Underappreciated role of regionally poor water quality on globally increasing antibiotic resistance

Methicillin Resistant Staphylococcus aureus: Molecular Mechanisms Underlying Drug Resistance Development and Novel Strategies to Combat

Antimicrobial resistance (AMR) represents a major threat to global health. Infection caused by Methicillin-resistant Staphylococcus aureus (MRSA) is one of the well-recognized global public health problem globally. In some regions, as many as 90% of S. aureus infections are reported to be MRSA, which cannot be treated with standard antibiotics. WHO reports indicated that MRSA is circulating in every province worldwide, significantly increasing the risk of death by 64% compared to drug-sensitive forms of the infection which is attributed to its antibiotic resistance. The emergence and spread of antibiotic-resistant MRSA strains have contributed to its increased prevalence in both healthcare and community settings. The resistance of S. aureus to methicillin is due to expression of penicillin-binding protein 2a (PBP2a), which renders it impervious to the action of β-lactam antibiotics including methicillin. The other is through the production of beta-lactamases. Although the treatment options for MRSA are limited, there are promising alternatives to antibiotics to combat the infections. Innovative therapeutic strategies with wide range of activity and modes of action are yet to be explored. The review highlights the global challenges posed by MRSA, elucidates the mechanisms underlying its resistance development, and explores mitigation strategies. Furthermore, it focuses on alternative therapies such as bacteriophages, immunotherapy, nanobiotics, and antimicrobial peptides, emphasizing their synergistic effects and efficacy against MRSA. By examining these alternative approaches, this review provides insights into the potential strategies for tackling MRSA infections and combatting the escalating threat of AMR. Ultimately, a multifaceted approach encompassing both conventional and novel interventions is imperative to mitigate the impact of MRSA and ensure a sustainable future for global healthcare.

Leveraging the COVID-19 pandemic as a natural experiment to assess changes in antibiotic use and antibiotic-resistant E. coli carriage in semi-rural Ecuador

The coronavirus 2019 (COVID-19) pandemic has had significant impacts on health systems, population dynamics, public health awareness, and antibiotic stewardship, which could affect antibiotic resistant bacteria (ARB) emergence and transmission. In this study, we aimed to compare knowledge, attitudes, and practices (KAP) of antibiotic use and ARB carriage in Ecuadorian communities before versus after the COVID-19 pandemic began. We leveraged data collected for a repeated measures observational study of third-generation cephalosporin-resistant E. coli (3GCR-EC) carriage among children in semi-rural communities in Quito, Ecuador between July 2018 and September 2021. We included 241 households that participated in surveys and child stool sample collection in 2019, before the pandemic, and in 2021, after the pandemic began. We estimated adjusted Prevalence Ratios (aPR) and 95% Confidence Intervals (CI) using logistic and Poisson regression models. Child antibiotic use in the last 3 months declined from 17% pre-pandemic to 5% in 2021 (aPR: 0.30; 95% CI 0.15, 0.61) and 3GCR-EC carriage among children declined from 40 to 23% (aPR: 0.48; 95% CI 0.32, 0.73). Multi-drug resistance declined from 86 to 70% (aPR: 0.32; 95% CI 0.13; 0.79), the average number of antibiotic resistance genes (ARGs) per 3GCR-EC isolate declined from 9.9 to 7.8 (aPR of 0.79; 95% CI 0.65, 0.96), and the diversity of ARGs was lower in 2021. In the context of Ecuador, where COVID-19 prevention and control measures were strictly enforced after its major cities experienced some of the world's the highest mortality rates from SARS-CoV-2 infections, antibiotic use and ARB carriage declined in semi-rural communities of Quito from 2019 to 2021.

Antimicrobial susceptibility of Salmonella and Escherichia coli from equids sampled in the NAHMS 2015-16 equine study and association of management factors with resistance

Several studies have investigated antimicrobial resistance (AMR) in Salmonella spp. and Escherichia coli isolated from hospitalized horses, but studies conducted on community-based populations of equids are limited. The factors associated with AMR in these bacteria in the general horse population are not well understood. The primary objective of our study was to estimate the prevalence of Salmonella and describe antimicrobial susceptibility of Salmonella and E. coli from equids across the United States. The second objective was to identify associations between health management and biosecurity practices and AMR. Fecal samples submitted from 1357 equids on 199 operations were tested for Salmonella, identifying 27 positive samples with 29 isolates belonging to 18 serotypes. Fecal sample and operation-level prevalence of Salmonella was 2.0% (27/1357) and 7.0% (14/199), respectively. Most (25/29) isolates were pan-susceptible while four isolates exhibited resistance, three of which were multidrug resistant. Of the 721 samples cultured for E. coli, 85% (613/721) were positive. Eighty-six percent of the E. coli isolates recovered were pan-susceptible (529/612). Ten isolates were intermediate to one antimicrobial drug and susceptible to all others. Seventy-three E. coli isolates (11.9%, SE=1.3) were resistant to one or more antimicrobials, corresponding to a 33.0% (64/194) operation-level prevalence. Resistance to sulfonamide drugs was most common with 63 isolates (10.3%) resistant to sulfisoxazole, 57 of which (9.3%) were resistant to trimethoprim-sulfamethoxazole. MDR in E. coli was rare (1.8%, SE=0.5). Univariate and multivariable regression were used to evaluate associations between health management and biosecurity questionnaire items and AMR in E. coli. The outcome modeled was resistance to any of the 14 tested antimicrobials. Depending on the operation type, operations with greater than 20 resident equids were significantly associated with resistance. In addition, performance operations were significantly associated with resistance when compared to farm/ranch operations. Operations with feed containers that prevent fecal contamination and those that had treated any equids for illness or injury were associated with a lower AMR. The study results suggest that equids in the general population appear to pose low risk of shedding antimicrobial resistant strains of Salmonella and E. coli, and therefore low transmission potential to other equids, animals, humans, or the environment. However, it is prudent to practice good hand hygiene to prevent spread of Salmonella as well as AMR, and to protect both animal and human health. Despite study limitations, potential management factors that may influence prevalence and prevent spread of AMR shed by equids were identified.

