Herbicide ingredients change Salmonella enterica sv. Typhimurium and Escherichia coli antibiotic responses

Treatment with Glyphosate Induces Tolerance of Citrus Pathogens to Glyphosate and Fungicides but Not to 1,8-Cineole

During the postharvest period, citrus fruits are exposed to Penicillium italicum, Penicillium digitatum, and Geotrichum candidum. Pesticides such as imazalil (IMZ), thiabendazole (TBZ), orthophenylphenol (OPP), and guazatine (GUA) are commonly used as antifungals. Glyphosate (GP) is also used in citrus fields to eliminate weed growth. The sensitivity of fungal pathogens of citrus fruit to these pesticides and 1,8-cineole was evaluated, and the effect of GP on the development of cross-resistance to other chemicals was monitored over a period of 3 weeks. IMZ most effectively inhibited the mycelial growth and spore germination of P. digitatum and P. italicum, with minimum inhibitory concentrations (MICs) of 0.01 and 0.05 mg/mL, respectively, followed by 1,8-cineole, GP, and TBZ. 1,8-Cineole and GP more effectively inhibited the mycelial growth and spore germination of G. candidum, with minimum inhibitory concentrations (MICs) of 0.2 and 1.0 mg/mL, respectively, than OPP or GUA. For the spore germination assay, all substances tested showed a total inhibitory effect. Subculturing the fungal strains in culture media containing increasing concentrations of GP induced fungal tolerance to GP as well as to the fungicides. In soil, experiments confirmed that GP induced the tolerance of P. digitatum to TBZ and GP and the tolerance of P. italicum to IMZ, TBZ, and GP. However, no tolerance was recorded against 1,8-cineole. In conclusion, it can be said that 1,8-cineole may be recommended as an alternative to conventional fungicides. In addition, these results indicate that caution should be taken when using GP in citrus fields.

Glyphosate and glyphosate-based herbicides (GBHs) induce phenotypic imipenem resistance in Pseudomonas aeruginosa

GBHs are the most widely used herbicides for weed control worldwide that potentially affect microorganisms, but the role of their sublethal exposure in the development of antibiotic resistance of Pseudomonas aeruginosa is still not fully investigated. Here, the effects of glyphosate acid (GLY), five glyphosate-based herbicides (GBHs), and POE(15), a formerly used co-formulant, on susceptibility to imipenem, a potent carbapenem-type antibiotic, in one clinical and four non-clinical environmental P. aeruginosa isolates were studied. Both pre-exposure in broth culture and co-exposure in solid media of the examined P. aeruginosa strains with 0.5% GBHs resulted in a decreased susceptibility to imipenem, while other carbapenems (doripenem and meropenem) retained their effectiveness. Additionally, the microdilution chequerboard method was used to examine additive/antagonistic/synergistic effects between GLY/POE(15)/GBHs and imipenem by determining the fractional inhibitory concentration (FIC) indexes. Based on the FIC index values, glyphosate acid and Total demonstrated a potent antagonistic effect in all P. aeruginosa strains. Dominator Extra 608 SL and Fozat 480 reduced the activity of imipenem in only one strain (ATCC10145), while POE(15) and three other GBHs did not have any effect on susceptibility to imipenem. Considering the simultaneous presence of GBHs and imipenem in various environmental niches, the detected interactions between these chemicals may affect microbial communities. The mechanisms of the glyphosate and GBH-induced imipenem resistance in P. aeruginosa are yet to be investigated.

Copper and nanostructured anatase rutile and carbon coatings induce adaptive antibiotic resistance

Contaminated surfaces are vehicles for the spread of infectious disease-causing microorganisms. A strategy to prevent their spread is applying antimicrobial coatings to surfaces. Both nanostructured anatase rutile and carbon (NsARC), a TiO₂ formulation, and copper are examples of antimicrobial agents that are used in making or coating door handles and similar surfaces, to reduce microbial loads. Antimicrobial surfaces have been extensively tested for antimicrobial activity but not sublethal effects, such as exposure-associated multiple antibiotic resistance phenotypes usually caused by induction of efflux pump genes. The possibility of NsARC and copper inducing indicative efflux pump pathways was investigated by monitoring the expression of mScarlet fluorescent protein (FP) in two reporter strains of Escherichia coli. There was an increase in the expression of FP in the reporter strains exposed to NsARC and copper relative to the inert control composed of stainless steel. Furthermore we tested E. coli and Staphylococcus aureus following 8 h of exposure to NsARC for changes in resistance to selected antibiotics. E. coli that were exposed to NsARC became more susceptible to kanamycin but there was no significant change in susceptibility of S. aureus to any tested antibiotics. These findings suggests that even though NsARC and copper are antimicrobial, they also have some potential to cause unintended phenotypes.

