Synergistic potential of Leu10-teixobactin and cefepime against multidrug-resistant Staphylococcus aureus.

Staphylococcus aureus (S. aureus) is a significant Gram-positive opportunistic pathogen behind many debilitating infections. ß-lactam antibiotics are conventionally prescribed for treating S. aureus infections. However, the adaptability of S. aureus in evolving resistance to multiple ß-lactams contributed to the persistence and spread of infections, exemplified in the emergence of methicillin-resistant S. aureus (MRSA). In the present study, we investigated the efficacies of the synthetic teixobactin analogue, Leu10-teixobactin, combined with the penicillinase-resistant cephalosporin cefepime against MRSA strains. The Leu10-teixobactin and cefepime combination exerted synergism against most strains tested in broth microdilution assay. Time-kill profiles showed that both Leu10-teixobactin and cefepime predominantly exhibited synergistic activity, with > 2.0-log10CFU decrease compared to monotherapy at 24 h. Moreover, biofilm assays revealed a significant inhibition of biofilm production in ATCC™43300 cells treated with sub-MICs of Leu10-teixobactin and cefepime. Subsequent electron microscopy studies showed more extensive damage with the combination therapy compared to monotherapies, including aberrant bacterial morphology, vesicle formation and substantial lysis, indicating combined damage to the cell wall. Quantitative real-time PCR revealed marked perturbation of genes mecA, sarA, atlA, and icaA, substantiating the apparent mode of combined antibacterial action of both antibiotics against peptidoglycan synthesis and initial biofilm production. Hence, the study highlights the prospective utility of the Leu10-teixobactin-cefepime combination in treating MRSA infections via ß-lactam potentiation.

Metabolomics Study of the Synergistic Killing of Polymyxin B in Combination with Amikacin against Polymyxin-Susceptible and -Resistant Pseudomonas aeruginosa.

In the present study, we employed untargeted metabolomics to investigate the synergistic killing mechanism of polymyxin B in combination with an aminoglycoside, amikacin, against a polymyxin-susceptible isolate of Pseudomonas aeruginosa, FADDI-PA111 (MIC = 2 mg/liter for both polymyxin B and amikacin), and a polymyxin-resistant Liverpool epidemic strain (LES), LESB58 (the corresponding MIC for both polymyxin B and amikacin is 16 mg/liter). The metabolites were extracted 15 min, 1 h, and 4 h following treatment with polymyxin B alone (2 mg/liter for FADDI-PA111; 4 mg/liter for LESB58), amikacin alone (2 mg/liter), and both in combination and analyzed using liquid chromatography-mass spectrometry (LC-MS). At 15 min and 1 h, polymyxin B alone induced significant perturbations in glycerophospholipid and fatty acid metabolism pathways in FADDI-PA111 and, to a lesser extent, in LESB58. Amikacin alone at 1 and 4 h induced significant perturbations in peptide and amino acid metabolism, which is in line with the mode of action of aminoglycosides. Pathway analysis of FADDI-PA111 revealed that the synergistic effect of the combination was largely due to the inhibition of cell envelope biogenesis, which was driven initially by polymyxin B via suppression of key metabolites involved in lipopolysaccharide, peptidoglycan, and membrane lipids (15 min and 1 h) and later by amikacin (4 h). Overall, these novel findings demonstrate that the disruption of cell envelope biogenesis and central carbohydrate metabolism, decreased levels of amino sugars, and a downregulated nucleotide pool are the metabolic pathways associated with the synergistic killing of the polymyxin-amikacin combination against P. aeruginosa This mechanistic study might help optimize synergistic polymyxin B combinations in the clinical setting.

The impact of backbone N-methylation on the structure-activity relationship of Leu10 -teixobactin.

Antimicrobial resistance is a serious threat to global human health; therefore, new anti-infective therapeutics are required. The cyclic depsi-peptide teixobactin exhibits potent antimicrobial activity against several Gram-positive pathogens. To study the natural product's mechanism of action and improve its pharmacological properties, efficient chemical methods for preparing teixobactin analogues are required to expedite structure-activity relationship studies. Described herein is a synthetic route that enables rapid access to analogues. Furthermore, our new N-methylated analogues highlight that hydrogen bonding along the N-terminal tail is likely to be important for antimicrobial activity.

