreover, antibiotic concentrations were also measured to evaluate the level of contamination of these pharmaceuticals in the sampling area. Antibiotics were found in the range of ng L(-1) in WWTP effluents, but most of them were no longer found in downstream river. However, some fluoroquinolones were detected in sediment downstream demonstrating their high persistence and their capacity to be retained in the river sediments. Most of the ciprofloxacin-resistant isolates belonged to the Gammaproteobacteria class and 17 of them, 8 (7.6%) from the first sampling and 9 (6.1%) from the second sampling, carried a qnr gene. In particular, 15 isolates carried the qnrS gene and 2 carried the qnrB gene. Among the qnr-positive isolates, 12 harboured the aac(6')-lb-cr gene and 2 of them also carried a β-lactamase on the same plasmid, indicating that they may be transferred simultaneously. It is also noteworthy that all qnr-positive isolates identified as Aeromonas species harboured the same qnrS allele, namely the qnrS2. This study reinforces the importance of environmental bacteria as vehicles for dissemination of antibiotic resistance genes.

Increased survival of experimentally evolved antimicrobial peptide-resistant Staphylococcus aureus in an animal host

Antimicrobial peptides (AMPs) have been proposed as new class of antimicrobial drugs, following the increasing prevalence of bacteria resistant to antibiotics. Synthetic AMPs are functional analogues of highly evolutionarily conserved immune effectors in animals and plants, produced in response to microbial infection. Therefore, the proposed therapeutic use of AMPs bears the risk of 'arming the enemy': bacteria that evolve resistance to AMPs may be cross-resistant to immune effectors (AMPs) in their hosts. We used a panel of populations of Staphylococcus aureus that were experimentally selected for resistance to a suite of individual AMPs and antibiotics to investigate the 'arming the enemy' hypothesis. We tested whether the selected strains showed higher survival in an insect model (Tenebrio molitor) and cross-resistance against other antimicrobials in vitro. A population selected for resistance to the antimicrobial peptide iseganan showed increased in vivo survival, but was not more virulent. We suggest that increased survival of AMP-resistant bacteria almost certainly poses problems to immune-compromised hosts.

Occurrence of avian pathogenic Escherichia coli and antimicrobial-resistant E. coli in red-legged partridges (Alectoris rufa): sanitary concerns of farming

Red-legged partridges (Alectoris rufa) are a significant part of the culture, diet and income for many people in central and southern Spain. Due to declining populations in the wild, intensive farming is common and 4 million juvenile partridges are released each autumn. Intensive management and high densities result in high prevalence of enteric disease and the use of antimicrobials as preventive measures on partridge farms and prior to restocking in the wild. We determined the occurrence of avian pathogenic Escherichia coli (APEC), and screened phenotypic resistance of E. coli against enrofloxacin, gentamicin and cefotaxim in farmed, restocked and wild partridges. Prevalence of APEC in farmed and restocked red-legged partridges was significantly higher than in natural populations. Phenotypic resistance against both gentamicin and enrofloxacin was significantly more frequent in farmed (75%) and restocked (43%) partridges than in wild partridges, while most E. coli isolated from natural populations were susceptible to all three antimicrobials tested (65%). This indicates that farmed and restocked partridges carry APEC that could be a reason for disease outbreaks on farms, and that E. coli carried by farmed and restocked partridges can acquire resistance to frequently used antimicrobials, thus being a concern for the environment, wild birds and consumers. Management in farms and restocking procedures may create a hazard not only for spreading APEC, but also as a potential source of resistant E. coli in the environment.

Prevalence of antibiotic resistance in bacteria isolated from drinking well water available in Guinea-Bissau (West Africa)

The dissemination of antibiotic-resistant bacteria and the spread of antibiotic resistance genes are a major public health concern worldwide, being even proposed as emerging contaminants. The aquatic environment is a recognized reservoir of antibiotic resistant bacteria, and antibiotic resistance genes have been recently detected in drinking water. In this study, the water quality and the prevalence of antibiotic resistance of heterotrophic culturable bacteria were characterized seasonally in wells that serve the population of Guinea-Bissau (West Africa) as the sole source of water for drinking and other domestic proposes. The results revealed that well water was unfit for human consumption independently of the season, owing to high acidity and heavy fecal contamination. Moreover, potentially pathogenic bacteria, which showed resistance to the most prescribed antibiotics in Guinea-Bissau, were isolated from well water, posing an additional health risk. Our results suggest that well water not only fosters the transmission of potential pathogenic bacteria, but also represents an important reservoir for the proliferation of antibiotic resistant bacteria, that can aggravate the potential to cause disease in a very vulnerable population that has no other alternative but to consume such water.

Adsorption behavior of sulfamethazine in an activated sludge process treating swine wastewater

Swine wastewater is an important pollution source of antibiotics entering the aquatic environment. In this work, the adsorption behavior of sulfamethazine (SMN), a commonly-used sulfonamide antibiotic, on activated sludge from a sequencing batch reactor treating swine wastewater was investigated. The results show that the adsorption of SMN on activated sludge was an initially rapid process and reached equilibrium after 6hr. The removal efficiency of SMN from the water phase increased with an increasing concentration of mixed liquor suspended solids, while the adsorbed concentration of SMN decreased. Solution pH influenced both the speciation of SMN and the surface properties of activated sludge, thus significantly impacting the adsorption process. A linear partition model could give a good fit for the equilibrium concentrations of SMN at the test temperatures (i.e., 10, 20 and 30°C). The partition coefficient (Kd) was determined to be 100.5L/kg at 20°C, indicating a quite high adsorption capacity for SMN. Thermodynamic analysis revealed that SMN adsorption on activated sludge was an exothermic process. This study could help to clarify the fate and behavior of sulfonamide antibiotics in the activated sludge process and assess consequent environmental risks arising from sludge disposal as well.