New antimicrobial material NsARC based on TiO₂ compared to copper.

Both NsARC and copper induce efflux pump gene transcription.

Species-specific changes in antibiotic resistance from exposure to antimicrobial surface coatings.

Does Glyphosate Affect the Human Microbiota?

Glyphosate is the world’s most widely used agrochemical. Its use in agriculture and gardening has been proclaimed safe because humans and other animals do not have the target enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). However, increasing numbers of studies have demonstrated risks to humans and animals because the shikimate metabolic pathway is present in many microbes. Here, we assess the potential effect of glyphosate on healthy human microbiota. Our results demonstrate that more than one-half of human microbiome are intrinsically sensitive to glyphosate. However, further empirical studies are needed to determine the effect of glyphosate on healthy human microbiota.

Herbicide promotes the conjugative transfer of multi-resistance genes by facilitating cellular contact and plasmid transfer

The global dissemination of antibiotic resistance genes (ARGs), especially via plasmid-mediated horizontal transfer, is becoming a pervasive health threat. While our previous study found that herbicides can accelerate the horizontal gene transfer (HGT) of ARGs in soil bacteria, the underlying mechanisms by which herbicides promote the HGT of ARGs across and within bacterial genera are still unclear. Here, the underlying mechanism associated with herbicide-promoted HGT was analyzed by detecting intracellular reactive oxygen species (ROS) production, extracellular polymeric substance composition, cell membrane integrity and proton motive force combined with genome-wide RNA sequencing. Exposure to herbicides induced a series of the above bacterial responses to promote HGT except for the ROS response, including compact cell-to-cell contact by enhancing pilus-encoded gene expression and decreasing cell surface charge, increasing cell membrane permeability, and enhancing the proton motive force, providing additional power for DNA uptake. This study provides a mechanistic understanding of the risk of bacterial resistance spread promoted by herbicides, which elucidates a new perspective on nonantibiotic agrochemical acceleration of the HGT of ARGs.

A Glyphosate-Based Herbicide Cross-Selects for Antibiotic Resistance Genes in Bacterioplankton Communities

Agrochemicals often contaminate freshwater bodies, affecting microbial communities that underlie aquatic food webs. For example, the herbicide glyphosate has the potential to indirectly select for antibiotic-resistant bacteria. Such cross-selection could occur if the same genes (encoding efflux pumps, for example) confer resistance to both glyphosate and antibiotics. To test for cross-resistance in natural aquatic bacterial communities, we added a glyphosate-based herbicide (GBH) to 1,000-liter mesocosms filled with water from a pristine lake. Over 57 days, we tracked changes in bacterial communities with shotgun metagenomic sequencing and annotated metagenome-assembled genomes (MAGs) for the presence of known antibiotic resistance genes (ARGs), plasmids, and resistance mutations in the enzyme targeted by glyphosate (enolpyruvyl-shikimate-3-phosphate synthase; EPSPS). We found that high doses of GBH significantly increased ARG frequency and selected for multidrug efflux pumps in particular. The relative abundance of MAGs after a high dose of GBH was predictable based on the number of ARGs in their genomes (17% of variation explained) and, to a lesser extent, by resistance mutations in EPSPS. Together, these results indicate that GBHs can cross-select for antibiotic resistance in natural freshwater bacteria. IMPORTANCE Glyphosate-based herbicides (GBHs) such as Roundup formulations may have the unintended consequence of selecting for antibiotic resistance genes (ARGs), as demonstrated in previous experiments. However, the effects of GBHs on ARGs remain unknown in natural aquatic communities, which are often contaminated with pesticides from agricultural runoff. Moreover, the resistance provided by ARGs compared to canonical mutations in the glyphosate target enzyme, EPSPS, remains unclear. Here, we performed a freshwater mesocosm experiment showing that a GBH strongly selects for ARGs, particularly multidrug efflux pumps. These selective effects were evident after just a few days, and the ability of bacteria to survive and thrive after GBH stress was predictable by the number of ARGs in their genomes and, to a lesser extent, by mutations in EPSPS. Intensive GBH application may therefore have the unintended consequence of selecting for ARGs in natural freshwater communities.

