A broad-spectrum antibiotic adjuvant reverses multidrug-resistant Gram-negative pathogens

Antimicrobial peptide mimic 329 potentiates minocycline against carbapenem-resistant Klebsiella pneumoniae

As antibiotic resistance increases and new drug development lags, the effectiveness of single antibiotics has drastically diminished for clinical infection treatment. The resistance crisis is exacerbated by the swift development and dissemination of Gram-negative bacteria that are extensively drug-resistant (XDR), particularly strains resistant to carbapenems in clinical settings. In this scenario, antibiotic adjuvants play a crucial role in revitalizing existing treatments to combat carbapenem-resistant bacterial infections. In this study, we synthesized ten small molecular antimicrobial peptide mimics and identified antimicrobial peptide mimic 329 (A329), which exhibited a synergistic effect with minocycline (FICI = 0.023), enhancing its efficacy by 4- to 128-fold, and significantly enhanced the antibacterial efficacy of minocycline against carbapenem-resistant Klebsiella pneumoniae (CRKP, 0.015 ≤ FICI ≤0.141), prevented the emergence of minocycline resistance, improved the survival rate of mice, and decreased bacterial load in tissues at 8 + 8 mg/kg. Mechanistic studies revealed that A329 increases bacterial membrane permeability and disrupts the proton-motive force. Additionally, A329 combined with minocycline boosts intracellular minocycline accumulation, induces intracellular production of reactive oxygen species (ROS), and ultimately triggers bacterial death. These findings advised that A329 in combination with minocycline is a potential combination therapy against XDR-associated infections.

The antibacterial efficacy of nitroxoline against multidrug resistant Escherichia coli associated with copper binding

Nitroxoline (NIT) has been approved for the treatment of uncomplicated urinary tract infections (UTIs) for more than half a century, yet its antimicrobial properties remain incompletely understood. Here, we determined the intricate connections between NIT's metal-chelating capabilities and its antibacterial activity. Metal ion binding characteristics were measured by Ultraviolet-visible (UV-vis) spectroscopy. Biochemical assays and molecular docking studies were performed to elucidate the underlying mechanism. We found that NIT could interact with a diverse array of metal ions, including Cu2+, Fe2+, Zn2+ and Mn2+. While, the addition of Cu2+ significantly decreased NIT's antibacterial effect against uropathogenic Escherichia coli (UPEC) strain J96 and multidrug resistant E coli B2, with the minimum inhibitory concentration (MIC) increased from 8 mg/L to 64 mg/L. Mechanically, NIT significantly decreased the intracellular copper ion levels and reduced bacterial transmembrane electrical potential. Furthermore, NIT promoted production of nitric oxide, peroxynitrite (ONOO-), and reactive oxygen species (ROS). However, the interaction of Cu2+ with NIT suppressed the induced generation of ROS but not the generation of ONOO- in E coli, suggesting that the antibacterial activity of NIT arose from multiple functional groups within its molecular structure. Moreover, NIT triggered intracellular acidification concomitant with enhanced glucose uptake, yet paradoxically suppressed ATP generation, suggesting a potential uncoupling between glycolytic flux and oxidative phosphorylation. Finally, the action of NIT was predicted to bind to the CuB-metal redox centers of cytochrome bo(3) ubiquinol oxidase through molecular docking analyses. Collectively, these data illuminate the antibacterial activity of NIT as a potent copper-related metalloantibiotic against UPEC.

Nitazoxanide inhibits pili assembly by targeting BamB to synergize with polymyxin B against drug-resistant Escherichia coli

Gram-negative bacteria rely on pili assembly for pathogenicity, with the chaperone-usher (CU) pathway regulating pilus biogenesis. Nitazoxanide (NTZ) inhibits CU pathway-mediated P pilus biogenesis by specifically interfering with the proper folding of the outer membrane protein (OMP) usher, primarily mediated by the β-barrel assembly machinery (BAM) complex. In this study, we identified the BAM complex components BamB and the BamA POTRA2 domain as key binding targets for NTZ. Molecular dynamics simulations and Bio-Layer Interferometry revealed that BamB residues S61 and R195 are critical for NTZ binding. NTZ activated the Cpx two-component system and induced inner membrane perturbations, which resulted from the accumulation of misfolded P pilus subunits. Upregulation of the ibpAB gene, which protects the bacteria against NTZ-induced oxidative stress, was also observed. Importantly, NTZ combined with polymyxin B enhanced the latter's antibacterial activity against both susceptible and MCR-positive E. coli strains. This enhancement was achieved through NTZ-induced increases in inner membrane permeability, oxidative stress, and inhibition of efflux pump activity and biofilm formation. This study provides new insights into the antimicrobial mechanism of NTZ and highlights its potential as an antibiotic adjuvant by targeting BamB to inhibit the CU pathway, restoring the efficacy of polymyxin B against multidrug-resistant bacteria.

Antibacterial activity of a plant natural poly-phenol against zoonotic Streptococcus suis

The increasing emergence and dissemination of multi-drugs resistant bacterial pathogens accelerate the desires for novel antimicrobials. Natural products are great resources for the discovery of antimicrobial compound. In this study, pyrogallol was screened from 25 poly-phenols for its antibacterial activity against multi-drugs resistant Streptococcus suis (S. suis), particularly, pyrogallol had synergistic antimicrobial effect with doxycycline, sulfafurazole and clindamycin, respectively. Pyrogallol showed significant inhibitory effects on bacterial biofilm formation, and caused cell wall and cell membrane injury to S. suis. Furthermore, mechanistic studies demonstrated that pyrogallol might interact with peptidoglycan and decreased the expression of virulence and growth-related genes, such as ftsZ, stK, sly, fbps and luxS. In cell model, pyrogallol protected Nptr cells from S. suis-mediated cell damage. Finally, in mouse model, the pyrogallol and antibiotics combination groups with dosage given in the half could be as effective as antibiotics groups. In summary, these results demonstrated the capacity of pyrogallol serving as a candidate for novel antibiotic alternative and antibiotic adjuvant to circumvent the antibiotics resistance and reduced antibiotic consumption.

Highly Efficient Thiol-Michael Addition Post-Modification toward Potent Degradable Antibacterial Polyesters with Guanidine Moiety

We have previously synthesized poly(3-methylene-1,5-dioxepan-2-one) (PMDXO) that could be modified through the thiol-Michael addition reaction to afford versatile degradable polymers. Herein, we find that the γ-oxa in PMDXO exerts a dramatically accelerating effect on the thiol-Michael addition post-modification, which makes PMDXO a promising platform polymer for synthesizing guanidinium-functionalized aliphatic polyesters under mild and approximately stoichiometric conditions. The relationship between polymer structure and antibacterial performance was investigated. A promising cationic polyester, P20-2C, which shows extremely low hemolytic activity, moderate cytotoxicity, and broad-spectrum potent bactericidal capability against 214 clinically isolated ESKAPE strains, is obtained. The good biocompatibility and potent in vivo antibacterial efficacy of P20-2C have been demonstrated in mice using three bacterial infection models, including MDR E. coli-infected peritonitis and MRSA-infected subcutaneous abscess and skin wound. Finally, a multimodal bactericidal mechanism of membrane disruption plus reactive oxygen species upregulation is proposed for P20-2C against E. coli and S. aureus.

The discovery of novel antimicrobial peptides against drug-resistant bacteria based on fragments fusion strategy

Since the escalating prevalence of multidrug-resistant (MDR) bacterial infections posing global health challenges, novel antimicrobial agents are urgently needed. This study designed a series of antimicrobial peptides by fusing two fragments of antimicrobial peptides sC184b (1-9) and MSI-78 (10-16). Among these peptides, 13DKallDab exhibited broad-spectrum antimicrobial efficacy against six different MDR bacterial strains with relatively low MICs. It exerted antibacterial effects through a membrane-disruption mechanism and maintained high stability in serum environment. Moreover, 13DKallDab displayed low cytotoxicity and hemolysis in vitro, and significant therapeutic efficacy in a mouse acute peritonitis model. These findings demonstrate that 13DKallDab is a promising antimicrobial agent in counteracting multidrug-resistant bacterial infections.

