HIV Drugs Inhibit Transfer of Plasmids Carrying Extended-Spectrum β-Lactamase and Carbapenemase Genes

Acetylshikonin reduces the spread of antibiotic resistance via plasmid conjugation

The plasmid-mediated conjugative transfer of antibiotic resistance genes (ARGs) stands out as the primary driver behind the dissemination of antimicrobial resistance (AMR). Developing effective inhibitors that target conjugative transfer represents an potential strategy for addressing the issue of AMR. Here, we studied the effect of acetylshikonin (ASK), a botanical derivative, on plasmid conjugation. The conjugative transfer of RP4-7 plasmid inter and intra species was notably reduced by ASK. The conjugation process of IncI2 and IncX4 plasmids harbouring the mobile colistin resistance gene (mcr-1), IncX4 and IncX3 plasmids containing the carbapenem resistance gene (blaNDM-5), and IncFI and IncFII plasmids possessing the tetracycline resistance gene [tet(X4)] were also reduced by ASK. Importantly, the conjugative transfer frequency of mcr-1 positive IncI2 plasmid in mouse peritoneal conjugation model and gut conjugation model was reduced by ASK. The mechanism investigation showed that ASK disrupted the functionality of the bacterial cell membrane. Furthermore, the proton motive force (PMF) was dissipated. In addition, ASK blocked the electron transmission in bacteria's electron transport chain (ETC) through disturbing the quinone interaction, resulting in an insufficient energy supply for conjugation. Collectively, ASK is a potential conjugative transfer inhibitor, providing novel strategies to prevent the spread of AMR.

CRISPR-AMRtracker: A novel toolkit to monitor the antimicrobial resistance gene transfer in fecal microbiota

The spread of antibiotic resistance genes (ARGs), particularly those carried on plasmids, poses a major risk to global health. However, the extent and frequency of ARGs transfer in microbial communities among human, animal, and environmental sectors is not well understood due to a lack of effective tracking tools. We have developed a novel fluorescent tracing tool, CRISPR-AMRtracker, to study ARG transfer. It combines CRISPR/Cas9 fluorescence tagging, fluorescence-activated cell sorting, 16S rRNA gene sequencing, and microbial community analysis. CRISPR-AMRtracker integrates a fluorescent tag immediately downstream of ARGs, enabling the tracking of ARG transfer without compromising the host cell's antibiotic susceptibility, fitness, conjugation, and transposition. Notably, our experiments demonstrate that sfGFP-tagged plasmid-borne mcr-1 can transfer across diverse bacterial species within fecal samples. This innovative approach holds the potential to illuminate the dynamics of ARG dissemination and provide valuable insights to shape effective strategies in mitigating the escalating threat of antibiotic resistance.

Non-antibiotic compounds associated with humans and the environment can promote horizontal transfer of antimicrobial resistance genes

Horizontal gene transfer plays a key role in the global dissemination of antimicrobial resistance (AMR). AMR genes are often carried on self-transmissible plasmids, which are shared amongst bacteria primarily by conjugation. Antibiotic use has been a well-established driver of the emergence and spread of AMR. However, the impact of commonly used non-antibiotic compounds and environmental pollutants on AMR spread has been largely overlooked. Recent studies found common prescription and over-the-counter drugs, artificial sweeteners, food preservatives, and environmental pollutants, can increase the conjugative transfer of AMR plasmids. The potential mechanisms by which these compounds promote plasmid transmission include increased membrane permeability, upregulation of plasmid transfer genes, formation of reactive oxygen species, and SOS response gene induction. Many questions remain around the impact of most non-antibiotic compounds on AMR plasmid conjugation in clinical isolates and the long-term impact on AMR dissemination. By elucidating the role of routinely used pharmaceuticals, food additives, and pollutants in the dissemination of AMR, action can be taken to mitigate their impact by closely monitoring use and disposal. This review will discuss recent progress on understanding the influence of non-antibiotic compounds on plasmid transmission, the mechanisms by which they promote transfer, and the level of risk they pose.