Pesticide Importation in Sierra Leone, 2010–2021: Implications for Food Production and Antimicrobial Resistance

There are no previous studies reporting the type and quantity of pesticides for farming from Sierra Leone and the impact of Ebola or COVID-19 on importation. This study reviewed imported farming pesticides by the Sierra Leone, Ministry of Agriculture and Forestry (MAF), between 2010–2021. It was a descriptive study using routinely collected importation data. We found the MAF imported pesticides for farming only during 2010, 2014 and 2021, in response to growing food insecurity and associated with Ebola and COVID-19 outbreaks. Results showed insecticide importation increased from 6230 L in 2010 to 51,150 L in 2021, and importation of antimicrobial pesticides (including fungicides) increased from 150 kg in 2010 to 23,560 kg in 2021. The hazard class risk classification of imported pesticides decreased over time. Increasing amounts of imported fungicides could increase the risk of future fungal resistance among humans. We found that in responding to escalating food insecurity, the government dramatically increased the amount of pesticide importation to improve crop production. Further support is necessary to decrease the risk of worsening food shortages and the possible threat of emerging antimicrobial resistance. We recommend continued monitoring and surveillance, with further studies on the most appropriate response to these multiple challenges.

Prevalence of Escherichia coli strains in horticultural farms from Argentina: antibiotic resistance, biofilm formation, and phylogenetic affiliation

Escherichia coli is the bacteria most commonly used as an indicator of fecal contamination in agricultural environments. Moreover, E. coli is categorized as a priority pathogen due to its widespread antibiotic resistance. This study aimed to characterize E. coli strains isolated from 10 horticultural farms. Isolates were obtained from samples of vegetable crops (n = 62), the surrounding soil (n = 62), poultry litter (n = 8), and groundwater (n = 6). Phyllo-grouping assignment was performed on the total of E. coli isolates. Antibiograms and quantification of the minimal inhibitory concentration (MIC) were performed with antibiotics commonly used in humans. Biofilm formation capacity was studied by quantifying cells attached to culture tubes. Overall, 21 E. coli isolates were obtained. Three phylogenetic groups (A, B1, and C) and two Escherichia clade IV and IV-V were identified in the collection by polymerase chain reaction. Sixty-seven percent of the E. coli isolates were resistant to amoxicillin-clavulanic acid and/or ampicillin. Amoxicillin MIC values ranged from 11.9 to >190.5 µg/mL and ampicillin MIC values ranged from 3 to >190.5 µg/mL. All the E. coli isolates, resistant and non-resistant, had biofilm forming capacity. The presence of phenotypic resistance on fresh produce and environmental matrices could present significant opportunities for contamination that result in health risks for consumers. To the authors' best knowledge, this is the first environmental assessment of resistant E. coli occurrence in horticultural farms in South America.

Antimicrobial Resistance and Environmental Health: A Water Stewardship Framework for Global and National Action

Antimicrobial resistance (AMR) is a global health crisis that affects all life on Earth. In 2015, the World Health Organization developed guidance to combat AMR in accordance with a One Health framework considering human, animal, and environment sectors of planetary health. This study reviewed global guidance and 25 National Action Plans to evaluate thematic priorities in One Health AMR approaches using a novel framework that additionally facilitated the identification of water-related stewardship gaps, as water resources are recognized as the primary environmental AMR reservoir and dissemination pathway. This review found that global and national stewardship primarily focuses on mitigating antibiotic use in the human and animal sectors, overlooking environmental drivers, particularly diverse environmental waters. The findings of this study highlight the need to broaden the scope of water-related AMR concerns beyond water, sanitation, and hygiene (WASH) infrastructure for water supply and wastewater treatment, and account for environmental waters in AMR development and dissemination, particularly in low-income countries where half a billion people rely on environmental waters to meet daily needs. Equitably accounting for water environments, supplies, and waste in AMR prevention, mitigation, surveillance, and innovation can significantly enhance the integration of environmental objectives in One Health AMR stewardship.