Trapping effect of surface deficient cocrystal synergizes with bimetallic nanoparticles against bacterial infection in wounds

Metal nanoparticles exert broad-spectrum antimicrobial effects through in situ generation of reactive oxygen species (ROS). However, the limited penetrability of ROS restricts the scope of antimicrobial activity of these nanoparticles. Herein, we develop core-shell nanoparticles composed of a surface-defective cocrystal shell and a Cu/Zn bimetallic core. Surface defects are generated by etching myricetin from a berberine-dihydromyricetin cocrystal, and bacterial adsorption efficiency peaks when the cocrystal contains 40 % myricetin. Similarly, Cu2+ doping on the surface of Zn nanoparticles to form a bimetallic core can optimize the ROS generation efficiency by facilitating effective electron transfer. Nanoparticles with this combined core-shell structure not only capture bacteria effectively but also draw bacteria into the ROS-killing range of the metal particles, thereby enhancing activity against drug-resistant bacteria. The feasibility of antibacterial infection was further validated in wounds of mice infected with Escherichia coli and Staphylococcus aureus. This strategy could be used to optimize antimicrobial nanoparticles with ROS-generating functionality and could have an impact on combating bacterial resistance.

Navigating Antibiotic Resistance in Gram-Negative Bacteria: Current Challenges and Emerging Therapeutic Strategies

The rapid rise of antibiotic resistance poses a severe global health crisis, necessitating new approaches to counter this growing threat. The problem is exacerbated in Gram-negative bacterial pathogens as many antibiotics are unable to enter these cells owing to their unique additional outer membrane barrier. In this review, we discuss the challenges of targeting Gram-negative bacteria, including the complexity of the outer membrane, as well as the presence of efflux pumps and β-lactamases that contribute to resistance. We also review solutions proposed to facilitate the entry and accumulation of antibiotics in Gram-negative bacteria. These involve using existing antibiotics in combination with other inhibitors to attack the bacterial cell synergistically. We also highlight approaches to target Gram-negative pathogens via novel modes of action, providing new strategies to tackle antibiotic resistance.

Effect of emodin on Streptococcus suis by targeting β-ketoacyl-acyl carrier protein synthase Ⅱ

BACKGROUND

Streptococcus suis is a zoonotic pathogen that causes meningitis, septicaemia, endocarditis, arthritis, and pneumonia in human beings. With the increasing prevalence of S. suis infections and a general decline in the effectiveness of antibiotics, the development of novel drugs that have effect on S. suis is extremely urgent. Emodin, a natural anthraquinone derivative of Rheum palmatum L., Reynoutria japonica Houtt., Polygonum multiflorum Thunb. and Cassia obtusifolia L., has been reported to exert anti-S. suis effect; however, the specific mechanism of the anti-S. suis action by targeting β-ketoacyl-acyl carrier protein synthase Ⅱ (FabF) in the fatty acid synthesis pathway remains unexplored.

PURPOSE

We sought to reveal the potential role of emodin to prevent S. suis infection, investigate its mechanism of anti-S. suis action, and provide further evidence of emodin as an alternative to traditional antibiotic agents.

METHODS

The in vitro anti-S. suis properties of emodin were assessed through minimum inhibitory concentration (MIC) assays, and time-kill assays. Subsequently, the mechanisms underlying emodin's mode of action at the molecular level by targeting FabF were elucidated using molecular docking, site-directed mutagenesis, bio-layer interferometry assays, and cellular thermal shift assays. Finally, metabolomics, cell membrane phospholipid content assay and biochemical parameters assays were used to detect emodin disrupting cell membrane integrity and function by affecting fatty acid biosynthesis.

RESULTS

In this study, we have identified that emodin inhibits S. suis by suppressing free fatty acids (FFAs) synthesis and disrupting phospholipid production by targeting FabF, a key enzyme in the fatty acid biosynthesis pathway. This interference compromises the integrity and functionality of the cell membranes of S. suis. Emodin also triggers the dissipation of the proton motive force, accelerates the tricarboxylic acid cycle, and enhances cellular respiration, ultimately leading to S. suis cell death.

CONCLUSION

This study suggested that emodin inhibits the growth of S. suis via targeting FabF and the inhibition of fatty acid biosynthesis through enzyme-targeted drug design. This represents a novel strategy for developing antimicrobial agents against S. suis and addressing the challenge of antibiotic resistance.

Copper(II) enhances the antibacterial activity of nitroxoline against MRSA by promoting aerobic glycolysis

Nitroxoline (NIT) is an FDA-approved antibiotic with numerous pharmacological properties. However, the intricate connections between its metal-chelating ability and antimicrobial efficacy remain incompletely understood. The specific interactions of NIT with different metal ions were measured via UV-vis absorption spectroscopy. Here, we found that NIT can bind to various metal ions, including Cu2+, Fe2+, Zn2+ and Mn2+. However, the antimicrobial activity of NIT against methicillin-resistant Staphylococcus aureus (MRSA) was significantly enhanced by the inclusion of Cu2+ as determined by a minimal inhibitory concentration (MIC) assay in Mueller-Hinton broth. The enhanced antibacterial effect was not influenced by the availability of oxygen. Mechanistically, Cu2+ promoted bacterial proliferation, increased the bacterial transmembrane electrical potential, and increased intracellular acidification. In addition, Cu2+ rewired bacterial metabolism, promoting the uptake of glucose with a lower level of ATP production. Pharmacological upregulation of glycolysis by VLX600 could potentiate the susceptibility of MRSA to NIT. Moreover, Cu2+ also significantly increased the survival rate of acutely infected larvae. These collective results underscore that the enhanced antibacterial efficacy of NIT by Cu2+ intricately involves aerobic glycolysis in MRSA.

De novo designed mini-binders targeting glyceraldehyde-3-phosphate dehydrogenase of Streptococcus equi ssp. zooepidemicus provided partial protection in mice model of infection

Streptococcus equi ssp. zooepidemicus (Streptococcus zooepidemicus, SEZ) is an important zoonotic pathogen that greatly threatens the health of pigs in China. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been identified as a critical virulence factor that contributes to the adhesion of SEZ to host. Effectively blocking the GAPDH mediated adhesion is of high significance for the treatment of SEZ infection. In this study, we de novo designed mini-binders targeting GAPDH by RFdiffusion approach and three binder candidates targeting two hydrophobic sites on GAPDH were screened out. Among them, binder 1and binder 9 presented micromolar affinities to GAPDH, and were thermostable in solution. The two binders significantly inhibited the adhesion of SEZ to HEp-2 cells, while binder 1 showed higher potency. We estimated the protection efficiency of the two binders in vivo with different administration programs. Binder 1 improved the survival (60 %) of mice infected with a lethal dose of SEZ when preventive and therapeutic administration combined, while binder 9 failed to reverse the death of mice in any of the dosing procedures. This work provided new insights for the rapid development of highly efficient and easy-to-prepare anti-SEZ agents and a paradigm for the application of protein de novo design in agricultural field.

The role of NhaA protein in modulating antibiotic tolerance in Escherichia coli

As microbial resistance and recurrent bacterial infections escalate, the growing understanding of the interplay between antibiotic resistance and tolerance has sparked significant interest in the latter. Previous studies have demonstrated that the deletion of cation/proton antiporters (CPAs) induces bacterial phenotypes, such as slow growth and prolonged lag phases, which contribute to the development of tolerance. This study investigates the role of the NhaA protein in antibiotic tolerance in Escherichia coli using CRISPR/Cas9 gene editing to delete the NhaA protein. Our results suggest that the NhaA protein plays a key role in modulating antibiotic tolerance. In response to NhaA deletion, E. coli adapts through multiple mechanisms, including changes in membrane permeability, enhanced efflux activity, increased membrane fluidity, disruption of the proton motive force (PMF), and a reduction in intracellular ATP levels. These adaptive changes collectively promote the development of antibiotic tolerance. Understanding these tolerance mechanisms could uncover new therapeutic targets, help prevent the emergence of tolerance, or sustain bacteria cells in a tolerant state, providing crucial strategies to combat the rise of antibiotic-resistant bacteria.

Discovery of a novel sea snake antimicrobial peptide Hydrostatin-AMP3 with dual-mechanism against multidrug-resistant Klebsiella pneumoniae

Klebsiella pneumoniae (K. pneumoniae) has ranked in the top three pathogens responsible for bacteria-related mortal infections. The emergence of multi-drug resistant (MDR) K. pneumoniae strains highlights an urgent need for novel antimicrobial agents. In this study, a series of antimicrobial peptides (AMPs) were screened based on gene annotation and sequence profiling via high-quality whole genome maps of sea snakes Hydrophis curtus and Hydrophis cyanocinctus. The most potent Hydrostatin-AMP3 showed efficient antimicrobial capacity against a panel of pathogenic bacteria, particularly MDR K. pneumoniae strains. Moreover, Hydrostatin-AMP3 exhibited remarkable efficacy in infection models of MDR K. pneumoniae, while demonstrating favourable profiles in safety and resistance development both in vitro and in vivo studies. Mechanistically, Hydrostatin-AMP3 exerted a bactericidal effect through a unique dual-mechanism: bacterial membrane disruption and DNA-targeting. Overall, this study presented Hydrostatin-AMP3 as the potential antimicrobial candidate for the treatment of MDR K. pneumoniae infection.