Waterborne polyurethane nanoparticles incorporating linoleic acid as a potential strategy for controlling antibiotic resistance spread in the mammalian intestine

Plasmid-mediated conjugative transfer of antibiotic resistance genes (ARGs) within the human and animal intestine represents a substantial global health concern. linoleic acid (LA) has shown promise in inhibiting conjugation in vitro, but its in vivo effectiveness in the mammalian intestinal tract is constrained by challenges in efficiently reaching the target site. Recent advancements have led to the development of waterborne polyurethane nanoparticles for improved drug delivery. In this study, we synthesized four waterborne polyurethane nanoparticles incorporating LA (WPU@LA) using primary raw materials, including N-methyldiethanolamine, 2,2'-(piperazine-1,4-diyl) diethanol, isophorone diisocyanate, castor oil, and acetic acid. These nanoparticles, identified as WPU0.89@LA, WPU0.99@LA, WPU1.09@LA, and WPU1.19@LA, underwent assessment for their pH-responsive release property and biocompatibility. Among these, WPU0.99@LA displayed superior pH-responsive release properties and biocompatibility towards Caco-2 and IPEC-J2 cells. In a mouse model, a dosage of 10 mg/kg/day WPU0.99@LA effectively reduced the conjugation of IncX4 plasmids carrying the mobile colistin resistance gene (mcr-1) by more than 45.1-fold. In vivo toxicity assessment demonstrated that 10 mg/kg/day WPU0.99@LA maintains desirable biosafety and effectively preserves gut microbiota homeostasis. In conclusion, our study provides crucial proof-of-concept support, demonstrating that WPU0.99@LA holds significant potential in controlling the spread of antibiotic resistance within the mammalian intestine.

Natural products from food sources can alter the spread of antimicrobial resistance plasmids in Enterobacterales

Antimicrobial resistance (AMR) poses a significant threat to global public health. Notably, resistance to carbapenem and extended-spectrum β-lactam antibiotics in Gram-negative bacteria is a major impediment to treating infections. Genes responsible for antibiotic resistance are frequently carried on plasmids, which can transfer between bacteria. Therefore, exploring strategies to prevent this transfer and the prevalence of AMR plasmids is timely and pertinent. Here, we show that certain natural product extracts and associated pure compounds can reduce the conjugation of AMR plasmids into new bacterial hosts. Using our established high-throughput fluorescence-based flow cytometry assay, we found that the natural products were more active in reducing transmission of the IncK extended-spectrum β-lactamase-encoding plasmid pCT in Escherichia coli EC958c, compared to Klebsiella pneumoniae Ecl8 carrying the IncFII carbapenemase-encoding plasmid pKpQIL. The exception was the natural product rottlerin, also active in K. pneumoniae. In classical conjugation assays, rottlerin also reduced the conjugation frequency of the IncFII bla NDM-1 carrying plasmid pCPE16_3 from a clinical K. pneumoniae isolate. Our data indicate that the natural products tested here, in their current molecular structure, reduced conjugation by a small amount, which is unlikely to achieve a large-scale reduction in AMR in bacterial populations. However, certain natural products like rottlerin could provide a foundation for further research into compounds with effective anti-plasmid activity.

Non-Canonical Aspects of Antibiotics and Antibiotic Resistance

The understanding of antibiotic resistance, one of the major health threats of our time, is mostly based on dated and incomplete notions, especially in clinical contexts. The "canonical" mechanisms of action and pharmacodynamics of antibiotics, as well as the methods used to assess their activity upon bacteria, have not changed in decades; the same applies to the definition, acquisition, selective pressures, and drivers of resistance. As a consequence, the strategies to improve antibiotic usage and overcome resistance have ultimately failed. This review gathers most of the "non-canonical" notions on antibiotics and resistance: from the alternative mechanisms of action of antibiotics and the limitations of susceptibility testing to the wide variety of selective pressures, lateral gene transfer mechanisms, ubiquity, and societal factors maintaining resistance. Only by having a "big picture" view of the problem can adequate strategies to harness resistance be devised. These strategies must be global, addressing the many aspects that drive the increasing prevalence of resistant bacteria aside from the clinical use of antibiotics.

