Mechanism of action of oritavancin and related glycopeptide antibiotics

A classic antibiotic reimagined: Rationally designed bacitracin variants exhibit potent activity against vancomycin-resistant pathogens

Bacitracin is a macrocyclic peptide antibiotic that is widely used as a topical treatment for infections caused by gram-positive bacteria. Mechanistically, bacitracin targets bacteria by specifically binding to the phospholipid undecaprenyl pyrophosphate (C55PP), which plays a key role in the bacterial lipid II cycle. Recent crystallographic studies have shown that when bound to C55PP, bacitracin adopts a highly ordered amphipathic conformation. In doing so, all hydrophobic side chains align on one face of the bacitracin-C55PP complex, presumably interacting with the bacterial cell membrane. These insights led us to undertake structure-activity investigations into the individual contribution of the nonpolar amino acids found in bacitracin. To achieve this we designed, synthesized, and evaluated a series of bacitracin analogues, a number of which were found to exhibit significantly enhanced antibacterial activity against clinically relevant, drug-resistant pathogens. As for the natural product, these next-generation bacitracins were found to form stable complexes with C55PP. The structure-activity insights thus obtained serve to inform the design of C55PP-targeting antibiotics, a key and underexploited antibacterial strategy.

Rational construction of a high-quality and high-efficiency biosynthetic system and fermentation optimization for A82846B based on combinatorial strategies in Amycolatopsis orientalis

BACKGROUND

Oritavancin is a new generation of semi-synthetic glycopeptide antibiotics against Gram-positive bacteria, which served as the first and only antibiotic with a single-dose therapeutic regimen to treat ABSSSI. A naturally occurring glycopeptide A82846B is the direct precursor of oritavancin. However, its application has been hampered by low yields and homologous impurities. This study established a multi-step combinatorial strategy to rationally construct a high-quality and high-efficiency biosynthesis system for A82846B and systematically optimize its fermentation process to break through the bottleneck of microbial fermentation production.

RESULTS

Firstly, based on the genome sequencing and analysis, we deleted putative competitive pathways and constructed a better A82846B-producing strain with a cleaner metabolic background, increasing A82846B production from 92 to 174 mg/L. Subsequently, the PhiC31 integrase system was introduced based on the CRISPR-Cas12a system. Then, the fermentation level of A82846B was improved to 226 mg/L by over-expressing the pathway-specific regulator StrR via the constructed PhiC31 system. Furthermore, overexpressing glycosyl-synthesis gene evaE enhanced the production to 332 mg/L due to the great conversion of the intermediate to target product. Finally, the scale-up production of A82846B reached 725 mg/L in a 15 L fermenter under fermentation optimization, which is the highest reported yield of A82846B without the generation of homologous impurities.

CONCLUSION

Under approaches including blocking competitive pathways, inserting site-specific recombination system, overexpressing regulator, overexpressing glycosyl-synthesis gene and optimizing fermentation process, a multi-step combinatorial strategy for the high-level production of A82846B was developed, constructing a high-producing strain AO-6. The combinatorial strategies employed here can be widely applied to improve the fermentation level of other microbial secondary metabolites, providing a reference for constructing an efficient microbial cell factory for high-value natural products.

Case analysis of hepatotoxicity caused by vancomycin

BACKGROUND

Although the correlation between liver toxicity and vancomycin is generally considered low, it has been observed that the use of vancomycin can lead to abnormal liver function indicators, such as elevated aspartate aminotransferase, alanine aminotransferase, alpha fetoprotein, and jaundice. To further understand the clinical features associated with vancomycin-induced liver toxicity and to provide clinical guidance, we conducted an analysis of the characteristics and clinical manifestations of vancomycin-induced liver injury.

METHODS

Patients with liver function injury who received vancomycin treatment at the Third Xiangya Hospital of Central South University and Hunan Maternal and Child Health Hospital between 2016 and 2021 were selected for retrospective analysis of their general characteristics, vancomycin course, dose, liver function index, severity of liver injury, and concomitant medications.

RESULTS

Of the 4562 patients who received vancomycin, 17 patients were finally included, with an incidence rate of 0.37%. Of these patients, 12 were male (70.6%) and 5 were female (29.4%), ranging in age from 17 to 84 years with a mean average age of 45.41 ± 20.405 years. All patients were evaluated using Naranjo's score, with score ≥ 3. The dosage, time, and plasma concentration of vancomycin were analyzed and it was found that nine patients (52.94%) had abnormal liver function when initially given a dose of 1 g every 12 hours. In total, 14 patients (82.35%) with liver injury were taking vancomycin in combination with two to four drugs, and severe liver injury occurred in patients taking vancomycin in combination with two drugs. The occurrence time of liver injury was 2-12 days after starting vancomycin, with a mean of 4.53 ± 2.401 days. Of these patients, 16 patients (94.1%) showed liver function abnormalities within 7 days of taking the drug, and 2 patients with grade 3-4 liver injury both showed liver function abnormalities within 3 days of taking the drug. Only 4 of the 17 patients (23.53%) had vancomycin blood concentrations within the normal range, and there was no correlation found between blood concentration and severity of liver injury. Analysis of the correlation between the severity of liver injury and vancomycin showed that none of the patients had allergies such as rash, two patients (11.76%) had jaundice, and fatigue occurred in five patients (29.41%). The remaining ten patients (58.82%) had no symptoms related to liver injury. All 17 patients had abnormal aspartate aminotransferase/alanine aminotransferase levels and 9 patients also had abnormal bilirubin levels. In 15 patients (88.24%), the severity of liver injury was grade 1, indicating mild liver injury, and no correlation was observed between the severity of liver injury and creatinine. Of the 17 patients, 1 patient received no intervention, 4 patients stopped taking vancomycin after developing liver injury, 1 patient reduced the dose, and 11 patients (64.7%) were treated with hepatic protectant.

CONCLUSION

Although the study concluded that the incidence of liver injury was not high, the liver toxicity of vancomycin should still be considered and liver function indicators should be monitored during the clinical use of vancomycin.