Glyphosate escalates horizontal transfer of conjugative plasmid harboring antibiotic resistance genes

Glyphosate has been frequently detected in water environments because of the wide use for controlling weed in farm lands and urban areas. Presently, the focus of the majority of studies is placed on the toxicity of glyphosate on humans and animals. However, the effects of glyphosate on horizontal transfer of conjugative plasmid carrying antibiotic resistance gene (ARG) are largely unknown. Here, we explored the ability and potential mechanism of glyphosate for accelerating horizontal transfer of conjugative plasmid-mediated ARG. The results showed that glyphosate can effectively boost horizontal transfer rate of conjugative plasmid carrying ARG. The possible mechanism analysis demonstrated that over-production of reactive oxygen species and reactive nitrogen species effectively regulated expression levels of bacterial outer membrane protein and conjugative transfer-related genes, thereby resulting into elevated horizontal transfer rate of plasmid-mediated ARG. In conclusion, this study casts new understanding into the biological effects of glyphosate on ARG.

Knowledge Gaps in the Understanding of Antimicrobial Resistance in Canada

Current limitations in the understanding and control of antimicrobial resistance (AMR) in Canada are described through a comprehensive review focusing on: (1) treatment optimization; (2) surveillance of antimicrobial use and AMR; and (3) prevention of transmission of AMR. Without addressing gaps in identified areas, sustained progress in AMR mitigation is unlikely. Expert opinions and perspectives contributed to prioritizing identified gaps. Using Canada as an example, this review emphasizes the importance and necessity of a One Health approach for understanding and mitigating AMR. Specifically, antimicrobial use in human, animal, crop, and environmental sectors cannot be regarded as independent; therefore, a One Health approach is needed in AMR research and understanding, current surveillance efforts, and policy. Discussions regarding addressing described knowledge gaps are separated into four categories: (1) further research; (2) increased capacity/resources; (3) increased prescriber/end-user knowledge; and (4) policy development/enforcement. This review highlights the research and increased capacity and resources to generate new knowledge and implement recommendations needed to address all identified gaps, including economic, social, and environmental considerations. More prescriber/end-user knowledge and policy development/enforcement are needed, but must be informed by realistic recommendations, with input from all relevant stakeholders. For most knowledge gaps, important next steps are uncertain. In conclusion, identified knowledge gaps underlined the need for AMR policy decisions to be considered in a One Health framework, while highlighting critical needs to achieve realistic and meaningful progress.

Herbicide Selection Promotes Antibiotic Resistance in Soil Microbiomes

Herbicides are one of the most widely used chemicals in agriculture. While they are known to be harmful to nontarget organisms, the effects of herbicides on the composition and functioning of soil microbial communities remain unclear. Here we show that application of three widely used herbicides—glyphosate, glufosinate, and dicamba—increase the prevalence of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soil microbiomes without clear changes in the abundance, diversity and composition of bacterial communities. Mechanistically, these results could be explained by a positive selection for more tolerant genotypes that acquired several mutations in previously well-characterized herbicide and ARGs. Moreover, herbicide exposure increased cell membrane permeability and conjugation frequency of multidrug resistance plasmids, promoting ARG movement between bacteria. A similar pattern was found in agricultural soils across 11 provinces in China, where herbicide application, and the levels of glyphosate residues in soils, were associated with increased ARG and MGE abundances relative to herbicide-free control sites. Together, our results show that herbicide application can enrich ARGs and MGEs by changing the genetic composition of soil microbiomes, potentially contributing to the global antimicrobial resistance problem in agricultural environments.

Antimicrobials and Food-Related Stresses as Selective Factors for Antibiotic Resistance along the Farm to Fork Continuum

Antimicrobial resistance (AMR) is a global problem and there has been growing concern associated with its widespread along the animal-human-environment interface. The farm-to-fork continuum was highlighted as a possible reservoir of AMR, and a hotspot for the emergence and spread of AMR. However, the extent of the role of non-antibiotic antimicrobials and other food-related stresses as selective factors is still in need of clarification. This review addresses the use of non-antibiotic stressors, such as antimicrobials, food-processing treatments, or even novel approaches to ensure food safety, as potential drivers for resistance to clinically relevant antibiotics. The co-selection and cross-adaptation events are covered, which may induce a decreased susceptibility of foodborne bacteria to antibiotics. Although the available studies address the complexity involved in these phenomena, further studies are needed to help better understand the real risk of using food-chain-related stressors, and possibly to allow the establishment of early warnings of potential resistance mechanisms.