Cobalt complexes modulate plasmid conjugation in Escherichia coli and Klebsiella pneumoniae

Antimicrobial resistance genes (ARG), such as extended-spectrum β-lactamase (ESBL) and carbapenemase genes, are commonly carried on plasmids. Plasmids can transmit between bacteria, disseminate globally, and cause clinically important resistance. Therefore, targeting plasmids could reduce ARG prevalence, and restore the efficacy of existing antibiotics. Cobalt complexes possess diverse biological activities, including antimicrobial and anticancer properties. However, their effect on plasmid conjugation has not been explored yet. Here, we assessed the effect of four previously characterised bis(N-picolinamido)cobalt(II) complexes lacking antibacterial activity on plasmid conjugation in Escherichia coli and Klebsiella pneumoniae. Antimicrobial susceptibility testing of these cobalt complexes confirmed the lack of antibacterial activity in E. coli and K. pneumoniae. Liquid broth and solid agar conjugation assays were used to screen the activity of the complexes on four archetypical plasmids in E. coli J53. The cobalt complexes significantly reduced the conjugation of RP4, R6K, and R388 plasmids, but not pKM101, on solid agar in E. coli J53. Owing to their promising activity, the impact of cobalt complexes was tested on the conjugation of fluorescently tagged extended-spectrum β-lactamase encoding pCTgfp plasmid in E. coli and carbapenemase encoding pKpQILgfp plasmid in K. pneumoniae, using flow cytometry. The complexes significantly reduced the conjugation of pKpQILgfp in K. pneumoniae but had no impact on pCTgfp conjugation in E. coli. The cobalt complexes did not have plasmid-curing activity, suggesting that they target conjugation rather than plasmid stability. To our knowledge, this is the first study to report reduced conjugation of clinically relevant plasmids with cobalt complexes. These cobalt complexes are not cytotoxic towards mammalian cells and are not antibacterial, therefore they could be optimised and employed as inhibitors of plasmid conjugation.

Co-selection for antibiotic resistance by environmental contaminants

The environment is increasingly recognised as a hotspot for the selection and dissemination of antibiotic resistant bacteria and antibiotic resistance genes. These can be selected for by antibiotics and non-antibiotic agents (such as metals and biocides), with the evidence to support this well established by observational and experimental studies. However, there is emerging evidence to suggest that plant protection products (such as herbicides), and non-antibiotic drugs (such as chemotherapeutic agents), can also co-select for antibiotic resistance. This review aims to provide an overview of four classes of non-antibiotic agents (metals, biocides, plant protection products, and non-antibiotic drugs) and how they may co-select for antibiotic resistance, with a particular focus on the environment. It also aims to identify key knowledge gaps that should be addressed in future work, to better understand these potential co-selective agents.

In vitro synergy screens of FDA-approved drugs reveal novel zidovudine- and azithromycin-based combinations with last-line antibiotics against Klebsiella pneumoniae

Treatment of infections caused by multi-drug resistant (MDR) enterobacteria remains challenging due to the limited therapeutic options available. Drug repurposing could accelerate the development of new urgently needed successful interventions. This work aimed to identify and characterise novel drug combinations against Klebsiella pneumoniae based on the concepts of synergy and drug repurposing. We first performed a semi-qualitative high-throughput synergy screen (sHTSS) with tigecycline, colistin and fosfomycin (last-line antibiotics against MDR Enterobacteriaceae) against a FDA-library containing 1430 clinically approved drugs; a total of 109 compounds potentiated any of the last-line antibiotics. Selected hits were further validated by secondary checkerboard (CBA) and time-kill (TKA) assays, obtaining 15.09% and 65.85% confirmation rates, respectively. Accordingly, TKA were used for synergy classification based on determination of bactericidal activities at 8, 24 and 48 h, selecting 27 combinations against K. pneumoniae. Among them, zidovudine or azithromycin combinations with last-line antibiotics were further evaluated by TKA against a panel of 12 MDR/XDR K. pneumoniae strains, and their activities confronted with those clinical combinations currently used for MDR enterobacteria treatment; these combinations showed better bactericidal activities than usual treatments without added cytotoxicity. Our studies show that sHTSS paired to TKA are powerful tools for the identification and characterisation of novel synergistic drug combinations against K. pneumoniae. Further pre-clinical studies might support the translational potential of zidovudine- and azithromycin-based combinations for the treatment of these infections.

