Glycopeptide antibiotics: Back to the future

The power of DNA-encoded chemical libraries in the battle against drug-resistant bacteria

Drug-resistant bacteria are increasingly posing an imminent existential threat, as many bacteria have developed resistance mechanisms that render most antibiotics ineffective. In the meantime, the number of newly approved antibiotics or new clinical antibacterial drug candidates is sharply declining. A key challenge is finding effective pharmacophores that can penetrate and accumulate inside bacterial cells. DNA-encoded chemical libraries (DECLs) play vital roles in accelerating hit identification and screening against various bacterial protein targets. In this review, we highlight the pivotal role of DECLs in accelerating the identification of new pharmacophores and hit compounds against drug-resistant bacteria. This review focuses on the protein targets, where DECLs have directly contributed to the rapid identification of new inhibitors. In addition, this review explores the methods used to screen DECLs against various bacterial targets and discusses the current outlook and perspectives on the role of DECLs in tackling antimicrobial resistance.

Fe(OTf)3 or Photosensitizer-free blue light activated diazo-thioglycoside donors for Iterative and stereoselective glycosylations

Conventional methods for thioglycoside activation often rely on precious and toxic platinum group metals. Here, we report a catalytic glycosylation strategy employing diazo-thioglycoside donors activated by earth-abundant iron or photosensitizer-free blue light conditions. It confers orthogonal reactivity relative to most glycosyl donors, including widely used thioglycosides and alkyne-based donors, thereby enabling one-pot orthogonal synthesis of glycans. The Thorpe-Ingold-like effect drives the proximity of iron- or blue-light-generated carbenes to the sulfur atom of thioglycosides. This approach accommodates diverse protecting groups and nucleophiles. It applies to various glycosyl donors derived from glucose, mannose, galactose, rhamnose, xylose, lactose, 2-deoxyamino glucose, and furanose derivatives such as ribose and arabinose. Moreover, we demonstrate the robustness of this methodology through challenging 1,2-cis furanosides, late-stage modifications of biomolecules like cholesterol, and the drug simvastatin on a gram scale, along with the iterative synthesis of challenging hexasaccharides.

Saarvienin A-A Novel Glycopeptide with Potent Activity against Drug-Resistant Bacteria

A member of a new family of glycopeptides, named saarvienin A, was isolated from a rare actinomycete Amycolatopsis sp. YIM10. Extensive NMR and MS analyses revealed a halogenated peptide core comprising four amino acids cyclized via a ureido linkage with an exocyclic 2-hydroxy-3-(4-hydroxyphenyl)propyl residue connected to a five-sugar/aminosugar chain. Two of the three aminosugars constitute the N-methylated and N,O-dimethylated derivatives of eremosamine (4-epi-vancosamine) that have not been reported in any natural product. Saarvienin A exhibits potent activity against a range of Gram-positive bacteria, effectively overcoming resistance to several frontline antibiotics in clinical isolates. It demonstrates an eight-fold reduction in minimum inhibitory concentrations (MICs) against methicillin-resistant, vancomycin-intermediate, and daptomycin-resistant Staphylococcus aureus compared to vancomycin.

An experimental study on the lytic bacteriophage MSP15 with wide-spectrum targeting methicillin-resistant Staphylococcus aureus

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is identified as one of the main drug-resistant pathogens, increasing the risk of no antibiotic availability in clinical settings and necessitating the urgent search for alternative antibacterial treatments. Phage therapy has been proposed as a therapeutic approach for bacterial infections, offering numerous advantages and broad application prospects. However, the efficacy of phage therapy in treating drug-resistant infections in humans remains uncertain. Given the current advances in phage therapy and the grim situation posed by MRSA infections, the application of lytic bacteriophages with wide-spectrum activity to treat difficult MRSA infections is proposed.

OBJECTIVE

The objective is to isolate, purify, and screen lytic bacteriophages targeting MRSA from the environment and to assess their efficacy and safety through in vitro and in vivo experiments, with the aim of providing another therapy for MRSA infection.

METHODS

Firstly, representative MRSA strains were selected, and their corresponding phages were isolated and purified from hospital sewage. Secondly, the isolated phages were screened to identify lytic bacteriophages with broad-spectrum activity, and their biological characteristics were analyzed. Thirdly, a systemic infection mouse model was established to evaluate the efficacy and safety of phage MSP15 against MRSA infection.

RESULTS

In this study, Staphylococcus aureus Phage MSP15, a lytic bacteriophage with broad-spectrum activity targeting MRSA, was successfully isolated, purified and screened. Furthermore, in the systemic infection mouse model, administration of phage MSP15 led to prolonged survival time of MRSA-infected mice. A 100% survival rate was observed in infected mice with both immediate and delayed administration of high doses of phage MSP15 (MOI = 1), although efficacy may potentially be reduced with delayed treatment compared to immediate treatment. Additionally, an immune response was induced by phage MSP15, resulting in the production of IgG against phage MSP15, while no adverse events such as changes in core body temperature, allergic reactions, or other adverse effects were observed in mice.

CONCLUSION

Lytic bacteriophages with a wide spectrum can become an auxiliary approach for treating MRSA infection.

Novel antimicrobial strategies for diabetic foot infections: addressing challenges and resistance

AIMS

This review examines the challenges posed by Diabetic Foot Infections (DFIs), focusing on the impact of neuropathy, peripheral arterial disease, immunopathy, and the polymicrobial nature of these infections. The aim is to explore the factors contributing to antimicrobial resistance and assess the potential of novel antimicrobial treatments and drug delivery systems in improving patient outcomes.

METHOD

A comprehensive analysis of existing literature on DFIs was conducted, highlighting the multifactorial pathogenesis and polymicrobial composition of these infections. The review delves into the rise of antimicrobial resistance due to the overuse of antimicrobials, biofilm formation, and microbial genetic adaptability. Additionally, it considers glycemic control, patient adherence, and recurrence rates as contributing factors to treatment failure. Emerging therapies, including new antimicrobial classes and innovative drug delivery systems, were evaluated for their potential efficacy.

RESULTS

DFIs present unique treatment challenges, with high rates of antimicrobial resistance and poor response to standard therapies. Biofilm formation and the genetic adaptability of pathogens worsen resistance, complicating treatment. Current antimicrobial therapies are further hindered by poor glycemic control and patient adherence, leading to recurrent infections. Novel antimicrobial classes and innovative delivery systems show promise in addressing these challenges by offering more targeted, effective treatments. These new approaches aim to reduce resistance and improve treatment outcomes.

CONCLUSION

DFIs remain a clinical challenge due to their multifactorial nature and antimicrobial resistance. The development of novel antimicrobials and drug delivery systems is crucial to improving patient outcomes and combating resistance. Future research should focus on enhancing treatment efficacy, reducing resistance, and addressing patient adherence to reduce the burden of DFIs.

FDA-Approved Antibacterials and Echinocandins

Since 1955, a total of 12 peptide-based drugs with antimicrobial or antifungal properties have received approval from the Food and Drug Administration (FDA). Peptides present a promising opportunity to address serious infections that may be challenging to manage through other means. Peptides exhibit the capability to leverage various mechanisms, and in some cases, multiple mechanisms are employed for this purpose. Despite the initial approval dating back to 1955, the FDA recently approved an echinocandin peptide just last year. The ongoing approvals underscore the significance of peptides in addressing ongoing medical challenges. Approximately 22 peptide therapeutics with an antibacterial and antifungal spectrum are currently undergoing various phases of clinical trials, showing promising results. In this review, antimicrobial and antifungal peptides are analyzed in terms of their chemical structure, indication, mode of action, and development journey, concluding with their arrival in the pharmaceutical market.