Emergence and spread of antibiotic resistance: setting a parameter space

The emergence and spread of antibiotic resistance among human pathogens is a relevant problem for human health and one of the few evolution processes amenable to experimental studies. In the present review, we discuss some basic aspects of antibiotic resistance, including mechanisms of resistance, origin of resistance genes, and bottlenecks that modulate the acquisition and spread of antibiotic resistance among human pathogens. In addition, we analyse several parameters that modulate the evolution landscape of antibiotic resistance. Learning why some resistance mechanisms emerge but do not evolve after a first burst, whereas others can spread over the entire world very rapidly, mimicking a chain reaction, is important for predicting the evolution, and relevance for human health, of a given mechanism of resistance. Because of this, we propose that the emergence and spread of antibiotic resistance can only be understood in a multi-parameter space. Measuring the effect on antibiotic resistance of parameters such as contact rates, transfer rates, integration rates, replication rates, diversification rates, and selection rates, for different genes and organisms, growing under different conditions in distinct ecosystems, will allow for a better prediction of antibiotic resistance and possibilities of focused interventions.

The gull (Chroicocephalus brunnicephalus) as an environmental bioindicator and reservoir for antibiotic resistance on the coastlines of the Bay of Bengal

The presence and frequency of multiresistant bacteria in wild birds act as indicators of the environmental contamination of antibiotic resistance. To explore the rate of contamination mediated by Escherichia coli, 150 fecal samples from the brown-headed gull (Chroicocephalus brunnicephalus) and 8 water samples from the Bay of Bengal area were collected, cultured, and tested for antibiotic susceptibility. Special attention was paid to extended-spectrum beta-lactamase (ESBL)-producing isolates, which were further characterized genetically. Antibiotic resistance was found in 42.3% (36/85) of the E. coli isolates and multidrug resistance in 11.8%. Isolates from the area with a higher human activity were more resistant than those from an area with a lower level of activity. Most frequent was resistance to ampicillin (29.4%), followed by trimethoprim-sulfamethoxazole (24.7%) and quinolones (22.4%). Carriage of ESBL-producing E. coli was relatively high (17.3%) in the gulls, whereas no ESBL producers were found in the water. All ESBL-producing E. coli isolates, but one, carried bla(CTX-M-15) or bla(CTX-M-15)-like genes. A bla(CTX-M-14)-like enzyme was found as an exception. Gulls from two different colonies shared E. coli clones and harbored the clinically relevant sequence types ST10, ST48, and ST131. The high frequency of antibiotic resistance and ESBL production among E. coli isolates from gulls indicates that the environmental contamination of antibiotic resistance has already gone far on the coastlines of the Bay of Bengal. Considering the limited control over the antibiotic consumption and waste from human activities in Bangladesh, there is no easy solution in sight.

Metabolic compensation of fitness costs associated with overexpression of the multidrug efflux pump MexEF-OprN in Pseudomonas aeruginosa

The acquisition of antibiotic resistance has been associated with a possible nonspecific, metabolic burden that is reflected in decreased fitness among resistant bacteria. We have recently demonstrated that overexpression of the MexEF-OprN multidrug efflux pump does not produce a metabolic burden when measured by classical competitions tests but rather leads to a number of changes in the organism's physiology. One of these changes is the untimely activation of the nitrate respiratory chain under aerobic conditions. MexEF-OprN is a proton/substrate antiporter. Overexpression of this element should result in a constant influx of protons, which may lead to cytoplasmic acidification. Acidification was not observed in aerobiosis, a situation in which the MexEF-overproducing mutant increases oxygen consumption. This enhanced oxygen uptake serves to eliminate intracellular proton accumulation, preventing the cytoplasmic acidification that was observed exclusively under anaerobic conditions, a situation in which the fitness of the MexEF-OprN-overproducing mutant decreases. Finally, we determined that the early activation of the nitrate respiratory chain under aerobic conditions plays a role in preventing a deleterious effect associated with the overexpression of MexEF-OprN. Our results show that metabolic rewiring may assist in overcoming the potential fitness cost associated with the acquisition of antibiotic resistance. Furthermore, the capability to metabolically compensate for this effect is habitat dependent, as demonstrated by our results under anaerobic conditions. The development of drugs that prevent metabolic compensation of fitness costs may help to reduce the persistence and dissemination of antibiotic resistance.

The marine environment as a reservoir of enterococci carrying resistance and virulence genes strongly associated with clinical strains

To gain insights into the relationships and the genetic exchange among environmental and clinical enterococci, 59 strains (29 from marine aquaculture sites and 30 from clinical settings) resistant to tetracycline, erythromycin, ampicillin and/or gentamicin were analysed for the antibiotic resistance tet(M), tet(L), tet(O), erm(A), erm(B), mef blaZ, aac(6')-Ie aph(2″)-Ia and virulence gelE, cylB, efaA and esp genes, and for the copper resistance gene tcrB. Antibiotic resistance and virulence genes were detected more frequently in clinical than in environmental enterococci; the opposite was true for copper resistance. Conjugation experiments demonstrated the transfer of antibiotic resistance genes from marine to clinical enterococci in interspecific mating and the uncommon joint transfer of tet(L) and erm(B). Enterobacterial repetitive intergenic consensus polymerase chain reaction typing evidenced a cluster (90% similarity) encompassing strains carrying multiple antibiotic resistance genes from both sets; the others marine isolates exhibited polyclonality and bore tcrB. Our results demonstrate that antibiotic-resistant marine enterococci bear antibiotic resistance genes transferable to humans and suggest that copper resistance, not observed among clinical strains, may be useful for survival in the environment, whereas virulence genes likely confer no advantage to enterococcal populations adapted to a lifestyle outside the host.