Bacteria exposed to antiviral drugs develop antibiotic cross-resistance and unique resistance profiles

Antiviral drugs are used globally as treatment and prophylaxis for long-term and acute viral infections. Even though antivirals also have been shown to have off-target effects on bacterial growth, the potential contributions of antivirals to antimicrobial resistance remains unknown. Herein we explored the ability of different classes of antiviral drugs to induce antimicrobial resistance. Our results establish the previously unrecognized capacity of antivirals to broadly alter the phenotypic antimicrobial resistance profiles of both gram-negative and gram-positive bacteria Escherichia coli and Bacillus cereus. Bacteria exposed to antivirals including zidovudine, dolutegravir and raltegravir developed cross-resistance to commonly used antibiotics including trimethoprim, tetracycline, clarithromycin, erythromycin, and amoxicillin. Whole genome sequencing of antiviral-resistant E. coli isolates revealed numerous unique single base pair mutations, as well as multi-base pair insertions and deletions, in genes with known and suspected roles in antimicrobial resistance including those coding for multidrug efflux pumps, carbohydrate transport, and cellular metabolism. The observed phenotypic changes coupled with genotypic results indicate that bacteria exposed to antiviral drugs with antibacterial properties in vitro can develop multiple resistance mutations that confer cross-resistance to antibiotics. Our findings underscore the potential contribution of wide scale usage of antiviral drugs to the development and spread of antimicrobial resistance in humans and the environment.

Plasmid permissiveness of wastewater microbiomes can be predicted from 16S rRNA sequences by machine learning

MOTIVATION

Wastewater treatment plants (WWTPs) harbor a dense and diverse microbial community. They constantly receive antimicrobial residues and resistant strains, and therefore provide conditions for horizontal gene transfer (HGT) of antimicrobial resistance (AMR) determinants. This facilitates the transmission of clinically important genes between, e.g. enteric and environmental bacteria, and vice versa. Despite the clinical importance, tools for predicting HGT remain underdeveloped.

RESULTS

In this study, we examined to which extent water cycle microbial community composition, as inferred by partial 16S rRNA gene sequences, can predict plasmid permissiveness, i.e. the ability of cells to receive a plasmid through conjugation, based on data from standardized filter mating assays using fluorescent bio-reporter plasmids. We leveraged a range of machine learning models for predicting the permissiveness for each taxon in the community, representing the range of hosts a plasmid is able to transfer to, for three broad host-range resistance IncP plasmids (pKJK5, pB10, and RP4). Our results indicate that the predicted permissiveness from the best performing model (random forest) showed a moderate-to-strong average correlation of 0.49 for pB10 [95% confidence interval (CI): 0.44-0.55], 0.43 for pKJK5 (0.95% CI: 0.41-0.49), and 0.53 for RP4 (0.95% CI: 0.48-0.57) with the experimental permissiveness in the unseen test dataset. Predictive phylogenetic signals occurred despite the broad host-range nature of these plasmids. Our results provide a framework that contributes to the assessment of the risk of AMR pollution in wastewater systems.

AVAILABILITY AND IMPLEMENTATION

The predictive tool is available as an application at https://github.com/DaneshMoradigaravand/PlasmidPerm.

Characterizations of blaCTX-M-14 and blaCTX-M-64 in a clinical isolate of Escherichia coli from China

Extended-spectrum beta-lactamase-producing Gram-negative bacteria are common in the community and hospitals. To monitor ESBLs mediated by the CTX-M genotype, we collected clinical ESBL pathogenic strains from a hospital in central China and observed a strain of Escherichia coli, namely Ec15103 carrying blaCTX-M-14, blaCTX-M-64 and blaTEM-1, isolated from the blood of a 7-day-old infant in 2015. Strain Ec15103 contains two drug resistance plasmids: pEc15103A, an IncFI-type plasmid that cannot be conjugatively transferred and carries the drug resistance genes blaTEM-1, aacC2, aadA5, sul1, mph(A), sul2, strAB, and tetA(A); and pEc15103B, an IncK2/Z-type plasmid that carries the conjugation transfer gene and blaCTX-M-14. In addition, blaCTX-M-64 is located on the chromosome of Ec15103, and it is the first report of pathogen with blaCTX-M-64 located on its chromosome (the search terms used "blaCTX-M-64" and "chromosome"). blaCTX-M-14 and blaCTX-M-64 are carried by ISEcp1-mediated transposon Tn6503a and Tn6502, respectively. The conjugation transfer ability of pEc15103B was significantly inhibited by zidovudine (AZT) and linoleic acid (LA) and that expression of blaCTX-M-14, blaCTX-M-64 and blaTEM-1 at the mRNA level did not change based on the concentration of cefotaxime or ampicillin. Co-occurrence of blaCTX-M-14 and blaCTX-M-64 in a single isolate will enhance the drug resistance of bacteria, and the presence of blaCTX-M-64 in the chromosome may make the resistance more maintain. This fact will facilitate its dissemination and persistence under different antimicrobial selection pressures. It is essential to prevent these strains from further spreading in a hospital environment.