De novo design of ribosomally synthesized and post-translationally modified peptides

In nature, peptides are enzymatically modified to constrain their structure and introduce functional moieties. De novo peptide structures could be built by combining enzymes from different pathways, but determining the rules of their use is difficult. We present a biophysical model to combine enzymes sourced from bacterial ribosomally synthesized and post-translationally modified peptide (RiPP) gene clusters. Using a pipeline to evaluate more than 1,000 peptides, the model was parameterized under uniform conditions in Escherichia coli for enzymes from different classes (graspetide, spliceotide, pantocin, cyanobactin, glycocin, lasso peptide and lanthipeptide). Synthetic leader peptides with recognition sequences for up to three enzymes were designed to modify core sequences sharing no identity to natural RiPPs. Empirically, RiPPs with the desired modifications constituted 7-67% of the total peptides produced, and 6 of our 8 peptide designs were successfully modified. This work is an example of the design of enzyme-modified peptides and libraries, using a framework that can be expanded to include new enzymes and chemical moieties.

A Long Fluorescence Lifetime Probe for Labeling of Gram-Negative Bacteria

Bacterial resistance, primarily stemming from misdiagnosis, misuse, and overuse of antibacterial medications in humans and animals, is a pressing issue. To address this, we focused on developing a fluorescent probe for the detection of bacteria, with a unique feature-an exceptionally long fluorescence lifetime, to overcome autofluorescence limitations in biological samples. The polymyxin-based probe (ADOTA-PMX) selectively targets Gram-negative bacteria and used the red-emitting fluorophore azadioxatriangulenium (with a reported fluorescence lifetime of 19.5 ns). Evaluation of ADOTA-PMX's bacterial labeling efficacy revealed strong specificity for Gram-negative bacteria, and full spectral fluorescence lifetime imaging microscopy demonstrated the potential of ADOTA-PMX for bacterial imaging applications. The probe exhibited a lifetime of 4.5 ns when bound to bacteria, possibly indicating interactions with the bacterial outer membrane. Furthermore, the fluorescence lifetime measurements of ADOTA-PMX labeled bacteria could be performed using a benchtop fluorimeter without the need of sophisticated microscopes. This study represents the first targeted probe for fluorescence lifetime imaging, offering sensitivity for detecting Gram-negative bacteria and enabling multiplexing via fluorescence lifetime imaging.

Electrochemical aptasensor for the selective detection of vancomycin based on nanostructured "in-lab" printed electrodes

A label-free, flexible, and disposable aptasensor was designed for the rapid on-site detection of vancomycin (VAN) levels. The electrochemical sensor was based on lab-printed carbon electrodes (C-PE) enriched with cauliflower-shaped gold nanostructures (AuNSs), on which VAN-specific aptamers were immobilized as biorecognition elements and short-chain thiols as blocking agents. The AuNSs, characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), enhanced the electrochemical properties of the platform and the aptamer immobilization active sites. The developed disposable aptasensor allowed label-free detection of VAN via electrochemical impedance spectroscopy (EIS) across a wide range of concentrations (50-1000 nM), with a limit of detection (LOD) of 1.721 nM. The aptasensor presented good selectivity against some commonly found interferences in human serum and milk and was successfully applied to the analysis of these samples.

Vancomycin and linezolid: severe cutaneous adverse reactions to drugs

BACKGROUND

Severe cutaneous adverse reactions (SCARs), including Stevens-Johnson Syndrome (SJS), Toxic Epidermal Necrolysis (TEN), Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), and Acute Generalized Exanthematous Pustulosis (AGEP), pose significant therapeutic challenges. Vancomycin and linezolid have been linked to these life-threatening conditions, necessitating a better understanding of their associated risks.

METHODS

We conducted a retrospective analysis using data from the FDA Adverse Event Reporting System (FAERS) database. Disproportionality and Bayesian statistical analyses were applied to evaluate the associations between vancomycin, linezolid, and SCARs, comparing the outcomes induced by these drugs.

RESULTS

Of the 11,737,133 data, there were a total of 1024 vancomycin-associated SCARs and 125 cases of linezolid-associated SCARs. Vancomycin was strongly associated with DRESS, showing a Reporting Odds Ratio (ROR) of 53.79 (95% CI: 49.75-58.16), Proportional Reporting Ratio (PRR) of 50.38, and Empirical Bayesian Geometric Mean (EBGM) of 2.32. For SJS and TEN, vancomycin reported RORs of 8.04 and 15.63, respectively. Linezolid demonstrated lower associations, with RORs of 5.14 for DRESS and 2.36 for SJS.

CONCLUSIONS

Vancomycin presents a higher risk of SCARs compared to linezolid, particularly for DRESS. Underscoring the need for cautious use and the potential benefit of personalized medicine practices to improve patient safety.

Animating insights into the biosynthesis of glycopeptide antibiotics

The realm of natural product (NP) research is constantly expanding, with diverse applications in both medicine and industry. In this interdisciplinary field, scientists collaborate to investigate various aspects of NPs, including understanding the mode of action of these compounds, unraveling their biosynthetic pathways, studying evolutionary aspects, and biochemically characterizing the enzymes involved. However, this collaboration can be challenging as all parties involved come from very different backgrounds (such as microbiology, synthetic chemistry, biochemistry, or bioinformatics) and may not use the same terminology. Fortunately, contemporary technologies, such as videos, provide novel avenues for effective engagement. Recognizing the potency of visual stimuli in explaining complex processes, we envision a future where animations become more and more common in interdisciplinary communication, accompanying perspectives, and reviews. To demonstrate how such approaches can enhance the understanding of complex processes, we have animated the biosynthesis of the glycopeptide antibiotic vancomycin (https://youtu.be/TGAgC4c8hvo).

Therapeutic applications of carbohydrate-based compounds: a sweet solution for medical advancement

Carbohydrates, one of the most abundant biomolecules found in nature, have been seen traditionally as a dietary component of foods. Recent findings, however, have unveiled their medicinal potential in the form of carbohydrates-derived drugs. Their remarkable structural diversity, high optical purity, bioavailability, low toxicity and the presence of multiple functional groups have positioned them as a valuable scaffold and an exciting frontier in contemporary therapeutics. At present, more than 170 carbohydrates-based therapeutics have been granted approval by varying regulatory agencies such as United States Food and Drug Administration (FDA), Japan Pharmaceuticals and Medical Devices Agency (PMDA), Chinese National Medical Products Administration (NMPA), and the European Medicines Agency (EMA). This article explores an overview of the fascinating potential and impact of carbohydrate-derived compounds as pharmacological agents and drug delivery vehicles.

Chemical structure metagenomics of microbial natural products: surveying nonribosomal peptides and beyond

Bioactivity-guided fractionation (BGF) has historically been a fruitful natural product discovery workflow. However, it is plagued by increasing rediscovery rates in recent years and new methods capable of exploring the natural product chemical space more broadly and more efficiently is in urgent need. Chemical structure metagenomics as one such method is the theme of this Perspective. It emphasizes a chemical-structure-centered viewpoint toward natural product research. Key to chemical structure metagenomics is the ability to predict the structure of a natural product based on its biosynthetic gene sequences, which facilitated the discovery of numerous new bioactive molecules and helped uncover oversampled/underexplored niches of decades of BGF based discovery. While microbial nonribosomal peptides have been the focus of chemical structure metagenomics efforts thus far, it is in principle applicable to other natural product families. The future outlook of this new approach will also be discussed.