Interplay between intrinsic and acquired resistance to quinolones in Stenotrophomonas maltophilia

To analyse whether the mutation-driven resistance-acquisition potential of a given bacterium might be a function of its intrinsic resistome, quinolones were used as selective agents and Stenotrophomonas maltophilia was chosen as a bacterial model. S. maltophilia has two elements - SmQnr and SmeDEF - that are important in intrinsic resistance to quinolones. Using a battery of mutants in which either or both of these elements had been removed, the apparent mutation frequency for quinolone resistance and the phenotype of the selected mutants were found to be related to the intrinsic resistome and also depended on the concentration of the selector. Most mutants had phenotypes compatible with the overexpression of multidrug efflux pump(s); SmeDEF overexpression was the most common cause of quinolone resistance. Whole genome sequencing showed that mutations of the SmeRv regulator, which result in the overexpression of the efflux pump SmeVWX, are the cause of quinolone resistance in mutants not overexpressing SmeDEF. These results indicate that the development of mutation-driven antibiotic resistance is highly dependent on the intrinsic resistome, which, at least for synthetic antibiotics such as quinolones, did not develop as a response to the presence of antibiotics in the natural ecosystems in which S. maltophilia evolved.

Occurrence and fate of pharmaceutically active compounds in the largest municipal wastewater treatment plant in Southwest China: mass balance analysis and consumption back-calculated model

The occurrence and fate of twenty-one pharmaceutically active compounds (PhACs) were investigated in different steps of the largest wastewater treatment plant (WWTP) in Southwest China. Concentrations of these PhACs were determined in both wastewater and sludge phases by a high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Results showed that 21 target PhACs were present in wastewater and 18 in sludge. The calculated total mass load of PhACs per capita to the influent, the receiving water and sludge were 4.95mgd(-1)person(-1), 889.94μgd(-1)person(-1) and 78.57μgd(-1)person(-1), respectively. The overall removal efficiency of the individual PhACs ranged from "negative removal" to almost complete removal. Mass balance analysis revealed that biodegradation is believed to be the predominant removal mechanism, and sorption onto sludge was a relevant removal pathway for quinolone antibiotics, azithromycin and simvastatin, accounting for 9.35-26.96% of the initial loadings. However, the sorption of the other selected PhACs was negligible. The overall pharmaceutical consumption in Chongqing, China, was back-calculated based on influent concentration by considering the pharmacokinetics of PhACs in humans. The back-estimated usage was in good agreement with usage of ofloxacin (agreement ratio: 72.5%). However, the back-estimated usage of PhACs requires further verification. Generally, the average influent mass loads and back-calculated annual per capita consumption of the selected antibiotics were comparable to or higher than those reported in developed countries, while the case of other target PhACs was opposite.

Antimicrobial susceptibility of Vibrio vulnificus and Vibrio parahaemolyticus recovered from recreational and commercial areas of Chesapeake Bay and Maryland Coastal Bays

Vibrio vulnificus and V. parahaemolyticus in the estuarine-marine environment are of human health significance and may be increasing in pathogenicity and abundance. Vibrio illness originating from dermal contact with Vibrio laden waters or through ingestion of seafood originating from such waters can cause deleterious health effects, particularly if the strains involved are resistant to clinically important antibiotics. The purpose of this study was to evaluate antimicrobial susceptibility among these pathogens. Surface-water samples were collected from three sites of recreational and commercial importance from July to September 2009. Samples were plated onto species-specific media and resulting V. vulnificus and V. parahaemolyticus strains were confirmed using polymerase chain reaction assays and tested for antimicrobial susceptibility using the Sensititre® microbroth dilution system. Descriptive statistics, Friedman two-way Analysis of Variance (ANOVA) and Kruskal-Wallis one-way ANOVA were used to analyze the data. Vibrio vulnificus (n = 120) and V. parahaemolyticus (n = 77) were isolated from all sampling sites. Most isolates were susceptible to antibiotics recommended for treating Vibrio infections, although the majority of isolates expressed intermediate resistance to chloramphenicol (78% of V. vulnificus, 96% of V. parahaemolyticus). Vibrio parahaemolyticus also demonstrated resistance to penicillin (68%). Sampling location or month did not significantly impact V. parahaemolyticus resistance patterns, but V. vulnificus isolates from St. Martin's River had lower overall intermediate resistance than that of the other two sampling sites during the month of July (p = 0.0166). Antibiotics recommended to treat adult Vibrio infections were effective in suppressing bacterial growth, while some antibiotics recommended for pediatric treatment were not effective against some of the recovered isolates. To our knowledge, these are the first antimicrobial susceptibility data of V. vulnificus and V. parahaemolyticus recovered from the Chesapeake Bay. These data can serve as a baseline against which future studies can be compared to evaluate whether susceptibilities change over time.

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.

Simultaneous removal of cadmium and sulfamethoxazole from aqueous solution by rice straw biochar

The simultaneous sorption behavior and characteristics of cadmium (Cd) and sulfamethoxazole (SMX) on rice straw biochar were investigated. Isotherms of Cd and SMX were well modeled by the Langmuir equation (R(2)>0.95). The calculated maximum adsorption parameter (Q) of Cd was similar in single and binary systems (34129.69 and 35919.54 mg/kg, respectively). However, the Q of SMX in a binary system (9182.74 mg/kg) was much higher than that in a single system (1827.82 mg/kg). The presence of Cd significantly promoted the sorption of SMX on rice straw biochar. When the pH ranged from 3 to 7.5, the sorption of Cd had the characteristics of a parabola pattern with maximum adsorption at pH 5, while the adsorption quantity of SMX decreased with increasing pH, with maximum adsorption at pH 3. The amount of SMX adsorbed on biochar was positively correlated with the surface area of the biochar, and the maximum adsorption occurred with d 250 biochar (biochar with a diameter of 150-250 μm). Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) showed that the removal of Cd and SMX by rice straw biochar may be attributed to precipitation and the formation of surface complexes between Cd or SMX and carboxyl or hydroxyl groups. The results of this study indicate that rice straw biochar has the potential for simultaneous removal of Cd and SMX from co-contaminated water.