A Streamlined Approach for Fluorescence Labelling of Low-Copy-Number Plasmids for Determination of Conjugation Frequency by Flow Cytometry

Bacterial conjugation plays a major role in the dissemination of antibiotic resistance and virulence traits through horizontal transfer of plasmids. Robust measurement of conjugation frequency of plasmids between bacterial strains and species is therefore important for understanding the transfer dynamics and epidemiology of conjugative plasmids. In this study, we present a streamlined experimental approach for fluorescence labelling of low-copy-number conjugative plasmids that allows plasmid transfer frequency during filter mating to be measured by flow cytometry. A blue fluorescent protein gene is inserted into a conjugative plasmid of interest using a simple homologous recombineering procedure. A small non-conjugative plasmid, which carries a red fluorescent protein gene with a toxin–antitoxin system that functions as a plasmid stability module, is used to label the recipient bacterial strain. This offers the dual advantage of circumventing chromosomal modifications of recipient strains and ensuring that the red fluorescent protein gene-bearing plasmid can be stably maintained in recipient cells in an antibiotic-free environment during conjugation. A strong constitutive promoter allows the two fluorescent protein genes to be strongly and constitutively expressed from the plasmids, thus allowing flow cytometers to clearly distinguish between donor, recipient, and transconjugant populations in a conjugation mix for monitoring conjugation frequencies more precisely over time.

Characteristics of Probiotic Preparations and Their Applications

The probiotics market is one of the fastest growing segments of the food industry as there is growing scientific evidence of the positive health effects of probiotics on consumers. Currently, there are various forms of probiotic products and they can be categorized according to dosage form and the site of action. To increase the effectiveness of probiotic preparations, they need to be specifically designed so they can target different sites, such as the oral, upper respiratory or gastrointestinal tracts. Here we review the characteristics of different dosage forms of probiotics and discuss methods to improve their bioavailability in detail, in the hope that this article will provide a reference for the development of probiotic products.

Nanoparticle-Enabled Combination Therapy Showed Superior Activity against Multi-Drug Resistant Bacterial Pathogens in Comparison to Free Drugs

The emergence of multidrug-resistant (MDR) bacterial pathogens in farm animals and their zoonotic spread is a concern to both animal agriculture and public health. Apart from antimicrobial resistance (AMR), bacterial pathogens from the genera of Salmonella and Staphylococcus take refuge inside host cells, thereby demanding intervention strategies that can eliminate intracellular MDR pathogens. In this study, seven clinical isolates of Salmonella and Staphylococcus from swine farms were characterized for antibiotic (n = 24) resistance, resistance mechanisms, and virulence characteristics. All isolates showed resistance to one or more antibiotics and S. enterica ser. Typhimurium isolate had the highest resistance to the panel of antibiotics tested. Major resistance mechanisms identified were efflux pump and beta-lactamase enzyme activities. Staphylococcus isolates showed complete hemolysis and strong biofilm formation, while Salmonella isolates caused partial hemolysis, but showed no or weak biofilm formation. MDR isolates of S. aureus M12 and S. enterica ser. Typhimurium bacteria were subsequently tested against combinations of antibiotics and potentiating adjuvants for improved antibacterial efficacy using a checkerboard assay, and their fractional inhibitory concentration index (FICI) was calculated. A combination of chitosan and silica nanoparticles containing tetracycline (TET) and efflux pump inhibitor chlorpromazine (CPZ), respectively, was characterized for physicochemical properties and effectiveness against MDR Salmonella enterica ser. Typhimurium isolate. This combination of nano-encapsulated drugs improved the antibacterial efficacy by inhibiting AMR mechanisms (efflux activity, beta-lactamase enzyme activity, and hydrogen sulfide (H₂S) production) and reducing intracellular pathogen load by 83.02 ± 14.35%. In conclusion, this study sheds light on the promising applicability of nanoparticle-enabled combination therapy to combat multidrug-resistant pathogens encountered in animal agriculture.