The Clinical Efficacy of Multidose Oritavancin: A Systematic Review

Oritavancin (ORI) is a semisynthetic lipoglycopeptide approved as a single 1200 mg dose intravenous infusion for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) caused by Gram-positive organisms in adults. The pharmacokinetic/pharmacodynamic (PK/PD) linear kinetic profile and long terminal half-life (~393 h) of ORI make it therapeutically attractive for the treatment of other Gram-positive infections for which prolonged therapy is needed. Multidose regimens are adopted in real-world clinical practice with promising results, but aggregated efficacy data are still lacking. A comprehensive search on PubMed/Medline, Scopus, Cochrane and Google Scholar databases was performed to include papers published up to the end of January 2023. All articles on ORI multiple doses usage, including case reports, with quantitative data and relevant clinical information were included. Two reviewers independently assessed papers against the inclusion/exclusion criteria and for methodological quality. Differences in opinion were adjudicated by a third party. From 1751 potentially relevant papers identified by this search, a total of 16 studies met the inclusion criteria and were processed further in the final data analysis. We extracted data concerning clinical response, bacteriologic response, mortality and adverse events (AEs). From the 16 included papers, 301 cases of treatment with multidose ORIs were identified. Multidose regimens comprised an initial ORI dose of 1200 mg followed by 1200 mg or 800 mg subsequent doses with a varying total number and frequency of reinfusions. The most often treated infections and isolates were osteomyelitis (148; 54.4%), ABSSSI (35; 12.9%) and cellulitis (14; 5.1%); and MRSA (121), MSSA (66), CoNS (17), E. faecalis (13) and E. faecium (12), respectively. Clinical cure and improvement by multidose ORI regimens were observed in 85% (231/272) and 8% (22/272) patients, respectively. Multidose ORI was safe and well tolerated; the most frequent AEs were infusion-related reactions and hypoglycemia. A multidose ORI regimen may be beneficial in treating other Gram-positive infections besides ABSSSIs, with a good safety profile. Further studies are warranted to ascertain the superiority of one multidose ORI scheme or posology over the other.

Tetrachlorovancomycin: Total Synthesis of a Designed Glycopeptide Antibiotic of Reduced Synthetic Complexity

A technically straightforward total synthesis of a new class of vancomycin analogues of reduced synthetic complexity was developed that provided tetrachlorovancomycin (1, LLS = 15 steps, 15% overall yield) and its precursor aglycon 29 (nearly 20% overall yield). The class retains all the intricate vancomycin structural features that contribute to its target binding affinity and selectivity, maintains the antimicrobial activity of vancomycin, and achieves the simplification by an unusual addition, not removal, of benign substituents to the core structure. The modification, accomplished by addition of two aryl chloride substituents to provide 1, permitted a streamlined total synthesis of the new glycopeptide antibiotic class by removing the challenges associated with CD and DE ring system atropisomer stereochemical control. This also enabled their simultaneous and further-activated SNAr macrocyclizations that establish the tricyclic skeleton of 1. Key elements of the approach include catalyst-controlled diastereoselective formation of the AB biaryl axis of chirality (>30:1 dr), an essentially instantaneous macrolactamization of the AB ring system free of competitive epimerization (>30:1 dr), racemization free coupling of the E ring tetrapeptide, room temperature simultaneous CD and DE ring system cyclizations, a highly refined 4-step conversion of the cyclization product to the aglycon, and a protecting-group-free one-pot enzymatic glycosylation for disaccharide introduction. In addition to the antimicrobial evaluation of tetrachlorovancomycin (1), the preparation of key peripherally modified derivatives, which introduce independent and synergistic mechanisms of action, revealed their exceptional antimicrobial potency and provide the foundation for future use of this new class of synthetic glycopeptide analogues.

Nano-Biotechnology for Bacteria Identification and Potent Anti-bacterial Properties: A Review of Current State of the Art

Sepsis is a critical disease caused by the abrupt increase of bacteria in human blood, which subsequently causes a cytokine storm. Early identification of bacteria is critical to treating a patient with proper antibiotics to avoid sepsis. However, conventional culture-based identification takes a long time. Polymerase chain reaction (PCR) is not so successful because of the complexity and similarity in the genome sequence of some bacterial species, making it difficult to design primers and thus less suitable for rapid bacterial identification. To address these issues, several new technologies have been developed. Recent advances in nanotechnology have shown great potential for fast and accurate bacterial identification. The most promising strategy in nanotechnology involves the use of nanoparticles, which has led to the advancement of highly specific and sensitive biosensors capable of detecting and identifying bacteria even at low concentrations in very little time. The primary drawback of conventional antibiotics is the potential for antimicrobial resistance, which can lead to the development of superbacteria, making them difficult to treat. The incorporation of diverse nanomaterials and designs of nanomaterials has been utilized to kill bacteria efficiently. Nanomaterials with distinct physicochemical properties, such as optical and magnetic properties, including plasmonic and magnetic nanoparticles, have been extensively studied for their potential to efficiently kill bacteria. In this review, we are emphasizing the recent advances in nano-biotechnologies for bacterial identification and anti-bacterial properties. The basic principles of new technologies, as well as their future challenges, have been discussed.

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

Structural diversity, biosynthesis, and biological functions of lipopeptides from Streptomyces

Covering: up to 2022Streptomyces are ubiquitous in terrestrial and marine environments, where they display a fascinating metabolic diversity. As a result, these bacteria are a prolific source of active natural products. One important class of these natural products is the nonribosomal lipopeptides, which have diverse biological activities and play important roles in the lifestyle of Streptomyces. The importance of this class is highlighted by the use of related antibiotics in the clinic, such as daptomycin (tradename Cubicin). By virtue of recent advances spanning chemistry and biology, significant progress has been made in biosynthetic studies on the lipopeptide antibiotics produced by Streptomyces. This review will serve as a comprehensive guide for researchers working in this multidisciplinary field, providing a summary of recent progress regarding the investigation of lipopeptides from Streptomyces. In particular, we highlight the structures, properties, biosynthetic mechanisms, chemical and chemoenzymatic synthesis, and biological functions of lipopeptides. In addition, the application of genome mining techniques to Streptomyces that have led to the discovery of many novel lipopeptides is discussed, further demonstrating the potential of lipopeptides from Streptomyces for future development in modern medicine.

Recent Advances in the Development of Semisynthetic Glycopeptide Antibiotics: 2014-2022

The accelerated appearance of drug-resistant bacteria poses an ever-growing threat to modern medicine's capacity to fight infectious diseases. Gram-positive species such as methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae continue to contribute significantly to the global burden of antimicrobial resistance. For decades, the treatment of serious Gram-positive infections relied upon the glycopeptide family of antibiotics, typified by vancomycin, as a last line of defense. With the emergence of vancomycin resistance, the semisynthetic glycopeptides telavancin, dalbavancin, and oritavancin were developed. The clinical use of these compounds is somewhat limited due to toxicity concerns and their unusual pharmacokinetics, highlighting the importance of developing next-generation semisynthetic glycopeptides with enhanced antibacterial activities and improved safety profiles. This Review provides an updated overview of recent advancements made in the development of novel semisynthetic glycopeptides, spanning the period from 2014 to today. A wide range of approaches are covered, encompassing innovative strategies that have delivered semisynthetic glycopeptides with potent activities against Gram-positive bacteria, including drug-resistant strains. We also address recent efforts aimed at developing targeted therapies and advances made in extending the activity of the glycopeptides toward Gram-negative organisms.