Amphiphilic mPEG-PLGA copolymer nanoparticles co-delivering colistin and niclosamide to treat colistin-resistant Gram-negative bacteria infections

Colistin is the last line of defense against multidrug-resistant (MDR) Gram-negative bacterial infections, yet it is restricted due to high drug resistance and toxicity. The combination therapy of colistin and niclosamide exhibits excellent synergistic antibacterial activity against Gram-negative bacteria. How to co-deliver these two drugs with vastly different pharmacokinetic properties in sufficient amounts to the infection site is the core issue that must be resolved for the clinical translation of this drug combination. Here, we designed and prepared a nanosystem capable of co-loading colistin and niclosamide with different physicochemical properties into mPEG-PLGA nanoparticles (COL/NIC-mPEG-PLGA-NPs) to overcome the resistance of multiple colistin-resistant bacteria to colistin and alleviate its toxicity. Mechanistic studies revealed that the COL/NIC-mPEG-PLGA-NPs enhanced the affinity of delivered COL to the modified membrane of colistin-resistant bacteria. The increased membrane permeability caused by colistin promotes an influx of niclosamide, which reduces efflux pump activity and generates intracellular ROS stress, eliminating colistin-resistant bacteria. In addition, the nanoparticles proved non-toxic both in vitro and in vivo. Overall, our study has profound insights into the use of nanosystems with high biosafety for the treatment of infections caused by colistin-resistant bacteria.

Cecropin A-Derived Peptide for the Treatment of Osteomyelitis by Inhibiting the Growth of Multidrug-Resistant Bacteria and Eliminating Inflammation

Osteomyelitis poses substantial therapeutic challenges due to the prevalence of multidrug-resistant bacterial infections and associated inflammation. Current treatment regimens often rely on a combination of corticosteroids and antibiotics, which can lead to complications and impede effective bacterial clearance. In this study, we present CADP-10, a Cecropin A-derived peptide, designed to target methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Escherichia coli (MRE), while simultaneously addressing inflammatory responses. CADP-10 self-assembles into nanobacterial net (NBacN) that selectively identify and bind to bacterial endotoxins (LPS and LTA), disrupting membrane integrity and depolarizing membrane potential, which culminates in bacterial death. Importantly, these NBacN are bound to LPS and LTA from dead bacteria, preventing their engagement with TLR receptors and effectively blocking downstream inflammatory pathways. Our assessments of CADP-10 demonstrate good biosafety in both in vitro and in vivo models. Notably, in a rabbit osteomyelitis model, CADP-10 eliminated MRSA-induced bone infections, mitigated inflammation, and promoted bone tissue regeneration. This research highlights the potential of CADP-10 as a multifunctional antimicrobial agent for the management of infectious inflammatory diseases.

Synergistic activity of menadione in combination with colistin against colistin-susceptible and colistin-resistant Gram-negative bacteria

OBJECTIVE

Antibiotic resistance poses a formidable challenge, especially with the emergence of multidrug-resistant Gram-negative bacteria. Colistin serves as a last-resort antibiotic to combat multidrug-resistance, but it is limited by its nephrotoxicity and rising resistance. This study introduces menadione, a synthetic form of vitamin K, as a potential adjuvant to enhance colistin's efficacy against both susceptible and resistant strains of Gram-negative bacteria.

METHODS

Through checkerboard dilution assays, we demonstrate that menadione significantly lowers the MICs of colistin, with fractional inhibitory concentration indices ranging from 0.031 to 0.375. Furthermore, synergistic effects were confirmed via time-kill kinetics, indicating effective bacterial growth inhibition. The study also explores the mechanism underlying this synergy, revealing that menadione in combination with colistin disrupts the bacterial outer membrane, reduces the proton motive force and adenosine triphosphate content, and amplify the production of reactive oxygen species, contributing to bacterial cell death.

RESULTS

Menadione was shown to prevent the evolution of colistin resistance.

CONCLUSIONS

This research highlights the potential of using menadione as a colistin adjuvant to combat antibiotic-resistant Gram-negative bacteria, providing a promising approach to extend the utility of existing antibiotics in clinical settings.

Tissue geometry spatiotemporally drives bacterial infections

Epithelial tissues serve as the first line of host against bacterial infections. The self-organization of epithelial tissues continuously adapts to the architecture and mechanics of microenvironments, thereby dynamically impacting the initial niche of infections. However, the mechanism by which tissue geometry regulates bacterial infection remains poorly understood. Here, we showed geometry-guided infection patterns of bacteria in epithelial tissues using bioengineering strategies. We discovered that cellular traction forces play a crucial role in the regulation of bacterial invasive sites and marginal infection patterns in epithelial monolayers through triggering co-localization of mechanosensitive ion channel protein Piezo1 with bacteria. Further, we developed precise mechanobiology-based strategies to potentiate the antibacterial efficacy in animal models of wound and intestinal infection. Our findings demonstrate that tissue geometry exerts a key impact on mediating spatiotemporal infections of bacteria, which has important implications for the discovery and development of alternative strategies against bacterial infections.

Bacteria-Responsive Drug Delivery System Utilizing Carboxymethyl Cellulose-Functionalized Metal-Organic Framework for Enhanced Antibacterial Efficacy

Bacterial infections pose a significant threat to human health and economic stability. The overuse of antibiotics has exacerbated bacterial resistance, highlighting the urgent need for innovative strategies to combat this issue. Bacteria-responsive drug delivery systems present a promising solution to overcoming bacterial resistance. Metal-organic frameworks (MOFs), versatile porous materials created by linking metal clusters with organic ligands, are ideal candidates for such applications. Here, we employed the zeolite imidazole framework 8 (ZIF-8) as a carrier for ceftiofur (EFT), enhanced with carboxymethyl cellulose to develop a smart drug delivery system (CMC-EFT@ZIF-8) responsive to pH and cellulase. In vitro tests demonstrated that this system released a higher quantity of EFT under acidic conditions and in the presence of cellulase, leading to more effective disruption of bacterial membranes and subsequent bacterial death. The CMC-EFT@ZIF-8 system achieved a 99% clearance of Pseudomonas aeruginosa within 6 h and showed superior efficacy in a mouse skin wound model. These findings underscore the potential of our smart drug delivery system to significantly improve treatment outcomes for bacterial infections, representing a significant advancement in the fight against antibiotic resistance.

Revitalizing Antibiotics with Macromolecular Engineering: Tackling Gram-Negative Superbugs and Mixed Species Bacterial Biofilm Infections In Vivo

The escalating prevalence of multidrug-resistant Gram-negative pathogens, coupled with dwindling antibiotic development, has created a critical void in the clinical pipeline. This alarming issue is exacerbated by the formation of biofilms by these superbugs and their frequent coexistence in mixed-species biofilms, conferring extreme antibiotic tolerance. Herein, we present an amphiphilic cationic macromolecule, ACM-AHex, as an innovative antibiotic adjuvant to rejuvenate and repurpose resistant antibiotics, for instance, rifampicin, fusidic acid, erythromycin, and chloramphenicol. ACM-AHex mildly perturbs the bacterial membrane, enhancing antibiotic permeability, hampers efflux machinery, and produces reactive oxygen species, resulting in a remarkable 64-1024-fold potentiation in antibacterial activity. The macromolecule reduces bacterial virulence and macromolecule-drug cocktail significantly eradicate both mono- and multispecies bacterial biofilms, achieving >99.9% bacterial reduction in the murine biofilm infection model. Demonstrating potent biocompatibility across multiple administration routes, ACM-AHex offers a promising strategy to restore obsolete antibiotics and combat recalcitrant Gram-negative biofilm-associated infections, advocating for further clinical evaluation as a next-generation macromolecular antibiotic adjuvant.