New tools to mitigate drug resistance in Enterobacteriaceae - Escherichia coli and Klebsiella pneumoniae

Treatment to common bacterial infections are becoming ineffective of late, owing to the emergence and dissemination of antibiotic resistance globally. Escherichia coli and Klebsiella pneumoniae are the most notorious microorganisms and are among the critical priority pathogens listed by WHO in 2017. These pathogens are the predominant cause of sepsis, urinary tract infections (UTIs), pneumonia, meningitis and pyogenic liver abscess. Concern arises due to the resistance of bacteria to most of the beta lactam antibiotics like penicillin, cephalosporin, monobactams and carbapenems, even to the last resort antibiotics like colistin. Preventing influx by modulation of porins, extruding the antibiotics by overexpression of efflux pumps, mutations of drug targets/receptors, biofilm formation, altering the drug molecules and rendering them ineffective are few resistance mechanisms that are adapted by Enterobacteriaeceae upon exposure to antibiotics. The situation is exacerbated due to the process of horizontal gene transfer (HGT), wherein the genes encoding resistance mechanisms are transferred to the neighbouring bacteria through plasmids/phages/uptake of free DNA. Carbapenemases, other beta lactamases and mcr genes coding for colistin resistance are widely disseminated leading to limited/no therapeutic options against those infections. Development of new antibiotics can be viewed as a possible solution but it involves major investment, time and labour despite which, the bacteria can easily adapt to the new antibiotic and evolve resistance in a relatively short time. Targeting the resistance mechanisms can be one feasible alternative to tackle these multidrug resistant (MDR) pathogens. Removal of plasmid (plasmid curing) causing resistance, use of bacteriophages and bacteriotherapy can be other potential approaches to combat infections caused by MDR E. coli and K. pneumoniae. The present review discusses the efficacies of these therapies in mitigating these infections, which can be potentially used as an adjuvant therapy along with existing antibiotics.

New perspectives on mobile genetic elements: a paradigm shift for managing the antibiotic resistance crisis

Mobile genetic elements (MGEs) are primary facilitators in the global spread of antibiotic resistance. Here, we present novel ecological and evolutionary perspectives to understand and manage these elements: as selfish entities that exhibit biological individuality, as pollutants that replicate and as invasive species that thrive under human impact. Importantly, each viewpoint suggests new means to control their activity and spread. When seen as biological individuals, MGEs can be regarded as therapeutic targets in their own right. We highlight promising conjugation-inhibiting compounds that could be administered alongside antibiotic treatment. Viewed as pollutants, sewage treatment methods could be modified to efficiently remove antimicrobials and the resistance genes that they select. Finally, by recognizing the invasive characteristics of MGEs, we might apply strategies developed for the management of invasive species. These include environmental restoration to reduce antimicrobial selection, early detection to help inform appropriate antibiotic usage, and biocontrol strategies that target MGEs, constituting precision antimicrobials. These actions, which embody the One Health approach, target different characteristics of MGEs that are pertinent at the cellular, community, landscape and global levels. The strategies could act on multiple fronts and, together, might provide a more fruitful means to combat the global resistance crisis.

This article is part of the theme issue ‘The secret lives of microbial mobile genetic elements’.