Selection for Resistance to a Glyphosate-Containing Herbicide in Salmonella enterica Does Not Result in a Sustained Activation of the Tolerance Response or Increased Cross-Tolerance and Cross-Resistance to Clinically Important Antibiotics

Evolution of bacterial tolerance to antimicrobials precedes evolution of resistance and may result in cross-tolerance, cross-resistance, or collateral sensitivity to other antibiotics. Transient exposure of gut bacteria to glyphosate, the world's most widely used herbicide, has been linked to the activation of the stress response and changes in susceptibility to antibiotics. In this study, we investigated whether chronic exposure to a glyphosate-based herbicide (GBH) results in resistance, a constitutive activation of the tolerance and stress responses, and cross-tolerance or cross-resistance to antibiotics. Of the 10 farm animal-derived clinical isolates of Salmonella enterica subjected to experimental evolution in increasing concentrations of GBH, three isolates showed stable resistance with mutations associated with the glyphosate target gene aroA and no fitness costs. Global quantitative proteomics analysis demonstrated activation of the cellular tolerance and stress response during the transient exposure to GBH but not constitutively in the resistant mutants. Resistant mutants displayed no cross-resistance or cross-tolerance to antibiotics. These results suggest that while transient exposure to GBH triggers cellular tolerance response in Salmonella enterica, this response does not become genetically fixed after selection for resistance to GBH and does not result in increased cross-tolerance or cross-resistance to clinically important antibiotics under our experimental conditions.IMPORTANCE Glyphosate-based herbicides (GBH) are among the world's most popular, with traces commonly found in food, feed, and the environment. Such high ubiquity means that the herbicide may come into contact with various microorganisms, on which it acts as an antimicrobial, and it may select for resistance and cross-resistance to clinically important antibiotics. It is therefore important to estimate whether the widespread use of pesticides may be an underappreciated source of antibiotic-resistant microorganisms that may compromise efficiency of antibiotic treatments in humans and animals.

Exposure to Environmental Levels of Pesticides Stimulates and Diversifies Evolution in Escherichia coli toward Higher Antibiotic Resistance

Antibiotic resistance is one of the most challenging issues in public health. Antibiotics have been increasingly used not only for humans and animals but also for crop protection as pesticides. Thus, antibiotics often coexist with pesticides in some environments. To investigate the effects of the co-occurring, nonantibiotic pesticides on the development of antibiotic resistance, we conducted long-term exposure experiments using an Escherichia coli K-12 model strain. The results reveal that (1) the exposure to pesticides (in mg/L) alone led to the emergence of mutants with significantly higher resistance to streptomycin; (2) the exposure to pesticides (in μg/L) together with a subinhibitory level (in high μg/L) of ampicillin synergistically stimulated the selection of ampicillin resistance and the cross-resistance to other antibiotics (i.e., ciprofloxacin, chloramphenicol, and tetracycline). Distinct and diversified genetic mutations emerged in the resistant mutants selected from the coexposure to both pesticides and ampicillin. The genetic mutations likely caused a holistic transcriptional regulation (e.g., biofilm formation, oxidative stress defense) when grown under antibiotic stress and led to increased antibiotic resistance. Together, these findings provide important fundamental insights into the development of antibiotic resistance and the resistance mechanisms under environmentally relevant conditions where antibiotics and nonantibiotic micropollutants coexist.

Antimicrobial resistance in freshwater Plesiomonas shigelloides isolates: Implications for environmental pollution and risk assessment