Antibiotic resistance, plasmid-mediated quinolone resistance (PMQR) genes and ampC gene in two typical municipal wastewater treatment plants

Antibiotic resistant bacteria and plasmid-mediated quinolone resistance genes and ampC gene were investigated for Escherichia coli isolates from two typical municipal wastewater treatment plants in both dry and wet seasons by using the antibiotic susceptibility test and PCR assay, respectively. The results showed that 98.4% of the isolates (1056) were found resistant to antibiotic(s) tested and 90.6% showed multiple resistances to at least three antibiotics. Tetracycline was found to have the highest resistance frequency (70.8%), followed by ampicillin (65.1%), whereas ceftazidime had the lowest resistance frequency of 9.0%. Moreover, 39.2% of the E. coli isolates were carrying plasmids. intI1 had the highest detection rate in the plasmids (38.1%), followed by qnrS, ampC, qnrB, intI2 and aac(6')-Ib-cr. The disinfection process (UV and chlorination) could significantly reduce the number of bacteria, but percentage of the resistant bacteria, resistance frequency for each antibiotic, MAR index and detection rate of the plasmid-mediated resistance genes were all found increasing in the effluents of biological units. The results of this study showed that a more frequent horizontal gene transfer occurred in the biological units. Wastewater treatment plants were an important medium for the recombination and dissemination of antibiotic resistance genes in the environment.

Occurrence, fate and ecotoxicological assessment of pharmaceutically active compounds in wastewater and sludge from wastewater treatment plants in Chongqing, the Three Gorges Reservoir Area

The occurrence, removal and ecotoxicological assessment of 21 pharmaceutically active compounds (PhACs) including antibiotics, analgesics, antiepileptics, antilipidemics and antihypersensitives, were studied at four municipal wastewater treatment plants (WWTP) in Chongqing, the Three Gorges Reservoir Area. Individual treatment unit effluents, as well as primary and secondary sludge, were sampled and analyzed for the selected PhACs to evaluate their biodegradation, persistence and partitioning behaviors. PhACs were identified and quantified using high performance liquid chromatography/tandem mass spectrometry after solid-phase extraction. All the 21 analyzed PhACs were detected in wastewater and the target PhACs except acetaminophen, ibuprofen and gemfibrozil, were also found in sludge. The concentrations of the antibiotics and SVT were comparable to or even higher than those reported in developed countries, while the case of other target PhACs was opposite. The elimination of PhACs except acetaminophen was incomplete and a wide range of elimination efficiencies during the treatment were observed, i.e. from "negative removal" to 99.5%. The removal of PhACs was insignificant in primary and disinfection processes, and was mainly achieved during the biological treatment. Based on the mass balance analysis, biodegradation is believed to be the primary removal mechanism, whereas only about 1.5% of the total mass load of the target PhACs was removed by sorption. Experimentally estimated distribution coefficients (<500 L/kg, with a few exceptions) also indicate that biodegradation/transformation was responsible for the removal of the target PhACs. Ecotoxicological assessment indicated that the environment concentrations of single compounds (including sulfadiazine, sulfamethoxazole, ofloxacin, azithromycin and erythromycin-H2O) in effluent and sludge, as well as the mixture of the 21 detected PhACs in effluent, sludge and receiving water had a significant ecotoxicological risk to algae. Therefore, further control of PhACs in effluent and sludge is required before their discharge and application to prevent their introduction into the environment.

Molecular insights into the pH-dependent adsorption and removal of ionizable antibiotic oxytetracycline by adsorbent cyclodextrin polymers

Effects of pH on adsorption and removal efficiency of ionizable organic compounds (IOCs) by environmental adsorbents are an area of debate, because of its dual mediation towards adsorbents and adsorbate. Here, we probe the pH-dependent adsorption of ionizable antibiotic oxytetracycline (comprising OTCH₂⁺, OTCH^±, OTC⁻, and OTC²⁻) onto cyclodextrin polymers (CDPs) with the nature of molecular recognition and pH inertness. OTCH^± commonly has high adsorption affinity, OTC⁻ exhibits moderate affinity, and the other two species have negligible affinity. These species are evidenced to selectively interact with structural units (e.g., CD cavity, pore channel, and network) of the polymers and thus immobilized onto the adsorbents to different extents. The differences in adsorption affinity and mechanisms of the species account for the pH-dependent adsorption of OTC. The mathematical equations are derived from the multiple linear regression (MLR) analysis of quantitatively relating adsorption affinity of OTC at varying pH to adsorbent properties. A combination of the MLR analysis for OTC and molecular recognition of adsorption of the species illustrates the nature of the pH-dependent adsorption of OTC. Based on this finding, γ-HP-CDP is chosen to adsorb and remove OTC at pH 5.0 and 7.0, showing high removal efficiency and strong resistance to the interference of coexisting components.

Transfer of antibiotic resistance plasmids in pure and activated sludge cultures in the presence of environmentally representative micro-contaminant concentrations

The presence of antibiotics in the natural environment has been a growing issue. This presence could also account for the influence that affects microorganisms in such a way that they develop resistance against these antibiotics. The aim of this study was to evaluate whether the antibiotic resistant gene (ARG) plasmid transfer can be facilitated by the impact of 1) environmentally representative micro-contaminant concentrations in ppb (part per billion) levels and 2) donor-recipient microbial complexity (pure vs. mixed). For this purpose, the multidrug resistant plasmid, pB10, and Escherichia coli DH5α were used as a model plasmid and a model donor, respectively. Based on conjugation experiments with pure (Pseudomonas aeruginosa PAKexoT) and mixed (activated sludge) cultures as recipients, increased relative plasmid transfer frequencies were observed at ppb (μg/L) levels of tetracycline and sulfamethoxazole micro-contaminant exposure. When sludge, a more complex community, was used as a recipient, the increases of the plasmid transfer rate were always statistically significant but not always in P. aeruginosa. The low concentration (10 ppb) of tetracycline exposure led to the pB10 transfer to enteric bacteria, which are clinically important pathogens.