Quantification of tricyclic glycopeptide in human plasma by UHPLC-MS3 coupled with counter-extraction follow by protein precipitation to enhance sensitivity

An ultra-high performance liquid chromatography tandem mass spectrometry cubed (UHPLC/MS3) assay coupled with protein precipitation and counter-extraction for detection of tricyclic glycopeptide vancomycin in human plasma was established and validated in this study. After protein precipitation and counter-extraction with dichloromethane, chromatographic separation of vancomycin and norvancomycin were performed on a reversed phase column (XBridge Peptide BEH C18 column, 2.1 × 100 mm I.D, 3.5 μm). The transition (parent ions → fragment ions → further fragment ions) at m/z 725.3 → 144.1 → 100.1 was used for quantification of vancomycin. The transition (parent ions → fragment ions) at m/z 718.3 → 144.2 was used for detection of norvancomycin. The linear range of the developed analytical method for quantification of vancomycin was 0.5-100 µg/mL (r = 0.9989). The range of intra- and inter-day precisions of the assay among low, medium and high concentrations is between 1.88 % and 6.33 %. The sensitivity of the analytical method was significantly improved by using MS3 technique as monitoring mode and counter-extraction with dichloromethane followed by protein precipitation as sample processing assay. The developed UHPLC/MS3 assay was successfully applied for clinical therapeutic drug monitoring (TDM) of vancomycin in 45 human plasma samples.

Comparison of vancomycin assays in patients undergoing hemodialysis

Vancomycin is a glycopeptide antibiotic mainly excreted by glomerular filtration. Therefore, patients undergoing hemodialysis tend to accumulate its crystalline degradation product, which has been associated with cross-reaction in commercial immunoassays. The aim of this study was to assess the performance of two commercial immunoassays for measuring vancomycin levels in patients undergoing hemodialysis. This method-comparison study enrolled patients undergoing hemodialysis at two hospitals in Porto Alegre, Brazil. Vancomycin serum concentrations measured by Chemiluminescent Microparticle Assay (CMIA) and measured by Kinetic Interaction of Microparticles in Solution (KIMS) were compared with Liquid Chromatography coupled with Tandem Mass Spectrometry (LC-MS/MS). A total of 64 samples from 42 patients and 54 samples from 23 patients were included in CMIA and KIMS groups. Both measurements were highly correlated with LC-MS/MS, with Spearman rank correlation coefficient r = 0.840 (p < 0.001) and r = 0.926 (p < 0.001), respectively. No deviation of linearity was observed (p = 0.81 and p = 0.49, respectively). The mean difference between CMIA and LC-MS/MS was -1.19 μg/mL and between KIMS and LC-MS/MS was -2.28 μg/mL. LC-MS/MS measured levels were, on average, 2.64 % higher than CMIA and 8.81 % higher than KIMS. CMIA and KIMS revealed accurate commercial methods to measure vancomycin serum concentrations in patients undergoing hemodialysis.

Antibiotics: From Mechanism of Action to Resistance and Beyond

Antibiotics are the super drugs that have revolutionized modern medicine by curing many infectious diseases caused by various microbes. They efficiently inhibit the growth and multiplication of the pathogenic microbes without causing adverse effects on the host. However, prescribing suboptimal antibiotic and overuse in agriculture and animal husbandry have led to the emergence of antimicrobial resistance, one of the most serious threats to global health at present. The efficacy of a new antibiotic is high when introduced; however, a small bacterial population attains resistance gradually and eventually survives. Understanding the mode of action of these miracle drugs, as well as their interaction with targets is very complex. However, it is necessary to fulfill the constant need for novel therapeutic alternatives to address the inevitable development of resistance. Therefore, considering the need of the hour, this article has been prepared to discuss the mode of action and recent advancements in the field of antibiotics. Efforts has also been made to highlight the current scenario of antimicrobial resistance and drug repurposing as a fast-track solution to combat the issue.

Agents Targeting the Bacterial Cell Wall as Tools to Combat Gram-Positive Pathogens

The cell wall is an indispensable element of bacterial cells and a long-known target of many antibiotics. Penicillin, the first discovered beta-lactam antibiotic inhibiting the synthesis of cell walls, was successfully used to cure many bacterial infections. Unfortunately, pathogens eventually developed resistance to it. This started an arms race, and while novel beta-lactams, either natural or (semi)synthetic, were discovered, soon upon their application, bacteria were developing resistance. Currently, we are facing the threat of losing the race since more and more multidrug-resistant (MDR) pathogens are emerging. Therefore, there is an urgent need for developing novel approaches to combat MDR bacteria. The cell wall is a reasonable candidate for a target as it differentiates not only bacterial and human cells but also has a specific composition unique to various groups of bacteria. This ensures the safety and specificity of novel antibacterial agents that target this structure. Due to the shortage of low-molecular-weight candidates for novel antibiotics, attention was focused on peptides and proteins that possess antibacterial activity. Here, we describe proteinaceous agents of various origins that target bacterial cell wall, including bacteriocins and phage and bacterial lysins, as alternatives to classic antibiotic candidates for antimicrobial drugs. Moreover, advancements in protein chemistry and engineering currently allow for the production of stable, specific, and effective drugs. Finally, we introduce the concept of selective targeting of dangerous pathogens, exemplified by staphylococci, by agents specifically disrupting their cell walls.

Dual Antibiotic Approach: Synthesis and Antibacterial Activity of Antibiotic-Antimicrobial Peptide Conjugates

In recent years, bacterial resistance to conventional antibiotics has become a major concern in the medical field. The global misuse of antibiotics in clinics, personal use, and agriculture has accelerated this resistance, making infections increasingly difficult to treat and rendering new antibiotics ineffective more quickly. Finding new antibiotics is challenging due to the complexity of bacterial mechanisms, high costs and low financial incentives for the development of new molecular scaffolds, and stringent regulatory requirements. Additionally, innovation has slowed, with many new antibiotics being modifications of existing drugs rather than entirely new classes. Antimicrobial peptides (AMPs) are a valid alternative to small-molecule antibiotics offering several advantages, including broad-spectrum activity and a lower likelihood of inducing resistance due to their multifaceted mechanisms of action. However, AMPs face challenges such as stability issues in physiological conditions, potential toxicity to human cells, high production costs, and difficulties in large-scale manufacturing. A reliable strategy to overcome the drawbacks associated with the use of small-molecule antibiotics and AMPs is combination therapy, namely the simultaneous co-administration of two or more antibiotics or the synthesis of covalently linked conjugates. This review aims to provide a comprehensive overview of the literature on the development of antibiotic-AMP conjugates, with a particular emphasis on critically analyzing the design and synthetic strategies employed in their creation. In addition to the synthesis, the review will also explore the reported antibacterial activity of these conjugates and, where available, examine any data concerning their cytotoxicity.

Altering glycopeptide antibiotic biosynthesis through mutasynthesis allows incorporation of fluorinated phenylglycine residues

Glycopeptide antibiotics (GPAs) are peptide natural products used as last resort treatments for antibiotic resistant bacterial infections. They are produced by the sequential activities of a linear nonribosomal peptide synthetase (NRPS), which assembles the heptapeptide core of GPAs, and cytochrome P450 (Oxy) enzymes, which perform a cascade of cyclisation reactions. The GPAs contain proteinogenic and nonproteinogenic amino acids, including phenylglycine residues such as 4-hydroxyphenylglycine (Hpg). The ability to incorporate non-proteinogenic amino acids in such peptides is a distinctive feature of the modular architecture of NRPSs, with each module selecting and incorporating a desired amino acid. Here, we have exploited this ability to produce and characterise GPA derivatives containing fluorinated phenylglycine (F-Phg) residues through a combination of mutasynthesis, biochemical, structural and bioactivity assays. Our data indicate that the incorporation of F-Phg residues is limited by poor acceptance by the NRPS machinery, and that the phenol moiety normally present on Hpg residues is essential to ensure both acceptance by the NRPS and the sequential cyclisation activity of Oxy enzymes. The principles learnt here may prove useful for the future production of GPA derivatives with more favourable properties through mixed feeding mutasynthesis approaches.