Melatonin prevents conjugative transfer of plasmid-mediated antibiotic resistance genes by disrupting proton motive force

The widespread dissemination of antibiotic resistance genes (ARGs) is a serious problem and constitutes a threat for public health. Plasmid-mediated conjugative transfer of ARGs is recognized as one of the most important pathways accounting for this global crisis. Inhibiting the conjugative transfer of resistant gene-bearing plasmids provides a feasible strategy to prevent the spread of antibiotic resistance. Here we found that melatonin, a neurohormone secreted from pineal gland, substantially inhibited the horizontal transfer of RP4-7 plasmid in a dose-dependent manner. Furthermore, melatonin could also suppress the conjugal frequency of different types of clinical plasmids that carrying colistin resistance gene mcr-1 rather than blaNDM or tet(X) genes. Next, we investigated the mechanisms underlying the inhibitory effect of melatonin on conjugation. As a result, we showed that the addition of melatonin markedly reduced bacterial membrane permeability and inhibited the oxidative stress. In line with these observations, the conjugative transfer-related genes were regulated accordingly. Most importantly, we uncovered that melatonin disrupted bacterial proton motive force (PMF), which is an essential bacterial energy metabolism substance and is important for conjugative process. Collectively, these results provide implications that some non-antibiotics such as melatonin are effective inhibitors of transmission of ARGs and raise a promising strategy to confront the increasing resistant infections.

Zidovudine in synergistic combination with fosfomycin: an in vitro and in vivo evaluation against multidrug-resistant Enterobacterales

Multidrug-resistant (MDR) Enterobacterales are a priority health issue with few treatment options. Recently, fosfomycin has been reconsidered for MDR bacterial infections. Zidovudine, licensed for the treatment of human immunodeficiency virus (HIV), has unexploited antibacterial properties and has been considered for drug repurposing. The aim of this study was to assess the effect of the combination of fosfomycin plus zidovudine against clinical MDR Enterobacterales isolates. Minimum inhibitory concentration (MIC) determination and checkerboard assays for 36 MDR Enterobacterales strains were performed. In addition, fosfomycin-resistant strains were evaluated using time-kill assay and in an in vivo Galleria mellonella infection model. Zidovudine and fosfomycin MICs ranged between 0.06 to >64 mg/L and 0.125 to >512 mg/L, respectively. A synergistic effect [fractional inhibitory concentration index (FICI) ≤0.5] was observed in 25 isolates and no antagonistic effect was observed in the remaining isolates. For 7 of 8 fosfomycin-resistant strains (MIC > 32 mg/L), zidovudine combination was able to restore fosfomycin susceptibility. These results were confirmed by time-kill assays. Fosfomycin + zidovudine presented greater larval survival (20-50%) than monotherapy. Synergistic activity was observed for fosfomycin + zidovudine in 69.4% of the tested strains. In vivo experiments confirmed the enhanced effectiveness of the combination. The zidovudine concentrations tested here can be reached in human serum using the actual licensed dosage, therefore this combination deserves further clinical investigation.

Detection of mcr-1-positive Escherichia coli in slaughterhouse wastewater collected from Dawen river

BACKGROUND

Low levels of mcr-1 were detected in Escherichia coli from wastewater samples across the world; hence, further monitoring and management of accumulation of mcr-1-positive bacteria in wastewater are urgently recommended.

OBJECTIVES

In this study, we have reported the detection of E. coli strains carrying the colistin resistance gene mcr-1 in slaughterhouse wastewater discharged into Dawen river.

METHODS

Twenty samples were collected aseptically and subjected to polymerase chain reaction (PCR) analysis, multilocus sequence typing and antibiotic resistance tests. Conjugation tests were also performed.

RESULTS

The screening results showed a positive rate of 20% (4/20), which suggested that the mcr-1 gene had polluted the environment of the river. The mcr-1 gene had successfully transferred from the donor to recipient cells, which showed the possibility of horizontal transfer of mcr-1 and subsequently, the formation of multidrug resistant bacteria in the river.

CONCLUSIONS

Our findings demonstrated a high occurrence of colistin-resistant E. coli carrying the mcr-1 gene on transferrable plasmids in slaughterhouses and indicated their dissemination into river. Large-scale cross-border cooperation would be required for the effective control of the spread of antibiotic-resistant bacteria.