Lipidomic Analysis of the Outer Membrane Vesicles from Paired Polymyxin-Susceptible and -Resistant Klebsiella pneumoniae Clinical Isolates.

Gram-negative bacteria produce outer membrane vesicles (OMVs) as delivery vehicles for nefarious bacterial cargo such as virulence factors, which are antibiotic resistance determinants. This study aimed to investigate the impact of polymyxin B treatment on the OMV lipidome from paired polymyxin-susceptible and -resistant Klebsiella pneumoniae isolates. K. pneumoniae ATCC 700721 was employed as a reference strain in addition to two clinical strains, K. pneumoniae FADDI-KP069 and K. pneumoniae BM3. Polymyxin B treatment of the polymyxin-susceptible strains resulted in a marked reduction in the glycerophospholipid, fatty acid, lysoglycerophosphate and sphingolipid content of their OMVs. Conversely, the polymyxin-resistant strains expressed OMVs richer in all of these lipid species, both intrinsically and increasingly under polymyxin treatment. The average diameter of the OMVs derived from the K. pneumoniae ATCC 700721 polymyxin-susceptible isolate, measured by dynamic light scattering measurements, was ~90.6 nm, whereas the average diameter of the OMVs isolated from the paired polymyxin-resistant isolate was ~141 nm. Polymyxin B treatment (2 mg/L) of the K. pneumoniae ATCC 700721 cells resulted in the production of OMVs with a larger average particle size in both the susceptible (average diameter ~124 nm) and resistant (average diameter ~154 nm) strains. In light of the above, we hypothesize that outer membrane remodelling associated with polymyxin resistance in K. pneumoniae may involve fortifying the membrane structure with increased glycerophospholipids, fatty acids, lysoglycerophosphates and sphingolipids. Putatively, these changes serve to make the outer membrane and OMVs more impervious to polymyxin attack.

High-level nitrofurantoin resistance in a clinical isolate of Klebsiella pneumoniae: a comparative genomics and metabolomics analysis.

Nitrofurantoin is a commonly used chemotherapeutic agent in the treatment of uncomplicated urinary tract infections caused by the problematic multidrug resistant Gram-negative pathogen Klebsiella pneumoniae. The present study aims to elucidate the mechanism of nitrofurantoin action and high-level resistance in K. pneumoniae using whole-genome sequencing (WGS), qPCR analysis, mutation structural modeling and untargeted metabolomic analysis. WGS profiling of evolved highly resistant mutants (nitrofurantoin minimum inhibitory concentrations > 256 mg/L) revealed modified expression of several genes related to membrane transport (porin ompK36 and efflux pump regulator oqxR) and nitroreductase activity (ribC and nfsB, involved in nitrofurantoin reduction). Untargeted metabolomics analysis of total metabolites extracted at 1 and 4 h post-nitrofurantoin treatment revealed that exposure to the drug caused a delayed effect on the metabolome which was most pronounced after 4 h. Pathway enrichment analysis illustrated that several complex interrelated metabolic pathways related to nitrofurantoin bacterial killing (aminoacyl-tRNA biosynthesis, purine metabolism, central carbohydrate metabolism, and pantothenate and CoA biosynthesis) and the development of nitrofurantoin resistance (riboflavin metabolism) were significantly perturbed. This study highlights for the first time the key role of efflux pump regulator oqxR in nitrofurantoin resistance and reveals global metabolome perturbations in response to nitrofurantoin, in K. pneumoniae.IMPORTANCEA quest for novel antibiotics and revitalizing older ones (such as nitrofurantoin) for treatment of difficult-to-treat Gram-negative bacterial infections has become increasingly popular. The precise antibacterial activity of nitrofurantoin is still not fully understood. Furthermore, although the prevalence of nitrofurantoin resistance remains low currently, the drug's fast-growing consumption worldwide highlights the need to comprehend the emerging resistance mechanisms. Here, we used multidisciplinary techniques to discern the exact mechanism of nitrofurantoin action and high-level resistance in Klebsiella pneumoniae, a common cause of urinary tract infections for which nitrofurantoin is the recommended treatment. We found that the expression of multiple genes related to membrane transport (including active efflux and passive diffusion of drug molecules) and nitroreductase activity was modified in nitrofurantoin-resistant strains, including oqxR, the transcriptional regulator of the oqxAB efflux pump. Furthermore, complex interconnected metabolic pathways that potentially govern the nitrofurantoin-killing mechanisms (e.g., aminoacyl-tRNA biosynthesis) and nitrofurantoin resistance (riboflavin metabolism) were significantly inhibited following nitrofurantoin treatment. Our study could help inform the improvement of nitrofuran derivatives, the development of new pharmacophores, or drug combinations to support the resurgence of nitrofurantoin in the management of multidrug resistant K. pneumouniae infection.