Enterococci as a One Health indicator of antimicrobial resistance

The rapid increase of antimicrobial-resistant bacteria in humans and livestock is concerning. Antimicrobials are essential for the treatment of disease in modern day medicine, and their misuse in humans and food animals has contributed to an increase in the prevalence of antimicrobial-resistant bacteria. Globally, antimicrobial resistance is recognized as a One Health problem affecting humans, animals, and environment. Enterococcal species are Gram-positive bacteria that are widely distributed in nature. Their occurrence, prevalence, and persistence across the One Health continuum make them an ideal candidate to study antimicrobial resistance from a One Health perspective. The objective of this review was to summarize the role of enterococci as an indicator of antimicrobial resistance across One Health sectors. We also briefly address the prevalence of enterococci in human, animal, and environmental settings. In addition, a 16S RNA gene-based phylogenetic tree was constructed to visualize the evolutionary relationship among enterococcal species and whether they segregate based on host environment. We also review the genomic basis of antimicrobial resistance in enterococcal species across the One Health continuum.

Detection of a Kinetically Competent Compound-I Intermediate in the Vancomycin Biosynthetic Enzyme OxyB

Cytochrome P450 enzymes are abundantly encoded in microbial genomes. Their reactions have two general outcomes, one involving oxygen insertion via a canonical "oxygen rebound" mechanism and a second that diverts from this pathway and leads to a wide array of products, notably intramolecular oxidative cross-links. The antibiotic of-last-resort, vancomycin, contains three such cross-links, which are crucial for biological activity and are installed by the P450 enzymes OxyB, OxyA, and OxyC. The mechanisms of these enzymes have remained elusive in part because of the difficulty in spectroscopically capturing transient intermediates. Using stopped-flow UV/visible absorption and rapid freeze-quench electron paramagnetic resonance spectroscopies, we show that OxyB generates the highly reactive compound-I intermediate, which can react with a model vancomycin peptide substrate in a kinetically competent fashion to generate product. Our results have implications for the mechanism of OxyB and are in line with the notion that oxygen rebound and oxidative cross-links share early steps in their catalytic cycles.

Genome-wide CRISPRi screens for high-throughput fitness quantification and identification of determinants for dalbavancin susceptibility in Staphylococcus aureus

Antibiotic resistance and tolerance remain a major problem for the treatment of staphylococcal infections. Identifying genes that influence antibiotic susceptibility could open the door to novel antimicrobial strategies, including targets for new synergistic drug combinations. Here, we developed a genome-wide CRISPR interference library for Staphylococcus aureus, demonstrated its use by quantifying gene fitness in different strains through CRISPRi-seq, and used it to identify genes that modulate susceptibility to the lipoglycopeptide dalbavancin. By exposing the library to sublethal concentrations of dalbavancin using both CRISPRi-seq and direct selection methods, we not only found genes previously reported to be involved in antibiotic susceptibility but also identified genes thus far unknown to affect antibiotic tolerance. Importantly, some of these genes could not have been detected by more conventional transposon-based knockout approaches because they are essential for growth, stressing the complementary value of CRISPRi-based methods. Notably, knockdown of a gene encoding the uncharacterized protein KapB specifically sensitizes the cells to dalbavancin, but not to other antibiotics of the same class, whereas knockdown of the Shikimate pathway showed the opposite effect. The results presented here demonstrate the promise of CRISPRi-seq screens to identify genes and pathways involved in antibiotic susceptibility and pave the way to explore alternative antimicrobial treatments through these insights.IMPORTANCEAntibiotic resistance is a challenge for treating staphylococcal infections. Identifying genes that affect how antibiotics work could help create new treatments. In our study, we made a CRISPR interference library for Staphylococcus aureus and used this to find which genes are critical for growth and also mapped genes that are important for antibiotic sensitivity, focusing on the lipoglycopeptide antibiotic dalbavancin. With this method, we identified genes that altered the sensitivity to dalbavancin upon knockdown, including genes involved in different cellular functions. CRISPRi-seq offers a means to uncover untapped antibiotic targets, including those that conventional screens would disregard due to their essentiality. This paves the way for the discovery of new ways to fight infections.

Pharmacotherapies for multidrug-resistant gram-positive infections: current options and beyond

INTRODUCTION

Infections due to multidrug-resistant organisms (MDRO) are a serious concern for public health with high morbidity and mortality. Though many antibiotics have been introduced to manage these infections, there are remaining concerns regarding the optimal management of Gram-positive MDROs.

AREAS COVERED

A literature search on the PubMed/Medline database was conducted. We applied no language and time limits for the search strategy. In this narrative review, we discuss the current options for managing Gram-positive MDROs as well as non-traditional antibacterial agents in development.

EXPERT OPINION

Despite their introduction more than 70 years ago, glycopeptides are still the cornerstone in treating Gram-positive infections: all registrative studies of new antibiotics have glycopeptides as control; these studies are designed as not inferior studies, therefore it is almost impossible to give recommendations other than the use of glycopeptides in the treatment of Gram-positive infections. The best evidence on treatments different from glycopeptides comes from post-hoc analysis and meta-analysis. Non-traditional antibacterial agents are being studied to aid in short and effective antibiotic therapies. The use of non-traditional antibacterial agents is not restricted to replacing traditional antibacterial agents with alternative therapies; instead, they should be used in combination with antibiotic therapies.

Fluorescence detecting glycopeptide antibiotics via a dynamic molecular switch

BACKGROUND

Glycopeptide antibiotics (GPAs) represented by vancomycin (VAN) are clinically used as a first-line treatment for serious infections caused by Gram-positive pathogens. The use and dosing methods of GPAs are rigorously managed for safety considerations, which calls for fast and accurate quantification approaches.

RESULT

A new sort of fluorescent probes for GPAs has been proposed, each of which was integrated by a fluorescein-based reporter and a GPAs' recognition peptide D-alanyl-D-alanine (D-Ala-D-Ala). These probes work as dynamic molecular switches, which mainly exist as non-fluorescent spirolactam forms in the absence of GPAs. GPAs binding with the dipeptide regulates the dynamic balance between fluorescence OFF lactam form and fluorescence ON ring-opened form, rendering these probes capable of GPAs detecting. The most promising one P1 exhibits excellent sensitivity and selectivity towards GPAs detection.

SIGNIFICANCE

Different to previous developments, P1 consists of a single fluorophore without the need of a fluorescence-quenching group or a secondary dye, which is the smallest fluorescent probe for GPAs up to now. P1 realizes direct VAN quantification from complex biological samples including real serums, dispensing with additional drug extraction. More interestingly, both P1 and P6 can distinguish GPAs with different peptide backbones, which has not been achieved previously.

A Vancomycin-Templated DNA-Encoded Library for Combating Drug-Resistant Bacteria

It is an urgent need to tackle the global crisis of multidrug-resistant bacterial infections. We report here an innovative strategy for large-scale screening of new antibacterial agents using a whole bacteria-based DNA-encoded library (DEL) of vancomycin derivatives via peripheral modifications. A bacterial binding affinity assay was established to select the modification fragments in high-affinity compounds. The optimal resynthesized derivatives demonstrated excellently enhanced activity against various resistant bacterial strains and provided useful structures for vancomycin derivatization. This work presents the new concept in a natural product-templated DEL and in antibiotic discovery through bacterial affinity screening, which promotes the fight against drug-resistant bacteria.