Combining Functional Genomics and Whole-Genome Sequencing to Detect Antibiotic Resistance Genes in Bacterial Strains Co-Occurring Simultaneously in a Brazilian Hospital

(1) Background: The rise of multi-antibiotic resistant bacteria represents an emergent threat to human health. Here, we investigate antibiotic resistance mechanisms in bacteria of several species isolated from an intensive care unit in Brazil. (2) Methods: We used whole-genome analysis to identify antibiotic resistance genes (ARGs) and plasmids in 34 strains of Gram-negative and Gram-positive bacteria, providing the first genomic description of Morganella morganii and Ralstonia mannitolilytica clinical isolates from South America. (3) Results: We identified a high abundance of beta-lactamase genes in resistant organisms, including seven extended-spectrum beta-lactamases (OXA-1, OXA-10, CTX-M-1, KPC, TEM, HYDRO, BLP) shared between organisms from different species. Additionally, we identified several ARG-carrying plasmids indicating the potential for a fast transmission of resistance mechanism between bacterial strains. Furthermore, we uncovered two pairs of (near) identical plasmids exhibiting multi-drug resistance. Finally, since many highly resistant strains carry several different ARGs, we used functional genomics to investigate which of them were indeed functional. In this sense, for three bacterial strains (Escherichia coli, Klebsiella pneumoniae, and M. morganii), we identified six beta-lactamase genes out of 15 predicted in silico as those mainly responsible for the resistance mechanisms observed, corroborating the existence of redundant resistance mechanisms in these organisms. (4) Conclusions: Systematic studies similar to the one presented here should help to prevent outbreaks of novel multidrug-resistant bacteria in healthcare facilities.

Linoleic acid and α-linolenic acid inhibit conjugative transfer of an IncX4 plasmid carrying mcr-1

AIMS

The aim of this study was to determine the effects of unsaturated fatty acids on clinical plasmids.

METHODS AND RESULTS

Two unsaturated fatty acids, linoleic acid (LA) and α-linolenic acid (ALA) at final concentration 0, 0·03, 0·3 and 3 mmol l^-1 , respectively, were used to assess the effects on conjugative transfer of a mcr-1-harbouring plasmid pCSZ4 (IncX4) in conjugation experiment. The inhibitory mechanisms were analysed by molecular docking and the gene expression of virB11 was quantitated by qRT-PCR. Target plasmid diversity was carried out by TrwD/VirB11 homology protein sequence prediction analysis. Our results showed that LA and ALA inhibit plasmid pCSZ4 transfer by binding to the amino acid residues (Phe124 and Thr125) of VirB11 with dose-dependent effects. The expression levels of virB11 gene were also significantly inhibited by LA and ALA treatment. Protein homology analysis revealed a wide distribution of TrwD/VirB11-like genes among over 37 classes of plasmids originated from both Gram-negative and Gram-positive bacteria.

CONCLUSIONS

This study demonstrates representing a diversity of plasmids that may be potentially inhibited by unsaturated fatty acids.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our work reported here provides additional support for application of curbing the spread of multiple plasmids by unsaturated fatty acids.

Correlation between Exogenous Compounds and the Horizontal Transfer of Plasmid-Borne Antibiotic Resistance Genes

The global spread of antibiotic resistance has posed a serious threat to public healthcare and undermined decades of progress made in the fight against bacterial infections. It has been demonstrated that the lack of novel effective antibiotics and rapid spread of antibiotic resistance genes via horizontal transfer in the ecosystem are mainly responsible for this crisis. Notably, plasmid-mediated horizontal transfer of antibiotic resistance genes (ARGs) is recognized as the most dominant dissemination pathway of ARGs in humans, animals and environmental settings. Antibiotic selective pressure has always been regarded as one of the crucial contributors to promoting the dissemination of antibiotic resistance through horizontal gene transfer (HGT). However, the roles of exogenous compounds and particularly non-antibiotic drugs in the spread of ARGs are still underappreciated. In this review, we first summarize the major pathways of HGT in bacteria, including conjugation, transformation, transduction and vesiduction. Subsequently, an overview of these compounds capable of promoting the HGT is presented, which guides to the formulation of more reasonable dosing regimens and drug residue standards in clinical practice. By contrast, these compounds that display an inhibition effect on HGT are also highlighted, which provides a unique strategy to minimize the spread of ARGs. Lastly, we discuss the implementations and challenges in bringing these HGT inhibitors into clinical trials.