Molecular dynamics simulations of the secondary-binding site in disaccharide-modified glycopeptide antibiotics

Oritavancin is a semisynthetic glycopeptide antibiotic used to treat severe infections by multidrug-resistant Gram-positive pathogens. Oritavancin is known to be a thousand times more potent than vancomycin against Gram-positive bacteria due to the additional interactions with bacterial peptidoglycan (PG) facilitated by a secondary-binding site. The presence of this secondary-binding site is evident in desleucyl-oritavancin, an Edman degradation product of oritavancin, still retaining its potency against Gram-positive bacteria, whereas desleucyl-vancomycin is devoid of any antimicrobial activities. Herein, using explicit solvent molecular dynamics (MD) simulations, steered MD simulations, and umbrella sampling, we show evidence of a secondary-binding site mediated by the disaccharide-modified hydrophobic sidechain of oritavancin interactions with the pentaglycyl-bridge segment of the PG. The interactions were characterized through comparison to the interaction of PG with chloroeremomycin, vancomycin, and the desleucyl analogs of the glycopeptides. Our results show that the enhanced binding of oritavancin to PG over the binding of the other complexes studied is due to an increase in the hydrophobic effect, electrostatic and van der Waals interactions, and not the average number of hydrogen bonds. Our ranking of the binding interactions of the biomolecular complexes directly correlates with the order based on their experimental minimum inhibitory concentrations. The results of our simulations provide insight into the modification of glycopeptides to increase their antimicrobial activities or the design of novel antibiotics against pathogenic Gram-positive bacteria.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

Mycobacterial Membranes as Actionable Targets for Lipid-Centric Therapy in Tuberculosis

Infectious diseases remain significant health concerns worldwide, and resistance is particularly common in patients with tuberculosis caused by Mycobacterium tuberculosis. The development of anti-infectives with novel modes of action may help overcome resistance. In this regard, membrane-active agents, which modulate membrane components essential for the survival of pathogens, present attractive antimicrobial agents. Key advantages of membrane-active compounds include their ability to target slow-growing or dormant bacteria and their favorable pharmacokinetics. Here, we comprehensively review recent advances in the development of membrane-active chemotypes that target mycobacterial membranes and discuss clinically relevant membrane-active antibacterial agents that have shown promise in counteracting bacterial infections. We discuss the relationship between the membrane properties and the synthetic requirements within the chemical scaffold, as well as the limitations of current membrane-active chemotypes. This review will lay the chemical groundwork for the development of membrane-active antituberculosis agents and will foster the discovery of more effective antitubercular agents.

The First Dimeric Derivatives of the Glycopeptide Antibiotic Teicoplanin

Various dimeric derivatives of the glycopeptide antibiotic teicoplanin were prepared with the aim of increasing the activity of the parent compound against glycopeptide-resistant bacteria, primarily vancomycin-resistant enterococci. Starting from teicoplanin, four covalent dimers were prepared in two orientations, using an α,ω-bis-isothiocyanate linker. Formation of a dimeric cobalt coordination complex of an N-terminal L-histidyl derivative of teicoplanin pseudoaglycone has been detected and its antibacterial activity evaluated. The Co(III)-induced dimerization of the histidyl derivative was demonstrated by DOSY experiments. Both the covalent and the complex dimeric derivatives showed high activity against VanA teicoplanin-resistant enterococci, but their activity against other tested bacterial strains did not exceed that of the monomeric compounds.

Cyclic peptide drugs approved in the last two decades (2001-2021)

In contrast to the major families of small molecules and antibodies, cyclic peptides, as a family of synthesizable macromolecules, have distinct biochemical and therapeutic properties for pharmaceutical applications. Cyclic peptide-based drugs have increasingly been developed in the past two decades, confirming the common perception that cyclic peptides have high binding affinities and low metabolic toxicity as antibodies, good stability and ease of manufacture as small molecules. Natural peptides were the major source of cyclic peptide drugs in the last century, and cyclic peptides derived from novel screening and cyclization strategies are the new source. In this review, we will discuss and summarize 18 cyclic peptides approved for clinical use in the past two decades to provide a better understanding of cyclic peptide development and to inspire new perspectives. The purpose of the present review is to promote efforts to resolve the challenges in the development of cyclic peptide drugs that are more effective.

Photodynamic inactivation (PDI) as a promising alternative to current pharmaceuticals for the treatment of resistant microorganisms

Although the whole world is currently observing the global battle against COVID-19, it should not be underestimated that in the next 30 years, approximately 10 million people per year could be exposed to infections caused by multi-drug resistant bacteria. As new antibiotics come under pressure from unpredictable resistance patterns and relegation to last-line therapy, immediate action is needed to establish a radically different approach to countering resistant microorganisms. Among the most widely explored alternative methods for combating bacterial infections are metal complexes and nanoparticles, often in combination with light, but strategies using monoclonal antibodies and bacteriophages are increasingly gaining acceptance. Photodynamic inactivation (PDI) uses light and a dye termed a photosensitizer (PS) in the presence of oxygen to generate reactive oxygen species (ROS) in the field of illumination that eventually kill microorganisms. Over the past few years, hundreds of photomaterials have been investigated, seeking ideal strategies based either on single molecules (e.g., tetrapyrroles, metal complexes) or in combination with various delivery systems. The present work describes some of the most recent advances of PDI, focusing on the design of suitable photosensitizers, their formulations, and their potential to inactivate bacteria, viruses, and fungi. Particular attention is focused on the compounds and materials developed in our laboratories that are capable of killing in the exponential growth phase (up to seven logarithmic units) of bacteria without loss of efficacy or resistance, while being completely safe for human cells. Prospectively, PDI using these photomaterials could potentially cure infected wounds and oral infections caused by various multidrug-resistant bacteria. It is also possible to treat the surfaces of medical equipment with the materials described, in order to disinfect them with light, and reduce the risk of nosocomial infections.