Improved pharmacokinetics and enhanced efficacy of the vancomycin derivative FU002 using a liposomal nanocarrier

Antibiotic resistance still represents a global health concern which diminishes the pool of effective antibiotics. With the vancomycin derivative FU002, we recently reported a highly potent substance active against Gram-positive bacteria with the potential to overcome vancomycin resistance. However, the translation of its excellent antimicrobial activity into clinical efficiency could be hampered by its rapid elimination from the blood stream. To improve its pharmacokinetics, we encapsulated FU002 in PEGylated liposomes. For PEG-liposomal FU002, no relevant cytotoxicity on liver, kidney and red blood cells was observed. Studies in Wistar rats revealed a significantly prolonged blood circulation of the liposomal antibiotic. In microdilution assays it could be demonstrated that encapsulation does not diminish the antimicrobial activity against staphylococci and enterococci. Highlighting its great potency, liposomal FU002 exhibited a superior therapeutic efficacy when compared to the free form in a Galleria mellonella larvae infection model.

The Impact of Heterologous Regulatory Genes from Lipodepsipeptide Biosynthetic Gene Clusters on the Production of Teicoplanin and A40926

StrR-like pathway-specific transcriptional regulators (PSRs) function as activators in the biosynthesis of various antibiotics, including glycopeptides (GPAs), aminoglycosides, aminocoumarins, and ramoplanin-like lipodepsipeptides (LDPs). In particular, the roles of StrR-like PSRs have been previously investigated in the biosynthesis of streptomycin, novobiocin, GPAs like balhimycin, teicoplanin, and A40926, as well as LDP enduracidin. In the current study, we focused on StrR-like PSRs from the ramoplanin biosynthetic gene cluster (BGC) in Actinoplanes ramoplaninifer ATCC 33076 (Ramo5) and the chersinamycin BGC in Micromonospora chersina DSM 44151 (Chers28). Through the analysis of the amino acid sequences of Ramo5 and Chers28, we discovered that these proteins are phylogenetically distant from other experimentally investigated StrR PSRs, although all StrR-like PSRs found in BGCs for different antibiotics share a conserved secondary structure. To investigate whether Ramo5 and Chers28, given their phylogenetic positions, might influence the biosynthesis of other antibiotic pathways governed by StrR-like PSRs, the corresponding genes (ramo5 and chers28) were heterologously expressed in Actinoplanes teichomyceticus NRRL B-16726 and Nonomuraea gerenzanensis ATCC 39727, which produce the clinically-relevant GPAs teicoplanin and A40926, respectively. Recombinant strains of NRRL B-16726 and ATCC 39727 expressing chers28 exhibited improved antibiotic production, although the expression of ramo5 did not yield the same effect. These results demonstrate that some StrR-like PSRs can "cross-talk" between distant biosynthetic pathways and might be utilized as tools for the activation of silent BGCs regulated by StrR-like PSRs.

Biocatalytic role of cytochrome P450s to produce antibiotics: A review

Cytochrome P450s belong to a family of heme-binding monooxygenases, which catalyze regio- and stereospecific functionalisation of C-H, C-C, and C-N bonds, including heteroatom oxidation, oxidative C-C bond cleavages, and nitrene transfer. P450s are considered useful biocatalysts for the production of pharmaceutical products, fine chemicals, and bioremediating agents. Despite having tremendous biotechnological potential, being heme-monooxygenases, P450s require either autologous or heterologous redox partner(s) to perform chemical transformations. Randomly distributed P450s throughout a bacterial genome and devoid of particular redox partners in natural products biosynthetic gene clusters (BGCs) showed an extra challenge to reveal their pharmaceutical potential. However, continuous efforts have been made to understand their involvement in antibiotic biosynthesis and their modification, and this review focused on such BGCs. Here, particularly, we have discussed the role of P450s involved in the production of macrolides and aminocoumarin antibiotics, nonribosomal peptide (NRPSs) antibiotics, ribosomally synthesized and post-translationally modified peptide (RiPPs) antibiotics, and others. Several reactions catalyzed by P450s, as well as the role of their redox partners involved in the BGCs of various antibiotics and their derivatives, have been primarily addressed in this review, which would be useful in further exploration of P450s for the biosynthesis of new therapeutics.

Rapid Colloidal Gold Immunoassay for Pharmacokinetic Evaluation of Vancomycin in the Cerebrospinal Fluid and Plasma of Beagle Dogs

Vancomycin (VAN), a glycopeptide antibiotic, is the preferred therapeutic agent for treating Gram-positive bacteria. Rapid and precise quantification of VAN levels in cerebrospinal fluid (CSF) and plasma is crucial for optimized drug administration, particularly among elderly patients. Herein, we introduce a novel clinical test strip utilizing colloidal gold competitive immunoassay technology for the expedient detection of VAN. This test strip enables the detection of VAN concentrations in clinical samples such as plasma within 10 min and has a limit of detection of 10.3 ng/mL, with an inhibitory concentration 50% (IC50) value of 44.5 ng/mL. Furthermore, we used the test strip for pharmacokinetic analysis of VAN in the CSF and plasma of beagle dogs. Our results provide valuable insights into the fluctuations of the drug concentration in the CSF and plasma over a 24 h period after a single intravenous dose of 12 mg/kg. The test strip results were compared with the results obtained via liquid chromatography-mass spectrometry methods, and the measured VAN concentrations in the CSF and plasma via both of the methods showed excellent agreement.

Natural products acting against S. aureus through membrane and cell wall disruption

Covering: 2015 to 2022Staphylococcus aureus (S. aureus) is responsible for several community and hospital-acquired infections with life-threatening complications such as bacteraemia, endocarditis, meningitis, liver abscess, and spinal cord epidural abscess. In recent decades, the abuse and misuse of antibiotics in humans, animals, plants, and fungi and the treatment of nonmicrobial diseases have led to the rapid emergence of multidrug-resistant pathogens. The bacterial wall is a complex structure consisting of the cell membrane, peptidoglycan cell wall, and various associated polymers. The enzymes involved in bacterial cell wall synthesis are established antibiotic targets and continue to be a central focus for antibiotic development. Natural products play a vital role in drug discovery and development. Importantly, natural products provide a starting point for active/lead compounds that sometimes need modification based on structural and biological properties to meet the drug criteria. Notably, microorganisms and plant metabolites have contributed as antibiotics for noninfectious diseases. In this study, we have summarized the recent advances in understanding the activity of the drugs or agents of natural origin that directly inhibit the bacterial membrane, membrane components, and membrane biosynthetic enzymes by targeting membrane-embedded proteins. We also discussed the unique aspects of the active mechanisms of established antibiotics or new agents.

Age and Sex-Related Differences in Teicoplanine Isoform Concentrations in SARS-CoV-2 Patients

Teicoplanin, a glycopeptide antibiotic commonly used to treat bacterial infections, was discovered to be active in vitro against SARS-CoV-2. The aim of this study was to assess the levels of teicoplanin and its components in a cohort of adult and pediatric SARS-CoV-2 patients, evaluating the effect of sex and age on analyte concentrations. The levels of AST, ALT and leukocytes were shown to be higher in females, while the C reactive protein was higher in males. Evaluating the absence/presence of teicoplanin isoforms, we observed that A2-2_3 is the only one consistently present in pediatrics and adults. In adult men and all pediatrics, A2-4_5 is always present. In pediatrics, except for A3-1, median isoform concentrations were higher in females; on the contrary, in adult patients, males showed higher levels. This is the first study to describe levels of teicoplanin isoforms in SARS-CoV-2 infected patients in males and females, and pediatrics and adults, despite the small sample size of our cohort. The observed results imply that additional testing, via therapeutic drug monitoring, may be helpful to more effectively manage infections, particularly those caused by the most recent viruses.