Ligilactobacillus salivarius regulating translocation of core bacteria to enrich mouse intrinsic microbiota of heart and liver in defense of heat stress

The aim of this study was to elucidate the intrinsic microbiota residing in the heart and liver, which was enriched with Ligilactobacillus salivarius supplementation and its roles in defending anti-oxidation of heat stress. The specific pathogen free (SPF) mice were employed to perform the study. Genomic sequencing showed that the intrinsic microbes in the heart and liver of SPF mice, which were primarily of the genera Burkholderia and Ralstonia, functioned in organic metabolism, environmental information processing, cellular processes, and genetic information processing. Lactobacillus sp. were found in the liver but not in the heart. The heart had a lower bacterial abundance than the liver. A culturomic assay of the heart flushing liquid indicated that the dominant species of bacteria were Ralstonia pickettii, Ralstonia sp._3PA37C10, Ralstonia insidiosa, Burkholderia lata, unclassified _g_ Ralstonia, and unclassified _p_ Pseudomonadota. Intrinsic bacteria exist in the heart due to their inhibitory action against pathogenic Escherichia coli. After, the mice were supplemented with Ligilactobacillus salivarius to optimize the microbiota levels. The dominant bacterial phyla in the liver and heart were Bacillota, Bacteroidota, Pseudomonadota, Thermodesulfobacteriota, andActinomycetota, which comprised 98.2% of total bacteria. The genus Lactobacillus was also abundant. Core bacteria such as Lactobacillus reuteri are translocated from the intestine to the heart and liver. The enriched bacterial composition up-regulated anti-oxidation capacities in the heart and liver. The levels of reactive oxygen species and superoxide dismutase (SOD) were significantly improved compared to those in control (P < 0.01). In conclusion, intrinsic bacteria present in the heart and liver alleviate infection by pathogens, environmental and genetic information processing, and cellular processes during heat stress exposure. Diet with Ligilactobacillus salivarius supplementation regulated the translocation of core bacteria to the heart and liver, improved bacterial composition, and induced a higher anti-oxidative capacity under heat stress.

Synergistic Antibacterial Activity of Amorolfine Combined with Colistin Against Acinetobacter baumannii

Emerging resistance to colistin in Acinetobacter baumannii is concerning because of the limited therapeutic options for this important clinical pathogen. Given the shortage of new antibiotics, one strategy that has been proven to be therapeutically effective is to overcome antibiotic-resistant pathogens by combining existing antibiotics with another antibiotic or non-antibiotic. This study was designed to investigate the potential synergistic antibacterial activity of amorolfine, a morpholine antifungal drug, in combination with colistin against A. baumannii. In this work, antibiotic susceptibility testing, checkerboard assays, and time-kill curves were used to investigate the synergistic efficacy of colistin combined with amorolfine. The molecular mechanisms of combination therapy were analyzed using fluorometric assays, UV-vis spectroscopy, and molecular docking. Finally, we evaluated the in vivo efficacy of combination therapy against A. baumannii. In brief, the combination therapy showed significant synergistic activity against A. baumannii (FICI = 0.094). In addition, the combination of amorolfine improved the membrane disruption of colistin, and amorolfine exhibited the capacity of binding to DNA. Moreover, in a mouse sepsis model, this combination therapy increased survival compared to colistin monotherapy. Our findings demonstrated that amorolfine serves as a potential colistin adjuvant against Acinetobacter baumannii.

Mechanistic insights into the multitarget synergistic efficacy of farrerol and β-lactam antibiotics in combating methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA), a principal causative agent of infections worldwide, urgently requires innovative interventions to counter its increasing risk. The present study revealed the profound impact of farrerol (FA), a robust bioactive agent, on the virulence and resistance mechanisms of MRSA. Our in-depth investigation revealed that FA significantly mitigated the β-lactam resistance of MRSA USA300, an achievement attributed to its precise interference with the BlaZ and Pbp2a protein. Additionally, FA indirectly diminishes the oligomerization of PBP2a by disrupting pigment synthesis, further contributing to its efficacy. In addition, FA extends its functional footprint beyond resistance modulation, exhibiting substantial antivirulence efficacy through selective inhibition of the accessory gene regulator (Agr) system, thereby significantly curbing MRSA pathogenicity in A549 cell and murine models. This study comprehensively explored the multiple impacts of FA on MRSA, shedding light on its versatile role as a BlaZ suppressor, pigment synthesis regulator, and AgrA activity modulator. These intricate findings firmly position FA as a compelling therapeutic candidate for addressing MRSA infections in the clinic.

Rational Design of Natural Xanthones Against Gram-negative Bacteria

Most antibiotics are ineffective against Gram-negative bacteria owing to the existence of the outer membrane (OM) barrier. The rational design of compounds to expand their antibacterial spectra of antibiotics solely targeting Gram-positive pathogens remains challenging. Here, the design of skeletons from natural products to penetrate the OM are deciphered. Structure-activity relationship analysis shows the optimization of the model of natural xanthones α-mangostin endows the broad-spectrum antibacterial activity. Mechanistic studies demonstrate the lead compound A20 penetrates the OM in a self-promoted pathway through electronic and hydrophobic interactions with lipopolysaccharides and phospholipids in OM. A20 displays rapid bactericidal activity by targeting the cofactor heme in the respiratory complex. The therapeutic efficacy of A20 is demonstrated in two animal models infected with multidrug-resistant Gram-negative bacterial pathogens. The findings elucidate the structural property and self-promoted transportation of a class of antibacterial compounds, to facilitate the design and discovery of antibacterial agents against increasingly prevalent Gram-negative pathogens associated with infections.

Glabridin restore the sensitivity of colistin against mcr-1-positive Escherichia coli by polypharmacology mechanism

The clinical effectiveness of colistin against multidrug-resistant Gram-negative pathogen infections has been threatened by the emergence of the plasmid-mediated colistin-resistant gene mcr-1. This development underscores the urgent need for innovative therapeutic strategies that target resistance mechanisms. In this study, we demonstrated that glabridin can restore the sensitivity of colistin to mcr-1-positive Escherichia coli (E. coli) and exhibits a reduced propensity for resistance development. Our investigation into the underlying mechanisms revealed that glabridin may re-sensitize E. coli to colistin by targeting MCR-1 to inhibit its activity, regulating the expression of mcr-1, and restoring the Zeta potential at the cell membrane surface. Furthermore, the combination of glabridin and colistin increased bacterial membrane permeability, decreased membrane fluidity, disrupted transmembrane proton motive force (PMF), reduced the ratios of NAD+/NADH and FAD/FADH2, facilitated the tricarboxylic acid (TCA) cycle, and led to the accumulation of reactive oxygen species (ROS) in E. coli cells, ultimately resulting in bacterial death. In animal models, glabridin significantly enhanced the efficacy of colistin in treating E. coli infections. Our findings suggest that glabridin is a promising polypharmacological antibiotic adjuvant for addressing infections associated with colistin-resistant E. coli.

Mini-binders targeting Streptococcus equi ssp. zooepidemicus M-like protein inhibit the bacterial adhesion and exert protective effects in vivo

Streptococcus equi ssp. zooepidemicus (Streptococcus zooepidemicus, SEZ) is one of the most common pathogens causing streptococcal disease in pigs in China and has been identified as a zoonotic pathogen, and thus poses great threat to the health of humans and pigs. The M-like protein (SzM) is the primary virulence factor of SEZ. Monoclonal antibodies (mAbs) targeting SzM have been demonstrated to provide effective protection against SEZ infection, but their preparation is cumbersome. Here, we designed mini-binders targeting SzM from scratch based on the RFdiffusion approach. Four potential binders were obtained in a short period of time, among which binder 3 showed the highest binding affinity to SzM protein. In vitro adhesion inhibition analysis demonstrated that binder 3 significantly suppressed the adhesion of SEZ to fibrinogen and HEp-2 cells. In vivo experiments showed that binder 3 treatment improved the survival rate (80 %) of mice infected with a 100-fold lethal dose of SEZ and significantly reduced the organ bacterial load. Our study provides new insights into the rapid development of stable anti-SEZ agents, which are expected to be ideal alternatives to mAbs.

Non-Membrane Active Peptide Resensitizes MRSA to β-Lactam Antibiotics and Inhibits S. aureus Virulence

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious global health threat due to its high morbidity and mortality rates, creating a dire need for novel therapeutic strategies. Antimicrobial peptides (AMPs), with broad-spectrum activity and low propensity for resistance development, show promise as effective antibiotic adjuvants to reverse multidrug-resistance in bacteria. Herein, it is uncovered that a potent and non-toxic AMP termed GN1 substantially resensitizes MRSA to multiple β-lactam antibiotics at low concentrations. Mechanistic studies indicate that GN1 functions by suppressing both the production and enzymatic activity of MRSA-associated resistance determinants, including penicillin-binding protein 2a (PBP2a) and β-lactamase. Additionally, GN1 exhibits a robust anti-virulence profile by inhibiting MRSA biofilm formation and staphyloxanthin production. Furthermore, GN1 induces bacterial metabolic perturbation, resulting in glutamate accumulation and oxidative damage. Importantly, the combination of GN1 with β-lactam antibiotics effectively mitigates MRSA-induced infections in the animal infection models. Collectively, these findings suggest that GN1 represents a potent β-lactam adjuvant and anti-virulence agent, offering a safe and versatile solution to combat MRSA infections.