Evaluation of FEAST for metagenomics-based source tracking of antibiotic resistance genes

A metagenomics-based technological framework has been proposed for evaluating the potential and utility of FEAST as an ARG profile-based source apportionment tool. To this end, a large panel of metagenomic data sets was analyzed, associating with eight source types of ARGs in environments. Totally, 1089 different ARGs were found in the 604 source metagenomes, and 396 ARG indicators were identified as the source-specific fingerprints to characterize each of the source types. With the source fingerprints, predictive performance of FEAST was checked using "leave-one-out" cross-validation strategy. Furthermore, artificial sink communities were simulated to evaluate the FEAST for source apportionment of ARGs. The prediction of FEAST showed high accuracy values (0.933 ± 0.046) and specificity values (0.959 ± 0.041), confirming its suitability to discriminate samples from different source types. The apportionment results reflected well the expected output of artificial communities which were generated with different ratios of source types to simulate various contamination levels. Finally, the validated FEAST was applied to track the sources of ARGs in river sediments. Results showed STP effluents were the main contributor of ARGs, with an average contribution of 76 %, followed by sludge (10 %) and aquaculture effluent (2.7 %), which were basically consistent with the actual environment in the area.

Comparison of Extended-Spectrum Beta-Lactamase-Producing Escherichia coli Isolates From Rooks (Corvus frugilegus) and Contemporary Human-Derived Strains: A One Health Perspective

During winter, a large number of rooks gather and defecate at the park of a university clinic. We investigated the prevalence of extended-spectrum beta-lactamase (ESBL)–producing Escherichia coli in these birds and compared recovered isolates with contemporary human isolates. In 2016, fecal samples were collected from 112 trap-captured rooks and investigated for presence of ESBL producers using eosin methylene blue agar supplemented by 2 mg/L cefotaxime; 2,455 contemporary human fecal samples of patients of the clinics sent for routine culturing were tested similarly. In addition, 42 ESBL-producing E. coli isolates collected during the same period from inpatients were also studied. ESBL genes were sought for by PCR and were characterized by sequencing; E. coli ST131 clones were identified. Epidemiological relatedness was determined by pulsed-field gel electrophoresis and confirmed using whole genome sequencing in selected cases. Thirty-seven (33%) of sampled rooks and 42 (1.7%) of human stools yielded ESBL-producing E coli. Dominant genes were blaCTX–M–55 and blaCTX–M–27 in corvid, blaCTX–M–15 and blaCTX–M–27 in human isolates. ST162 was common among rooks. Two rook-derived E. coli belonged to ST131 C1-M27, which was also predominant (10/42) among human fecal and (15/42) human clinical isolates. Another potential link between rooks and humans was a single ST744 rook isolate grouped with one human fecal and three clinical isolates. Despite possible contact, genotypes shared between rooks and humans were rare. Thus, rooks are important as long-distance vectors and reservoirs of ESBL-producing E. coli rather than direct sources of infections to humans in our setting.

Antibiotic Resistance: One Health One World Outlook

Antibiotic resistance (ABR) is a growing public health concern worldwide, and it is now regarded as a critical One Health issue. One Health's interconnected domains contribute to the emergence, evolution, and spread of antibiotic-resistant microorganisms on a local and global scale, which is a significant risk factor for global health. The persistence and spread of resistant microbial species, and the association of determinants at the human-animal-environment interface can alter microbial genomes, resulting in resistant superbugs in various niches. ABR is motivated by a well-established link between three domains: human, animal, and environmental health. As a result, addressing ABR through the One Health approach makes sense. Several countries have implemented national action plans based on the One Health approach to combat antibiotic-resistant microbes, following the Tripartite's Commitment Food and Agriculture Organization (FAO)-World Organization for Animal Health (OIE)-World Health Organization (WHO) guidelines. The ABR has been identified as a global health concern, and efforts are being made to mitigate this global health threat. To summarize, global interdisciplinary and unified approaches based on One Health principles are required to limit the ABR dissemination cycle, raise awareness and education about antibiotic use, and promote policy, advocacy, and antimicrobial stewardship.

Improved quantitative microbiome profiling for environmental antibiotic resistance surveillance

BACKGROUND

Understanding environmental microbiomes and antibiotic resistance (AR) is hindered by over reliance on relative abundance data from next-generation sequencing. Relative data limits our ability to quantify changes in microbiomes and resistomes over space and time because sequencing depth is not considered and makes data less suitable for Quantitative Microbial Risk Assessments (QMRA), critical in quantifying environmental AR exposure and transmission risks.