Antibiotic resistance is known to impact treatment efficiency of Plesiomonas infections negatively with fatal outcomes. This study investigated antibiogram fingerprint of P. shigelloides (n = 182) isolated from three South Africa rivers using the disc diffusion technique. Environmental pollution and analogous health risk (given infections) that could associate with the freshwaters and empirical treatment of Plesiomonas were assessed using Antibiotic Resistance Index (ARI) and Multiple Antibiotic Resistance Indices (MARI), respectively. Thirteen EUCAST recommended (ERAs) and eleven non-recommended antibiotics (NAs) used as first line agents in the treatment of gastroenteritis and extraintestinal infections were tested. Resistance against ERAs decreased from cefoxitin (37.91%), cefuroxime (35.17%), cefepime (31.87%), ceftriaxone (29.67%), ciprofloxacin (18.13%), trimethoprim-sulfamethoxazole (10.44%), piperacillin/tazobactam (8.79%), ertapenem (4.95%), norfloxacin (4.40%), levofloxacin (2.75%), meropenem (1.10%) to imipenem (0.55%). The isolates had higher resistance (≥36.07%) against NAs but were susceptible to amikacin (67.58%), gentamycin (73.08%), and tetracycline (80.77%). MARI of the isolates were significantly different between ERAs and NAs (P-value < 0.05) and had an average of 0.17 ± 0.18 and 0.45 ± 0.13, respectively. About 33.87% and 95.63% of the isolates had MARI value from 0.23 to 0.62 and 0.27-0.82 to ERAs and NAs, respectively. Also, ERAs-based and NAs-based ARI across sampling units showed significantly different (P-value < 0.05) means of 0.18 ± 0.09 and 0.46 ± 0.05, respectively. MARI attributed low risk of empirical treatment to recommended antibiotics but higher risk to non-recommended antibiotics. Model estimated successful and unsuccessful empirical treatment of infections risks due to resistance in the isolates using recommended antibiotics as 65.93% and 34.07%, respectively; 1.65% and 98.35% in the case of non-recommended antibiotics, respectively. ARI based on recommended antibiotics identified potential environmental pollutions in a number of sites. Resistance in freshwater P. shigelloides especially against cephalosporin, quinolones and fluoroquinolones is distressing and might suggests high pollution of the freshwaters in the Eastern Cape Province.

Antimicrobial resistance in water in Latin America and the Caribbean: a scoping review protocol

OBJECTIVE

The objective of this scoping review is to identify and map existing evidence of antimicrobial resistance (AMR) in water in Latin America and the Caribbean (LAC), while also identifying the gaps in AMR information in the region in eight themes of interest.

INTRODUCTION

Antimicrobial resistance is a public health concern that has gained increasing global awareness. Concerns have been raised toward the importance of the environment's role in the dissemination of clinically relevant AMR. Although studies on AMR have been conducted, the reality of the role of the environment in the LAC region has not been studied.

INCLUSION CRITERIA

Articles that examine AMR in water in the LAC region will be considered for inclusion. Antimicrobial resistance will be defined as a natural process that arises when the microorganisms that cause infection (e.g. bacteria) survive exposure to a drug that would normally kill them or stop their growth. The search will focus on eight themes of interest, as defined in the protocol, relating to the presence of resistant microorganisms in water sources and reported negative health effects. Qualitative and quantitative studies will be considered for inclusion. Reviews and gray literature will be excluded.

METHODS

The proposed scoping review will be conducted in accordance with the JBI methodology for scoping reviews. A search for published literature will be performed in PubMed, Web of Science and Scopus. Independent screening of articles will be performed by examining the abstracts and then the full texts, utilizing pre-defined inclusion and exclusion criteria. Data for specific variables will be extracted, and descriptive examination will be performed.

Translating antibiotic prescribing into antibiotic resistance in the environment: A hazard characterisation case study

The environment receives antibiotics through a combination of direct application (e.g., aquaculture and fruit production), as well as indirect release through pharmaceutical manufacturing, sewage and animal manure. Antibiotic concentrations in many sewage-impacted rivers are thought to be sufficient to select for antibiotic resistance genes. Yet, because antibiotics are nearly always found associated with antibiotic-resistant faecal bacteria in wastewater, it is difficult to distinguish the selective role of effluent antibiotics within a 'sea' of gut-derived resistance genes. Here we examine the potential for macrolide and fluoroquinolone prescribing in England to select for resistance in the River Thames catchment, England. We show that 64% and 74% of the length of the modelled catchment is chronically exposed to putative resistance-selecting concentrations (PNEC) of macrolides and fluoroquinolones, respectively. Under current macrolide usage, 115 km of the modelled River Thames catchment (8% of total length) exceeds the PNEC by 5-fold. Similarly, under current fluoroquinolone usage, 223 km of the modelled River Thames catchment (16% of total length) exceeds the PNEC by 5-fold. Our results reveal that if reduced prescribing was the sole mitigating measure, that macrolide and fluoroquinolone prescribing would need to decline by 77% and 85%, respectively, to limit resistance selection in the catchment. Significant reductions in antibiotic prescribing are feasible, but innovation in sewage-treatment will be necessary for achieving substantially-reduced antibiotic loads and inactivation of DNA-pollution from resistant bacteria. Greater confidence is needed in current risk-based targets for antibiotics, particularly in mixtures, to better inform environmental risk assessments and mitigation.