Providing insight into the mechanism of action of cationic lipidated oligomers using metabolomics.

The increasing resistance of clinically relevant microbes against current commercially available antimicrobials underpins the urgent need for alternative and novel treatment strategies. Cationic lipidated oligomers (CLOs) are innovative alternatives to antimicrobial peptides and have reported antimicrobial potential. An understanding of their antimicrobial mechanism of action is required to rationally design future treatment strategies for CLOs, either in monotherapy or synergistic combinations. In the present study, metabolomics was used to investigate the potential metabolic pathways involved in the mechanisms of antibacterial activity of one CLO, C12-o-(BG-D)-10, which we have previously shown to be effective against methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300. The metabolomes of MRSA ATCC 43300 at 1, 3, and 6 h following treatment with C12-o-(BG-D)-10 (48 µg/mL, i.e., 3× MIC) were compared to those of the untreated controls. Our findings reveal that the studied CLO, C12-o-(BG-D)-10, disorganized the bacterial membrane as the first step toward its antimicrobial effect, as evidenced by marked perturbations in the bacterial membrane lipids and peptidoglycan biosynthesis observed at early time points, i.e., 1 and 3 h. Central carbon metabolism and the biosynthesis of DNA, RNA, and arginine were also vigorously perturbed, mainly at early time points. Moreover, bacterial cells were under osmotic and oxidative stress across all time points, as evident by perturbations of trehalose biosynthesis and pentose phosphate shunt. Overall, this metabolomics study has, for the first time, revealed that the antimicrobial action of C12-o-(BG-D)-10 may potentially stem from the dysregulation of multiple metabolic pathways.IMPORTANCEAntimicrobial resistance poses a significant challenge to healthcare systems worldwide. Novel anti-infective therapeutics are urgently needed to combat drug-resistant microorganisms. Cationic lipidated oligomers (CLOs) show promise as new antibacterial agents against Gram-positive pathogens like methicillin-resistant Staphylococcus aureus (MRSA). Understanding their molecular mechanism(s) of antimicrobial action may help design synergistic CLO treatments along with monotherapy. Here, we describe the first metabolomics study to investigate the killing mechanism(s) of CLOs against MRSA. The results of our study indicate that the CLO, C12-o-(BG-D)-10, had a notable impact on the biosynthesis and organization of the bacterial cell envelope. C12-o-(BG-D)-10 also inhibits arginine, histidine, central carbon metabolism, and trehalose production, adding to its antibacterial characteristics. This work illuminates the unique mechanism of action of C12-o-(BG-D)-10 and opens an avenue to design innovative antibacterial oligomers/polymers for future clinical applications.

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.

Comparative Proteomics of Outer Membrane Vesicles from Polymyxin-Susceptible and Extremely Drug-Resistant Klebsiella pneumoniae.

