Environmental Concentrations Of Antibiotics Research Articles

Environmental concentrations of antibiotics, biocides, and heavy metals fail to induce phenotypic antimicrobial resistance in Escherichia coli

Most anthropogenically affected environments contain mixtures of pollutants from different sources. The impact of these pollutants is usually the combined effect of the individual polluting constituents. However, how these stressors contribute to the development of antimicrobial resistance in environmental microorganisms is poorly understood. Thus, a 30-day exposure experiment to environmental and sub-inhibitory concentrations of oxytetracycline, amoxicillin, zinc, copper, BAC (benzalkonium chloride) 10 and DADMAC (diallyldimethylammonium chloride) 12, was conducted using fully susceptible E. coli ATCC 25922 to ascertain any development of phenotypic or genotypic resistance. Furthermore, wild-type isolates were collected from the same aquatic environment as the stressors, analysed for phenotypic resistance using the disk diffusion method and genotypically through whole genome sequencing. Exposure to the various concentrations and combinations of the stressors did not trigger phenotypic resistance in the experimental bacteria. Furthermore, genotypic analysis of the WGS on the exposed isolates only found the macrolide resistance mdf(A) gene (also present in the control strain) and the disinfectant resistance gene sitABCD. With further analysis for single nucleotide variants (SNV), mutations were detected for 19 genes that encoded for oxidative stress, DNA repair, membrane proteins efflux systems, growth and persister formations except for the robA, a transcription protein subset of the ArcC/XylS family of proteins, which confer multidrug resistance in E. coli. This indicates that exposure to sub-inhibitory concentrations of antibiotics, heavy metals and biocide residues in the aquatic environmental concentrations of the stressors identified in the current study could not induce phenotypic or genotypic resistance but encoded for genes responsible for the development of persistence and tolerance in bacteria, which could be a precursor to the development of resistance in environmental bacteria.

Sub-MIC antibiotics affect microbial ferrihydrite reduction by extracellular membrane vesicles

Environmental concentrations of antibiotics, usually below MIC, have significant biological effects on bacterial cells. Sub-MIC antibiotics exposure induces bacteria to produce outer membrane vesicles (OMVs). Recently, OMVs is discovered as a novel pathway for dissimilatory iron reducing bacteria (DIRB) to mediate extracellular electron transfer (EET). Whether and how the antibiotic-induced OMVs modulate iron oxides reduction by DIRB have not been studied. This study showed the sub-MIC antibiotics (ampicillin or ciprofloxacin) increased OMVs secretion in Geobacter sulfurreducens, and the antibiotic-induced OMVs contained more redox active cytochromes facilitating iron oxides reduction, especially for the ciprofloxacin-induced OMVs. Deduced from a combination of electron microscopy and proteomic analysis, the influence of ciprofloxacin on SOS response triggered prophage induction and led to the formation of outer-inner membrane vesicles (OIMVs) in, which was a first report in Geobacter species. While ampicillin disrupting cell membrane integrity resulted in more formation of classic OMVs from outer membrane blebbing. The results indicated that the different structure and composition of vesicles were responsible for the antibiotic-dependent regulation on iron oxides reduction. This newly identified regulation on EET-mediated redox reactions by sub-MIC antibiotics expands our knowledge about the impact of antibiotics on microbial processes or “non-target” organisms.

Knowledge gaps in the assessment of antimicrobial resistance in surface waters.

ABSTRACTThe spread of antibiotic resistance in the water environment has been widely described. However, still many knowledge gaps exist regarding the selection pressure from antibiotics, heavy metals and other substances present in surface waters as a result of anthropogenic activities, as well as the extent and impact of this phenomenon on aquatic organisms and humans. In particular, the relationship between environmental concentrations of antibiotics and the acquisition of ARGs by antibiotic-sensitive bacteria as well as the impact of heavy metals and other selective agents on antimicrobial resistance (AMR) need to be defined. Currently, established safety values are based on the effects of antibiotic toxicity neglecting the question of AMR spread. In turn, risk assessment of antibiotics in waterbodies remains a complex question implicating multiple variables and unknowns reinforced by the lack of harmonized protocols and official guidelines. In the present review, we discussed current state-of-the-art and the knowledge gaps related to pressure exerted by antibiotics and heavy metals on aquatic environments and their relationship to the spread of AMR. Along with this latter, we reflected on (i) the risk assessment in surface waters, (ii) selective pressures contributing to its transfer and propagation and (iii) the advantages of metagenomics in investigating AMR. Furthermore, the role of microplastics in co-selection for metal and antibiotic resistance, together with the need for more studies in freshwater are highlighted.

Risk assessment of infectious diseases in rural population associated with chronic exposure to sub-therapeutic concentrations of antibiotics in environment.