A plant peptide with dual activity against multidrug-resistant bacterial and fungal pathogens

Multidrug-resistant (MDR) bacteria pose a major threat to public health, and additional sources of antibacterial candidates are urgently needed. Noncanonical peptides (NCPs), derived from noncanonical small open reading frames, represent small biological molecules with important roles in biology. However, the antibacterial activity of NCPs remains largely unknown. Here, we discovered a plant-derived noncanonical antibacterial peptide (NCBP1) against both Gram-positive and Gram-negative bacteria. NCBP1 is composed of 11 amino acid residues with cationic surface potential and favorable safety and stability. Mechanistic studies revealed that NCBP1 displayed antibacterial activity by targeting phosphatidylglycerol and cardiolipin in bacterial membrane, resulting in membrane damage and dysfunction. Notably, NCBP1 showed promising efficacy in mice. Furthermore, NCBP1 effectively inhibited the growth of plant fungal pathogens and enhanced disease resistance in maize. Our results demonstrate the unexplored antimicrobial potential of plant-derived NCPs and provide an accessible source for the discovery of antimicrobial substances against MDR bacterial and fungal pathogens.

Vitamin B6 resensitizes mcr-carrying Gram-negative bacteria to colistin

Antimicrobial resistance poses a severe threat to human health, with colistin serving as a critical medication in clinical trials against multidrug-resistant Gram-negative bacteria. However, the efficacy of colistin is increasingly compromised due to the rise of MCR-positive bacteria worldwide. Here, we reveal a notable metabolic disparity between mcr-positive and -negative bacteria through transcriptome and metabolomics analysis. Specifically, pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, was significantly diminished in mcr-positive bacteria. Conversely, supplementing with PLP could reverse the metabolic profile of drug-resistant bacteria and effectively restore colistin's bactericidal properties. Mechanistically, PLP was found to augment bacterial proton motive force by inhibiting the Kdp transport system, a bacterial K+ transport ATPase, thereby facilitating the binding of the positively charged colistin to the negatively charged bacterial membrane components. Furthermore, PLP supplementation triggers ferroptosis-like death by accumulating ferrous ions and inducing lipid peroxidation. These two modes of action collectively resensitize mcr-harboring Gram-negative bacteria to colistin therapy. Altogether, our study provides a novel metabolic-driven antibiotic sensitization strategy to tackle antibiotic resistance and identifies a potentially safe antibiotic synergist.

Antibacterial and anti-biofilm activities of Derazantinib (ARQ-087) against Staphylococcus aureus

The global rise of multidrug-resistant pathogens, particularly methicillin-resistant Staphylococcus aureus (MRSA), represents a critical public health challenge. This study evaluates the antibacterial and anti-biofilm activities of Derazantinib (ARQ-087) against S. aureus. ARQ-087 exhibited minimum inhibitory concentration (MIC) values ranging from 4 to 16 µM against S. aureus reference laboratory strains and diverse clinical MRSA isolates, demonstrating strong antibacterial activity with minimal resistance development. Time-kill assays demonstrated a concentration- and time-dependent reduction in bacterial viability. Crystal violet staining assays revealed that ARQ-087 significantly inhibited MRSA biofilm formation in a dose-dependent manner. Additionally, ARQ-087 exhibited strong anti-biofilm activity against pre-formed biofilms, as shown by colony counts and confocal laser scanning microscopy, which indicated extensive biofilm disruption and bacterial cell death. Mechanistic studies revealed that ARQ-087 disrupts bacterial membrane integrity, as evidenced by SYTOX Green and DISC3(5) fluorescence assays, while inducing intracellular ATP depletion and reactive oxygen species generation, contributing to bacterial death. ARQ-087 also displayed negligible hemolytic activity and no acute toxicity observed in a Galleria mellonella infection model. In this model, ARQ-087 prolonged the survival of larvae infected with S. aureus. These findings highlight ARQ-087 as a promising therapeutic candidate for treating MRSA infections and biofilm-associated diseases. Further preclinical studies are needed to confirm its potential for clinical application.

Zwitterionic Photosensitizer-Assembled Nanocluster Produces Efficient Photogenerated Radicals via Autoionization for Superior Antibacterial Photodynamic Therapy

Photodynamic therapy (PDT) holds significant promise for antibacterial treatment, with its potential markedly amplified when using Type I photosensitizers (PSs). However, developing Type I PSs remains a significant challenge due to a lack of reliable design strategy. Herein, a Type I PS nanocluster is developed via self-assembly of zwitterionic small molecule (C3TH) for superior antibacterial PDT in vivo. Mechanism studies demonstrate that unique cross-arranged C3TH within nanocluster not only shortens intermolecular distance but also inhibits intermolecular electronic-vibrational coupling, thus facilitating intermolecular photoinduced electron transfer to form PS radical cation and anion via autoionization reaction. Subsequently, these highly oxidizing or reducing PS radicals engage in cascade photoredox to generate efficient ·OH and O2‾·. As a result, C3TH nanoclusters achieve a 97.6% antibacterial efficacy against MRSA at an ultralow dose, surpassing the efficacy of the commercial antibiotic Vancomycin by more than 8.8-fold. These findings deepen the understanding of Type I PDT, providing a novel strategy for developing Type I PSs.

Alisol A 24-Acetate combats Methicillin-Resistant Staphylococcus aureus infection by targeting the mevalonate biosynthesis

Infections caused by Methicillin-resistant Staphylococcus aureus (MRSA) have emerged as one of the most pressing global public health challenges. In concert with global rise of antimicrobial resistance at alarming rate, there is an urgent need for alternative strategies to combat MRSA. Here, the high throughput screening indicated that the Alisol A 24-acetate (AA) effectively inhibits the mevalonate (MVA) synthesis in MRSA. The mechanistic analysis revealed that AA competitively inhibits the 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMGR) protein to blockade the MVA pathway, thereby disrupting the bacterial membrane integrity and functions. Further investigations showed that this disruption consequently restores the β-lactam susceptibility in MRSA by retarding the expression of PBP2a protein and dampens the virulence of MRSA by reducing the exotoxins secretion. In addition to the effect on MRSA, AA has been found to exert host-acting activity to reduce the MRSA-induced inflammation. The promising anti-MRSA activity of AA was further confirmed in vivo. Collectively, the current study highlighted the potential of AA as a proposing drug for combating MRSA and emphasize the MVA pathway as an ideal therapeutic target for MRSA treatment.

Association of idealized amphiphiles and protease inhibitors: Conferring antimicrobial peptides with stable antibacterial activity under physiological conditions to combat multidrug-resistant bacteria

AIMS

The unstable antimicrobial activity of antimicrobial peptides (AMPs) under physiological conditions (especially the degradation instigated proteases) seems to be a persistent impediment for their successful implementation in clinical trials. Consequently, our objective was to devise AMP engineering frameworks that could sustain robust antibacterial efficacy within physiological environments.

METHODS

In this work, we harvested AMPs with stable antimicrobial activity under the physiological barriers through the combination of idealized amphiphiles and trypsin inhibitors.

RESULTS

We screened and identified the lead peptides IK3-A and IK3-S, which showed potent activity against Gram-negative bacteria, including multidrug-resistant (MDR) bacteria, and exhibited promising biocompatibility with mammalian cells. Remarkably, IK3-A and IK3-S maintained sustained antibacterial potency under physiological salts, serum, and protease conditions. Furthermore, both IK3-A and IK3-S kill Gram-negative bacteria by attacking the bacterial cell membrane and inducing oxidative damage (at high concentrations). Crucially, IK3-A and IK3-S have optimal safety and efficacy in mice.

CONCLUSIONS

This is the first work to compare the effects of different trypsin inhibitors on the resistance of AMPs to protease hydrolysis on the same sequence platform. In conclusion, these findings provide guidance for the molecular design of AMPs with stable antibacterial activity under physiological conditions and facilitates the process of clinical translation of AMPs as antimicrobial biomaterials against MDR bacteria. Moreover, this may stimulate a more general interest in protease inhibitors as molecular scaffolds in the creation of highly stable peptide-based biomaterials.

