Specific Antibiotic Resistance Genes Research Articles

Determining the composition of bacterial community and relative abundance of specific antibiotics resistance genes via thermophilic anaerobic digestion of sewage sludge

In this study, the effects of different temperature transitions on the dynamics of antibiotic resistance genes (ARGs) and bacterial community were investigated during start-up of thermophilic anaerobic digestion (AD) of sewage sludge. Although two thermophilic reactors showed dissimilar removal efficiencies of ARGs in batch mode, both the removal efficiency and reduction patterns of ARGs were similar in continuous stirred tank reactor (CSTR) mode, resulting in significant reduction of the total sum of the relative abundance of ARGs. Using network analysis to explore the correlation between bacterial community and some specific ARGs revealed that composition of the bacterial community played a vital role in the fluctuations in the relative abundance of the antibiotic resistome, demonstrating that shaping the development of ARGs was facilitated by vertical gene transfer. To facilitate eliminating ARGs, minimizing their hosts which persist even under long-term operations is vital in thermophilic AD.

A rapid and accurate method for the detection of four aminoglycoside modifying enzyme drug resistance gene in clinical strains of Escherichia coli by a multiplex polymerase chain reaction.

BackgroundAntibiotics are highly effective drugs used in the treatment of infectious diseases. Aminoglycoside antibiotics are one of the most common antibiotics in the treatment of bacterial infections. However, the development of drug resistance against those medicines is becoming a serious concern.AimThis study aimed to develop an efficient, rapid, accurate, and sensitive detection method that is applicable for routine clinical use.MethodsEscherichia coli was used as a model organism to develop a rapid, accurate, and reliable multiplex polymerase chain reaction (M-PCR) for the detection of four aminoglycoside modifying enzyme (AME) resistance genes Aac(6′)-Ib, Aac(3)-II, Ant(3″)-Ia, and Aph(3′)-Ia. M-PCR was used to detect the distribution of AME resistance genes in 237 clinical strains of E. coli. The results were verified by simplex polymerase chain reaction (S-PCR).ResultsResults of M-PCR and S-PCR showed that the detection rates of Aac(6′)-Ib, Aac(3)-II, Ant(3″)-Ia, and Aph(3′)-Ia were 32.7%, 59.2%, 23.5%, and 16.8%, respectively, in 237 clinical strains of E. coli. Compared with the traditional methods for detection and identification, the rapid and accurate M-PCR detection method was established to detect AME drug resistance genes. This technique can be used for the clinical detection as well as the surveillance and monitoring of the spread of those specific antibiotic resistance genes.

Environmental fate of Bacteroidetes, with particular emphasis on Bacteroides fragilis group bacteria and their specific antibiotic resistance genes, in activated sludge wastewater treatment plants

The aim of this study was to determine the effect of the activated sludge process on the abundance of anaerobic bacteria of the phylum Bacteroidetes, with special emphasis on Bacteroides fragilis group (BFG) bacteria, in twelve full-scale wastewater treatment plants. The composition of bacterial phyla and classes in wastewater samples were analyzed by next-generation sequencing. The presence of specific to BFG bacteria genes and the abundance of ARGs and genes encoding class 1 integrase in wastewater samples were determined by qPCR. Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes were dominant bacterial phyla in wastewater samples. Next-generation sequencing revealed similar proportions of Bacteroidia (<1.0-8.2 % of all bacteria) in wastewater influents and effluents, which suggest that these microorganisms are not completely eliminated in the activated sludge process. The average copy numbers of specific to BFG bacteria gene, were 106, and 104 copies in 1 mL of wastewater influents and effluents, respectively. The results revealed a correlation between the abundance of BFG bacteria and BFG-specific genes encoding resistance to antibiotics. The observed changes in the prevalence of BFG-specific genes and ARGs in untreated and treated wastewater indicate that the activated sludge process decreases the number of gene copies in the effluent evacuated to the environment.

Growth rate assays reveal fitness consequences of β-lactamases.