Long-Acting Lipoglycopeptides Can Interfere With Vancomycin Therapeutic Drug Monitoring

Oritavancin and dalbavancin are long-acting lipoglycopeptides with activity against susceptible gram-positive bacteria, including methicillin-resistant Staphylococcus aureus. Though similar in structure to traditional glycopeptide antibiotics like vancomycin, these antibiotics have terminal half-lives >10 days, and, as a result, there is potential for administration of vancomycin to a patient while oritavancin or dalbavancin are still appreciably present in serum. Given the structural similarities, this creates an opportunity for lab assay interference when performing therapeutic drug monitoring for vancomycin. Following higher-than-expected serum vancomycin concentrations in a patient who received both oritavancin and vancomycin within a short time frame, we evaluated the potential for lipoglycopeptide interference with clinical vancomycin assays. Five platforms covering 3 immunoassay technologies were used to quantify vancomycin concentrations in serum spiked with oritavancin or dalbavancin. Oritavancin generated spurious vancomycin concentrations (20%-84% increase) in both enzyme-multiplied immunoassay technique and a particle-enhanced turbidimetric inhibition immunoassay. However, the improper detection of oritavancin was not consistent across all particle-enhanced turbidimetric inhibition immunoassay platforms. Dalbavancin interference was not detected on any of the platforms tested. The interference from oritavancin may result in falsely elevated vancomycin concentrations and, subsequently, inappropriately adjusted vancomycin doses.

Alkyl-Aryl-Vancomycins: Multimodal Glycopeptides with Weak Dependence on the Bacterial Metabolic State

Resistance to last-resort antibiotics such as vancomycin for Gram-positive bacterial infections necessitates the development of new therapeutics. Furthermore, the ability of bacteria to survive antibiotic therapy through formation of biofilms and persister cells complicates treatment. Toward this, we report alkyl-aryl-vancomycins (AAVs), with high potency against vancomycin-resistant enterococci and staphylococci. Unlike vancomycin, the lead compound AAV-qC10 was bactericidal and weakly dependent on bacterial metabolism. This resulted in complete eradication of non-growing cells of MRSA and disruption of its biofilms. In addition to inhibiting cell wall biosynthesis like vancomycin, AAV-qC10 also depolarizes and permeabilizes the membrane. More importantly, the compound delocalized the cell division protein MinD, thereby impairing bacterial growth through multiple pathways. The potential of AAV-qC10 is exemplified by its superior efficacy against MRSA in a murine thigh infection model as compared to vancomycin. This work paves the way for structural optimization and drug development for combating drug-resistant bacterial infections.

Aminoalkylamides of Eremomycin Exhibit an Improved Antibacterial Activity

After decades, the glycopeptide vancomycin is still the preferred antibiotic against resistant strains of Gram-positive bacteria. Although its clinical use is strictly regulated, the gradual spread of vancomycin-resistant bacteria, such as glycopeptide-resistant and glycopeptide-intermediate Staphylococcus aureus and vancomycin-resistant Enterococcus spp., is a serious health problem. Based on the literature data and previous studies, our main goal was to assess the antimicrobial potential and to study the structure-activity relationship of new eremomycin aminoalkylamides. We designed and synthesized a series of new eremomycin amides in which eremomycin is conjugated with a hydrophobic arylalkyl group via an alkylenediamine spacer, and tested their antibacterial activities on a panel of Gram-positive strains that were sensitive and resistant to a "gold-standard" vancomycin. Based on the data obtained, the structure-activity relationships were investigated, and a lead compound was selected for in-depth testing. Research carried out using an in vivo model of staphylococcus sepsis, acute toxicity studies, and the estimated therapeutic index also showed the advantage of the selected eremomycin amide derivative in particular, as well as the chosen direction in general.

A synergistic antibacterial platform: combining mechanical and photothermal effects based on Van-MoS2-Au nanocomposites

Herein, we successfully developed a new multifunctional antibacterial system, which combined mechano-bactericidal (Au-nanostars) and photothermal (MoS₂) mechanism. Meanwhile, the targeting molecule of vancomycin was modified on the surface of MoS₂-Au nanocomposites (Van-MoS₂-Au), that generally yield high efficiency in antibacterial performance due to their effective working radii. Van-MoS₂-Au nanocomposites were capable of completely destroying both gram-negative (E. coli) and gram-positive (B. subtilis) bacteria under 808 NIR laser irradiation for 20 min, and nearly no bacterial growth was detected after 12 h incubation. Moreover, these nanocomposites could destruct the refractory biofilm as well, which was a much more difficult medical challenge. The new antibacterial nanomaterials might offer many biomedical applications because of the biocompatibility and strong antibacterial ability.

Bacterial Cell Wall Analogue Peptides Control the Oligomeric States and Activity of the Glycopeptide Antibiotic Eremomycin: Solution NMR and Antimicrobial Studies

For some time, glycopeptide antibiotics have been considered the last line of defense against Methicillin-resistant Staphylococcus aureus (MRSA). However, vancomycin resistance of Gram-positive bacteria is an increasingly emerging worldwide health problem. The mode of action of glycopeptide antibiotics is essentially the binding of peptidoglycan cell-wall fragments terminating in the d-Ala-d-Ala sequence to the carboxylate anion binding pocket of the antibiotic. Dimerization of these antibiotics in aqueous solution was shown to persist and even to enhance the antibacterial effect in a co-operative manner. Some works based on solid state (ss) Nuclear Magnetic Resonance (NMR) studies questioned the presence of dimers under the conditions of ssNMR while in a few cases, higher-order oligomers associated with contiguous back-to-back and face-to-face dimers were observed in the crystal phase. However, it is not proved if such oligomers persist in aqueous solutions. With the aid of ¹⁵N-labelled eremomycin using ¹⁵N relaxation and diffusion NMR methods, we observed tetramers and octamers when the N-Ac-d-Ala-d-Ala dipeptide was added. To the contrary, the N-Ac-d-Ala or (N-Ac)₂-l-Lys-d-Ala-d-Ala tripeptide did not induce higher-order oligomers. These observations are interesting examples of tailored supramolecular self-organization. New antimicrobial tests have also been carried out with these self-assemblies against MRSA and VRE (resistant) strains.

Attenuating the Selection of Vancomycin Resistance Among Enterococci through the Development of Peptide-Based Vancomycin Antagonists

The emergence and spread of multidrug resistant (MDR) pathogens with acquired resistance to almost all available antimicrobial agents has severely threatened the international healthcare community over the last two decades. The last resort antibiotic vancomycin is critical for treatment of several of these pathogens; howeverc vancomycin resistance is spreading due to the undesired accumulation of IV vancomycin in the colon post-treatment. This accumulation exerts selective pressure upon members of the colonic microflora, including Enterococci, which possess vancomycin resistance genes. To ensure the continual effectiveness of vancomycin in the clinical setting by preventing the spread of antibiotic resistance, it is crucial to develop strategies that reduce selective pressure on the colonic microflora while allowing vancomycin to maintain its desired activity at the site of infection. Herein we report that modification of the native l-Lys-d-Ala-d-Ala vancomycin binding site can be used to produce peptides with the ability to competitively bind vancomycin, reducing its activity against susceptible Enterococci. Moreover, several modifications to the N-termini of the native tripeptide have produced compounds with enhanced vancomycin binding activity, including several analogs that were designed to covalently bind vancomycin, thereby acting as suicide inhibitors. Finally, in a mixed culture of susceptible and resistant bacteria, a single lead compound was found to protect high ratios of susceptible bacteria from vancomycin over the course of a week-long period, preventing the selection for vancomycin-resistant Enterococci. These findings demonstrate the ability of these peptides as potential therapeutic adjuvants for counteracting the undesired accumulation of colonic vancomycin, allowing for protection of the colonic microflora.