Background: Various antibiotics are being continuously added in different environmental compartments from point and non-point sources. The rural settings are more vulnerable to this addition. Since, antibiotics are very sensitive compound which are also degraded in natural environment spontaneously as well as by means of microbial activity. Therefore, the concentrations of antibiotics reported in these compartments are perhaps below WHO regulatory limits but chronic exposure to these sub-therapeutic concentrations may cause antimicrobial resistance (AMR). The resistant microorganisms are potential threat in rural population that cause various infectious diseases in them. Aims:This study aimed to (i) assess the indirect exposure of rural population to antibiotics, (ii) assess the effect of exposure on human gut microbiome, and (iii) assess the risk of infectious diseases in exposed rural population.Method:Agricultural soil, sewage water, livestock waste, poultry waste and human feces samples in triplicate were collected fortnightly for three months and analyzed for ciprofloxacin and Co-amoxiclav (target antibiotics) through HPLC. Population exposure to antibiotics in rural population was characterized using self-structured questionnaire included livestock handlers, poultry workers, agricultural farmers, female households and children (n=300). Human fecal samples were also collected to assess the AMR in their gut microbiome against the target antibiotics. Results: Ciprofloxacin and Co-amoxiclav were estimated at concentration ranging between 0.90 and 3.88 ng/L in sewage water, 0.6 and 2.68 μg/kg in Agricultural soil, 1.12 and 3.82 μg/kg in livestock waste, 0.92 and 3.51 μg/kg in poultry waste and 0.65 and 1.41 μg/kg in human feces. Conclusion:Based upon antibiotic resistance percentages against target antibiotics, low risk of E.coli related infections in households and children, moderate risk in agricultural farmers and high risk in poultry workers and livestock handlers were concluded.

Inhibition of staphylococci and S. aureus in wastewater by ferrates and electrochemical methods

Abstract Increasing concentration of antibiotics in environment and their subinhibitory concentrations in wastewater may result in increased antibiotic resistance of present bacteria. Therefore, this study was aimed to analyze the efficiency of coagulase-positive staphylococci and Staphylococcus aureus inhibition in wastewater by electrochemical methods and addition of ferrates. Advanced electrochemical oxidation by boron doped diamond electrodes in anode; cathode and anode-cathode connection were used for wastewater disinfection. Results showed that the most effective connection was the anodic one, as complete inhibition of coagulase-positive staphylococci as well as of S. aureus was observed after 40 min. Energy consumption was 3.69 kWh/m3 for effluent wastewater disinfection. The second studied method of wastewater disinfection was the application of powdered ferrates. Addition of 100 mg of ferrates resulted in the inhibition of 84—96 % of coagulase-positive staphylococci and 97—99 % of S. aureus in influent water, while the inhibition of coagulase-positive staphylococci and S. aureus was 61—83 % and 83—86 %, respectively, in effluent wastewater.

The 'SELection End points in Communities of bacTeria' (SELECT) Method: A Novel Experimental Assay to Facilitate Risk Assessment of Selection for Antimicrobial Resistance in the Environment.

Background:Antimicrobial resistance (AMR) is one of the most significant health threats to society. A growing body of research demonstrates selection for AMR likely occurs at environmental concentrations of antibiotics. However, no standardized experimental approaches for determining selective concentrations of antimicrobials currently exist, preventing appropriate environmental and human health risk assessment of AMR.Objectives:We aimed to design a rapid, simple, and cost-effective novel experimental assay to determine selective effect concentrations of antibiotics and to generate the largest experimental data set of selective effect concentrations of antibiotics to date.Methods:Previously published methods and data were used to validate the assay, which determines the effect concentration based on reduction of bacterial community (wastewater) growth. Risk quotients for test antibiotics were generated to quantify risk.Results:The assay (SELection End points in Communities of bacTeria, or the SELECT method) was used to rapidly determine selective effect concentrations of antibiotics. These were in good agreement with quantitative polymerase chain reaction effect concentrations determined within the same experimental system. The SELECT method predicted no effect concentrations were minimally affected by changes in the assay temperature, growth media, or microbial community used as the inoculum. The predicted no effect concentrations for antibiotics tested ranged from for ciprofloxacin to for erythromycin.Discussion:The lack of evidence demonstrating environmental selection for AMR, and of associated human health risks, is a primary reason for the lack of action in the mitigation of release of antibiotics into the aquatic environment. We present a novel method that can reliably and rapidly fill this data gap to enable regulation and subsequent mitigation (where required) to lower the risk of selection for, and human exposure to, AMR in aquatic environments. In particular, ciprofloxacin and, to a lesser extent, azithromycin, cefotaxime, and trimethoprim all pose a significant risk for selection of AMR in the environment. https://doi.org/10.1289/EHP6635

Preventing Antibiotic Resistance in the Wild: A New End Point for Environmental Risk Assessment