Antibiotic resistance is a powerful model for studying evolutionary biology and population genetics. For the purpose of these evolutionary studies, fitness data have been approximated through susceptibility testing methods designed for clinical use in providing appropriate antibiotic therapies. An alternative approach for measuring fitness of microbes has experienced growing popularity: growth rates are a highly sensitive approach for measuring the fitness effects of antibiotics and resistance genes, but they differ from susceptibility testing in that a single concentration of antibiotic is used for the assay. Here we show that despite this key difference, the results of growth rates correlate well with clinical determination of resistance by minimum inhibitory concentration (MIC), while providing the sensitivity required for direct input as fitness values into mathematical models. This means that growth rates at a single sublethal inhibitory concentration can help us understand the fitness effects that result in clinical antibiotic resistance. By measuring the growth rates of sequenced clinical isolates obtained from Dignity Health Mercy Medical Center, we detected the fitness effects of individual resistance genes on bacteria exposed to different antibiotics. In our study, the CTX-M-15 gene conferred the highest fitness in assays with cephalosporins. These results show the strong fitness benefit conferred by CTX-M-15.Non-technical summaryAntibiotic resistance is a global human health problem. We partnered with Dignity Health Mercy Medical Center to study antibiotic resistance in clinical isolates. We tested whether growth rates, a sensitive assay used to measure the fitness of bacterial samples, correlate with a clinical test to measure antibiotic resistance. We found a strong correlation between these two methods suggesting that growth rates could be reliably applied to evolutionary studies of clinically relevant problems. Moreover, the sensitivity of the growth rates assay enabled us to identify fitness effects of specific antibiotic resistance genes.

Gene pool transmission of multidrug resistance among Campylobacter from livestock, sewage and human disease.

SummaryThe use of antimicrobials in human and veterinary medicine has coincided with a rise in antimicrobial resistance (AMR) in the food‐borne pathogens Campylobacter jejuni and Campylobacter coli. Faecal contamination from the main reservoir hosts (livestock, especially poultry) is the principal route of human infection but little is known about the spread of AMR among source and sink populations. In particular, questions remain about how Campylobacter resistomes interact between species and hosts, and the potential role of sewage as a conduit for the spread of AMR. Here, we investigate the genomic variation associated with AMR in 168 C. jejuni and 92 C. coli strains isolated from humans, livestock and urban effluents in Spain. AMR was tested in vitro and isolate genomes were sequenced and screened for putative AMR genes and alleles. Genes associated with resistance to multiple drug classes were observed in both species and were commonly present in multidrug‐resistant genomic islands (GIs), often located on plasmids or mobile elements. In many cases, these loci had alleles that were shared among C. jejuni and C. coli consistent with horizontal transfer. Our results suggest that specific antibiotic resistance genes have spread among Campylobacter isolated from humans, animals and the environment.

Dairy farm soil presents distinct microbiota and varied prevalence of antibiotic resistance across housing areas

Dairy cattle of different ages experience different living conditions and varied frequency of antibiotic administration that likely influence the distribution of microbiome and resistome in ways that reflect different risks of microbial transmission. To assess the degree of variance in these distributions, fecal and soil samples were collected from six distinct housing areas on commercial dairy farms (n = 7) in Washington State. 16S rRNA gene sequencing indicated that the microbiota differed between different on-farm locations in feces and soil, and in both cases, the microbiota of dairy calves was often distinct from others (P < 0.05). Thirty-two specific antibiotic resistance genes (ARGs) were widely distributed on dairies, of which several clinically relevant ARGs (including cfr, cfrB, and optrA) were identified for the first time at U.S. dairies. Overall, ARGs were observed more frequently in feces and soil from dairy calves and heifers than from hospital, fresh, lactation and dry pens. Droplet-digital PCR demonstrated that the absolute abundance of floR varied greatly across housing areas and this gene was enriched the most in calves and heifers. Furthermore, in an extended analysis with 14 dairies, environmental soils in calf pens had the most antibiotic-resistant Escherichia coli followed by heifer and hospital pens. All soil E. coli isolates (n = 1,905) are resistant to at least 4 different antibiotics, and the PFGE analysis indicated that florfenicol-resistant E. coli is probably shared across geographically-separated farms. This study identified a discrete but predictable distribution of antibiotic resistance genes and organisms, which is important for designing mitigation for higher risk areas on dairy farms.

Metagenomic assembly provides a deep insight into the antibiotic resistome alteration induced by drinking water chlorination and its correlations with bacterial host changes.