Tackling Antibiotic Resistance with Compounds of Natural Origin: A Comprehensive Review

Drug-resistant bacteria pose a serious threat to human health worldwide. Current antibiotics are losing efficacy and new antimicrobial agents are urgently needed. Living organisms are an invaluable source of antimicrobial compounds. The antimicrobial activity of the most representative natural products of animal, bacterial, fungal and plant origin are reviewed in this paper. Their activity against drug-resistant bacteria, their mechanisms of action, the possible development of resistance against them, their role in current medicine and their future perspectives are discussed. Electronic databases such as PubMed, Scopus and ScienceDirect were used to search scientific contributions until September 2020, using relevant keywords. Natural compounds of heterogeneous origins have been shown to possess antimicrobial capabilities, including against antibiotic-resistant bacteria. The most commonly found mechanisms of antimicrobial action are related to protein biosynthesis and alteration of cell walls and membranes. Various natural compounds, especially phytochemicals, have shown synergistic capacity with antibiotics. There is little literature on the development of specific resistance mechanisms against natural antimicrobial compounds. New technologies such as -omics, network pharmacology and informatics have the potential to identify and characterize new natural antimicrobial compounds in the future. This knowledge may be useful for the development of future therapeutic strategies.

Synthesis of Antiviral Perfluoroalkyl Derivatives of Teicoplanin and Vancomycin

The limited scope of antiviral drugs and increasing problem of antiviral drug resistance represent a global health threat. Glycopeptide antibiotics and their lipophilic derivatives have emerged as relevant inhibitors of diverse viruses. Herein, we describe a new strategy for the synthesis of dual hydrophobic and lipophobic derivatives of glycopeptides to produce selective antiviral agents without membrane-disrupting activity. Perfluorobutyl and perfluorooctyl moieties were attached through linkers of different length to azido derivatives of vancomycin aglycone and teicoplanin pseudoaglycone, and the new derivatives were evaluated against a diverse panel of viruses. The teicoplanin derivatives displayed strong anti-influenza virus activity at nontoxic concentrations. Some of the perfluoroalkylated glycopeptides were also active against a few other viruses such as herpes simplex virus or coronavirus. These data encourage further exploration of glycopeptide analogues for broad antiviral application.

Combinations of (lipo)glycopeptides with β-lactams against MRSA: susceptibility insights

Background

Increasing application of vancomycin due to the high prevalence of MRSA infections has led to the emergence of vancomycin intermediate-resistant Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA). Consequently, the need for alternative therapies that target MRSA has become evident.

Objectives

To evaluate the synergy between (lipo)glycopeptides (LGP/GPs) (vancomycin, teicoplanin, telavancin, dalbavancin and oritavancin) and β-lactams (ceftaroline, cefepime, cefazolin and oxacillin) against MRSA, hVISA, VISA and daptomycin non-susceptible (DNS) phenotypes.

Methods

Twenty randomly selected clinical MRSA strains (i.e. 5 MRSA, 5 hVISA, 5 VISA and 5 DNS) were assessed versus LGP/GPs alone and LGP/GPs in combination with β-lactams for MICs. Although verification of antibiotic potency against bacterial strains is assessed by the microbroth dilution (MBD) MIC method recommended by the CLSI, some antibiotics need modified assay conditions in order to demonstrate their optimal activity.

Results

Addition of β-lactams reduced MIC values of LGP/GPs against all strains (up to 160-fold reduction). In general, LGPs (dalbavancin, oritavancin and telavancin) were more active (significant differences in MIC values, up to 8-fold) compared with vancomycin and teicoplanin. The majority of these combinations were bactericidal and superior to any single agent.

Conclusions

This report has examined the susceptibility patterns of LGP/GPs and their combination with β-lactams. Of interest, the impact of susceptibility tests (in terms of MIC plates and their surface area) on the synergistic activity in 24 h time–kill experiments was apparent for LGPs. Further clinical research is required to investigate synergy with LGP/GPs and β-lactams against these Staphylococcus strains.

Antimicrobial peptides: new hope in the war against multidrug resistance

The discovery of antibiotics marked a golden age in the revolution of human medicine. However, decades later, bacterial infections remain a global healthcare threat, and a return to the pre-antibiotic era seems inevitable if stringent measures are not adopted to curb the rapid emergence and spread of multidrug resistance and the indiscriminate use of antibiotics. In hospital settings, multidrug resistant (MDR) pathogens, including carbapenem-resistant Pseudomonas aeruginosa, vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamases (ESBL) bearing Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae are amongst the most problematic due to the paucity of treatment options, increased hospital stay, and exorbitant medical costs. Antimicrobial peptides (AMPs) provide an excellent potential strategy for combating these threats. Compared to empirical antibiotics, they show low tendency to select for resistance, rapid killing action, broad-spectrum activity, and extraordinary clinical efficacy against several MDR strains. Therefore, this review highlights multidrug resistance among nosocomial bacterial pathogens and its implications and reiterates the importance of AMPs as next-generation antibiotics for combating MDR superbugs.

C1-CBP-vancomycin: Impact of a Vancomycin C-Terminus Trimethylammonium Cation on Pharmacological Properties and Insights into Its Newly Introduced Mechanism of Action

C1-CBP-vancomycin (3) was examined alongside CBP-vancomycin for susceptibility to acquired resistance upon serial exposure against two vancomycin-resistant enterococci strains where its activity proved more durable and remarkably better than many current therapies. Combined with earlier studies, this observation confirmed an added mechanism of action was introduced by incorporation of the trimethylammonium cation and that C1-CBP-vancomycin exhibits activity against vancomycin-resistant organisms through two synergistic mechanisms of action, both independent of d-Ala-d-Ala/d-Lac binding. New insights into this added mechanism of action, induced cell membrane permeabilization, can be inferred from studies that show added exogenous lipoteichoic acid reduces antimicrobial activity, rescues bacteria cell growth inhibition, and blocks induced cell permeabilization properties of C1-CBP-vancomycin, suggesting a direct binding interaction with embedded teichoic acid is responsible for the added mechanism of action and enhanced antimicrobial activity. Further studies indicate that the trimethylammonium cation does not introduce new liabilities in common pharmacological properties of the analogue and established that 3 is well tolerated in mice, displays substantial PK improvements over both vancomycin and CBP-vancomycin, and exhibits in vivo efficacy against a challenging multidrug-resistant and vancomycin-resistant S. aureus strain that is representative of the resistant pathogens all fear will emerge in the general population.