Dual-Functional Antibiotic Adjuvant Displays Potency against Complicated Gram-Negative Bacterial Infections and Exhibits Immunomodulatory Properties

The treatment of Gram-negative bacterial infections is challenged by antibiotic resistance and complicated forms of infection like persistence, multispecies biofilms, intracellular infection, as well as infection-associated hyperinflammation and sepsis. To overcome these challenges, a dual-functional antibiotic adjuvant has been developed as a novel strategy to target complicated forms of bacterial infection and exhibit immunomodulatory properties. The lead adjuvant, D-LBDiphe showed multimodal mechanisms of action like weak outer membrane permeabilization, weak membrane depolarization, and inhibition of efflux machinery, guided primarily by hydrogen bonding and electrostatic interactions, along with weak van der Waals forces. D-LBDiphe potentiated antibiotics up to ∼4100-fold, targeted phenotypic forms of antibiotic tolerance, and revitalized antibiotics against topical and systemic infections of P. aeruginosa in mice. The aromatic moiety in D-LBDiphe was instrumental for interaction with lipopolysaccharide (LPS) micelles, and this interaction was the driving factor in reducing pro-inflammatory cytokines by 61.8-79% in mice challenged with LPS. Such multifarious properties of a weak-membrane perturbing, nonactive and nontoxic adjuvant have been discussed for the first time, supported by detailed mechanistic understanding and elucidation of structure-guided properties. This work expands the scope of antibiotic adjuvants and validates them as a promising approach for treatment of complicated bacterial infections and inflammation.

In vitro potentiation of tetracyclines in Pseudomonas aeruginosa by RW01, a new cyclic peptide

The pipeline for new drugs against multidrug-resistant Pseudomonas aeruginosa remains limited, highlighting the urgent need for innovative treatments. New strategies, such as membrane-targeting molecules acting as adjuvants, aim to enhance antibiotic effectiveness and combat resistance. RW01, a cyclic peptide with low antimicrobial activity, was selected as an adjuvant to enhance drug efficacy through membrane permeabilization. RW01's activity was evaluated via antimicrobial susceptibility testing in combination with existing antibiotics on 10 P. aeruginosa strains and analog synthesis. Synergy was assessed using checkerboard assays, and one-step mutants were generated to identify altered pathways through whole-genome sequencing and variant analysis. Permeabilizing activity was studied using flow cytometry and real-time fluorescence measurement. In vivo toxicity was assessed in female C57BL/6J mice, and possible interaction with mouse serum was also evaluated. Susceptibility testing revealed specific synergy with tetracyclines, with up to a 16-fold reduction in minimum inhibitory concentrations. Sequencing revealed that resistance to the RW01-minocycline combination involved mutations in the pmrB gene, affecting outer membrane lipopolysaccharide composition. This was further confirmed by the identification of cross-resistance to colistin in these mutants. RW01 reduced the mutant prevention concentration of minocycline from 64 to 8 mg/L. RW01 was demonstrated to enhance membrane permeabilization and therefore minocycline uptake with statistical significance. Synthetic derivatives of RW01 showed a complete loss of activity, highlighting the importance of RW01's D-proline(NH2) residue. No acute or cumulative in vivo toxicity was observed in mice. These findings suggest that RW01 could revitalize obsolete antimicrobials and potentially expand therapeutic options against multidrug-resistant P. aeruginosa.

Self-assembling peptide with dual function of cell penetration and antibacterial as a nano weapon to combat intracellular bacteria

Intracellular bacterial infections and antimicrobial resistance are threatening global public health systems. Antimicrobial peptides are a potential solution to combat bacterial resistance, but the design of self-assembled nanopeptides with dual functions of cell penetration and antibacterial properties to combat intracellular bacteria remains a challenge. Here, we propose a strategy to develop self-assembled nanopeptides with dual functions through the chimerization of self-assembled core, hydrophobic motif, and cell-permeable unit. The optimal nanopeptides, F3FT and N3FT, exhibited potent antibacterial activity and excellent biocompatibility. Crucially, F3FT and N3FT are able to efficiently penetrate cells and eliminate intracellular bacteria and sniping inflammation. Moreover, F3FT and N3FT kill bacteria mainly by disrupting bacterial cell membranes and inducing excessive accumulation of reactive oxygen species. F3FT and N3FT have exhibited good safety and potent therapeutic potential in vivo. This scheme of constructing nanopeptides through multifunctional domains design provides a paradigm for dealing with escalating of intracellular bacteria and antimicrobial resistance.

Discovery, synthesis, and antibacterial activity of novel myrtucommulone analogs as inhibitors of DNA gyrase and topoisomerase IV

Drug-resistant bacterial infections have emerged as a new challenge in anti-infective treatment, posing a significant threat to public health. DNA gyrase and topoisomerase IV (Topo IV) are promising targets for designing new antibiotics. Myrtus communis L. has long been used as a traditional herb for antisepsis and disinfection; however, the underlying mechanism of the antibacterial activity remains unclear. In this study, a class of novel myrtucommulone derivatives was synthesized and evaluated for DNA gyrase and Topo IV inhibitions. Analog 27 was the most potent DNA gyrase and Topo IV inhibitor. In bioactivity assays, molecule 27 exhibited a significant antibacterial effect against methicillin-resistant Staphylococcus aureus (MRSA). Additionally, it exhibited rapid bactericidal properties, low toxicity, and low inducing bacterial resistance. It demonstrated synergistic effects with ofloxacin, amikacin, cefepime, and ceftazidime, which make it a potential candidate for antimicrobial application. This work will facilitate the future development of myrtucommulone-based DNA gyrase and Topo IV inhibitors as novel antimicrobials to combat the increasing prevalence of multidrug-resistant bacteria.

Investigation on the reversal effect of closantel on colistin resistance in MCR-1 positive Escherichia coli based on dose-response relationship

BACKGROUND

The lack of research on the dose-response relationship of adjuvants in reversing colistin resistance will lead to a lack of scientific theoretical basis for determining the dosage of adjuvants in clinical combination therapy plans or their compound formulations.

OBJECTIVES

This study investigates the dose-response relationship of the deworming drug closantel (CST) on the reversal of colistin resistance in mcr-1-positive Escherichia coli (E. coli).

METHODS

Firstly, the reversal effect of different concentrations of CST on colistin resistance in mcr-1-positive E. coli was analysed using broth microdilution method, checkerboard method and time-killing curves. Then, the inhibitory effect of CST on the development of colistin resistance, as well as the haemolytic and cytotoxic properties of CST, was analysed. Finally, the in vivo efficacy of the combination of CST and colistin was evaluated.

RESULTS

Both the checkerboard assays and the time-killing curves indicate that there is a special dose-response relationship between CST and its reversal effect on colistin resistance, which is not concentration-dependent. High reversal efficiency can be achieved within a low concentration range. However, as the CST concentration increases, the ability to reverse colistin resistance remains unchanged or decreases, which resulted in a gradual decrease in reversal efficiency. Additionally, CST can inhibit the development of colistin resistance and reduce the cytotoxicity of colistin. Importantly, in a mouse model of E. coli infection, the combination of CST and colistin showed a significant therapeutic effect.

CONCLUSIONS

This study indicates a special dose-response relationship between CST and its reversal effect on colistin resistance, which was not concentration-dependent.

A Milk Extracellular Vesicle-Based Nanoplatform Enhances Combination Therapy Against Multidrug-Resistant Bacterial Infections

The increasing occurrence of infections caused by multidrug-resistant (MDR) bacteria drives the need for new antibacterial drugs. Due to the current lack of antibiotic discovery and development, new strategies to fight MDR bacteria are urgently needed. Efforts to develop new antibiotic adjuvants to increase the effectiveness of existing antibiotics and design delivery systems are essential to address this issue. Here, a bioinspired delivery system equipped with combination therapy and paracellular transport is shown to enhance the efficacy against bacterial infections by improving oral delivery. A screening platform is established using an in vitro-induced high polymyxin-resistant strain to acquire plumbagin, which enhances the efficacy of polymyxin. Functionalized milk extracellular vesicles (FMEVs) coloaded with polymyxin and plumbagin cleared 99% of the bacteria within 4 h. Mechanistic studies revealed that the drug combination damaged the membrane, disrupted energy metabolism, and accelerated bacterial death. Finally, FMEVs are efficiently transported transcellularly through the citric acid-mediated reversible opening of the tight junctions and showed high efficacy against an MDR Escherichia coli-associated peritonitis-sepsis model in mice. These findings provide a potential therapeutic strategy to improve the efficacy of combination therapy by enhancing oral delivery using a biomimetic delivery platform.