Outer membrane vesicles (OMVs) secreted by Gram-negative bacteria serve as transporters for the delivery of cargo such as virulence and antibiotic resistance factors. OMVs play a key role in the defense against membrane-targeting antibiotics such as the polymyxin B. Herein, we conducted comparative proteomics of OMVs from paired Klebsiella pneumoniae ATCC 700721 polymyxin-susceptible (polymyxin B MIC = 0.5 mg/L) and an extremely resistant (polymyxin B MIC ≥128 mg/L), following exposure to 2 mg/L of polymyxin B. Comparative profiling of the OMV subproteome of each strain revealed proteins from multiple perturbed pathways, particularly in the polymyxin-susceptible strain, including outer membrane assembly (lipopolysaccharide, O-antigen, and peptidoglycan biosynthesis), cationic antimicrobial peptide resistance, ß-lactam resistance, and quorum sensing. In the polymyxin-susceptible strain, polymyxin B treatment reduced the expression of OMV proteins in the pathways related to adhesion, virulence, and the cell envelope stress responses, whereas, in the polymyxin-resistant strain, the proteins involved in LPS biosynthesis, RNA degradation, and nucleotide excision repair were significantly overexpressed in response to polymyxin B treatment. Intriguingly, the key polymyxin resistance enzymes 4-amino-4-deoxy-l-arabinose transferase and the PhoPQ two-component protein kinase were significantly downregulated in the OMVs of the polymyxin-susceptible strain. Additionally, a significant reduction in class A ß-lactamase proteins was observed following polymyxin B treatment in the OMVs of both strains, particularly the OMVs of the polymyxin-susceptible strain. These findings shed new light on the OMV subproteome of extremely polymyxin resistant K. pneumoniae, which putatively may serve as active decoys to make the outer membrane more impervious to polymyxin attack. IMPORTANCE OMVs can help bacteria to fight antibiotics not only by spreading antibiotic resistance genes but also by acting as protective armor against antibiotics. By employing proteomics, we found that OMVs have a potential role in shielding K. pneumoniae and acting as decoys to polymyxin attack, through declining the export of proteins (e.g., 4-amino-4-deoxy-l-arabinose transferase) involved in polymyxin resistance. Furthermore, polymyxin B treatment of both strains leads to shedding of the OMVs with perturbed proteins involved in outer membrane remodeling (e.g., LPS biosynthesis) as well as pathogenic potential of K. pneumoniae (e.g., quorum sensing). The problematic extended spectrum beta-lactamases SHV and TEM were significantly reduced in both strains, suggesting that polymyxin B may act as a potentiator to sensitize the bacterium to ß-lactam antibiotics. This study highlights the importance of OMVs as "molecular mules" for the intercellular transmission and delivery of resistance and cellular repair factors in the bacterial response to polymyxins.

Transcriptomic Mapping of Neurotoxicity Pathways in the Rat Brain in Response to Intraventricular Polymyxin B.

Intraventricular or intrathecal administration of polymyxins are increasingly used to treat multidrug-resistant (MDR) Gram-negative bacteria caused infections in the central nervous system (CNS). However, our limited knowledge of the mechanisms underpinning polymyxin-induced neurotoxicity significantly hinders the development of safe and efficacious polymyxin dosing regimens. To this end, we conducted transcriptomic analyses of the rat brain and spinal cord 1 h following intracerebroventricular administration of polymyxin B into rat lateral ventricle at a clinically relevant dose (0.5 mg/kg). Following the treatment, 66 differentially expressed genes (DEGs) were identified in the brain transcriptome while none for the spinal cord (FDR ≤ 0.05, fold-change ≥ 1.5). DEGs were enriched in signaling pathways associated with hormones and neurotransmitters, including dopamine and (nor)epinephrine. Notably, the expression levels of Slc6a3 and Gabra6 were decreased by 20-fold and 4.3-fold, respectively, likely resulting in major perturbations of dopamine and γ-aminobutyric acid signaling in the brain. Mass spectrometry imaging of brain sections revealed a distinct pattern of polymyxin B distribution with the majority accumulating in the injection-side lateral ventricle and subsequently into third and fourth ventricles. Polymyxin B was not detectable in the left lateral ventricle or brain tissue. Electrophysiological measurements on primary cultured rat neurons revealed a large inward current and significant membrane leakage following polymyxin B treatment. Our work demonstrates, for the first time, the key CNS signaling pathways associated with polymyxin neurotoxicity. This mechanistic insight combined with pharmacokinetic/pharmacodynamic dosing strategies will help guide the design of safe and effective intraventricular/intrathecal polymyxin treatment regimens for CNS infections caused by MDR Gram-negative pathogens.