The Continuing Threat of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus has been an exceptionally successful pathogen, which is still relevant in modern age-medicine due to its adaptability and tenacity. This bacterium may be a causative agent in a plethora of infections, owing to its abundance (in the environment and in the normal flora) and the variety of virulence factors that it possesses. Methicillin-resistant S. aureus (MRSA) strains—first described in 1961—are characterized by an altered penicillin-binding protein (PBP2a/c) and resistance to all penicillins, cephalosporins, and carbapenems, which makes the β-lactam armamentarium clinically ineffective. The acquisition of additional resistance determinants further complicates their eradication; therefore, MRSA can be considered as the first representative of multidrug-resistant bacteria. Based on 230 references, the aim of this review is to recap the history, the emergence, and clinical features of various MRSA infections (hospital-, community-, and livestock-associated), and to summarize the current advances regarding MRSA screening, typing, and therapeutic options (including lipoglycopeptides, oxazolidinones, anti-MRSA cephalosporins, novel pleuromutilin-, tetracycline- and quinolone-derivatives, daptomycin, fusidic acid, in addition to drug candidates in the development phase), both for an audience of clinical microbiologists and infectious disease specialists.

Synthesis and evaluation of new quinazolin-4(3H)-one derivatives as potent antibacterial agents against multidrug resistant Staphylococcus aureus and Mycobacterium tuberculosis

Staphylococcus aureus and Mycobacterium tuberculosis are major causative agents responsible for serious nosocomial and community-acquired infections impacting healthcare systems globally. Over several decades, these pathogens have developed resistance to multiple antibiotics significantly affecting morbidity and mortality. Thus, these recalcitrant pathogens are amongst the most formidable microbial pathogens for which international healthcare agencies have mandated active identification and development of new antibacterial agents for chemotherapeutic intervention. In our present work, a series of new quinazolin-4(3H)-one derivatives were designed, synthesized and evaluated for their antibacterial activity against ESKAP pathogens and pathogenic mycobacteria. The experiments revealed that 4'c, 4'e, 4'f and 4'h displayed selective and potent inhibitory activity against Staphylococcus aureus with MIC values ranging from 0.03-0.25 μg/mL. Furthermore, compounds 4'c and 4'e were found to be benign to Vero cells (CC₅₀ = >5 μg/mL) and displayed promising selectivity index (SI) > 167 and > 83.4 respectively. Additionally, 4'c and 4'e demonstrated equipotent MIC against multiple drug-resistant strains of S. aureus including VRSA, concentration dependent bactericidal activity against S. aureus and synergized with FDA approved drugs. Moreover, compound 4'c exhibited more potent activity in reducing the biofilm and exhibited a PAE of ∼2 h at 10X MIC which is comparable to levofloxacin and vancomycin. In vivo efficacy of 4'c in murine neutropenic thigh infection model revealed that 4'c caused a similar reduction in cfu as vancomycin. Gratifyingly, compounds 4d, 4e, 9a, 9b, 14a, 4'e and 4'f also exhibited anti-mycobacterial activity with MIC values in the range of 2-16 μg/mL. In addition, the compounds were found to be less toxic to Vero cells (CC₅₀ = 12.5->100 μg/mL), thus displaying a favourable selectivity index. The interesting results obtained here suggest the potential utilization of these new quinazolin-4(3H)-one derivatives as promising antibacterial agents for treating MDR-Staphylococcal and mycobacterial infections.

Toward Single-Peak Dalbavancin Analogs through Biology and Chemistry

Glycopeptide antibiotics are used to treat severe multidrug resistant infections caused by Gram-positive bacteria. Dalbavancin is a second generation glycopeptide approved for human use, which is obtained from A40926, a lipoglycopeptide produced by Nonomuraea sp. ATCC39727 as a mixture of biologically active congeners mainly differing in the fatty acid chains present on the glucuronic moiety. In this study, we constructed a double mutant of the A40926 producer strain lacking dbv23, and thus defective in mannose acetylation, a feature that increases A40926 production, and lacking the acyltransferases Dbv8, and thus incapable of installing the fatty acid chains. The double mutant afforded the desired deacyl, deacetyl A40926 intermediates, which could be converted by chemical reacylation yielding A40926 analogs with a greatly reduced number of congeners. The newly acylated analogs could then be transformed into dalbavancin analogs possessing the same in vitro properties as the approved drug.

Synthesis and Medicinal Chemistry of Muraymycins, Nucleoside Antibiotics

Muraymycins, isolated from a culture broth of Streptomyces sp., are members of a class of naturally occurring nucleoside antibiotics. They are strong inhibitors of the phospho-MurNAc-pentapeptide translocase (MraY), which is responsible for the peptidoglycan biosynthesis. Since MraY is an essential enzyme among bacteria, muraymycins are expected to be a novel antibacterial agent. In this review, our efforts to synthesize muraymycin D2, simplify the chemical structure, improve antibacterial spectrum, and solve the X-ray crystal structure of the muraymycin D2/MraY complex are described.

Magnetic Nanoconjugated Teicoplanin: A Novel Tool for Bacterial Infection Site Targeting

Nanoconjugated antibiotics can be regarded as next-generation drugs as they possess remarkable potential to overcome multidrug resistance in pathogenic bacteria. Iron oxide nanoparticles (IONPs) have been extensively used in the biomedical field because of their biocompatibility and magnetic properties. More recently, IONPs have been investigated as potential nanocarriers for antibiotics to be magnetically directed to/recovered from infection sites. Here, we conjugated the “last-resort” glycopeptide antibiotic teicoplanin to IONPs after surface functionalization with (3-aminopropyl) triethoxysilane (APTES). Classical microbiological methods and fluorescence and electron microscopy analysis were used to compare antimicrobial activity and surface interactions of naked IONPs, amino-functionalized NPs (NP-APTES), and nanoconjugated teicoplanin (NP-TEICO) with non-conjugated teicoplanin. As bacterial models, differently resistant strains of three Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis, and Bacillus subtilis) and a Gram-negative representative (Escherichia coli) were used. The results indicated that teicoplanin conjugation conferred a valuable and prolonged antimicrobial activity to IONPs toward Gram-positive bacteria. No antimicrobial activity was detected using NP-TEICO toward the Gram-negative E. coli. Although IONPs and NP-APTES showed only insignificant antimicrobial activity in comparison to NP-TEICO, our data indicate that they might establish diverse interaction patterns at bacterial surfaces. Sensitivity of bacteria to NPs varied according to the surface provided by the bacteria and it was species specific. In addition, conjugation of teicoplanin improved the cytocompatibility of IONPs toward two human cell lines. Finally, NP-TEICO inhibited the formation of S. aureus biofilm, conserving the activity of non-conjugated teicoplanin versus planktonic cells and improving it toward adherent cells.