RESULTS

Here we combine quantitative microbiome profiling (QMP; parallelization of amplicon sequencing and 16S rRNA qPCR to estimate cell counts) and absolute resistome profiling (based on high-throughput qPCR) to quantify AR along an anthropogenically impacted river. We show QMP overcomes biases caused by relative taxa abundance data and show the benefits of using unified Hill number diversities to describe environmental microbial communities. Our approach overcomes weaknesses in previous methods and shows Hill numbers are better for QMP in diversity characterisation.

CONCLUSIONS

Methods here can be adapted for any microbiome and resistome research question, but especially providing more quantitative data for QMRA and other environmental applications.

Multidrug-resistant bacteria and microbial communities in a river estuary with fragmented suburban waste management

River systems in developing and emerging countries are often fragmented relative to land and waste management in their catchment. The impact of inconsistent waste management and releases is a major challenge in water quality management. To examine how anthropogenic activities and estuarine effects impact water quality, we characterised water conditions, in-situ microbiomes, profiles of faecal pollution indicator, pathogenic and antibiotic resistant bacteria in the River Melayu, Southern Malaysia. Overall, upstream sampling locations were distinguished from those closer to the coastline by physicochemical parameters and bacterial communities. The abundances of bacterial DNA, total E. coli marker genes, culturable bacteria as well as antibiotic resistance ESBL-producing bacteria were elevated at upstream sampling locations especially near discharge of a wastewater oxidation pond. Furthermore, 85.7% of E. faecalis was multidrug-resistant (MDR), whereas 100% of E. cloacae, E. coli, K. pneumoniae were MDR. Overall, this work demonstrates how pollution in river estuaries does not monotonically change from inland towards the coast but varies according to local waste releases and tidal mixing. We also show that surrogate markers, such dissolved oxygen, Bacteroides and Prevotella abundances, and the rodA qPCR assay for total E. coli, can identify locations on a river that deserve immediate attention to mitigate AMR spread through improved waste management.

Diverse and abundant resistome in terrestrial and aquatic vertebrates revealed by transcriptional analysis

Despite increasing evidence that antibiotic resistant pathogens are shared among humans and animals, the diversity, abundance and patterns of spread of antibiotic resistance genes (ARGs) in wildlife remains unclear. We identified 194 ARGs associated with phenotypic resistance to 13 types of antibiotic in meta-transcriptomic data generated from a broad range of lower vertebrates residing in both terrestrial and aquatic habitats. These ARGs, confirmed by PCR, included those that shared high sequence similarity to clinical isolates of public health concern. Notably, the lower vertebrate resistome varied by ecological niche of the host sampled. The resistomes in marine fish shared high similarity and were characterized by very high abundance, distinct from that observed in other habitats. An assessment of ARG mobility found that ARGs in marine fish were frequently co-localized with mobile elements, indicating that they were likely spread by horizontal gene transfer. Together, these data reveal the remarkable diversity and transcriptional levels of ARGs in lower vertebrates, and suggest that these wildlife species might play an important role in the global spread of ARGs.

Analysis of Eurasian Stone curlew (Burhinus oedicnemus) microbial flora reveals the presence of multi-drug resistant pathogens in agro-pastoral areas of Sicily (Italy)

Spread of multi-drug resistant (MDR) bacteria in natural environments pose a risk to human and animal health. Wild birds are considered to be reservoirs of human pathogens and vectors of antimicrobial resistance distribution in the environment. The aim of this study is to assess the occurrence of antibiotic resistant bacteria in isolates from bird specimens living in three agro-pastoral areas of the southeastern Sicily. We analyzed the microbiomes of the Eurasian Stone curlew Burhinus oedicnemus (Charadriiformes, Aves) and identified 91 Gram positive and 212 Gram negative strains, whose antimicrobial susceptibility to 11 and 9 antibiotic classes (respectively) was evaluated using agar disk diffusion test. Isolates showed significant levels of antimicrobial resistance, and a high percentage of MDR strains was found both between the Gram positive (49.4%) and the Gram negative (34.9%). Multi-drug resistance levels are higher among strains isolated in the beak and the eye than among enteric (faeces and cloaca) strains. Our results indicate high levels of MDR strains among wild bird populations, with a potential threat to wildlife and human populations.

Mobility of β-Lactam Resistance Under Bacterial Co-infection and Ampicillin Treatment in a Mouse Model

Ingestion of food- or waterborne antibiotic-resistant bacteria may lead to the dissemination of antibiotic-resistance genes in the gut microbiota and the development of antibiotic-resistant bacterial infection, a significant threat to animal and public health. Food or water may be contaminated with multiple resistant bacteria, but animal models on gene transfer were mainly based on single-strain infections. In this study, we investigated the mobility of β-lactam resistance following infection with single- versus multi-strain of resistant bacteria under ampicillin treatment. We characterized three bacterial strains isolated from food-animal production systems, Escherichia coli O80:H26 and Salmonella enterica serovars Bredeney and Heidelberg. Each strain carries at least one conjugative plasmid that encodes a β-lactamase. We orally infected mice with each or all three bacterial strain(s) in the presence or absence of ampicillin treatment. We assessed plasmid transfer from the three donor bacteria to an introduced E. coli CV601gfp recipient in the mouse gut, and evaluated the impacts of the bacterial infection on gut microbiota and gut health. In the absence of ampicillin treatment, none of the donor or recipient bacteria established in the normal gut microbiota and plasmid transfer was not detected. In contrast, the ampicillin treatment disrupted the gut microbiota and enabled S. Bredeney and Heidelberg to colonize and transfer their plasmids to the E. coli CV601gfp recipient. E. coli O80:H26 on its own failed to colonize the mouse gut. However, during co-infection with the two Salmonella strains, E. coli O80:H26 colonized and transferred its plasmid to the E. coli CV601gfp recipient and a residential E. coli O2:H6 strain. The co-infection significantly increased plasmid transfer frequency, enhanced Proteobacteria expansion and resulted in inflammation in the mouse gut. Our findings suggest that single-strain infection models for evaluating in vivo gene transfer may underrepresent the consequences of multi-strain infections following the consumption of heavily contaminated food or water.