Bifunctional antibiotic hybrids: A review of clinical candidates

Antibiotic resistance is a top threat to human health and a priority across the globe. This problematic issue is accompanied by the decline of new antibiotics in the pipeline over the past 30 years. In this context, an urgent need to develop new strategies to combat antimicrobial resistance is in great demand. Lately, among the possible approaches used to deal with antimicrobial resistance is the covalent ligation of two antibiotic pharmacophores that target the bacterial cells through a dissimilar mode of action into a single hybrid molecule, namely hybrid antibiotics. This strategy exhibits several advantages, including better antibacterial activity, overcoming the existing resistance towards individual antibiotics, and may ultimately delay the onset of bacterial resistance. This review sheds light on the latest development of the dual antibiotic hybrids pipeline, their potential mechanisms of action, and challenges in their use.

Controlling the Evolution of Selective Vancomycin Resistance through Successful Ophthalmic Eye-Drop Preparation of Vancomycin-Loaded Nanoliposomes Using the Active-Loading Method

Vancomycin is the front-line defense and drug of choice for the most serious and life-threatening methicillin-resistant Staphylococcus aureus (MRSA) infections. However, poor vancomycin therapeutic practice limits its use, and there is a consequent rise of the threat of vancomycin resistance by complete loss of its antibacterial activity. Nanovesicles as a drug-delivery platform, with their featured capabilities of targeted delivery and cell penetration, are a promising strategy to resolve the shortcomings of vancomycin therapy. However, vancomycin's physicochemical properties challenge its effective loading. In this study, we used the ammonium sulfate gradient method to enhance vancomycin loading into liposomes. Depending on the pH difference between the extraliposomal vancomycin-Tris buffer solution (pH 9) and the intraliposomal ammonium sulfate solution (pH 5-6), vancomycin was actively and successfully loaded into liposomes (up to 65% entrapment efficiency), while the liposomal size was maintained at 155 nm. Vancomycin-loaded nanoliposomes effectively enhanced the bactericidal effect of vancomycin; the minimum inhibitory concentration (MIC) value for MRSA decreased 4.6-fold. Furthermore, they effectively inhibited and killed heteroresistant vancomycin-intermediate S.aureous (h-VISA) with an MIC of 0.338 μg mL^-1. Moreover, MRSA could not develop resistance against vancomycin that was loaded into and delivered by liposomes. Vancomycin-loaded nanoliposomes could be a feasible solution for enhancing vancomycin's therapeutic use and controlling the emerging vancomycin resistance.

Strategic Approaches to Improvise Peptide Drugs as Next Generation Therapeutics

In recent years, the occurrence of a wide variety of drug-resistant diseases has led to an increase in interest in alternate therapies. Peptide-based drugs as an alternate therapy hold researchers' attention in various therapeutic fields such as neurology, dermatology, oncology, metabolic diseases, etc. Previously, they had been overlooked by pharmaceutical companies due to certain limitations such as proteolytic degradation, poor membrane permeability, low oral bioavailability, shorter half-life, and poor target specificity. Over the last two decades, these limitations have been countered by introducing various modification strategies such as backbone and side-chain modifications, amino acid substitution, etc. which improve their functionality. This has led to a substantial interest of researchers and pharmaceutical companies, moving the next generation of these therapeutics from fundamental research to the market. Various chemical and computational approaches are aiding the production of more stable and long-lasting peptides guiding the formulation of novel and advanced therapeutic agents. However, there is not a single article that talks about various peptide design approaches i.e., in-silico and in-vitro along with their applications and strategies to improve their efficacy. In this review, we try to bring different aspects of peptide-based therapeutics under one article with a clear focus to cover the missing links in the literature. This review draws emphasis on various in-silico approaches and modification-based peptide design strategies. It also highlights the recent progress made in peptide delivery methods important for their enhanced clinical efficacy. The article would provide a bird's-eye view to researchers aiming to develop peptides with therapeutic applications.

Graphical Abstract

Gut microbiota interspecies interactions shape the response of Clostridioides difficile to clinically relevant antibiotics

In the human gut, the growth of the pathogen Clostridioides difficile is impacted by a complex web of interspecies interactions with members of human gut microbiota. We investigate the contribution of interspecies interactions on the antibiotic response of C. difficile to clinically relevant antibiotics using bottom-up assembly of human gut communities. We identify 2 classes of microbial interactions that alter C. difficile's antibiotic susceptibility: interactions resulting in increased ability of C. difficile to grow at high antibiotic concentrations (rare) and interactions resulting in C. difficile growth enhancement at low antibiotic concentrations (common). Based on genome-wide transcriptional profiling data, we demonstrate that metal sequestration due to hydrogen sulfide production by the prevalent gut species Desulfovibrio piger increases the minimum inhibitory concentration (MIC) of metronidazole for C. difficile. Competition with species that display higher sensitivity to the antibiotic than C. difficile leads to enhanced growth of C. difficile at low antibiotic concentrations due to competitive release. A dynamic computational model identifies the ecological principles driving this effect. Our results provide a deeper understanding of ecological and molecular principles shaping C. difficile's response to antibiotics, which could inform therapeutic interventions.

New Antibiotics for Staphylococcus aureus Infection: An Update from the World Association of Infectious Diseases and Immunological Disorders (WAidid) and the Italian Society of Anti-Infective Therapy (SITA)

Staphylococcus aureus is an extremely virulent pathogen that is capable of quickly evolving and developing antibiotic resistance. To overcome this problem, new antibiotics have been developed. Some of these have been licenced for use in clinical practice, mainly for the treatment of adults with acute skin and soft tissue infections, in addition to both community-acquired pneumonia (CAP) and nosocomial pneumonia (hospital-acquired bacterial pneumonia and ventilator-associated bacterial pneumonia). In this paper, the main characteristics and clinical use of new licenced anti-staphylococcal drugs have been discussed. In vitro studies have demonstrated that some new anti-staphylococcal antibiotics have better antimicrobial activity and, at least in certain cases, more favourable pharmacokinetic properties and higher safety and tolerability than the presently available anti-staphylococcal drugs. This suggests that they may have a potential use in reducing the risk of failure of S. aureus therapy. However, an in-depth analysis of microbiological and clinical studies carried out with these new drugs seems to indicate that further studies need to be conducted before the problem of resistance of S. aureus to the antibiotics available today can be completely solved. Considering the overall available research, the drugs that are active against S. aureus appear to present a great therapeutic opportunity for overcoming resistance to traditional therapy. There are advantages in the pharmacokinetic characteristics of some of these drugs and they have the potential to reduce hospital stays and economic costs associated with their use.