Oritavancin Retains a High Affinity for a Vancomycin-Resistant Cell-Wall Precursor via Its Bivalent Motifs of Interaction

Despite its potent antibacterial activities against drug-resistant Gram-positive pathogens, oritavancin remains partially understood with respect to its primary mode of hydrogen bond interaction with a cell-wall peptide regarding the role of its lipophilic 4'-chlorobiphenyl moiety. Here we report a surface plasmon resonance (SPR) study performed in two cell-wall model surfaces, each prepared by immobilization with a vancomycin-susceptible Lys-d-Ala-d-Ala or vancomycin-resistant Lys-d-Ala-d-Lac peptide. Analysis of binding kinetics performed on the peptide surface showed that oritavancin bound ∼100-1000-fold more tightly than vancomycin on each model surface. Ligand competition experiments conducted by SPR and fluorescence spectroscopy provided evidence that such affinity enhancement can be attributed to its 4'-chlorobiphenyl moiety, possibly through a hydrophobic interaction that led to a gain of free energy with a contribution from enthalpy as suggested by a variable-temperature SPR experiment. On the basis of these findings, we propose a model for the bivalent motifs of interaction of oritavancin with cell-wall peptides, by which the drug molecule can retain a strong interaction even with the vancomycin-resistant peptide. In summary, this study advances our understanding of oritavancin and offers new insight into the significance of bivalent motifs in the design of glycopeptide antibiotics.

Specificity of Induction of Glycopeptide Antibiotic Resistance in the Producing Actinomycetes

Glycopeptide antibiotics are drugs of last resort for treating severe infections caused by Gram-positive pathogens. It is widely believed that glycopeptide-resistance determinants (van genes) are ultimately derived from the producing actinomycetes. We hereby investigated the relationship between the antimicrobial activity of vancomycin and teicoplanins and their differential ability to induce van gene expression in Actinoplanes teichomyceticus—the producer of teicoplanin—and Nonomuraea gerenzanensis—the producer of the teicoplanin-like A40926. As a control, we used the well-characterized resistance model Streptomyces coelicolor. The enzyme activities of a cytoplasmic-soluble d,d-dipeptidase and of a membrane-associated d,d-carboxypeptidase (corresponding to VanX and VanY respectively) involved in resistant cell wall remodeling were measured in the actinomycetes grown in the presence or absence of subinhibitory concentrations of vancomycin, teicoplanin, and A40926. Results indicated that actinomycetes possess diverse self-resistance mechanisms, and that each of them responds differently to glycopeptide induction. Gene swapping among teicoplanins-producing actinomycetes indicated that cross-talking is possible and provides useful information for predicting the evolution of future resistance gene combinations emerging in pathogens.

Old and new glycopeptide antibiotics: From product to gene and back in the post-genomic era

Glycopeptide antibiotics are drugs of last resort for treating severe infections caused by multi-drug resistant Gram-positive pathogens. First-generation glycopeptides (vancomycin and teicoplanin) are produced by soil-dwelling actinomycetes. Second-generation glycopeptides (dalbavancin, oritavancin, and telavancin) are semi-synthetic derivatives of the progenitor natural products. Herein, we cover past and present biotechnological approaches for searching for and producing old and new glycopeptide antibiotics. We review the strategies adopted to increase microbial production (from classical strain improvement to rational genetic engineering), and the recent progress in genome mining, chemoenzymatic derivatization, and combinatorial biosynthesis for expanding glycopeptide chemical diversity and tackling the never-ceasing evolution of antibiotic resistance.

Novel Miniature Membrane Active Lipopeptidomimetics against Planktonic and Biofilm Embedded Methicillin-Resistant Staphylococcus aureus

Escalating multidrug resistance and highly evolved virulence mechanisms have aggravated the clinical menace of methicillin-resistant Staphylococcus aureus (MRSA) infections. Towards development of economically viable staphylocidal agents here we report eight structurally novel tryptophan-arginine template based peptidomimetics. Out of the designed molecules, three lipopeptidomimetics (S-6, S-7 and S-8) containing 12-amino dodecanoic acid exhibited cell selectivity and good to potent activity against clinically relevant pathogens MRSA, methicillin-resistant Staphylococcus epidermidis and vancomycin-resistant Enterococcus faecium (MIC: 1.4–22.7 μg/mL). Mechanistically, the active peptidomimetics dissipated membrane potential and caused massive permeabilization on MRSA concomitant with loss of viability. Against stationary phase MRSA under nutrient-depleted conditions, active peptidomimetics S-7 and S-8 achieved > 6 log reduction in viability upon 24 h incubation while both S-7 (at 226 μg/mL) and S-8 (at 28 μg/mL) also destroyed 48 h mature MRSA biofilm causing significant decrease in viability (p < 0.05). Encouragingly, most active peptidomimetic S-8 maintained efficacy against MRSA in presence of serum/plasma while exhibiting no increase in MIC over 17 serial passages at sub-MIC concentrations implying resistance development to be less likely. Therefore, we envisage that the current template warrants further optimization towards the development of cell selective peptidomimetics for the treatment of device associated MRSA infections.

Vancomycin-resistant enterococcus infection in the hematopoietic stem cell transplant recipient: an overview of epidemiology, management, and prevention

Vancomycin-resistant enterococcus (VRE) is now one of the leading causes of nosocomial infections in the United States. Hematopoietic stem cell transplantation (HSCT) recipients are at increased risk of VRE colonization and infection. VRE has emerged as a major cause of bacteremia in this population, raising important clinical questions regarding the role and impact of VRE colonization and infection in HSCT outcomes as well as the optimal means of prevention and treatment. We review here the published literature and scientific advances addressing these thorny issues and provide a rational framework for their approach.

Characterization of the tertiary structure of the peptidoglycan of Enterococcus faecalis

Solid-state NMR spectra of whole cells and isolated cell walls of Enterococcus faecalis grown in media containing combinations of 13C and 15N specific labels in d- and l-alanine and l-lysine (in the presence of an alanine racemase inhibitor alaphosphin) have been used to determine the composition and architecture of the cell-wall peptidoglycan. The compositional variables include the concentrations of (i) peptidoglycan stems without bridges, (ii) d-alanylated wall teichoic acid, (iii) cross-links, and (iv) uncross-linked tripeptide and tetra/pentapeptide stems. Connectivities of l-alanyl carbonyl‑carbon bridge labels to d-[3-13C]alanyl and l-[ε-15N]lysyl stem labels prove that the peptidoglycan of E. faecalis has the same hybrid short-bridge architecture (with a mix of parallel and perpendicular stems) as the FemA mutant of Staphylococcus aureus, in which the cross-linked stems are perpendicular to one another and the cross-linking is close to the ideal 50% value. This is the first determination of the cell-wall chemical and geometrical architecture of whole cells of E. faecalis, a major source of nosocomial infections worldwide.