Integrated Transcriptomic and Metabolomic Mapping Reveals the Mechanism of Action of Ceftazidime/Avibactam against Pan-Drug-Resistant Klebsiella pneumoniae.

Here, we employed an integrated metabolomics and transcriptomics approach to investigate the molecular mechanism(s) of action of ceftazidime/avibactam against a pan-drug-resistant K. pneumoniae clinical isolate from a patient with urinary tract infection. Ceftazidime/avibactam induced time-dependent perturbations in the metabolome and transcriptome of the bacterium, mainly at 6 h, with minimal effects at 1 and 3 h. Metabolomics analysis revealed a notable reduction in essential lipids involved in outer membrane glycerolipid biogenesis. This disruption effect extended to peptidoglycan and lipopolysaccharide biosynthetic pathways, including lipid A and O-antigen assembly. Importantly, ceftazidime/avibactam not only affected the final steps of peptidoglycan biosynthesis in the periplasm, a common mechanism of ceftazidime action, but also influenced the synthesis of lipid-linked intermediates and early stages of cytoplasmic peptidoglycan synthesis. Furthermore, ceftazidime/avibactam substantially inhibited central carbon metabolism (e.g., the pentose phosphate pathway and tricarboxylic acid cycle). Consistently, the dysregulation of genes governing these metabolic pathways aligned with the metabolomics findings. Certain metabolomics and transcriptomics signatures associated with ceftazidime resistance were also perturbed. Consistent with the primary target of antibiotic activity, biochemical assays also confirmed the direct impact of ceftazidime/avibactam on peptidoglycan production. This study explored the intricate interactions of ceftazidime and avibactam within bacterial cells, including their impact on cell envelope biogenesis and central carbon metabolism. Our findings revealed the complexities of how ceftazidime/avibactam operates, such as hindering peptidoglycan formation in different cellular compartments. In summary, this study confirms the existing hypotheses about the antibacterial and resistance mechanisms of ceftazidime/avibactam while uncovering novel insights, including its impact on lipopolysaccharide formation.

Drug Repurposing Approaches towards Defeating Multidrug-Resistant Gram-Negative Pathogens: Novel Polymyxin/Non-Antibiotic Combinations.

Multidrug-resistant (MDR) Gram-negative pathogens remain an unmet public health threat. In recent times, increased rates of resistance have been reported not only to commonly used antibiotics, but also to the last-resort antibiotics, such as polymyxins. More worryingly, despite the current trends in resistance, there is a lack of new antibiotics in the drug-discovery pipeline. Hence, it is imperative that new strategies are developed to preserve the clinical efficacy of the current antibiotics, particularly the last-line agents. Combining conventional antibiotics such as polymyxins with non-antibiotics (or adjuvants), has emerged as a novel and effective strategy against otherwise untreatable MDR pathogens. This review explores the available literature detailing the latest polymyxin/non-antibiotic combinations, their mechanisms of action, and potential avenues to advance their clinical application.

Intraventricular Drug Delivery and Sampling for Pharmacokinetics and Pharmacodynamics Study.

Although the blood-brain barrier (BBB) protects the brain from foreign entities, it also prevents some therapeutics from crossing into the central nervous system (CNS) to ameliorate diseases or infections. Drugs are administered directly into the CNS in animals and humans to circumvent the BBB. The present protocol describes a unique way of treating brain infections through intraventricular delivery of antibiotics, i.e., polymyxins, the last-line antibiotics to treat multi-drug resistant Gram-negative bacteria. A straightforward stereotaxic surgery protocol was developed to implant a guide cannula reaching into the lateral ventricle in rats. After a recovery period of 24 h, rats can be injected consciously and repeatedly through a cannula that is fitted to the guide. Injections can be delivered manually as a bolus or infusion using a microinjection pump to obtain a slow and controlled flow rate. The intraventricular injection was successfully confirmed with Evans Blue dye. Cerebrospinal fluid (CSF) can be drained, and the brain and other organs can be collected. This approach is highly amenable for studies involving drug delivery to the CNS and subsequent assessment of pharmacokinetic and pharmacodynamic activity.