Synergistic antimicrobial efficacy of glabrol and colistin through micelle-based co-delivery against multidrug-resistant bacterial pathogens

BACKGROUND

Widespread bacterial infection and the spread of multidrug resistance (MDR) exhibit increasing threats to the public and thus require new antibacterial strategies. Coupled with the current slow pace of antibiotic development, the use of antibiotic adjuvants to revitalize existing antibiotics offers great potential.

PURPOSE

We aim to explore the synergistic antimicrobial mechanism of glabrol (GLA) and colistin (COL) while developing an innovative multifunctional micelle-based drug delivery system to enhance therapeutic efficacy.

METHODS

The synergy between GLA and COL was assessed through a combination of high-throughput screening and checkerboard analysis techniques. Moreover, we performed fluorescence-based assays to investigate the underlying mechanisms of action of the GLA and COL combination. We also developed a multifunctional drug delivery platform that integrates GLA and COL into co-loaded composite micelles, aimed at improving antibacterial efficacy against peritoneal sepsis and chronic bacterial wound infections caused by diverse microbial pathogens.

RESULTS

We have discovered that natural flavonoids found in plants act synergistically with colistin against MDR bacterial infections, effectively improving its efficacy through a co-delivery strategy. The combination therapy consisting of GLA and COL exhibits enhanced antibacterial efficacy and is capable of clearing 99% of MDR Gram-positive and Gram-negative bacteria in 4 h. Mechanistic studies showed that COL increases the outer membrane permeability, which promotes the adhesion of GLA to the inner membrane, disrupting bacterial metabolism, and ultimately leading to bacterial death. Furthermore, a novel pH-responsive hydrogel system was developed and dispersed with GLA and COL co-loaded composite micelles to mitigate the selective pressure of antibiotics with fewer side effects. Lastly, such a system showed high efficacy in two animal models.

CONCLUSION

Our findings provide a potential therapeutic option using a co-delivery system functionalized with combination therapy, to address the prevalent infections caused by complex bacterial infections and even MDR bacterial infections.

The Evolution of Antimicrobial Resistance in Acinetobacter baumannii and New Strategies to Fight It

Acinetobacter baumannii is considered one of the prioritized ESKAPE microorganisms for the research and development of novel treatments by the World Health Organization, especially because of its remarkable persistence and drug resistance. In this review, we describe how this can be acquired by the enzymatic degradation of antibiotics, target site modification, altered membrane permeability, multidrug efflux pumps, and their ability to form biofilms. Also, the evolution of drug resistance in A. baumannii, which is mainly driven by mobile genetic elements, is reported, with particular reference to plasmid-associated resistance, resistance islands, and insertion sequences. Finally, an overview of existing, new, and alternative therapies is provided.

Cuminaldehyde Potentiates Antiproteolytic Peptide Efficacy via Parallel Pathways of Enhanced Inner Membrane-Damaging Activity and Inhibition of Bacterial Energy Metabolism

Antimicrobial peptides (AMPs) offer potential as antibiotic alternatives, but high cost, off-site cytotoxicity, and poor stability limit their application. Combining AMPs with adjuvants holds promise in surmounting these limitations. Among potentiators, terpenoids account for the highest proportion, yet their potential to enhance the AMPs efficacy and underlying mechanism remain unclear. Hence, we investigated the potential of monoterpenoids to enhance the efficacy of antiproteolytic AMPs N1 (NalAArIILrWrFR). Cuminaldehyde potentiated N1 activity against all tested strains, with FICI from 0.375 to 0.094. N1/cuminaldehyde combination also worked synergistically against drug-resistant bacteria, exhibited a low incidence of resistance development, and was not synergistically toxic to eukaryotes. Furthermore, cuminaldehyde enhanced N1 stability in salts, serum, and proteases. Mechanistically, cuminaldehyde enhanced the inner-membrane-damaging activity of N1 and inhibited bacterial energy metabolism. Finally, cuminaldehyde enhanced the efficacy of N1 against ETEC K88-induced enteritis in mice. Collectively, cuminaldehyde may be a promising N1 adjuvant to combat bacterial infections and circumvent antibiotic resistance.

Antimicrobial activity of ceftibuten/polymyxin B combination against polymyxin/carbapenem-resistant Klebsiella pneumoniae

OBJECTIVES

To evaluate the synergistic effect of a ceftibuten and polymyxin B combination and to determine its capacity to overcome polymyxin B resistance in polymyxin/carbapenem-resistant (PC-R) Klebsiella pneumoniae.

METHODS

To investigate the combination's antibacterial efficacy, antimicrobial susceptibility tests using broth microdilution methods, chequerboard assays and time-kill testing were performed. Antibiofilm activity was also assessed. The treatment's effect on the bacterial cell membrane was examined by quantifying intracellular protein leakage and conducting scanning electron microscopy. Haemocompatibility tests were conducted to evaluate toxicity. Additionally, an infection model was established using Swiss mice to assess in vivo antimicrobial activity.

RESULTS

The ceftibuten/polymyxin B combination demonstrated synergistic effects against several PC-R strains of K. pneumoniae, as determined by the FIC index (FICI) values, which ranged from 0.15 to 0.37. This combination was efficacious, exhibiting bactericidal activity at twice the MIC. Ceftibuten/polymyxin B also demonstrated antibiofilm activity. Additionally, ceftibuten/polymyxin B neither damaged the bacterial membrane nor exhibited haemolytic activity. Based on these findings, the in vivo therapeutic potential was investigated and it was found that ceftibuten/polymyxin B significantly decreased the bacterial load in the peritoneal lavage fluid of mice, revealing its effectiveness in treating infections caused by PC-R K. pneumoniae.

CONCLUSIONS

The ceftibuten/polymyxin B combination exhibited synergistic effects in vitro and in vivo, and thus might be a promising therapeutic alternative for treating PC-R K. pneumoniae infections. As the combination was efficacious in preclinical models, researchers may further investigate its potential in clinical studies.

Curcumin reverses high-level tigecycline resistance mediated by different mechanisms in Gram-negative bacteria

BACKGROUND

Tigecycline is one of the few effective treatments for multidrug-resistant bacteria. However, the recent emergence and spread of high-level tigecycline resistance in Enterobacteriaceae have significantly limited its clinical use. To combat this challenge, combining antibiotics with adjuvants has emerged as a promising strategy. Curcumin, known for its antibacterial properties and ability to enhance antibiotic efficacy, presents a viable option for reversing tigecycline resistance.

PURPOSE

This study aimed to evaluate the in vitro and in vivo synergistic effects of curcumin and tigecycline in gram-negative bacteria with different tigecycline resistance mechanisms and to elucidate the molecular mechanisms by which curcumin reverses tigecycline resistance.

METHODS

The checkerboard assay was used to evaluate the synergistic effects of tigecycline and curcumin, while the time-killing curves were used to assess their antibacterial activity. The study also examined their impact on biofilm eradication, the development of tigecycline resistance, and the conjugative transfer of tigecycline-resistant plasmids. The molecular mechanisms underlying the combined effect were investigated. Additionally, the in vivo efficacy of the tigecycline-curcumin combination against tigecycline-resistant Escherichia coli was assessed using a mouse peritonitis infection model.

RESULTS

This study revealed that curcumin and tigecycline exhibited synergistic effects against tigecycline-resistant gram-negative bacteria with various resistance mechanisms in vitro. Notably, the addition of curcumin delayed the development of tigecycline resistance in E. coli and impeded the horizontal transfer of tet(X4)-positive IncX1 plasmid. The curcumin-tigecycline combination significantly disrupted cell membrane integrity and reduced efflux pump activity by modulating proton dynamics and inhibiting ATP synthesis. Transcriptomic and proteomic analyses supported these findings, revealing disruptions in central carbon metabolism and substantial effects on the electron transport chain. In vivo experiments using a peritonitis model induced by the tet(X4)-carrying E. coli ZZ9DT16R demonstrated that the curcumin-tigecycline combination improved survival rates, reduced bacterial counts, and enhanced liver and spleen histopathology. Furthermore, the expression of the tet(X4) gene was reduced, and molecular docking studies indicated that curcumin binds to diverse tigecycline resistance proteins.

CONCLUSION

This study is the first to reveal the synergistic action of curcumin and tigecycline, highlighting its potential as a combined therapeutic strategy against tigecycline-resistant gram-negative pathogens with various resistance mechanisms.