Gut carriage of antimicrobial resistance genes among young children in urban Maputo, Mozambique: Associations with enteric pathogen carriage and environmental risk factors

Because poor sanitation is hypothesized as a major direct and indirect pathway of exposure to antimicrobial resistance genes (ARGs), we sought to determine a) the prevalence of and b) environmental risk factors for gut carriage of key ARGs in a pediatric cohort at high risk of enteric infections due to poor water, sanitation, and hygiene (WASH) conditions. We investigated ARGs in stool from young children in crowded, low-income settlements of Maputo, Mozambique, and explored potential associations with concurrent enteric pathogen carriage, diarrhea, and environmental risk factors, including WASH. We collected stool from 120 children <14 months old and tested specimens via quantal, multiplex molecular assays for common bacterial, viral, and protozoan enteric pathogens and 84 ARGs encoding potential resistance to 7 antibiotic classes. We estimated associations between ARG detection (number and diversity detected) and concurrently-measured enteric pathogen carriage, recently-reported diarrhea, and risk factors in the child's living environment. The most commonly-detected ARGs encoded resistance to macrolides, lincosamides, and streptogramins (100% of children); tetracyclines (98%); β-lactams (94%), aminoglycosides (84%); fluoroquinolones (48%); and vancomycin (38%). Neither concurrent diarrhea nor measured environmental (including WASH) conditions were associated with ARG detection in adjusted models. Enteric pathogen carriage and ARG detection were associated: on average, 18% more ARGs were detected in stool from children carrying bacterial pathogens than those without (adjusted risk ratio (RR): 1.18, 95% confidence interval (CI): 1.02, 1.37), with 16% fewer ARGs detected in children carrying parasitic pathogens (protozoans, adjusted RR: 0.84, 95% CI: 0.71, 0.99). We observed gut ARGs conferring potential resistance to a range of antibiotics in this at-risk cohort that had high rates of enteric infection, even among children <14 months-old. Gut ARGs did not appear closely correlated with WASH, though environmental conditions were generally poor. ARG carriage may be associated with concurrent carriage of bacterial enteric pathogens, suggesting indirect linkages to WASH that merit further investigation.

Water and sanitation: an essential battlefront in the war on antimicrobial resistance

Water and sanitation represent a key battlefront in combatting the spread of antimicrobial resistance (AMR). Basic water sanitation infrastructure is an essential first step towards protecting public health, thereby limiting the spread of pathogens and the need for antibiotics. AMR presents unique human health risks, meriting new risk assessment frameworks specifically adapted to water and sanitation-borne AMR. There are numerous exposure routes to AMR originating from human waste, each of which must be quantified for its relative risk to human health. Wastewater treatment plants play a vital role in centralized collection and treatment of human sewage, but there are numerous unresolved issues in terms of the microbial ecological processes occurring within them and the extent to which they attenuate or amplify AMR. Research is needed to advance understanding of the fate of resistant bacteria and antibiotic resistance genes in various waste management systems, depending on the local constraints and intended reuse applications. World Health Organization and national AMR action plans would benefit from a more holistic 'One Water' understanding. In this article we provide a framework for research, policy, practice and public engagement aimed at limiting the spread of AMR from water and sanitation in low-, medium- and high-income countries.

Understanding antimicrobial discovery and resistance from a metagenomic and metatranscriptomic perspective: advances and applications

Our inability to cultivate most microorganisms, specifically bacteria, in the laboratory has for many years restricted our view and understanding of the bacterial meta-resistome in all living and nonliving environments. As a result, reservoirs, sources and distribution of antibiotic resistance genes (ARGS) and antibiotic-producers, as well as the effects of human activity and antibiotics on the selection and dissemination of ARGs were not well comprehended. With the advances made in the fields of metagenomics and metatranscriptomics, many of the hitherto little-understood concepts are becoming clearer. Further, the discovery of antibiotics such as lugdinin and lactocillin from the human microbiota, buttressed the importance of these new fields. Metagenomics and metatranscriptomics are becoming important clinical diagnostic tools for screening and detecting pathogens and ARGs, assessing the effects of antibiotics, other xenobiotics and human activity on the environment, characterizing the microbiome and the environmental resistome with lesser turnaround time and decreasing cost, as well as discovering antibiotic-producers. However, challenges with accurate binning, skewed ARGs databases, detection of less abundant and allelic variants of ARGs and efficient mobilome characterization remain. Ongoing efforts in long-read, phased- and single-cell sequencing, strain-resolved binning, chromosomal-conformation capture, DNA-methylation binning and deep-learning bioinformatic approaches offer promising prospects in reconstructing complete strain-level genomes and mobilomes from metagenomes.