Rat Burn Model to Study Full-Thickness Cutaneous Thermal Burn and Infection.

Burn induction methodologies are inconsistently described in rat models. A uniform burn wound model, which represents the clinical scenario, is necessary to perform reproducible burn research. The present protocol describes a simple and reproducible method to create ~20% total body surface area (TBSA) full-thickness burns in rats. Here, a 22.89 cm2 (5.4 cm diameter) copper rod heated at 97 °C in a water bath was applied to the rat skin surface to induce the burn injury. A copper rod with a high thermal conductivity was able to dissipate the heat deeper in the skin tissue to create a full-thickness burn. Histology analysis shows attenuated epidermis with coagulative damage to the full-thickness extent of the dermis and the subcutaneous tissue. Additionally, this model is representative of the clinical situations observed in hospitalized burn patients following burn injury such as immune dysregulation and bacterial infections. The model can recapitulate the systemic bacterial infection by both Gram-positive and Gram-negative bacteria. In conclusion, this paper presents an easy-to-learn and robust rat burn model that mimics the clinical situations, including immune dysregulation and bacterial infections, which is of considerable utility for the development of new topical antibiotic drugs for burn wound and infections.

Mechanisms Underlying Synergistic Killing of Polymyxin B in Combination with Cannabidiol against Acinetobacter baumannii: A Metabolomic Study.

Polymyxins have resurged as the last-resort antibiotics against multidrug-resistant Acinetobacter baumannii. As reports of polymyxin resistance in A. baumannii with monotherapy have become increasingly common, combination therapy is usually the only remaining treatment option. A novel and effective strategy is to combine polymyxins with non-antibiotic drugs. This study aimed to investigate, using untargeted metabolomics, the mechanisms of antibacterial killing synergy of the combination of polymyxin B with a synthetic cannabidiol against A. baumannii ATCC 19606. The antibacterial synergy of the combination against a panel of Gram-negative pathogens (Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa) was also explored using checkerboard and static time-kill assays. The polymyxin B-cannabidiol combination showed synergistic antibacterial activity in checkerboard and static time-kill assays against both polymyxin-susceptible and polymyxin-resistant isolates. The metabolomics study at 1 h demonstrated that polymyxin B monotherapy and the combination (to the greatest extent) significantly perturbed the complex interrelated metabolic pathways involved in the bacterial cell envelope biogenesis (amino sugar and nucleotide sugar metabolism, peptidoglycan, and lipopolysaccharide (LPS) biosynthesis), nucleotides (purine and pyrimidine metabolism) and peptide metabolism; notably, these pathways are key regulators of bacterial DNA and RNA biosynthesis. Intriguingly, the combination caused a major perturbation in bacterial membrane lipids (glycerophospholipids and fatty acids) compared to very minimal changes induced by monotherapies. At 4 h, polymyxin B-cannabidiol induced more pronounced effects on the abovementioned pathways compared to the minimal impact of monotherapies. This metabolomics study for the first time showed that in disorganization of the bacterial envelope formation, the DNA and RNA biosynthetic pathways were the most likely molecular mechanisms for the synergy of the combination. The study suggests the possibility of cannabidiol repositioning, in combination with polymyxins, for treatment of MDR polymyxin-resistant Gram-negative infections.

Untargeted metabolomics to evaluate polymyxin B toxicodynamics following direct intracerebroventricular administration into the rat brain.