Investigation of residual fluoroquinolones in a soil-vegetable system in an intensive vegetable cultivation area in Northern China

One of the largest vegetable cultivation field sites in Northeast China was selected to investigate the occurrence and distribution pattern of fluoroquinolones (FQs) in the soil-vegetable system. A total of 100 surface soil samples and 68 vegetable samples were collected from this study area. The antibiotic concentration was analyzed using high-performance liquid chromatography tandem mass spectrometry. Results indicated the presence of FQs in all soil samples. Ciprofloxacin (CIP) had the highest mean concentration, at 104.4 μg · kg(-1) in the soil, a level that represents a relatively high risk to the environment and to human health. However, in the vegetable samples, norfloxacin (NOR) was significantly higher than CIP and enrofloxacin (ENR), ranging from 18.2 to 658.3 μg · kg(-1). The transfer ability of NOR in soil-vegetables is greater than that of CIP and ENR. Moreover, we found that the solanaceous fruits had a higher antibiotic accumulation ability than the leafy vegetables. Taken together, these data indicate that greater attention should be paid to the region in which vegetables with higher accumulation ability are grown.

Impact of reclaimed water irrigation on antibiotic resistance in public parks, Beijing, China

The abundance and distribution of antibiotics and antibiotic resistance genes (ARGs) in soils from six parks using reclaimed water in Beijing, China, were characterized. Three classes of commonly used antibiotics (tetracycles, quinolones, and sulfonamides) were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The highest concentrations of tetracyclines and quinolones were 145.2 μg kg(-1) and 79.2 μg kg(-1), respectively. Detected tetG, tetW, sulI, and sulII genes were quantified by quantitative PCR. ARGs exhibited various abundances for different park soils. The integrase gene (intI1) as an indicator of horizontal gene transfer potential was also detected in high abundance, and had significant positive correlation with tetG, sulI, and sulII genes, suggesting that intI1 may be involved in ARGs dissemination. Both sulII and intI1 clones had high homology with some classes of pathogenic bacteria, such as Klebsiella oxytoca, Acinetobacter baumannii, Shigella flexneri, which could trigger potential public health concern.

Balancing water sustainability and public health goals in the face of growing concerns about antibiotic resistance

Global initiatives are underway to advance the sustainability of urban water infrastructure through measures such as water reuse. However, there are growing concerns that wastewater effluents are enriched in antibiotics, antibiotic resistant bacteria, and antibiotic resistance genes, and thus could serve as a contributing factor to growing rates of antibiotic resistance in human infections. Evidence for the role of the water environment as a source and pathway for the spread of antimicrobial resistance is examined and key knowledge gaps are identified with respect to implications for sustainable water systems. Efforts on the part of engineers along with investment in research in epidemiology, risk assessment, water treatment and water delivery could advance current and future sustainable water strategies and help avoid unintended consequences.

Synthesis of core–shell structured Fe3O4@α-MnO2microspheres for efficient catalytic degradation of ciprofloxacin

Three-dimensional core–shell structured Fe₃O₄@α-MnO₂microspheres were successfully fabricated to activate persulfate for catalytic degradation of ciprofloxacin in wastewater.

Effect of antibiotics on redox transformations of arsenic and diversity of arsenite-oxidizing bacteria in sediment microbial communities

In the present study, we investigated the effect of antibiotics on microbial arsenate (As(V)) reduction and arsenite (As(III)) oxidation in sediments collected from a small pond and eutrophic lake. The As(V)-reducing activities were less susceptible to chloramphenicol in aerobic conditions than in anaerobic conditions. Aerobic As(V) reduction proceeded in the presence of diverse types of antibiotics, suggesting that As-resistant bacteria are widely antibiotic resistant. In contrast, some antibiotics, e.g., chloramphenicol, strongly inhibited aerobic As(III) oxidation. In addition, bacterial As(III) oxidase genes were scarcely amplified and Proteobacteria -related 16S rRNA genes drastically decreased in chloramphenicol-amended cultures. Erythromycin and lincomycin, which successfully target many Gram-positive bacteria, scarcely affected As(III) oxidation, although they decreased the diversity of As(III) oxidase genes. These results indicate that the aerobic As(III) oxidizers in the sediment cultures are mainly composed of Proteobacteria and are more sensitive to certain types of antibiotics than the aerobic As(V) reducers. Our results suggest that antibiotic disturbance of environmental microbial communities may affect the biogeochemical cycle of As.

Geo-Chip analysis reveals reduced functional diversity of the bacterial community at a dumping site for dredged Elbe sediment

The dumping of dredged sediments represents a major stressor for coastal ecosystems. The impact on the ecosystem function is determined by its complexity not easy to assess. In the present study, we evaluated the potential of bacterial community analyses to act as ecological indicators in environmental monitoring programmes. We investigated the functional structure of bacterial communities, applying functional gene arrays (GeoChip4.2). The relationship between functional genes and environmental factors was analysed using distance-based multivariate multiple regression. Apparently, both the function and structure of the bacterial communities are impacted by dumping activities. The bacterial community at the dumping centre displayed a significant reduction of its entire functional diversity compared with that found at a reference site. DDX compounds separated bacterial communities of the dumping site from those of un-impacted sites. Thus, bacterial community analyses show great potential as ecological indicators in environmental monitoring.

New strategies against Stenotrophomonas maltophilia: a serious worldwide intrinsically drug-resistant opportunistic pathogen

Stenotrophomonas maltophilia is a worldwide human opportunistic pathogen associated with serious infections in humans, and is most often recovered from respiratory tract infections. In addition to its intrinsic drug resistance, this organism may acquire resistance via multiple molecular mechanisms. New antimicrobial strategies are needed to combat S. maltophilia infections, particularly in immunocompromised patients, cystic fibrosis patients with polymicrobial infections of the lung, and in patients with chronic infections. This editorial reports on newer drugs and antimicrobial strategies and their potential for use in treatment of S. maltophilia infections, the development of new technologies to detect this organism, and identifies strategies currently in use to reduce transmission of this pathogen.