Effect of a Glyphosate-Containing Herbicide on Escherichia coli and Salmonella Ser. Typhimurium in an In Vitro Rumen Simulation System

Glyphosate (N-(phosphonomethyl)glycine) is the most-used herbicide worldwide. Many studies in the past have shown that residues of the herbicide can be found in many cultivated plants, including those used as livestock feed. Sensitivity to glyphosate varies with bacteria, particularly those residing in the intestine, where microbiota is exposed to glyphosate residues. Therefore, less susceptible pathogenic isolates could have a distinct advantage compared to more sensitive commensal isolates, probably leading to dysbiosis. To determine whether the ruminal growth and survival of pathogenic Escherichia coli or Salmonella serovar Typhimurium are higher when glyphosate residues are present in the feed, an in vitro fermentation trial with a "Rumen Simulation System" (RUSITEC) and a glyphosate-containing commercial formulation was performed. Colony forming units of E. coli and Salmonella ser. Typhimurium decreased steadily in all fermenters, regardless of the herbicide application. Minimum inhibitory concentrations of the studied Salmonella and E. coli strains did not change, and antibiotic susceptibility varied only slightly but independent of the glyphosate application. Overall, application of the glyphosate-containing formulation in a worst-case concentration of 10 mg/L neither increased the abundance for the tested E. coli and Salmonella strain in the in vitro fermentation system, nor promoted resistance to glyphosate or antibiotics.

Redox-Based Synthetic Biology Enables Electrochemical Detection of the Herbicides Dicamba and Roundup via Rewired Escherichia coli

Synthetic biology is typically exploited to endow bacterial cells with new biosynthetic capabilities. It can also serve to create "smart" bacteria such as probiotics that detect and treat disease. Here, we show how minimally rewiring the genetic regulation of bacterial cells can enable their ability to recognize and report on chemical herbicides, including those routinely used to clear weeds from gardens and crops. In so doing, we demonstrate how constructs of synthetic biology, in this case redox-based synthetic biology, can serve as a vector for information flow mediating molecular communication between biochemical systems and microelectronics. We coupled the common genetic reporter, β-galactosidase, with the E. coli superoxide response regulon promoter pSoxS, for detection of the herbicides dicamba and Roundup. Both herbicides activated our genetic construct in a concentration dependent manner. Results indicate robust detection using spectrophotometry, via the Miller assay, and electrochemistry using the enzymatic cleavage of 4-aminophenyl β-d-galactopyranoside into the redox active molecule p-aminophenol. We found that environmental components, in particular, the availability of glucose, are important factors for the cellular detection of dicamba. Importantly, both herbicides were detected at concentrations relevant for aquatic toxicity.

Minimum Inhibitory Concentration of Glyphosate and of a Glyphosate-Containing Herbicide Formulation for Escherichia coli Isolates - Differences Between Pathogenicand Non-pathogenic Isolates and Between Host Species

Glyphosate is the most extensively used herbicide in the world. However, concerns regarding its safety, side effects, and impact on other organisms have increased in recent years. This is the first study to analyze a large set of recent and historical Escherichia coli isolates varying in pathogenicity and beta-lactam resistance from different host species for their susceptibility to glyphosate isopropylamine salt (IPA), the active ingredient of the herbicide, and to a complete glyphosate-containing formulation (Roundup LB Plus). For this, minimum inhibitory concentrations (MIC) were determined for 238 E. coli isolates by broth microdilution in Mueller Hinton I media followed by the statistical analyses using Mann-Whitney-U test, multivariable analysis of variance (ANOVA) and a multivariable proportional-odds ordinal regression model. While the overall MIC distribution was narrow and lacked a highly resistant sub-population for both substances, statistical analyses revealed small but significant associations between glyphosate resistance levels and different factors tested. Mean MIC values for the entire dataset showed a higher level of resistance to the complete glyphosate-containing formulation (40 mg/ml IPA) than to pure glyphosate (10 mg/ml IPA) in E. coli. Isolates that originated from poultry had significantly higher MIC values for both pure glyphosate and the complete formulation. Pathogenic and non-extended-spectrum beta-lactamase (non-ESBL) E. coli isolates each showed significantly higher MIC values compared to commensals and ESBL-producing E. coli in pure glyphosate, but not in the complete formulation. Recently sampled isolates showed statistically higher MICs than the isolates of the historic standard E. coli collection of reference in pure glyphosate, when tested by nonparametric Mann-Whitney-U test, but not in the multivariable model. Further investigations are necessary to confirm whether these associations have a casual relationship with the glyphosate use or are the consequence of co-selection due to the increased application rates of antibiotics, heavy metals or other biocides. A possible accumulation of pathogenic bacteria in livestock animals fed with glyphosate-containing feed should also be considered.