Extended structure-activity relationship studies of the [1,2,5]oxadiazolo[3,4-b]pyrazine-containing colistin adjuvants

Antimicrobial resistance (AMR) is a formidable global health challenge. Multidrug-resistant (MDR) Gram-negative bacterial infections are of primary concern due to diminishing treatment options and high morbidity and mortality. Colistin, a polymyxin family antibiotic, is a last-resort treatment for MDR Gram-negative infections, but its wider use has resulted in escalating resistance. In 2022, using a screening approach, we discovered that a [1,2,5]oxadiazolo[3,4-b]pyrazine (ODP)-containing compound selectively re-sensitized various MDR Gram-negative bacteria to colistin. Initial structure-activity relationship (SAR) studies confirmed that bisanilino ODP compounds are colistin adjuvants with low mammalian toxicity. Herein, we report our extended SAR studies on a wide range of ODP analogs bearing alkyl- or arylalkylamines. Specifically, we discovered two new compounds, 5q and 8g, with potent colistin-potentiating activity and low mammalian toxicity in a wide range of clinically relevant pathogens.

Improving the Stability and Anti-Infective Activity of Sea Turtle AMPs Using Multiple Structural Modification Strategies

Antimicrobial peptides (AMPs) are regarded as promising candidates for combating antimicrobial resistance. Previously we identified an AMP named Cm-CATH2 from the green sea turtle, which exhibited potent antibacterial activity and attractive potential in application. However, natural AMPs including Cm-CATH2 frequently suffer from structural instability and sensitivity to physiological conditions, limiting their effectiveness. Herein, we explored various strategies to enhance the efficacy and stability of Cm-CATH2, including peptide truncation, non-natural amino acid substitutions, disulfide bond-based cyclization, and stapled peptide techniques. The results demonstrated that the truncated NCM4 significantly improved the antimicrobial capability of Cm-CATH2 while also enhancing its anti-inflammatory and antibiofilm activities with minimal cytotoxicity. Further ornithine-substituted peptide oNCM markedly enhanced the stability of NCM4 without compromising its antimicrobial efficacy. This study successfully designed a lead peptide oNCM with significant development potential, while providing valuable insights into the advantages and limitations associated with diverse strategies for enhancing the stability of AMPs.

Repurposing pinaverium bromide against Staphylococcus and its biofilms with new mechanisms

Antibiotic resistance by methicillin-resistant Staphylococcus aureus (MRSA) is an urgent threat to human health. The biofilm and persister cells formation ability of MRSA and Staphylococcus epidermidis often companied with extremely high antimicrobial resistance. Pinaverium bromide (PVB) is an antispasmodic compound mainly used for irritable bowel syndrome. Here we demonstrate that PVB could rapidly kill MRSA and S. epidermidis planktonic cells and persister cells avoiding resistance occurrence. Moreover, by crystal violet staining, viable cells counting and SYTO9/PI staining, PVB exhibited strong biofilm inhibition and eradication activities on the 96-well plates, glass surface or titanium discs. And the synergistic antimicrobial effects were observed between PVB and conventional antibiotics (ampicillin, oxacillin, and cefazolin). Mechanism study demonstrated the antimicrobial and antibiofilm effects by PVB were mainly mediated by proton motive force disrupting as well as reactive oxygen species inducing. Although, relatively poor pharmacokinetics were observed by systemic use, PVB could significantly reduce the viable bacterial cell loads and inflammatory infiltration in abscess in vivo caused by the biofilm forming strain ATCC 43,300. In all, our results indicated that PVB could be an alternative antimicrobial reagent for the treatment of MRSA, S. epidermidis and its biofilm related skin and soft tissue infections.

The Efficacy of Cecropin Against Multidrug-Resistant Bacteria Is Linked to the Destabilization of Outer Membrane Structure LPS of Gram-Negative Bacteria

The escalating prevalence of antibiotic-resistant bacteria has emerged as a formidable threat to global health, and the quest for alternative antimicrobial agents is imperative. Cecropins, a class of antimicrobial peptides (AMPs), have garnered attention due to their potent bactericidal properties. This investigation delves into the antibacterial prowess of Cecropin A (CA) and Cecropin AD (CAD), showcasing their robust activity against Gram-negative bacteria, inclusive of multidrug-resistant bacteria. The bactericidal efficacy of CA and CAD is characterized by a dose-responsive paradigm, affirming their potential as therapeutic agents. These peptides exhibit minimal cytotoxicity and hemolytic effects, underscoring their safety profile. Advanced experimentation has elucidated that cecropins could disrupt the outer bacterial membrane, targeting lipid A, a pivotal constituent of the lipopolysaccharides (LPS) in the outer membrane as their antimicrobial bullseye. The affinity of cecropins for LPS and their antimicrobial action underscore the therapeutic potential of these peptides in targeting Gram-negative bacterial infections. These insights accentuate the promise of cecropins as viable "antibiotic substitutes," paving the path for their expanded application in combating antibiotic resistance.

Novel 2-aminothiazole analogues both as polymyxin E synergist and antimicrobial agent against multidrug-resistant Gram-positive bacteria

The widespread emergence of antibiotic resistance poses a substantial challenge to global health. While polymyxin E serves as a final option in treatment, its effectiveness is hindered by dose-related toxicity. A crucial strategy for addressing this issue involves incorporating an antibiotic adjuvant to enhance the antibiotic's efficacy and decrease the required dosage. Here, we reported a multifunctional antibacterial compound A33, containing a 2-aminothiazole scaffold. In vitro studies demonstrated that A33 in combination with polymyxin E inhibited the growth of various Gram-negative bacteria, meanwhile with minimum inhibitory concentrations (MICs) of 0.5-4 μg/mL against twenty-three Gram-positive bacteria, including two drug-resistant strains. In vivo studies showed significant efficacy of the combined treatment of A33 and polymyxin E in a mouse infection model. The mice treated with compound A33 (64 mg/kg) and polymyxin E (0.5 mg/kg) in combination had a 100 % survival rate. Mechanistic studies suggested that A33 might exert its synergistic effect by targeting the outer membrane of Gram-negative bacteria. The ADMET data demonstrated that A33 possessed good pharmacokinetic profiles and drug-likeness properties. Overall, the optimized compound A33 assisted polymyxin E in combating various Gram-negative bacteria and exhibited bactericidal effects against drug-resistant Gram-positive bacteria, offering a new potential therapeutic approach for managing mixed bacterial infections.

Paeonol potentiates colistin efficacy against K. pneumoniae by promoting membrane disruption and oxidative damage

BACKGROUND

Although colistin is widely recognized as the last line of antibiotics against gram-negative bacteria, the emergence and spread of colistin resistance severely diminish its clinical efficacy and application. An alternative strategy to alleviate this crisis is to identify promising colistin adjuvants with enhanced antibacterial activity.

PURPOSE

In this study, the adjuvant effects of paeonol on colistin and the underlying mechanisms were investigated.

METHOD

Minimum Inhibitory Concentration (MIC) and checkerboard assays were used to investigate the adjuvant activity and structure-activity relationship of paeonol on the antibacterial effect of colistin in vitro. Time-dependent killing and resistance development assays were used to investigate the bactericidal effects and emergence of colistin resistance. Different fluorescent probes and competitive inhibition tests were used to investigate bacterial membrane functions and potential targets. Skin infection and peritonitis-sepsis models were used to evaluate the combined in vivo effects of colistin and paeonol in vivo.

RESULT

Paeonol enhanced the antibacterial effects of colistin against gram-negative bacteria, particularly Klebsiella pneumoniae. Structure-activity relationship analysis showed that the hydroxyl, 4-methoxy and ketone carbonyl side chains of the benzene ring contributed to the adjuvant effect of paeonol. Paeonol enhances the bactericidal effects of colistin and minimizes the emergence of colistin resistance. Notably, mechanistic studies demonstrated that the combination of colistin and paeonol enhances membrane disruption and oxidative damage, possibly via interactions with phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CAL). Importantly, paeonol enhanced the efficacy of colistin in both the skin and peritonitis infection models.

CONCLUSION

This is the first report on the adjuvant potential of paeonol in colistin to combat K. pneumoniae by promoting membrane disruption and oxidative damage via targeting membrane phospholipids. Notably, the verified target, PE, provides an additional avenue for screening new colistin adjuvants.The combination therapy of paeonol and colistin is a promising strategy for treating infections caused by gram-negative pathogens to address antibiotic resistance issues.