There is a dearth of studies focused on understanding pharmacokinetics, pharmacodynamics and toxicodynamics of polymyxins following direct administration to the central nervous system (CNS). In this study, for the first time, untargeted metabolomics were employed to ascertain the perturbations of brain metabolism in the rat cerebral cortex following direct brain injection of 0.75 mg/kg polymyxin B (1 and 4 h) through the right lateral ventricle. In the right cortex metabolome, ICV polymyxin B induced a greater perturbation at 1 h compared to negligible effect at 4 h. Pathway enrichment analysis showed that sphingolipid, arginine, and histidine metabolism, together with aminoacyl-tRNA biosynthesis were significantly affected in the right cortex metabolome. Furthermore, intracerebroventricular (ICV) polymyxin B dysregulated the two arms (CDP-choline and CDP-ethanolamine) of the Kennedy pathway that governs the de novo biosynthesis of neuronal phospholipids. Importantly, the key intermediates of metabolic pathways that maintain cellular redox balance (e.g., glutathione metabolism) and mitochondrial function (e.g., electron transport chain) were markedly depleted. The abundance of key metabolites (e.g., N-acetyl-l-glutamate) associated with diverse CNS disorders (e.g., neurodegenerative disease) were also significantly perturbed. The biological significance of these metabolic perturbations on the CNS includes impaired oxidant-antioxidant balance, impaired neuronal lipid homeostasis and mitochondrial dysfunction. Furthermore, ICV polymyxin B caused a significant alteration in the abundance of several metabolic biomarkers associated with cerebral ischemia, oxidative stress as well as certain neurological disorders. These findings may facilitate the development of new pharmacokinetic/pharmacodynamic strategies to attenuate polymyxins ICV related CNS toxicities and stimulate the discovery of safer next-generation polymyxin-like lipopeptide antibiotics.

Unique mechanistic insights into pathways associated with the synergistic activity of polymyxin B and caspofungin against multidrug-resistant Klebsiella pneumoniae.

Klebsiella pneumoniae is an opportunistic Gram-negative pathogen causing nosocomial infections. K. pneumoniae rapidly acquires antibiotic resistance and is known as a reservoir for resistance genes. Polymyxins remain effective as a last-line therapy against infections caused by multidrug-resistant (MDR) K. pneumoniae; however, resistance to polymyxins emerges rapidly with monotherapy. Synergistic combinations of polymyxins with FDA-approved non-antibiotics are a novel approach to preserve its efficacy whilst minimising the emergence of polymyxin resistance in K. pneumoniae. This study aimed to investigate the synergistic antibacterial activity of polymyxin B in combination with the anti-fungal caspofungin against K. pneumoniae. The combination of polymyxin B and caspofungin showed marked synergistic antibacterial killing activity in checkerboard broth microdilution and static time-kill assays at clinically relevant concentrations at early (0.5 and 1 h) and later (4 h) time points. The potential bacterial killing mechanism of the combination was studied against K. pneumoniae FADDI-KP001 using metabolomics and transcriptomics studies at 0.5, 1 and 4 h. The key pathways involved in the synergistic killing action of the combination were cell wall assembly (peptidoglycan and lipopolysaccharide biosynthesis), central carbon metabolism (glycolysis, pentose phosphate pathway and tricarboxylic acid cycle) and fatty acid biosynthesis. Moreover, the combination inhibited the most common bacterial virulence pathway (phosphotransferase system) as well as the multi-resistant efflux mechanisms, including ATP-binding cassette (ABC) transporter pathway. Overall, this study sheds light on the possibility of a polymyxin-caspofungin combination for the treatment of infections caused by K. pneumoniae and may help repurpose FDA-approved caspofungin against MDR K. pneumoniae infections.

The Antimicrobial Activity of Cannabinoids.

A post-antibiotic world is fast becoming a reality, given the rapid emergence of pathogens that are resistant to current drugs. Therefore, there is an urgent need to discover new classes of potent antimicrobial agents with novel modes of action. Cannabis sativa is an herbaceous plant that has been used for millennia for medicinal and recreational purposes. Its bioactivity is largely due to a class of compounds known as cannabinoids. Recently, these natural products and their analogs have been screened for their antimicrobial properties, in the quest to discover new anti-infective agents. This paper seeks to review the research to date on cannabinoids in this context, including an analysis of structure-activity relationships. It is hoped that it will stimulate further interest in this important issue.

Synthesis and structure-activity relationships of teixobactin.