Reversing resistance to counter antimicrobial resistance in the World Health Organisation's critical priority of most dangerous pathogens

The speed at which bacteria develop antimicrobial resistance far outpace drug discovery and development efforts resulting in untreatable infections. The World Health Organisation recently released a list of pathogens in urgent need for the development of new antimicrobials. The organisms that are listed as the most critical priority are all Gram-negative bacteria resistant to the carbapenem class of antibiotics. Carbapenem resistance in these organisms is typified by intrinsic resistance due to the expression of antibiotic efflux pumps and the permeability barrier presented by the outer membrane, as well as by acquired resistance due to the acquisition of enzymes able to degrade β-lactam antibiotics. In this perspective article we argue the case for reversing resistance by targeting these resistance mechanisms - to increase our arsenal of available antibiotics and drastically reduce antibiotic discovery times - as the most effective way to combat antimicrobial resistance in these high priority pathogens.

Effects of sub-lethal concentrations of copper ammonium acetate, pyrethrins and atrazine on the response of Escherichia coli to antibiotics

Background: Antibiotic resistance in human and animal pathogens is mainly the outcome of human use of antibiotics. However, bacteria are also exposed to thousands of other antimicrobial agents. Increasingly those exposures are being investigated as co-selective agents behind the rapid rise and spread of resistance in bacterial pathogens of people and our domesticated animals. Methods: We measured the sub-lethal effects on antibiotic tolerance of the human pathogen/commensal Escherichia coli caused by exposure to three common biocide formulations based on either copper, pyrethrins, or atrazine as active ingredients. The influence of the efflux pump AcrAB-TolC was investigated using deletion strains, and the persistence of observed effects was determined. Results: Some effects were seen for all biocides, but the largest effects were observed with copper in combination with the antibiotic tetracycline. The effect was caused by both the induction of the adaptive efflux system and by chelation of the antibiotic by copper. Finally, persistence of the adaptive response was measured and found to persist for about two generations. Conclusions: Through a combination of microbe-chemical and chemical-chemical interactions, humanity may be creating micro-environments in which resistance evolution is accelerated.

Agrichemicals and antibiotics in combination increase antibiotic resistance evolution

Antibiotic resistance in our pathogens is medicine's climate change: caused by human activity, and resulting in more extreme outcomes. Resistance emerges in microbial populations when antibiotics act on phenotypic variance within the population. This can arise from either genotypic diversity (resulting from a mutation or horizontal gene transfer), or from differences in gene expression due to environmental variation, referred to as adaptive resistance. Adaptive changes can increase fitness allowing bacteria to survive at higher concentrations of antibiotics. They can also decrease fitness, potentially leading to selection for antibiotic resistance at lower concentrations. There are opportunities for other environmental stressors to promote antibiotic resistance in ways that are hard to predict using conventional assays. Exploiting our previous observation that commonly used herbicides can increase or decrease the minimum inhibitory concentration (MIC) of different antibiotics, we provide the first comprehensive test of the hypothesis that the rate of antibiotic resistance evolution under specified conditions can increase, regardless of whether a herbicide increases or decreases the antibiotic MIC. Short term evolution experiments were used for various herbicide and antibiotic combinations. We found conditions where acquired resistance arises more frequently regardless of whether the exogenous non-antibiotic agent increased or decreased antibiotic effectiveness. This is attributed to the effect of the herbicide on either MIC or the minimum selective concentration (MSC) of a paired antibiotic. The MSC is the lowest concentration of antibiotic at which the fitness of individuals varies because of the antibiotic, and is lower than MIC. Our results suggest that additional environmental factors influencing competition between bacteria could enhance the ability of antibiotics to select antibiotic resistance. Our work demonstrates that bacteria may acquire antibiotic resistance in the environment at rates substantially faster than predicted from laboratory conditions.