Chlorination can contribute to the enrichment of specific antibiotic resistance genes (ARGs) in drinking water, but the underlying molecular ecological mechanisms remain unknown, which may hinder the assessment and control of the resulting health risks. In this study, metagenomic assembly and Resfams annotation were used to profile the co-occurrence patterns of ARGs, mobile genetic elements (MGEs) and their bacterial hosts, as well as the correlations of potential pathogens with the antibiotic resistome, in a full-scale drinking water treatment and transportation system. Seven ARG types involved in different resistance mechanisms occurred in drinking water and chlorination enhanced the total abundance of the ARGs (p < 0.05). The ARGs encoding resistance-nodulation-cell division and ATP-binding cassette antibiotic efflux pumps predominated in all the samples and were primarily responsible for the ARG accumulation. After chlorination, the ARGs were primarily carried by predominant Sphingomonas, Polaromonas, Hyphomicrobium, Acidovorax, Pseudomonas and Fluviicola. Further, enrichment of the bacterial hosts and MGEs greatly contributed to alteration of the antibiotic resistome. Pseudomonas alcaligenes, carrying multiple ARGs, was identified as a potential pathogen in the chlorinated drinking water. These findings provide novel insights into the host-ARG relationship and the mechanism underlying the resistome alteration during drinking water chlorination.

Degradation of extracellular genomic, plasmid DNA and specific antibiotic resistance genes by chlorination

There is a need to improve understanding of the effect of chlorine disinfection on antibiotic resistance genes (ARGs) in order to advance relevant drinking water, wastewater, and reuse treatments. However, few studies have explicitly assessed the physical effects on the DNA. Here we examined the effects of free chlorine (1–20 mg Cl2/L) on extracellular genomic, plasmid DNA and select ARGs. Chlorination was found to decrease the fluorometric signal of extracellular genomic and plasmid DNA (ranging from 0.005 to 0.05 μg/mL) by 70%, relative to a no-chlorine control. Resulting DNA was further subject to a fragment analysis using a Bioanalyzer, indicating that chlorination resulted in fragmentation. Moreover, chlorine also effectively deactivated both chromosomal- and plasmid-borne ARGs, mecA and tetA, respectively. For concentrations >2 mg Cl2//L × 30 min, chlorine efficiently reduced the qPCR signal when the initial concentration of ARGs was 105 copies/μL or less. Notably, genomic DNA and mecA gene signals were more readily reduced by chlorine than the plasmid-borne tetA gene (by ~2 fold). Based on the results of qPCR with short (~200 bps) and long amplicons (~1200 bps), chlorination could destroy the integrity of ARGs, which likely reduces the possibility of natural transformation. Overall, our findings strongly illustrate that chlorination could be an effective method for inactivating extracellular chromosomal- and plasmid-borne DNA and ARGs.

Quantitative contribution of efflux to multi-drug resistance of clinical Escherichia coli and Pseudomonas aeruginosa strains.

BackgroundEfflux pumps mediate antimicrobial resistance in several WHO critical priority bacterial pathogens. However, most available data come from laboratory strains. The quantitative relevance of efflux in more relevant clinical isolates remains largely unknown.MethodsWe developed a versatile method for genetic engineering in multi-drug resistant (MDR) bacteria, and used this method to delete tolC and specific antibiotic-resistance genes in 18 representative MDR clinical E. coli isolates. We determined efflux activity and minimal inhibitory concentrations for a diverse set of clinically relevant antibiotics in these mutants. We also deleted oprM in MDR P. aeruginosa strains and determined the impact on antibiotic susceptibility.FindingstolC deletion abolished detectable efflux activity in 15 out of 18 tested E. coli strains, and modulated antibiotic susceptibility in many strains. However, all mutant strains retained MDR status, primarily because of other, antibiotic-specific resistance genes. Deletion of oprM altered antibiotic susceptibility in a fraction of clinical P. aeruginosa isolates.InterpretationEfflux modulates antibiotic resistance in clinical MDR isolates of E. coli and P. aeruginosa. However, when other antimicrobial-resistance mechanisms are present, inhibition of MDR efflux pumps alone is often not sufficient to restore full susceptibility even for antibiotics with a dramatic impact of efflux in laboratory strains. We propose that development of novel antibiotics should include target validation in clinical MDR isolates.FundInnovative Medicines Initiative of European Union and EFPIA, Schweizerischer Nationalfonds, Swiss National Research Program 72, EU Marie Skłodowska-Curie program. The funders played no role in design, data collection, data analysis, interpretation, writing of the report, and in the decision to submit the paper for publication.

Antibiotic resistance profiling of pathogenic Enterobacteriaceae from Cluj-Napoca, Romania.