Occurrence and distribution of heavy metals and tetracyclines in agricultural soils after typical land use change in east China

Land use in east China tends to change from paddy rice to vegetables or other high-value cash crops, resulting in high input rates of organic manures and increased risk of contamination with both heavy metals (HMs) and antibiotics. This investigation was conducted to determine the accumulation, distribution and risks of HMs and tetracyclines (TCs) in surface soils and profiles receiving different amounts of farmyard manure. Soil samples collected from suburbs of Hangzhou city, Zhejiang province were introduced to represent three types of land use change from paddy rice to asparagus production, vineyards and field mustard cultivation, and divided into two portions, one of which was air-dried and sieved through 2-, 0.3- and 0.149-mm nylon mesh for determination of pH and heavy metals. The other portion was frozen at -20 °C, freeze-dried and sieved through a 0.3-mm nylon mesh for tetracyline determination. HM and TC concentrations in surface soils of 14-year-old mustard fields were the highest with total Cu, Zn, Cd and ∑TCs of 50.5, 196, 1.03 mg kg(-1) and 22.9 μg kg(-1), respectively, on average. The total Cu sequence was field mustard>vineyards>asparagus when duration of land use change was considered; oxytetracycline (OTC) and doxycycline were dominant in soils used for asparagus production; OTC was dominant in vineyards and chlortetracycline (CTC) was dominant in mustard soils. There were positive pollution relationships among Cu, Zn and ∑TCs, especially between Cu and Zn or Cu and ∑TCs. Repeated and excessive application of manures from intensive farming systems may produce combined contamination with HMs and TCs which were found in the top 20 cm of the arable soil profiles and also extended to 20-40 cm depth. Increasing manure application rate and cultivation time led to continuing increases in residue concentrations and movement down the soil profile.

Occurrence and sources of antibiotics and their metabolites in river water, WWTPs, and swine wastewater in Jiulongjiang River basin, south China

In this study, the occurrence and sources of five cataloged antibiotics and metabolites were studied in Jiulongjiang River basin, south China. Nineteen antibiotics and 13 metabolites were detected in water samples from 16 river sampling sites, wastewater from 5 swine-raising facilities, and effluent from 5 wastewater treatment plants (WWTPs). The results showed that 12 antibiotics and 6 metabolites were detected in river water samples. Sulfonamides (SAs) and their metabolites were detected at high concentrations (8.59-158.94 ng/L). Tetracyclines (TCs) and their metabolites were frequently detected in swine wastewater, and the maximum concentration was up to the level in milligram per liter. Macrolides (MLs) and β-lactams (β-Ls) were found in all WWTP effluent samples and some river samples, while they were never found in any of the swine wastewater samples. SAs and quinolones (QNs) were detected in all samples. Hierarchical cluster analysis of 16 surface water samples was applied to achieve the spatial distribution characteristics of antibiotics in the Jiulongjiang River. As a result, two categories were obviously obtained. Principal component analysis and redundancy analysis showed that TCs and SAs as well as their metabolites were the major antibiotics in Jiulongjiang River, and they mainly originated from swine wastewater, while the QNs, MLs, and β-Ls in the Jiulongjiang River came from WWTP effluent.

Exploring the risks of phage application in the environment

Interest in using bacteriophages to control the growth and spread of bacterial pathogens is being revived in the wake of widespread antibiotic resistance. However, little is known about the ecological effects that high concentrations of phages in the environment might have on natural microbial communities. We review the current evidence suggesting phage-mediated environmental perturbation, with a focus on agricultural examples, and describe the potential implications for human health and agriculture. Specifically, we examine the known and potential consequences of phage application in certain agricultural practices, discuss the risks of evolved bacterial resistance to phages, and question whether the future of phage therapy will emulate that of antibiotic treatment in terms of widespread resistance. Finally, we propose some basic precautions that could preclude such phenomena and highlight existing methods for tracking bacterial resistance to phage therapeutic agents.

Evidence and recommendations to support the use of a novel passive water sampler to quantify antibiotics in wastewaters

A novel passive water sampler (diffusive gradients in thin-films for organics, o-DGT) was previously developed and successfully tested in the laboratory, but has not yet been validated in the field. Here, o-DGT samplers were deployed in the influent and effluent of a typical UK wastewater treatment plant (WWTP); the influent was also sampled with a conventional automatic sampler (Auto) and by grab (Grab) sampling. All the samples were analyzed by LC-MS/MS for 40 target antibiotics (including 16 sulfonamides (SAs), 12 fluoroquinolones, 6 macrolides, 2 ionophores, 2 diaminopyimidines, 1 aminocoumarin, and 1 lincosamide). The diffusion coefficients (D) of these antibiotics in o-DGT, measured in the laboratory, ranged from 0.58 × 10(-06) to 6.24 × 10(-06) cm(2) s(-1). The derived surface area normalized sampling rates (RS/A, 0.54-5.74 mL d(-1) cm(-2)) were comparable with those for another passive sampler called POCIS. Fourteen antibiotics were detected in the actively sampled water samples, with 10 of the 14 detected in o-DGT devices deployed for more than 7 days. Most of the antibiotics detected in o-DGT, except sulfapyridine, were continually accumulated by o-DGT for ~10 days. Deployment for 7 days is recommended to integrate ambient concentrations over time, without risks of reaching capacity and significant biofouling. Diffusive boundary layer (DBL) thickness had less effect on the o-DGT measurement than reported for other passive samplers. The comparison between o-DGT and Auto and Grab samplings showed that o-DGT was more efficient in terms of cost, time, and labor. This study demonstrates for the first time in a real environment that o-DGT is an effective tool for the routine monitoring of antibiotics in wastewaters and provides a powerful approach to studying their occurrence, fate, and behavior in the environment.