Targeting a cell wall biosynthesis hot spot

Covering: up to 2017History points to the bacterial cell wall biosynthetic network as a very effective target for antibiotic intervention, and numerous natural product inhibitors have been discovered. In addition to the inhibition of enzymes involved in the multistep synthesis of the macromolecular layer, in particular, interference with membrane-bound substrates and intermediates essential for the biosynthetic reactions has proven a valuable antibacterial strategy. A prominent target within the peptidoglycan biosynthetic pathway is lipid II, which represents a particular "Achilles' heel" for antibiotic attack, as it is readily accessible on the outside of the cytoplasmic membrane. Lipid II is a unique non-protein target that is one of the structurally most conserved molecules in bacterial cells. Notably, lipid II is more than just a target molecule, since sequestration of the cell wall precursor may be combined with additional antibiotic activities, such as the disruption of membrane integrity or disintegration of membrane-bound multi-enzyme machineries. Within the membrane bilayer lipid II is likely organized in specific anionic phospholipid patches that form a particular "landing platform" for antibiotics. Nature has invented a variety of different "lipid II binders" of at least 5 chemical classes, and their antibiotic activities can vary substantially depending on the compounds' physicochemical properties, such as amphiphilicity and charge, and thus trigger diverse cellular effects that are decisive for antibiotic activity.

Peripheral modifications of [Ψ[CH2NH]Tpg4]vancomycin with added synergistic mechanisms of action provide durable and potent antibiotics

Subsequent to binding pocket modifications designed to provide dual d-Ala-d-Ala/d-Ala-d-Lac binding that directly overcome the molecular basis of vancomycin resistance, peripheral structural changes have been explored to improve antimicrobial potency and provide additional synergistic mechanisms of action. A C-terminal peripheral modification, introducing a quaternary ammonium salt, is reported and was found to provide a binding pocket-modified vancomycin analog with a second mechanism of action that is independent of d-Ala-d-Ala/d-Ala-d-Lac binding. This modification, which induces cell wall permeability and is complementary to the glycopeptide inhibition of cell wall synthesis, was found to provide improvements in antimicrobial potency (200-fold) against vancomycin-resistant Enterococci (VRE). Furthermore, it is shown that this type of C-terminal modification may be combined with a second peripheral (4-chlorobiphenyl)methyl (CBP) addition to the vancomycin disaccharide to provide even more potent antimicrobial agents [VRE minimum inhibitory concentration (MIC) = 0.01-0.005 μg/mL] with activity that can be attributed to three independent and synergistic mechanisms of action, only one of which requires d-Ala-d-Ala/d-Ala-d-Lac binding. Finally, it is shown that such peripherally and binding pocket-modified vancomycin analogs display little propensity for acquired resistance by VRE and that their durability against such challenges as well as their antimicrobial potency follow now predictable trends (three > two > one mechanisms of action). Such antibiotics are expected to display durable antimicrobial activity not prone to rapidly acquired clinical resistance.

Total Syntheses of Vancomycin-Related Glycopeptide Antibiotics and Key Analogues

A review of efforts that have provided total syntheses of vancomycin and related glycopeptide antibiotics, their agylcons, and key analogues is provided. It is a tribute to developments in organic chemistry and the field of organic synthesis that not only can molecules of this complexity be prepared today by total synthesis but such efforts can be extended to the preparation of previously inaccessible key analogues that contain deep-seated structural changes. With the increasing prevalence of acquired bacterial resistance to existing classes of antibiotics and with the emergence of vancomycin-resistant pathogens (VRSA and VRE), the studies pave the way for the examination of synthetic analogues rationally designed to not only overcome vancomycin resistance but provide the foundation for the development of even more powerful and durable antibiotics.

Surface mediated cooperative interactions of drugs enhance mechanical forces for antibiotic action

The alarming increase of pathogenic bacteria that are resistant to multiple antibiotics is now recognized as a major health issue fuelling demand for new drugs. Bacterial resistance is often caused by molecular changes at the bacterial surface, which alter the nature of specific drug-target interactions. Here, we identify a novel mechanism by which drug-target interactions in resistant bacteria can be enhanced. We examined the surface forces generated by four antibiotics; vancomycin, ristomycin, chloroeremomycin and oritavancin against drug-susceptible and drug-resistant targets on a cantilever and demonstrated significant differences in mechanical response when drug-resistant targets are challenged with different antibiotics although no significant differences were observed when using susceptible targets. Remarkably, the binding affinity for oritavancin against drug-resistant targets (70 nM) was found to be 11,000 times stronger than for vancomycin (800 μM), a powerful antibiotic used as the last resort treatment for streptococcal and staphylococcal bacteria including methicillin-resistant Staphylococcus aureus (MRSA). Using an exactly solvable model, which takes into account the solvent and membrane effects, we demonstrate that drug-target interactions are strengthened by pronounced polyvalent interactions catalyzed by the surface itself. These findings further enhance our understanding of antibiotic mode of action and will enable development of more effective therapies.

Lipophilic teicoplanin pseudoaglycon derivatives are active against vancomycin- and teicoplanin-resistant enterococci

A selection of nine derivatives of teicoplanin pseudoaglycon were tested in vitro against clinical vancomycin-resistant Enterococcus strains possessing vanA, vanB or both genes. The bacteria were characterized by PCR for the identification of their resistance genes. The tested compounds contain lipoic acid, different carbohydrates and aryl groups as lipophilic moieties. About one-third of the teicoplanin-resistant strains were shown to be susceptible to one or more of the glycopeptide derivatives.

A review on cell wall synthesis inhibitors with an emphasis on glycopeptide antibiotics

Cell wall biosynthesis inhibitors (CBIs) have historically been one of the most effective classes of antibiotics. They are the most extensively used class of antibiotics and their importance is exemplified by the β-lactams and glycopeptide antibiotics. However, this class of antibiotics has not received impunity from resistance development. In the wake of this predicament, this review presents the progress of CBIs, especially glycopeptide derivatives as antibiotics to confront antibacterial resistance. The various strategies used for the development of CBIs, their clinical status and possible directions in which this field can evolve have also been discussed.