Complexities in understanding antimicrobial resistance across domesticated animal, human, and environmental systems

Antimicrobial resistance (AMR) is a significant threat to both human and animal health. The spread of AMR bacteria and genes across systems can occur through a myriad of pathways, both related and unrelated to agriculture, including via wastewater, soils, manure applications, direct exchange between humans and animals, and food exposure. Tracing origins and drivers of AMR bacteria and genes is challenging due to the array of contexts and the complexity of interactions overlapping health practice, microbiology, genetics, applied science and engineering, as well as social and human factors. Critically assessing the diverse and sometimes contradictory AMR literature is a valuable step in identifying tractable mitigation options to stem AMR spread. In this article we review research on the nonfoodborne spread of AMR, with a focus on domesticated animals and the environment and possible exposures to humans. Attention is especially placed on delineating possible sources and causes of AMR bacterial phenotypes, including underpinning the genetics important to human and animal health.

One Health-Its Importance in Helping to Better Control Antimicrobial Resistance

Approaching any issue from a One Health perspective necessitates looking at the interactions of people, domestic animals, wildlife, plants, and our environment. For antimicrobial resistance this includes antimicrobial use (and abuse) in the human, animal and environmental sectors. More importantly, the spread of resistant bacteria and resistance determinants within and between these sectors and globally must be addressed. Better managing this problem includes taking steps to preserve the continued effectiveness of existing antimicrobials such as trying to eliminate their inappropriate use, particularly where they are used in high volumes. Examples are the mass medication of animals with critically important antimicrobials for humans, such as third generation cephalosporins and fluoroquinolones, and the long term, in-feed use of antimicrobials, such colistin, tetracyclines and macrolides, for growth promotion. In people it is essential to better prevent infections, reduce over-prescribing and over-use of antimicrobials and stop resistant bacteria from spreading by improving hygiene and infection control, drinking water and sanitation. Pollution from inadequate treatment of industrial, residential and farm waste is expanding the resistome in the environment. Numerous countries and several international agencies have now included a One Health Approach within their action plans to address antimicrobial resistance. Necessary actions include improvements in antimicrobial use, better regulation and policy, as well as improved surveillance, stewardship, infection control, sanitation, animal husbandry, and finding alternatives to antimicrobials.

Strategic Approach for Prioritising Local and Regional Sanitation Interventions for Reducing Global Antibiotic Resistance

Globally increasing antibiotic resistance (AR) will only be reversed through a suite of multidisciplinary actions (One Health), including more prudent antibiotic use and improved sanitation on international scales. Relative to sanitation, advanced technologies exist that reduce AR in waste releases, but such technologies are expensive, and a strategic approach is needed to prioritize more affordable mitigation options, especially for Low- and Middle-Income Countries (LMICs). Such an approach is proposed here, which overlays the incremental cost of different sanitation options and their relative benefit in reducing AR, ultimately suggesting the “next-most-economic” options for different locations. When considering AR gene fate versus intervention costs, reducing open defecation (OD) and increasing decentralized secondary wastewater treatment, with condominial sewers, will probably have the greatest impact on reducing AR, for the least expense. However, the best option for a given country depends on the existing sewerage infrastructure. Using Southeast Asia as a case study and World Bank/WHO/UNICEF data, the approach suggests that Cambodia and East Timor should target reducing OD as a national priority. In contrast, increasing decentralized secondary treatment is well suited to Thailand, Vietnam and rural Malaysia. Our approach provides a science-informed starting point for decision-makers, for prioritising AR mitigation interventions; an approach that will evolve and refine as more data become available.

Critical knowledge gaps and research needs related to the environmental dimensions of antibiotic resistance

There is growing understanding that the environment plays an important role both in the transmission of antibiotic resistant pathogens and in their evolution. Accordingly, researchers and stakeholders world-wide seek to further explore the mechanisms and drivers involved, quantify risks and identify suitable interventions. There is a clear value in establishing research needs and coordinating efforts within and across nations in order to best tackle this global challenge. At an international workshop in late September 2017, scientists from 14 countries with expertise on the environmental dimensions of antibiotic resistance gathered to define critical knowledge gaps. Four key areas were identified where research is urgently needed: 1) the relative contributions of different sources of antibiotics and antibiotic resistant bacteria into the environment; 2) the role of the environment, and particularly anthropogenic inputs, in the evolution of resistance; 3) the overall human and animal health impacts caused by exposure to environmental resistant bacteria; and 4) the efficacy and feasibility of different technological, social, economic and behavioral interventions to mitigate environmental antibiotic resistance.1.

The diversity of uncharacterized antibiotic resistance genes can be predicted from known gene variants-but not always

BACKGROUND

Antibiotic resistance is considered one of the most urgent threats to modern healthcare, and the role of the environment in resistance development is increasingly recognized. It is often assumed that the abundance and diversity of known resistance genes are representative also for the non-characterized fraction of the resistome in a given environment, but this assumption has not been verified. In this study, this hypothesis is tested, using the resistance gene profiles of 1109 metagenomes from various environments.

RESULTS

This study shows that the diversity and abundance of known antibiotic resistance genes can generally predict the diversity and abundance of undescribed resistance genes. However, the extent of this predictability is dependent on the type of environment investigated. Furthermore, it is shown that carefully selected small sets of resistance genes can describe total resistance gene diversity remarkably well.