Abundance and persistence of antibiotic resistance genes in livestock farms: a comprehensive investigation in eastern China

Increases of antibiotic resistance genes in the environment may pose a threat to public health. The purpose of this study was to investigate the abundance and diversity of tetracycline (tet) and sulfonamide (sul) resistance genes in eight livestock farms in Hangzhou, eastern China. Ten tet genes (tetA, tetB, tetC, tetG, tetL, tetM, tetO, tetQ, tetW, and tetX), two sul genes (sulI and sulII), and one genetic element associated with mobile antibiotic resistance genes [class 1 integron (intI1)] were quantified by real-time polymerase chain reaction. No significant difference was found in the abundance of the tet and sul genes in various scales of pig, chicken, and duck farms (P>0.05). The average abundance of ribosomal protection protein genes (tetQ, tetM, tetW, and tetO) in the manure and wastewater samples was higher than most of the efflux pump genes (tetA, tetB, tetC, and tetL) and enzymatic modification gene (tetX) (P<0.05), except for efflux pump gene tetG, which was abundant and showed no difference from tetM. Most ARGs had higher relative abundance in the wastewater lagoon than in manures even after treatment. Although the three ribosomal protection protein genes (tetQ, tetW, and tetO) had higher relative abundance, numbers were reduced during the complete wastewater treatment process in pig farms (P<0.05). The relative abundance of tetG, sulI, and sulII increased after the wastewater treatment and the removal of these three genes exhibited significant positive correlations with the intI1 gene (tetG: R(2)=0.60, P<0.05; sulI: R(2)=0.72, P<0.05; sulII: R(2)=0.62, P<0.05), suggesting that intI1 may be involved in their proliferation. As for tetM and sulII genes, a highly significant difference was found in manure samples between pig farms and duck farms (P<0.001). Phylogenetic analysis showed that tetM was more diverse in duck farms than in pig farms. Additionally, sulII sequence was conserved both in pig and duck farms. This is the first comprehensive study to detail the relative abundance of specific ARGs in animal manures and agricultural wastewater treatment systems, potentially providing knowledge for managing antibiotic resistance emanating from agricultural activities.

A treatment plant receiving waste water from multiple bulk drug manufacturers is a reservoir for highly multi-drug resistant integron-bearing bacteria

The arenas and detailed mechanisms for transfer of antibiotic resistance genes between environmental bacteria and pathogens are largely unclear. Selection pressures from antibiotics in situations where environmental bacteria and human pathogens meet are expected to increase the risks for such gene transfer events. We hypothesize that waste-water treatment plants (WWTPs) serving antibiotic manufacturing industries may provide such spawning grounds, given the high bacterial densities present there together with exceptionally strong and persistent selection pressures from the antibiotic-contaminated waste. Previous analyses of effluent from an Indian industrial WWTP that processes waste from bulk drug production revealed the presence of a range of drugs, including broad spectrum antibiotics at extremely high concentrations (mg/L range). In this study, we have characterized the antibiotic resistance profiles of 93 bacterial strains sampled at different stages of the treatment process from the WWTP against 39 antibiotics belonging to 12 different classes. A large majority (86%) of the strains were resistant to 20 or more antibiotics. Although there were no classically-recognized human pathogens among the 93 isolated strains, opportunistic pathogens such as Ochrobactrum intermedium, Providencia rettgeri, vancomycin resistant Enterococci (VRE), Aerococcus sp. and Citrobacter freundii were found to be highly resistant. One of the O. intermedium strains (ER1) was resistant to 36 antibiotics, while P. rettgeri (OSR3) was resistant to 35 antibiotics. Class 1 and 2 integrons were detected in 74/93 (80%) strains each, and 88/93 (95%) strains harbored at least one type of integron. The qPCR analysis of community DNA also showed an unprecedented high prevalence of integrons, suggesting that the bacteria living under such high selective pressure have an appreciable potential for genetic exchange of resistance genes via mobile gene cassettes. The present study provides insight into the mechanisms behind and the extent of multi-drug resistance among bacteria living under an extreme antibiotic selection pressure.

Prevalence of antibiotic resistance genes and bacterial community composition in a river influenced by a wastewater treatment plant

Antibiotic resistance represents a global health problem, requiring better understanding of the ecology of antibiotic resistance genes (ARGs), their selection and their spread in the environment. Antibiotics are constantly released to the environment through wastewater treatment plant (WWTP) effluents. We investigated, therefore, the effect of these discharges on the prevalence of ARGs and bacterial community composition in biofilm and sediment samples of a receiving river. We used culture-independent approaches such as quantitative PCR to determine the prevalence of eleven ARGs and 16S rRNA gene-based pyrosequencing to examine the composition of bacterial communities. Concentration of antibiotics in WWTP influent and effluent were also determined. ARGs such as qnrS, bla_TEM, bla_CTX-M, bla_SHV, erm(B), sul(I), sul(II), tet(O) and tet(W) were detected in all biofilm and sediment samples analyzed. Moreover, we observed a significant increase in the relative abundance of ARGs in biofilm samples collected downstream of the WWTP discharge. We also found significant differences with respect to community structure and composition between upstream and downstream samples. Therefore, our results indicate that WWTP discharges may contribute to the spread of ARGs into the environment and may also impact on the bacterial communities of the receiving river.

Sympatric inhibition and niche differentiation suggest alternative coevolutionary trajectories among Streptomycetes

Soil bacteria produce a diverse array of antibiotics, yet our understanding of the specific roles of antibiotics in the ecological and evolutionary dynamics of microbial interactions in natural habitats remains limited. Here, we show a significant role for antibiotics in mediating antagonistic interactions and nutrient competition among locally coexisting Streptomycete populations from soil. We found that antibiotic inhibition is significantly more intense among sympatric than allopatric Streptomycete populations, indicating local selection for inhibitory phenotypes. For sympatric but not allopatric populations, antibiotic inhibition is significantly positively correlated with niche overlap, indicating that inhibition is targeted toward bacteria that pose the greatest competitive threat. Our results support the hypothesis that antibiotics serve as weapons in mediating local microbial interactions in soil and suggest that coevolutionary niche displacement may reduce the likelihood of an antibiotic arms race. Further insight into the diverse roles of antibiotics in microbial ecology and evolution has significant implications for understanding the persistence of antibiotic inhibitory and resistance phenotypes in environmental microbes, optimizing antibiotic drug discovery and developing strategies for managing microbial coevolutionary dynamics to enhance inhibitory phenotypes.