Members of the family Enterobacteriaceae are commonly identified in the clinical laboratory, being responsible for a substantial range of infections. This study aimed to investigate phenotypic and genotypic resistance traits in pathogenic Enterobacteriaceae isolated from outpatients in Cluj-Napoca, Romania. Pathogenic Enterobacteriaceae were isolated from urinary tract infections, wound infections and persistent diarrhea in a private laboratory from Cluj-Napoca, Romania. Bacterial strains were biochemically identified and subjected to antimicrobial susceptibility testing by disk diffusion. The carriage of antibiotic resistance genes and of class 1 integron were assessed by PCR. E. coli and Enterobacter spp. were the most prevalent pathogens. High levels of resistance were observed against folate pathway inhibitors (74%), fluoroquinolones (49%) and penicillins (44%). The incidence of carbapenem resistance was 3%. The strains displaying phenotypic resistance were able to produce β-lactamase enzymes encoded by bla TEM, bla TEM-1, bla SHV-1 and bla CTX-M, aminoglycoside modifying enzymes due to the carriage of aac(3)-IIIa, aac(6')-II and aac(6')-Ie-aph(2"), to possess fluoroquinolones resistance due to qnrS DNA gyrase protection proteins and resistance to folate pathway inhibitors due to dihydropteroate synthases encoded by sul1, sul2 and sul3 genes. The high frequency of intI1 integrase was associated to sulphonamide resistance (r=0.48; p<0.001) and also to fluoroquinolone resistance (r=0.27; p=0.011), but no significant associations in the co-occurrence of specific antibiotic resistance genes and intI1 were found in pathogenic Enterobacteriaceae. An important proportion of pathogenic Enterobacteriaceae were multidrug resistant, due to a wide diversity of mechanisms encoding genetic resistance.

In vitro evalution of antibiotic resistance of Lactobacillus bulgaricus strains isolated from traditional dairy products

The antimicrobial susceptibility of 20 Lb. bulgaricus isolates from traditional fermented milk-originated was assessed and then determined the ability to transfer antibiotic resistance genes to other bacteria. The minimum inhibitory concentration of each strain was determined using a standardized dilution method. All the tested strains were found to be susceptible to gentamicin, erythromycin, clindamycin, neomycin, tetracycline, linezolid, chloramphenicol, rifampicin, and quinupristin/dalfopristin, while their susceptibilities to kanamycin, ciprofloxacin, streptomycin, trimethoprim, ampicillin, and vancomycin varied. Polymerase chain reaction (PCR) was used to check whether specific antibiotic resistance genes were present in these Lb. bulgaricus. We detected the rpoB, erm(B), aadA, bla, cat and vanX. Finally, a filter mating assay was applied to investigate the transferability of these resistance markers; and we observe no antibiotic resistance transfer between bacteria. This work demonstrates a low risk of lateral transfer of the antibiotic resistance gene of Lb. bulgaricus.

Maternal gut and breast milk microbiota affect infant gut antibiotic resistome and mobile genetic elements

The infant gut microbiota has a high abundance of antibiotic resistance genes (ARGs) compared to adults, even in the absence of antibiotic exposure. Here we study potential sources of infant gut ARGs by performing metagenomic sequencing of breast milk, as well as infant and maternal gut microbiomes. We find that fecal ARG and mobile genetic element (MGE) profiles of infants are more similar to those of their own mothers than to those of unrelated mothers. MGEs in mothers’ breast milk are also shared with their own infants. Termination of breastfeeding and intrapartum antibiotic prophylaxis of mothers, which have the potential to affect microbial community composition, are associated with higher abundances of specific ARGs, the composition of which is largely shaped by bacterial phylogeny in the infant gut. Our results suggest that infants inherit the legacy of past antibiotic consumption of their mothers via transmission of genes, but microbiota composition still strongly impacts the overall resistance load.

Antibiotic-mediated changes in the fecal microbiome of broiler chickens define the incidence of antibiotic resistance genes