CONCLUSIONS

The results of this study suggest that knowledge gained from large-scale quantifications of known resistance genes can be utilized as a proxy for unknown resistance factors. This is important for current and proposed monitoring efforts for environmental antibiotic resistance and has implications for the design of risk ranking strategies and the choices of measures and methods for describing resistance gene abundance and diversity in the environment.

Impact of Vegetative Treatment Systems on Multiple Measures of Antibiotic Resistance in Agricultural Wastewater

Wastewater is an important vector of antibiotic resistant bacteria and antibiotic resistance genes (ARB/G). While there is broad agreement that ARB/G from agricultural (ag) wastewaters can be transported through the environment and may contribute to untreatable infectious disease in humans and animals, there remain large knowledge gaps surrounding applied details on the types and amounts of ARB/G associated with different agricultural wastewater treatment options and different ag production systems. This study evaluates a vegetative treatment system (VTS) built to treat the wastewater from a beef cattle feedlot. Samples were collected for three years, and plated on multiple media types to enumerate tetracycline and cefotaxime-resistant bacteria. Enterobacteriaceae isolates (n = 822) were characterized for carriage of tetracycline resistance genes, and E. coli isolates (n = 673) were phenotyped to determine multi-drug resistance (MDR) profiles. Tetracycline resistance in feedlot runoff wastewater was 2-to-3 orders of magnitude higher compared to rainfall runoff from the VTS fields, indicating efficacy of the VTA for reducing ARB over time following wastewater application. Clear differences in MDR profiles were observed based on the specific media on which a sample was plated. This result highlights the importance of method, especially in the context of isolate-based surveillance and monitoring of ARB in agricultural wastewaters.

Antimicrobial Resistance: a One Health Perspective

One Health is the collaborative effort of multiple health science professions to attain optimal health for people, domestic animals, wildlife, plants, and our environment. The drivers of antimicrobial resistance include antimicrobial use and abuse in human, animal, and environmental sectors and the spread of resistant bacteria and resistance determinants within and between these sectors and around the globe. Most of the classes of antimicrobials used to treat bacterial infections in humans are also used in animals. Given the important and interdependent human, animal, and environmental dimensions of antimicrobial resistance, it is logical to take a One Health approach when addressing this problem. This includes taking steps to preserve the continued effectiveness of existing antimicrobials by eliminating their inappropriate use and by limiting the spread of infection. Major concerns in the animal health and agriculture sectors are mass medication of animals with antimicrobials that are critically important for humans, such as third-generation cephalosporins and fluoroquinolones, and the long-term, in-feed use of medically important antimicrobials, such as colistin, tetracyclines, and macrolides, for growth promotion. In the human sector it is essential to prevent infections, reduce over-prescribing of antimicrobials, improve sanitation, and improve hygiene and infection control. Pollution from inadequate treatment of industrial, residential, and farm waste is expanding the resistome in the environment. Numerous countries and several international agencies have included a One Health approach within their action plans to address antimicrobial resistance. Necessary actions include improvements in antimicrobial use regulation and policy, surveillance, stewardship, infection control, sanitation, animal husbandry, and alternatives to antimicrobials. WHO recently has launched new guidelines on the use of medically important antimicrobials in food-producing animals, recommending that farmers and the food industry stop using antimicrobials routinely to promote growth and prevent disease in healthy animals. These guidelines aim to help preserve the effectiveness of antimicrobials that are important for human medicine by reducing their use in animals.

Environmental factors influencing the development and spread of antibiotic resistance

Antibiotic resistance and its wider implications present us with a growing healthcare crisis. Recent research points to the environment as an important component for the transmission of resistant bacteria and in the emergence of resistant pathogens. However, a deeper understanding of the evolutionary and ecological processes that lead to clinical appearance of resistance genes is still lacking, as is knowledge of environmental dispersal barriers. This calls for better models of how resistance genes evolve, are mobilized, transferred and disseminated in the environment. Here, we attempt to define the ecological and evolutionary environmental factors that contribute to resistance development and transmission. Although mobilization of resistance genes likely occurs continuously, the great majority of such genetic events do not lead to the establishment of novel resistance factors in bacterial populations, unless there is a selection pressure for maintaining them or their fitness costs are negligible. To enable preventative measures it is therefore critical to investigate under what conditions and to what extent environmental selection for resistance takes place. In addition, understanding dispersal barriers is not only key to evaluate risks, but also to prevent resistant pathogens, as well as novel resistance genes, from reaching humans.

'Disperse abroad in the land': the role of wildlife in the dissemination of antimicrobial resistance

Antimicrobial resistance (AMR) has been detected in the microbiota of many wildlife species, including long-distance migrants. Inadequately treated wastes from humans and livestock dosed with antimicrobial drugs are often assumed to be the main sources of AMR to wildlife. While wildlife populations closely associated with human populations are more likely to harbour clinically important AMR related to that found in local humans and livestock, AMR is still common in remote wildlife populations with little direct human influence. Most reports of AMR in wildlife are survey based and/or small scale, so researchers can only speculate on possible sources and sinks of AMR or the impact of wildlife AMR on clinical resistance. This lack of quantitative data on the flow of AMR genes and AMR bacteria across the natural environment could reflect the numerous AMR sources and amplifiers in the populated world. Ecosystems with relatively simple and well-characterized potential inputs of AMR can provide tractable, but realistic, systems for studying AMR in the natural environment. New tools, such as animal tracking technologies and high-throughput sequencing of resistance genes and mobilomes, should be integrated with existing methodologies to understand how wildlife maintains and disperses AMR.