The discovery of antibiotics has led to the effective treatment of bacterial infections that were otherwise fatal and has had a transformative effect on modern medicine. Teixobactin is an unusual depsipeptide natural product that was recently discovered from a previously unculturable soil bacterium and found to possess potent antibacterial activity against several Gram positive pathogens, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci. One of the key features of teixobactin as an antibiotic lead is that resistance could not be generated in a laboratory setting. This is proposed to be a result of a mechanism of action that involves binding to essential cell wall synthesis building blocks, lipid II and lipid III. Since the initial isolation report in 2015, significant efforts have been made to understand its unique mechanism of action, develop efficient synthetic routes for its production, and thus enable the generation of analogues for structure-activity relationship studies and optimization of its pharmacological properties. Our review provides a comprehensive treatise on the progress in understanding teixobactin chemistry, structure-activity relationships, and mechanisms of antibacterial activity. Teixobactin represents an exciting starting point for the development of new antibiotics that can be used to combat multidrug-resistant bacterial ("superbug") infections.

Allosteric folding correction of F508del and rare CFTR mutants by elexacaftor-tezacaftor-ivacaftor (Trikafta) combination.

Based on its clinical benefits, Trikafta - the combination of folding correctors VX-661 (tezacaftor), VX-445 (elexacaftor), and the gating potentiator VX-770 (ivacaftor) - was FDA approved for treatment of patients with cystic fibrosis (CF) carrying deletion of phenylalanine at position 508 (F508del) of the CF transmembrane conductance regulator (CFTR) on at least 1 allele. Neither the mechanism of action of VX-445 nor the susceptibility of rare CF folding mutants to Trikafta are known. Here, we show that, in human bronchial epithelial cells, VX-445 synergistically restores F508del-CFTR processing in combination with type I or II correctors that target the nucleotide binding domain 1 (NBD1) membrane spanning domains (MSDs) interface and NBD2, respectively, consistent with a type III corrector mechanism. This inference was supported by the VX-445 binding to and unfolding suppression of the isolated F508del-NBD1 of CFTR. The VX-661 plus VX-445 treatment restored F508del-CFTR chloride channel function in the presence of VX-770 to approximately 62% of WT CFTR in homozygous nasal epithelia. Substantial rescue of rare misprocessing mutations (S13F, R31C, G85E, E92K, V520F, M1101K, and N1303K), confined to MSD1, MSD2, NBD1, and NBD2 of CFTR, was also observed in airway epithelia, suggesting an allosteric correction mechanism and the possible application of Trikafta for patients with rare misfolding mutants of CFTR.

Polymyxin B combinations with FDA-approved non-antibiotic phenothiazine drugs targeting multi-drug resistance of Gram-negative pathogens.

The status quo for combating uprising antibacterial resistance is to employ synergistic combinations of antibiotics. Nevertheless, the currently available combination therapies are fast becoming untenable. Combining antibiotics with various FDA-approved non-antibiotic drugs has emerged as a novel strategy against otherwise untreatable multi-drug resistant (MDR) pathogens. The apex of this study was to investigate the mechanisms of antibacterial synergy of the combination of polymyxin B with the phenothiazines against the MDR Gram-negative pathogens Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa. The synergistic antibacterial effects were tested using checkerboard and static time-kill assays. Electron microscopy (EM) and untargeted metabolomics were used to ascertain the mechanism(s) of the antibacterial synergy. The combination of polymyxin B and the phenothiazines showed synergistic antibacterial activity in checkerboard and static time-kill assays at clinically relevant concentrations against both polymyxin-susceptible and polymyxin-resistant isolates. EM revealed that the polymyxin B-prochlorperazine combination resulted in greater damage to the bacterial cell compared to each drug monotherapy. In metabolomics, at 0.5 h, polymyxin B monotherapy and the combination (to a greatest extent) disorganised the bacterial cell envelope as manifested by a major perturbation in bacterial membrane lipids (glycerophospholipids and fatty acids), peptidoglycan and lipopolysaccharide (LPS) biosynthesis. At the late time exposure (4 h), the aforementioned effects (except LPS biosynthesis) perpetuated mainly with the combination therapy, indicating the disorganising bacterial membrane biogenesis is potentially behind the mechanisms of antibacterial synergy. In conclusion, the study highlights the potential usefulness of the combination of polymyxin B with phenothiazines for the treatment of polymyxin-resistant Gram-negative infections (e.g. CNS infections).