Shapeshifting bullvalene-linked vancomycin dimers as effective antibiotics against multidrug-resistant gram-positive bacteria

The alarming rise in superbugs that are resistant to drugs of last resort, including vancomycin-resistant enterococci and staphylococci, has become a significant global health hazard. Here, we report the click chemistry synthesis of an unprecedented class of shapeshifting vancomycin dimers (SVDs) that display potent activity against bacteria that are resistant to the parent drug, including the ESKAPE pathogens, vancomycin-resistant Enterococcus (VRE), methicillin-resistant Staphylococcus aureus (MRSA), as well as vancomycin-resistant S. aureus (VRSA). The shapeshifting modality of the dimers is powered by a triazole-linked bullvalene core, exploiting the dynamic covalent rearrangements of the fluxional carbon cage and creating ligands with the capacity to inhibit bacterial cell wall biosynthesis. The new shapeshifting antibiotics are not disadvantaged by the common mechanism of vancomycin resistance resulting from the alteration of the C-terminal dipeptide with the corresponding d-Ala-d-Lac depsipeptide. Further, evidence suggests that the shapeshifting ligands destabilize the complex formed between the flippase MurJ and lipid II, implying the potential for a new mode of action for polyvalent glycopeptides. The SVDs show little propensity for acquired resistance by enterococci, suggesting that this new class of shapeshifting antibiotic will display durable antimicrobial activity not prone to rapidly acquired clinical resistance.

Side effects of antibiotics and perturbations of mitochondria functions

Antibiotics are one of the greatest discoveries of medicine of the past century. Despite their invaluable contribution to infectious disease, their administration could lead to side effects that in some cases are serious. The toxicity of some antibiotics is in part due to their interaction with mitochondria: these organelles derive from a bacterial ancestor and possess specific translation machinery that shares similarities with the bacterial counterpart. In other cases, the antibiotics could interfere with mitochondrial functions even if their main bacterial targets are not shared with the eukaryotic cells. The purpose of this review is to summarize the effects of antibiotics administration on mitochondrial homeostasis and the opportunity that some of these molecules could represent in cancer treatment. The importance of antimicrobial therapy is unquestionable, but the identification of interaction with eukaryotic cells and in particular with mitochondria is crucial to reduce the toxicity of these drugs and to explore other useful medical applications.

Cross-Talking of Pathway-Specific Regulators in Glycopeptide Antibiotics (Teicoplanin and A40926) Production

Teicoplanin and A40926 (natural precursor of dalbavancin) are clinically relevant glycopeptide antibiotics (GPAs) produced by Actinoplanes teichomyceticus NRRL B-16726 and Nonomuraea gerenzanensis ATCC 39727. Their biosynthetic enzymes are coded within large biosynthetic gene clusters (BGCs), named tei for teicoplanin and dbv for A40926, whose expression is strictly regulated by pathway-specific transcriptional regulators (PSRs), coded by cluster-situated regulatory genes (CSRGs). Herein, we investigated the "cross-talk" between the CSRGs from tei and dbv, through the analysis of GPA production levels in A. teichomyceticus and N. gerenzanensis strains, with knockouts of CSRGs cross-complemented by the expression of heterologous CSRGs. We demonstrated that Tei15* and Dbv4 StrR-like PSRs, although orthologous, were not completely interchangeable: tei15* and dbv4 were only partially able or unable to cross-complement N. gerenzanensis knocked out in dbv4 and A. teichomyceticus knocked out in tei15*, implying that the DNA-binding properties of these PSRs are more different in vivo than it was believed before. At the same time, the unrelated LuxR-like PSRs Tei16* and Dbv3 were able to cross-complement corresponding N. gerenzanensis knocked out in dbv3 and A. teichomyceticus knocked out in tei16*. Moreover, the heterologous expression of dbv3 in A. teichomyceticus led to a significant increase in teicoplanin production. Although the molecular background of these events merits further investigations, our results contribute to a deeper understanding of GPA biosynthesis regulation and offer novel biotechnological tools to improve their production.

Teicoplanin-Resistant Coagulase-Negative Staphylococci: Do the Current Susceptibility Testing Methods Reliably Detect This Elusive Phenotype?

Coagulase-negative staphylococci (CoNS), members of the skin commensal microbiota, are increasingly associated with local or systemic infections due to a shift in patient populations in recent decades. Subsequently, more CoNS strains have been subjected to antibiotic susceptibility testing (AST), thus leading to the increased detection of teicoplanin resistance. However, data concerning teicoplanin resistance among CoNS strains remain limited, heterogeneous, and inconclusive. We collected 162 consecutive CoNS strains identified using Vitek-2 as teicoplanin-resistant and tested them with a range of AST methods. The results of standard and high inoculum broth microdilution (sBMD; hBMD), agar dilution (AD) after 24 h and 48 h incubation, standard and macrogradient diffusion strip (sGDT, MET), screening agar, and disc diffusion were compared to assess their robustness and to establish a diagnostic algorithm to detect teicoplanin resistance. sBMD was used as the reference method, and the lowest number of strains were teicoplanin-resistant using this method. sGDT and disc diffusion generated similar results to sBMD. Compared with sBMD, AD-24 h generated the lowest number of false teicoplanin-resistant strains, followed by hBMD, AD-48 h, and Vitek-2. sGDT, a fast, easy, affordable method in diagnostic settings, generated the highest rate of false teicoplanin-susceptible strains. Vitek-2 testing produced the highest number of teicoplanin-resistant strains. Only in two strains was the initial Vitek-2 teicoplanin resistance confirmed using five other AST methods. In conclusion, the different antibiotic susceptibility testing methods generated inconsistent, inconclusive, and discrepant results, thus making it difficult to establish a diagnostic algorithm for suspected teicoplanin resistance. Teicoplanin testing proved to be challenging and easily influenced by technical factors. This study aimed not only to raise awareness of teicoplanin resistance testing but also of the need for future studies focusing on the clinical efficacy of teicoplanin in relation to its susceptibility results.

Single Modification at the N-Terminus of Norvancomycin to Combat Drug-Resistant Gram-Positive Bacteria

In the arsenal of glycopeptide antibiotics, norvancomycin, which differs from vancomycin by a single methyl group, has received much less attention. Facing the risks of serious antibiotic resistance and even the collapse of last-line defenses, we designed and synthesized 40 novel norvancomycin derivatives to combat the threat. 32 compounds are single N-terminally modified derivatives generated through simple and efficient methods. Diversity at the N-terminus was greatly enriched, mainly by lipophilic attachment and strategies for the introduction of lipo-sulfonium moieties for extensive structure-activity relationship analysis. The first incorporation of a sulfonium moiety into the norvancomycin structure gave rise to compounds that exhibited 4- to 2048-fold higher activity against vancomycin-resistant bacteria VISA and VRE. This N-terminal modification for norvancomycin provides an alternatively useful and promising strategy to restore the antibacterial activity of glycopeptide antibiotics against resistant bacteria, highlighting the same importance of the N-terminal site as well as the vancosamine position, which is worth further study and development.

Mechanisms of a Mycobacterium tuberculosis Active Peptide

Multidrug-resistant tuberculosis (MDR) continues to pose a threat to public health. Previously, we identified a cationic host defense peptide with activity against Mycobacterium tuberculosis in vivo and with a bactericidal effect against MDR M. tuberculosis at therapeutic concentrations. To understand the mechanisms of this peptide, we investigated its interactions with live M. tuberculosis and liposomes as a model. Peptide interactions with M. tuberculosis inner membranes induced tube-shaped membranous structures and massive vesicle formation, thus leading to bubbling cell death and ghost cell formation. Liposomal studies revealed that peptide insertion into inner membranes induced changes in the peptides' secondary structure and that the membranes were pulled such that they aggregated without permeabilization, suggesting that the peptide has a strong inner membrane affinity. Finally, the peptide targeted essential proteins in M. tuberculosis, such as 60 kDa chaperonins and elongation factor Tu, that are involved in mycolic acid synthesis and protein folding, which had an impact on bacterial proliferation. The observed multifaceted targeting provides additional support for the therapeutic potential of this peptide.