Human and veterinary antibiotics enter the environment through wastewater effluent, agricultural use of manure and treated sewage for fertilizer, and leakage from waste storage facilities. This antibiotic pollution may exert selective pressure on bacteria to develop drug resistance, which is especially concerning if it develops in pathogenic bacteria. A new study weighs known bacterial antibiotic sensitivities against the backdrop of antibiotic concentrations measured in the environment and suggests that resistance in clinically relevant bacteria may not be kept in check by current risk assessment action levels [EHP 120(8):1100–1106; Tello et al.]. Ciprofloxacin, erythromycin, and tetracycline were selected for the analysis from among the approximately 150 compounds for which minimum inhibitory concentrations (MICs) have been reported for different bacteria. An MIC is the amount of antibiotic needed to inhibit bacterial growth. Each of the three antibiotics affects a wide range of bacteria and represents a distinct class of antibiotics used in humans and animals. Concentrations of each antibiotic in various environmental compartments, or media, had been documented previously. Current guidelines for environmental risk assessment reflect the phase I action limits of the International Cooperation on Harmonisation of Technical Requirements for Registration of Veterinary Medicinal Products. This program, which evaluates the safety of veterinary drugs, calls for environmental risk assessment of antibiotics whose concentrations exceed 1 ppb in aquatic compartments or 100 ppb in terrestrial compartments. These guidelines have been implemented in regulations in the United States, Europe, Japan, and Australia. www.jasonschneider.com The researchers compared information on antibiotic levels in the environment with information on the MICs of clinically relevant bacteria to determine if current levels of antibiotic pollution might be high enough to promote the development of resistance. Within aquatic compartments, only a small fraction of the 27 bacterial genera included in the study were predicted to be affected by environmental concentrations of antibiotics, and results suggested that the phase I action level would protect against resistance. However, current levels of antibiotic pollution in terrestrial compartments—particularly in river sediments, liquid manure, and farmed soil—may be high enough to favor the evolution of bacterial resistance. The conclusions may be limited by long-term selective pressure and by the fact that MIC tests do not represent environmental conditions. Furthermore, the authors did not address bioavailability or the potential influences of antibiotic mixtures, metals, or disinfectants. Nevertheless, the potential for antibiotic pollution to increase antibiotic resistance in clinically relevant bacteria has important implications for public health and environmental health policy, and the authors demonstrate a possible framework for answering important outstanding questions about the environmental impact of antibiotics.

Selective Pressure of Antibiotic Pollution on Bacteria of Importance to Public Health

Background: Many bacteria of clinical importance survive and may grow in different environments. Antibiotic pollution may exert on them a selective pressure leading to an increase in the prevalence of resistance.Objectives: In this study we sought to determine whether environmental concentrations of antibiotics and concentrations representing action limits used in environmental risk assessment may exert a selective pressure on clinically relevant bacteria in the environment.Methods: We used bacterial inhibition as an assessment end point to link antibiotic selective pressures to the prevalence of resistance in bacterial populations. Species sensitivity distributions were derived for three antibiotics by fitting log-logistic models to end points calculated from minimum inhibitory concentration (MIC) distributions based on worldwide data collated by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). To place bacteria represented in these distributions in a broader context, we performed a brief phylogenetic analysis. The potentially affected fraction of bacterial genera at measured environmental concentrations of antibiotics and environmental risk assessment action limits was used as a proxy for antibiotic selective pressure. Measured environmental concentrations and environmental risk assessment action limits were also directly compared to wild-type cut-off values.Results: The potentially affected fraction of bacterial genera estimated based on antibiotic concentrations measured in water environments is ≤ 7%. We estimated that measured environmental concentrations in river sediments, swine feces lagoons, liquid manure, and farmed soil inhibit wild-type populations in up to 60%, 92%, 100%, and 30% of bacterial genera, respectively. At concentrations used as action limits in environmental risk assessment, erythromycin and ciprofloxacin were estimated to inhibit wild-type populations in up to 25% and 76% of bacterial genera.Conclusions: Measured environmental concentrations of antibiotics, as well as concentrations representing environmental risk assessment action limits, are high enough to exert a selective pressure on clinically relevant bacteria that may lead to an increase in the prevalence of resistance.

The toxicity of antibiotic agents to the luminescent bacterium Vibrio fischeri

Despite their common use the fate and effects of antibiotics in the environment are largely unknown. These compounds may enter the environment through different pathways, resulting in the contamination of waste water or fresh water, where bacteria are most likely the primarily affected organisms. In this paper the toxicity of several drugs, reflecting the most important groups of antibiotics and chemotherapeutics, towards Vibrio fischeri are presented. The chronic bioluminescence inhibition assay with Vibrio fischeri is shown to be sensitive against many of the high volume antibiotics used for veterinary purposes and in aquaculture. Thus the assay may be a valuable tool for an effects assessment and biomonitoring of these xenobiotics. The available data for both parts of the risk assessment procedure — exposure assessment and effects assessment — have to be regarded as insufficient for most antibiotics. When the available data about environmental concentrations of antibiotics are compared with their toxicity towards Vibrio fischeri, direct effects on natural microbial communities are to be expected.