BackgroundAntimicrobial agents have been widely used in animal farms to prevent and treat animal diseases and to promote growth. Antimicrobial agents may change the bacterial community and enhance the resistome in animal feces. We used metagenome-wide analysis to investigate the changes in bacterial community, variations in antibiotic resistance genes (ARGs), and their bacterial hosts in the feces of broiler chickens over a full-treatment course of chlortetracycline at low and therapeutic dose levels.ResultsThe effects of chlortetracycline on resistome were dependent on the specific ARG subtypes and not simply the overall community-level ARGs. Therapeutic dose of chlortetracycline promoted the abundance of tetracycline resistance genes (tetA and tetW) and inhibited multidrug resistance genes (mdtA, mdtC, mdtK, ompR, and TolC). The therapeutic dose of chlortetracycline led to loss of Proteobacteria mainly due to the decrease of Escherichia/Shigella (from 72 to 58%). Inhibition of Escherichia by chlortetracycline was the primary reason for the decrease of genes resistant to multiple drugs in the therapeutic dose group. The ARG host Bifidobacterium were enriched due to tetW harbored by Bifidobacterium under chlortetracycline treatment. Escherichia was always the major host for multidrug resistance genes, whereas the primary host was changed from Escherichia to Klebsiella for aminoglycoside resistance genes with the treatment of therapeutic dose of chlortetracycline.ConclusionsWe provided the first metagenomic insights into antibiotic-mediated alteration of ARG-harboring bacterial hosts at community-wide level in chicken feces. These results indicated that the changes in the structure of antibiotic-induced feces microbial communities accompany changes in the abundance of bacterial hosts carrying specific ARGs in the feces microbiota. These findings will help to optimize therapeutic schemes for the effective treatment of antibiotic resistant pathogens in poultry farms.Graphical abstractResistome variations in faecal microbiome of chickens exposed to chlortetracycline

Experimental Epidemiology of Antibiotic Resistance: Looking for an Appropriate Animal Model System.

Antibiotic resistance is recognized as one of the major challenges in public health. The global spread of antibiotic resistance is the consequence of a constant flow of information across multi-hierarchical interactions, involving cellular (clones), subcellular (resistance genes located in plasmids, transposons, and integrons), and supracellular (clonal complexes, genetic exchange communities, and microbiotic ensembles) levels. In order to study such multilevel complexity, we propose to establish an experimental epidemiology model for the transmission of antibiotic resistance with the cockroach Blatella germanica. This paper reports the results of five types of preliminary experiments with B. germanica populations that allow us to conclude that this animal is an appropriate model for experimental epidemiology: (i) the composition, transmission, and acquisition of gut microbiota and endosymbionts; (ii) the effect of different diets on gut microbiota; (iii) the effect of antibiotics on host fitness; (iv) the evaluation of the presence of antibiotic resistance genes in natural- and lab-reared populations; and (v) the preparation of plasmids harboring specific antibiotic resistance genes. The basic idea is to have populations with higher and lower antibiotic exposure, simulating the hospital and the community, respectively, and with a certain migration rate of insects between populations. In parallel, we present a computational model based on P-membrane computing that will mimic the experimental system of antibiotic resistance transmission. The proposal serves as a proof of concept for the development of more-complex population dynamics of antibiotic resistance transmission that are of interest in public health, which can help us evaluate procedures and design appropriate interventions in epidemiology.

Feed additives shift gut microbiota and enrich antibiotic resistance in swine gut

Antibiotic resistance genes (ARGs) are emerging environmental contaminants posing a threat to public health. Antibiotics and metals are widely used as feed additives and could consequently affect ARGs in swine gut. In this study, high-throughput quantitative polymerase chain reaction (HT-qPCR) based ARG chip and next-generation 16S rRNA gene amplicon sequencing data were analyzed using multiple statistical approaches to profile the antibiotic resistome and investigate its linkages to antibiotics and metals used as feed additives and to the microbial community composition in freshly collected swine manure samples from three large-scale Chinese pig farms. A total of 146 ARGs and up to 1.3×1010 total ARG copies per gram of swine feces were detected. ARGs conferring resistance to aminoglycoside, macrolide-lincosamide-streptogramin B (MLSB) and tetracycline were dominant in pig gut. Total abundance of ARGs was positively correlated with in-feed antibiotics, microbial biomass and abundance of mobile genetic elements (MGEs) (P<0.05). A significant correlation between microbial communities and ARG profiles was observed by Procrustes analysis. Network analysis revealed that Bacteroidetes and Firmicutes were the most dominant phyla co-occurring with specific ARGs. Partial redundancy analysis indicated that the variance in ARG profiles could be primarily attributed to antibiotics and metals in feed (31.8%), gut microbial community composition (23.3%) and interaction between feed additives and community composition (16.5%). These results suggest that increased levels of in-feed additives could aggravate the enrichment of ARGs and MGEs in swine gut.