Untreated urban waste contaminates Indian river sediments with resistance genes to last resort antibiotics

Efficient sewage treatment is critical for limiting environmental transmission of antibiotic-resistant bacteria. In many low and middle income countries, however, large proportions of sewage are still released untreated into receiving water bodies. In-depth knowledge of how such discharges of untreated urban waste influences the environmental resistome is largely lacking. Here, we highlight the impact of uncontrolled discharge of partially treated and/or untreated wastewater on the structure of bacterial communities and resistome of sediments collected from Mutha river flowing through Pune city in India. Using shotgun metagenomics, we found a wide array (n = 175) of horizontally transferable antibiotic resistance genes (ARGs) including carbapenemases such as NDM, VIM, KPC, OXA-48 and IMP types. The relative abundance of total ARGs was 30-fold higher in river sediments within the city compared to upstream sites. Forty four ARGs, including the tet(X) gene conferring resistance to tigecycline, OXA-58 and GES type carbapenemases, were significantly more abundant in city sediments, while two ARGs were more common at upstream sites. The recently identified mobile colistin resistance gene mcr-1 was detected only in one of the upstream samples, but not in city samples. In addition to ARGs, higher abundances of various mobile genetic elements were found in city samples, including integron-associated integrases and ISCR transposases, as well as some biocide/metal resistance genes. Virulence toxin genes as well as bacterial genera comprising many pathogens were more abundant here; the genus Acinetobacter, which is often associated with multidrug resistance and nosocomial infections, comprised up to 29% of the 16S rRNA reads, which to our best knowledge is unmatched in any other deeply sequenced metagenome. There was a strong correlation between the abundance of Acinetobacter and the OXA-58 carbapenemase gene. Our study shows that uncontrolled discharge of untreated urban waste can contribute to an overall increase of the abundance and diversity of ARGs in the environment, including those conferring resistance to last-resort antibiotics.

Does antifouling paint select for antibiotic resistance?

There is concern that heavy metals and biocides contribute to the development of antibiotic resistance via co-selection. Most antifouling paints contain high amounts of such substances, which risks turning painted ship hulls into highly mobile refuges and breeding grounds for antibiotic-resistant bacteria. The objectives of this study were to start investigate if heavy-metal based antifouling paints can pose a risk for co-selection of antibiotic-resistant bacteria and, if so, identify the underlying genetic basis. Plastic panels with one side painted with copper and zinc-containing antifouling paint were submerged in a Swedish marina and biofilms from both sides of the panels were harvested after 2.5-4weeks. DNA was isolated from the biofilms and subjected to metagenomic sequencing. Biofilm bacteria were cultured on marine agar supplemented with tetracycline, gentamicin, copper sulfate or zinc sulfate. Biofilm communities from painted surfaces displayed lower taxonomic diversity and enrichment of Gammaproteobacteria. Bacteria from these communities showed increased resistance to both heavy metals and tetracycline but not to gentamicin. Significantly higher abundance of metal and biocide resistance genes was observed, whereas mobile antibiotic resistance genes were not enriched in these communities. In contrast, we found an enrichment of chromosomal RND efflux system genes, including such with documented ability to confer decreased susceptibility to both antibiotics and biocides/heavy metals. This was paralleled by increased abundances of integron-associated integrase and ISCR transposase genes. The results show that the heavy metal-based antifouling paint exerts a strong selection pressure on marine bacterial communities and can co-select for certain antibiotic-resistant bacteria, likely by favoring species and strains carrying genes that provide cross-resistance. Although this does not indicate an immediate risk for promotion of mobile antibiotic resistance, the clear increase of genes involved in mobilizing DNA provides a foundation for increased opportunities for gene transfer in such communities, which might also involve yet unknown resistance mechanisms.

The antibiotic resistome: gene flow in environments, animals and human beings

The antibiotic resistance is natural in bacteria and predates the human use of antibiotics. Numerous antibiotic resistance genes (ARGs) have been discovered to confer resistance to a wide range of antibiotics. The ARGs in natural environments are highly integrated and tightly regulated in specific bacterial metabolic networks. However, the antibiotic selection pressure conferred by the use of antibiotics in both human medicine and agriculture practice leads to a significant increase of antibiotic resistance and a steady accumulation of ARGs in bacteria. In this review, we summarized, with an emphasis on an ecological point of view, the important research progress regarding the collective ARGs (antibiotic resistome) in bacterial communities of natural environments, human and animals, i.e., in the one health settings.We propose that the resistance gene flow in nature is "from the natural environments" and "to the natural environments"; human and animals, as intermediate recipients and disseminators, contribute greatly to such a resistance gene "circulation."

Towards a research agenda for water, sanitation and antimicrobial resistance

Clinically relevant antimicrobial resistant bacteria, genetic resistance elements, and antibiotic residues (so-called AMR) from human and animal waste are abundantly present in environmental samples. This presence could lead to human exposure to AMR. In 2015, the World Health Organization (WHO) developed a Global Action Plan for Antimicrobial Resistance with one of its strategic objectives being to strengthen knowledge through surveillance and research. With respect to a strategic research agenda on water, sanitation and hygiene and AMR, WHO organized a workshop to solicit input by scientists and other stakeholders. The workshop resulted in three main conclusions. The first conclusion was that guidance is needed on how to reduce the spread of AMR to humans via the environment and to introduce effective intervention measures. Second, human exposure to AMR via water and its health impact should be investigated and quantified, in order to compare with other human exposure routes, such as direct transmission or via food consumption. Finally, a uniform and global surveillance strategy that complements existing strategies and includes analytical methods that can be used in low-income countries too, is needed to monitor the magnitude and dissemination of AMR.