Self-association of the glycopeptide antibiotic teicoplanin A2 in aqueous solution studied by molecular hydrodynamics

The natural glycopeptide antibiotic teicoplanin is used for the treatment of serious Gram-positive related bacterial infections and can be administered intravenously, intramuscularly, topically (ocular infections), or orally. It has also been considered for targeting viral infection by SARS-CoV-2. The hydrodynamic properties of teicoplanin A2 (M₁ = 1880 g/mol) were examined in phosphate chloride buffer (pH 6.8, I = 0.10 M) using sedimentation velocity and sedimentation equilibrium in the analytical ultracentrifuge together with capillary (rolling ball) viscometry. In the concentration range, 0-10 mg/mL teicoplanin A2 was found to self-associate plateauing > 1 mg/mL to give a molar mass of (35,400 ± 1000) g/mol corresponding to ~ (19 ± 1) mers, with a sedimentation coefficient s_{20, w} =  ~ 4.65 S. The intrinsic viscosity [[Formula: see text]] was found to be (3.2 ± 0.1) mL/g: both this, the value for s_20,w and the hydrodynamic radius from dynamic light scattering are consistent with a globular macromolecular assembly, with a swelling ratio through dynamic hydration processes of ~ 2.

Breakthrough of glycobiology in the 21st century

As modern medicine began to emerge at the turn of the 20th century, glycan-based therapies advanced. DNA- and protein-centered therapies became widely available. The research and development of structurally defined carbohydrates have led to new tools and methods that have sparked interest in the therapeutic applications of glycans. One of the latest omics disciplines to emerge in the contemporary post-genomics age is glycomics. In addition, to providing hope for patients and people with different health conditions through a deeper understanding of the mechanisms of common complex diseases, this new specialty in system sciences has much to offer to communities involved in the development of diagnostics and therapeutics in medicine and life sciences.This review focuses on recent developments that have pushed glycan-based therapies into the spotlight in medicine and the technologies powering these initiatives, which we can take as the most significant success of the 21st century.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Newest perspectives of glycopeptide antibiotics: biosynthetic cascades, novel derivatives, and new appealing antimicrobial applications

Glycopeptide antibiotics (GPAs) are a family of non-ribosomal peptide natural products with polypeptide skeleton characteristics, which are considered the last resort for treating severe infections caused by multidrug-resistant Gram-positive pathogens. Over the past few years, an increasing prevalence of Gram-positive resistant strain "superbugs" has emerged. Therefore, more efforts are needed to study and modify the GPAs to overcome the challenge of superbugs. In this mini-review, we provide an overview of the complex biosynthetic gene clusters (BGCs), the ingenious crosslinking and tailoring modifications, the new GPA derivatives, the discoveries of new natural GPAs, and the new applications of GPAs in antivirus and anti-Gram-negative bacteria. With the development and interdisciplinary integration of synthetic biology, next-generation sequencing (NGS), and artificial intelligence (AI), more GPAs with new chemical structures and action mechanisms will constantly be emerging.

Heterologous Expression Reveals Ancient Properties of Tei3—A VanS Ortholog from the Teicoplanin Producer Actinoplanes teichomyceticus

Glycopeptide antibiotics (GPAs) are among the most clinically successful antimicrobials. GPAs inhibit cell-wall biosynthesis in Gram-positive bacteria via binding to lipid II. Natural GPAs are produced by various actinobacteria. Being themselves Gram-positives, the GPA producers evolved sophisticated mechanisms of self-resistance to avoid suicide during antibiotic production. These self-resistance genes are considered the primary source of GPA resistance genes actually spreading among pathogenic enterococci and staphylococci. The GPA-resistance mechanism in Actinoplanes teichomyceticus—the producer of the last-resort-drug teicoplanin—has been intensively studied in recent years, posing relevant questions about the role of Tei3 sensor histidine kinase. In the current work, the molecular properties of Tei3 were investigated. The setup of a GPA-responsive assay system in the model Streptomyces coelicolor allowed us to demonstrate that Tei3 functions as a non-inducible kinase, conferring high levels of GPA resistance in A. teichomyceticus. The expression of different truncated versions of tei3 in S. coelicolor indicated that both the transmembrane helices of Tei3 are crucial for proper functioning. Finally, a hybrid gene was constructed, coding for a chimera protein combining the Tei3 sensor domain with the kinase domain of VanS, with the latter being the inducible Tei3 ortholog from S. coelicolor. Surprisingly, such a chimera did not respond to teicoplanin, but indeed to the related GPA A40926. Coupling these experimental results with a further in silico analysis, a novel scenario on GPA-resistance and biosynthetic genes co-evolution in A. teichomyceticus was hereby proposed.

Undesired Effect of Vancomycin Prolonged Treatment: Enhanced Biofilm Production of the Nosocomial Pathogen Candida auris

Fungal infections are often consequent to prolonged antibiotic treatments. Vancomycin (Van) is the first-choice antibiotic in the treatment of Staphylococcus aureus infections associated with colonization of catheter surfaces. We demonstrate the direct effect of Van in promoting the formation of the biofilm of the emergent yeast pathogen Candida auris, developed in the conventional polystyrene microwell plate model, as well as on silicone surfaces (22 and 28% increase in total biomass, respectively) and on an S. aures biofilm, residual after vancomycin treatment, where C. auris achieved 99% of the mixed biofilm population. The effect of Van was assessed also in vivo, in the Galleria mellonella infection model, which showed higher mortality when infected with the yeast pathogen in the presence of the antibiotic. This evidence enhances awareness of the potential risk associated with prolonged antibiotic use in promoting fungal infections.

Vibrational Optical Activity Study of Four Antibiotic (Lipo)glycopeptides: Vancomycin, Oritavancin, Dalbavancin, and Teicoplanin

The antibiotic glycopeptide class, of which vancomycin is the original compound, has received due attention over the past few decades in search of antibiotics to overcome resistances developed by bacteria. Crucial for the understanding and further development of glycopeptides that possess desired antibacterial effects is the determination of their conformational behavior, as this sheds light on the mechanism of action of the compound. Among others, vibrational optical activity (VOA) techniques (vibrational circular dichroism and Raman optical activity) can be deployed for this, but the question remains to what extent these spectroscopic techniques can provide information concerning the molecular class under investigation. This contribution takes the last hurdle in the search for the capabilities of the VOA techniques in the conformational analysis of the antibiotic glycopeptide class by extending research that was previously conducted for vancomycin toward its three derivatives: oritavancin, dalbavancin, and teicoplanin. The principal information that can be drawn from VOA spectra is the conformation of the rigid cyclic parts of the glycopeptides and the aromatic rings that are part hereof. The addition or removal of carbohydrates does not induce noticeable VOA spectral responses, preventing the determination of the conformation they adopt.

Synthesis of an amphiphilic vancomycin aglycone derivative inspired by polymyxins: overcoming glycopeptide resistance in Gram-positive and Gram-negative bacteria in synergy with teicoplanin in vitro

Gram-negative bacteria possess intrinsic resistance to glycopeptide antibiotics so these important antibacterial medications are only suitable for the treatment of Gram-positive bacterial infections. At the same time, polymyxins are peptide antibiotics, structurally related to glycopeptides, with remarkable activity against Gram-negative bacteria. With the aim of breaking the intrinsic resistance of Gram-negative bacteria against glycopeptides, a polycationic vancomycin aglycone derivative carrying an n-decanoyl side chain and five aminoethyl groups, which resembles the structure of polymyxins, was prepared. Although the compound by itself was not active against the Gram-negative bacteria tested, it synergized with teicoplanin against Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii, and it was able to potentiate vancomycin against these Gram-negative strains. Moreover, it proved to be active against vancomycin- and teicoplanin-resistant Gram-positive bacteria.