Impact of intrapartum antimicrobial prophylaxis upon the intestinal microbiota and the prevalence of antibiotic resistance genes in vaginally delivered full-term neonates

BackgroundDisturbances in the early establishment of the intestinal microbiota may produce important implications for the infant’s health and for the risk of disease later on. Different perinatal conditions may be affecting the development of the gut microbiota. Some of them, such as delivery mode or feeding habits, have been extensively assessed whereas others remain to be studied, being critical to identify their impact on the microbiota and, if any, to minimize it. Antibiotics are among the drugs most frequently used in early life, the use of intrapartum antimicrobial prophylaxis (IAP), present in over 30% of deliveries, being the most frequent source of exposure. However, our knowledge on the effects of IAP on the microbiota establishment is still limited. The aim of the present work was to evaluate the impact of IAP investigating a cohort of 40 full-term vaginally delivered infants born after an uncomplicated pregnancy, 18 of which were born from mothers receiving IAP.ResultsFecal samples were collected at 2, 10, 30, and 90 days of age. We analyzed the composition of the fecal microbiota during the first 3 months of life by 16S rRNA gene sequencing and quantified fecal short chain fatty acids by gas chromatography. The presence of genes for resistance to antibiotics was determined by PCR in the samples from 1-month-old infants. Our results showed an altered pattern of intestinal microbiota establishment in IAP infants during the first weeks of life, with lower relative proportions of Actinobacteria and Bacteroidetes and increased of Preoteobacteria and Firmicutes. A delay in the increase on the levels of acetate was observed in IAP infants. The analyses of specific antibiotic resistance genes showed a higher occurrence of some β-lactamase coding genes in infants whose mothers received IAP.ConclusionsOur results indicate an effect of IAP on the establishing early microbiota during the first months of life, which represent a key moment for the development of the microbiota-induced host homeostasis. Understanding the impact of IAP in the gut microbiota development is essential for developing treatments to minimize it, favoring a proper gut microbiota development in IAP-exposed neonates.

Presence of antibiotic resistance genes in raw source water of a drinking water treatment plant in a rural community of USA

Very few studies have been reported on the presence of antibiotic resistance genes in the raw source water of rural communities in the USA. Therefore this study was conducted to study the presence of few specific antibiotic resistance genes, which imparts resistance to commonly used antibiotics in a rural drinking water plant in Louisiana, USA. Samples were taken from raw intake water, the treated water in holding tank at the water treatment facility, and an offsite consumer source serviced by the distribution line. Water quality analysis uncovered increase in organic carbon in distributed water. No live bacteria were found in the treated or distributed water, but bacterial DNA in the form of 16s rRNA was consistently found. Isolates of antibiotic resistant E. coli, Enterobacter cloacae, Pseudomonas aerugenosa, and Klebsiella pneumonia were found in the raw intake water. Antibiotic resistance genes, tetA and sul1 were observed in the raw intake showing the presence of antibiotic resistance genes (ARG) and antibiotic resistant bacteria (ARB) in the raw intake water. However, no ARGs or ARB were found in the treated and distributed water.

Occurrence and elimination of antibiotic resistance genes in a long-term operation integrated surface flow constructed wetland

Wetland construction is a recommended domestic sewage treatment technique, owing to its simplicity and cost efficiency. Concentrations of 14 antibiotic resistance genes (ARGs) in an integrated surface flow constructed wetland (ICW) steadily operated over 10 years were investigated in the winter and summer. Domestic sewage was observed to be the primary source of ARGs in the ICW, and 77.8% and 59.5% removal rates of total targeted ARGs in the ICW were achieved in the winter and summer, respectively. Concentrations of five ARGs (sul1, tetA, tetC, tetE, and qnrS) in the winter and of six ARGs (sul1, sul3, tetA, tetC, tetE, and qnrS) in the summer were increased throughout the treatment process. Strong correlations were found between ARGs in water and those found in sediments, especially in the summer, indicating that ARGs may be exchanged between water and sediment. Strong positive correlations were also observed between concentrations of intI1 and several ARGs, implying that mobile genetic elements may play a key role in the dissemination of ARGs in an ICW. Our study results suggest aqueous ARGs could be effectively removed via an ICW and that ICWs can also act as reservoirs of specific ARGs.

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, blaTEM and vanA and the bacterial community composition were analyzed.In general, the genes blaTEM 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, blaTEM and vanA were members of the classes Gammaproteobacteria, Bacilli or Bacteroidia. For blaTEM, 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.

Emerging contaminants in agricultural systems

Emerging contaminants in agricultural systems