[Multidrug-resistant bacteria in Germany. The impact of sources outside healthcare facilities]

BACKGROUND

Currently, there is an ongoing discussion about the question whether the emergence of multidrug-resistant microorganisms (MDRO) among humans is due to transfer of these bacteria from animals.

OBJECTIVES

This review summarizes data on the occurrence of methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum beta-lactamase (ESBL) producing enterobacteria in animals and humans, and describes knowledge about transmission pathways.

MATERIAL AND METHODS

After a scientific literature analysis, relevant articles were identified by screening of titles and abstracts, amended by publications of infection control authorities and the respective reference lists.

RESULTS

MDRO are both transmitted in the nosocomial setting and are increasingly detected as sources of infection outside healthcare facilities.

CONCLUSIONS

Due to new transmission pathways of MDRO an inter-disciplinary approach towards prevention is necessary, involving medical, pharmaceutical and veterinary expertise.

Persistence of antibiotic resistance and plasmid-associated genes in soil following application of sewage sludge and abundance on vegetables at harvest

Sewage sludge recovered from wastewater treatment plants contains antibiotic residues and is rich in antibiotic resistance genes, selected for and enriched in the digestive tracts of human using antibiotics. The use of sewage sludge as a crop fertilizer constitutes a potential route of human exposure to antibiotic resistance genes through consumption of contaminated crops. Several gene targets associated with antibiotic resistance (catA1, catB3, ereA, ereB, erm(B), str(A), str(B), qnrD, sul1, and mphA), mobile genetic elements (int1, mobA, IncW repA, IncP1 groups -α, -β, -δ, -γ, -ε), and bacterial 16S rRNA (rrnS) were quantified by qPCR from soil and vegetable samples obtained from unamended and sludge-amended plots at an experimental field in London, Ontario. The qPCR data reveals an increase in abundance of gene targets in the soil and vegetables samples, indicating that there is potential for additional crop exposure to antibiotic resistance genes carried within sewage sludge following field application. It is therefore advisable to allow an appropriate delay period before harvesting of vegetables for human consumption.

Multiple Discharges of Treated Municipal Wastewater Have a Small Effect on the Quantities of Numerous Antibiotic Resistance Determinants in the Upper Mississippi River

This study evaluated multiple discharges of treated wastewater on the quantities of antibiotic resistance genes (ARGs) in the Upper Mississippi River. Surface water and treated wastewater samples were collected along the Mississippi River during three different periods of 4 days during the summer of 2012, and quantitative real-time PCR (qPCR) was used to enumerate several ARGs and related targets. Even though the wastewater effluents contained 75- to 831-fold higher levels of ARGs than the river water, the quantities of ARGs in the Mississippi River did not increase with downstream distance. Plasmids from the incompatibility group A/C were detected at low levels in the wastewater effluents but not in the river water; synthetic DNA containing an ampicillin resistance gene (bla) from cloning vectors was not detected in either the wastewater effluent or river samples. A simple 1D model suggested that the primary reason for the small impact of the wastewater discharges on ARG levels was the large flow rate of the Mississippi River compared to that of the wastewater discharges. Furthermore, this model generally overpredicted the ARG levels in the Mississippi River, suggesting that substantial loss mechanisms (e.g., decay or deposition) were occurring in the river.

Screening Foodstuffs for Class 1 Integrons and Gene Cassettes

Antibiotic resistance is one of the greatest threats to health in the 21st century. Acquisition of resistance genes via lateral gene transfer is a major factor in the spread of diverse resistance mechanisms. Amongst the DNA elements facilitating lateral transfer, the class 1 integrons have largely been responsible for spreading antibiotic resistance determinants amongst Gram negative pathogens. In total, these integrons have acquired and disseminated over 130 different antibiotic resistance genes. With continued antibiotic use, class 1 integrons have become ubiquitous in commensals and pathogens of humans and their domesticated animals. As a consequence, they can now be found in all human waste streams, where they continue to acquire new genes, and have the potential to cycle back into humans via the food chain. This protocol details a streamlined approach for detecting class 1 integrons and their associated resistance gene cassettes in foodstuffs, using culturing and PCR. Using this protocol, researchers should be able to: collect and prepare samples to make enriched cultures and screen for class 1 integrons; isolate single bacterial colonies to identify integron-positive isolates; identify bacterial species that contain class 1 integrons; and characterize these integrons and their associated gene cassettes.

Fighting microbial drug resistance: a primer on the role of evolutionary biology in public health

Although microbes have been evolving resistance to antimicrobials for millennia, the spread of resistance in pathogen populations calls for the development of new drugs and treatment strategies. We propose that successful, long-term resistance management requires a better understanding of how resistance evolves in the first place. This is an opportunity for evolutionary biologists to engage in public health, a collaboration that has substantial precedent. Resistance evolution has been an important tool for developing and testing evolutionary theory, especially theory related to the genetic basis of new traits and constraints on adaptation. The present era is no exception. The articles in this issue highlight the breadth of current research on resistance evolution and also its challenges. In this introduction, we review the conceptual advances that have been achieved from studying resistance evolution and describe a path forward.