Comparing selection on S. aureus between antimicrobial peptides and common antibiotics

With a diminishing number of effective antibiotics, there has been interest in developing antimicrobial peptides (AMPs) as drugs. However, any new drug faces potential bacterial resistance evolution. Here, we experimentally compare resistance evolution in Staphylococcus aureus selected by three AMPs (from mammals, amphibians and insects), a combination of two AMPs, and two antibiotics: the powerful last-resort vancomycin and the classic streptomycin. We find that resistance evolves readily against single AMPs and against streptomycin, with no detectable fitness cost. However the response to selection from our combination of AMPs led to extinction, in a fashion qualitatively similar to vancomycin. This is consistent with the hypothesis that simultaneous release of multiple AMPs during immune responses is a factor which constrains evolution of AMP resistant pathogens.

Silver-doped manganese dioxide and trioxide nanoparticles inhibit both gram positive and gram negative pathogenic bacteria

Palladium, ruthenium and silver-doped MnO2 and silver doped Mn2O3 nanoparticles were synthesized by simple co-precipitation technique. SEM-TEM analysis revealed the nano-size of these synthesized samples. XPS data illustrates that Mn is present in 4+ and 3+ oxidation states in MnO2 and Mn2O3 respectively. Thermal analysis gave significant evidence for the phase changes with increasing temperature. Antibacterial activity of these synthesized nanoparticles on three Gram positive bacterial cultures (Staphylococcus aureus ATCC 6538, Streptococcus epidermis ATCC 12228, Bacillus subtilis ATCC 6633) and three Gram negative cultures (Escherichia coli ATCC 8739, Salmonella abony NCTC 6017 and Klebsiella pneumoniae ATCC 1003) was investigated using a disc diffusion method and live/dead assay. Only Ag-doped MnO2 and Ag-doped Mn2O3 nanoparticles showed antibacterial property against all six-test bacteria but Ag-doped MnO2 was found to be more effective than Ag-doped Mn2O3.

Exploring variation of antibiotic resistance genes in activated sludge over a four-year period through a metagenomic approach

In this study, the profiles of ARGs in activated sludge from the Shatin WWTP of Hong Kong were investigated using metagenomic analysis over a four-year period. Forty giga base pairs of metagenomic data were generated from eight activated sludge samples collected biannually at two seasons (winter and summer) from July 2007 to January 2011. A structured database of ARGs was proposed and constructed to facilitate the classification of ARGs in the collected samples from metagenomic data using a customized script. Analysis of the data showed the existence of a broad-spectrum of different ARGs, some of which have never been reported in activated sludge before. The most abundant ARGs were aminoglycoside and tetracycline resistance genes, followed by resistance genes of sulfonamide, multidrug, and chloramphenicol. Seasonal fluctuations were observed for 3 types of ARGs, that is, resistance genes of tetracycline, sulfonamide, and vancomycin. The abundances of these resistance genes were generally higher in the samples collected in the winters than the samples collected in the contiguous summer. Further analyses were carried out for the presence of subtypes of ARGs for aminoglycoside, tetracycline, and beta-lactam. The abundances of some ARGs subtypes were inconsistent with those reported in previous studies of activated sludge using the PCR approach. Statistical analyses showed that the activated sludge data sets from this study can be distinguished from other types of samples based on their ARGs profiles. Furthermore, the results of this study demonstrate that a high throughput-based metagenomic approach combined with a structured database of ARGs provides a powerful tool for a comprehensive survey of the various ARGs not only in the activated sludge of a WWTP but in other environmental samples as well. Thus, the profiling of ARGs in other ecologically important environmental matrixes may help elucidate those environmental factors contributing to the spread of ARGs.

Optical control of antibacterial activity

Bacterial resistance is a major problem in the modern world, stemming in part from the build-up of antibiotics in the environment. Novel molecular approaches that enable an externally triggered increase in antibiotic activity with high spatiotemporal resolution and auto-inactivation are highly desirable. Here we report a responsive, broad-spectrum, antibacterial agent that can be temporally activated with light, whereupon it auto-inactivates on the scale of hours. The use of such a 'smart' antibiotic might prevent the build-up of active antimicrobial material in the environment. Reversible optical control over active drug concentration enables us to obtain pharmacodynamic information. Precisely localized control of activity is achieved, allowing the growth of bacteria to be confined to defined patterns, which has potential for the development of treatments that avoid interference with the endogenous microbial population in other parts of the organism. 

Acquired genetic mechanisms of a multiresistant bacterium isolated from a treatment plant receiving wastewater from antibiotic production

The external environment, particularly wastewater treatment plants (WWTPs), where environmental bacteria meet human commensals and pathogens in large numbers, has been highlighted as a potential breeding ground for antibiotic resistance. We have isolated the extensively drug-resistant Ochrobactrum intermedium CCUG 57381 from an Indian WWTP receiving industrial wastewater from pharmaceutical production contaminated with high levels of quinolones. Antibiotic susceptibility testing against 47 antibiotics showed that the strain was 4 to >500 times more resistant to sulfonamides, quinolones, tetracyclines, macrolides, and the aminoglycoside streptomycin than the type strain O. intermedium LMG 3301T. Whole-genome sequencing identified mutations in the Indian strain causing amino acid substitutions in the target enzymes of quinolones. We also characterized three acquired regions containing resistance genes to sulfonamides (sul1), tetracyclines [tet(G) and tetR], and chloramphenicol/florfenicol (floR). Furthermore, the Indian strain harbored acquired mechanisms for horizontal gene transfer, including a type I mating pair-forming system (MPFI), a MOBP relaxase, and insertion sequence transposons. Our results highlight that WWTPs serving antibiotic manufacturing may provide nearly ideal conditions for the recruitment of resistance genes into human commensal and pathogenic bacteria.