Search Results (635)

Staphylococcus aureus is a leading cause of bacterial keratitis and antimicrobial resistance-associated death globally. This study aimed to evaluate the efficacy of CaD23, a human-derived hybrid antimicrobial peptide (AMP), in combination with antibiotics in treating S. aureus infections. The efficacy of CaD23 and six medically important antibiotics (amikacin, cefuroxime, chloramphenicol, fosfomycin, vancomycin and levofloxacin) was examined against six strains of methicillin-sensitive and methicillin-resistant S. aureus using a minimum inhibitory concentration (MIC) assay. CaD23–antibiotic interactions were evaluated using checkerboard and time–kill kinetics assays. 3,3′-dipropylthiadicarbocyanine iodide (DiSC_3,5) cytoplasmic membrane depolarisation assay was performed to examine the mechanism of action. Overall, CaD23 exhibited good efficacy against all MSSA and MRSA (MIC = 16–32 μg/mL [6.7–13.3 μM]). Of 20 peptide–antibiotic–organism combinations, 19 (95%) combinations demonstrated positive interactions, with six (31.6%) and 13 (68.4%) exhibiting synergistic (FICI = 0.293–0.412) and additive effects (FICI = 0.521–0.890), respectively. CaD23 was able to achieve complete bacterial eradication significantly faster than cefuroxime and levofloxacin (15 min vs. 8–24 h). When used at a sub-MIC concentration, CaD23 could accelerate the killing of S. aureus of cefuroxime from 8–24 h to within 1 h and enhance the activity of levofloxacin by 90%. CaD23 was shown to rapidly depolarise the inner membrane of S. aureus within seconds of the treatment. In conclusion, CaD23–antibiotic combination therapy serves as a useful strategy for tackling drug-resistant ocular and systemic S. aureus infections. Full article

Physiologically produced circulating β-amyloid (Aβ) exerts critical physiological functions. Although Aβ is a key player in Alzheimer’s disease (AD), it may initially be beneficial at the onset of infection. As an evolutionary conserved antimicrobial peptide (AMP), Aβ contributes to innate immune defense against pathogens. Host defense peptides such as Aβ and human cathelicidin (LL-37) not only kill pathogens through their antimicrobial activity but also exhibit high affinity for bacterial lipopolysaccharides (LPSs) and membrane receptors. LL-37, which is upregulated in the brain, binds to Aβ, modulating its aggregation; Aβ and LL-37 are protective under physiological conditions, but during chronic infection or dysregulation, their interaction becomes toxic and contributes to AD pathology. Similarly to Aβ, LL-37 can induce neuroinflammation by stimulating human microglia to release inflammatory cytokines, such as TNF-α and IL-6. Neuroinflammation is essential for protecting the brain from pathogens—when prolonged, it drives pathological processes underlying AD, Parkinson’s disease (PD), and other neurodegenerative disorders. Full article

Background/Objectives: Antimicrobial peptides (AMPs) are promising candidates against multidrug-resistant bacteria, although their clinical translation is frequently limited by cytotoxicity. In this study, we investigated whether combinations of structurally related oligomeric analogs could cooperatively enhance bacterial membrane targeting while redistributing the associated cytotoxic burden. Methods: Monomeric, dimeric, and tetrameric AMPs were evaluated through antimicrobial susceptibility testing, checkerboard interaction assays, RAW 264.7 macrophage cytotoxicity assays, and all-atom molecular dynamics simulations, including biased membrane insertion and umbrella sampling analyses. In addition, we introduced the Combinatorial Therapeutic Index (CTI) as an exploratory metric to estimate the predicted reduction in cytotoxic burden associated with peptide combinations. Results: Cytotoxicity varied substantially among oligomeric forms, with larger and more hydrophobic peptides, particularly tetramers, exhibiting the highest cytotoxicity. Additive effects were observed in checkerboard assays involving linear, dimeric, and tetrameric forms, supporting the redistribution of the toxic burden and enabling the beneficial membrane-interaction properties of hydrophobic linear peptides to be leveraged at lower cytotoxic cost. Predicted therapeutic improvement ranged from approximately twofold for the SET-M33:L33 combination to nearly ninefold for the SET-M33:DIM-33:L8 triple combination. Molecular dynamics simulations revealed non-redundant membrane interaction behaviors, with smaller peptides exhibiting deeper membrane insertion and the dimeric form favoring interfacial membrane engagement. Conclusions: These findings support a cooperative formulation strategy in which structurally related SET-M33 oligomers contribute complementary antibacterial functions while reducing the predicted cytotoxic burden. Further experimental validation using direct cytotoxicity assays of complete peptide mixtures will be necessary to confirm the therapeutic potential of these formulations. Full article

Serratia spp., particularly Serratia marcescens, have emerged as clinically important opportunistic pathogens and are increasingly recognized as causes of healthcare-associated infections, especially among critically ill and immunocompromised patients. Their remarkable ecological adaptability, persistence in hospital environments, and capacity to acquire multiple antimicrobial resistance determinants have contributed to the global emergence of multidrug-resistant strains and complicated therapeutic management. This review aims to comprehensively analyze the epidemiology, virulence mechanisms, antimicrobial resistance patterns, and current and emerging therapeutic strategies associated with Serratia spp. The manuscript is based on a critical review and analysis of previously published literature retrieved from electronic scientific databases focusing on clinically relevant Serratia spp. infections and resistance trends. The reviewed literature demonstrates that Serratia spp. combine intrinsic resistance mechanisms, particularly inducible chromosomal AmpC β-lactamases, with acquired resistance determinants including extended-spectrum β-lactamases, carbapenemases, aminoglycoside-modifying enzymes, and plasmid-mediated quinolone resistance. Horizontal gene transfer and biofilm formation further enhance bacterial persistence, dissemination, and adaptation within healthcare settings. Clinically, these pathogens are associated with device-related infections, bloodstream infections, pneumonia, urinary tract infections, and hospital outbreaks, where increasing multidrug and carbapenem resistance significantly limits therapeutic options. Novel β-lactam/β-lactamase inhibitor combinations and cefiderocol represent promising therapeutic approaches, although treatment success remains highly dependent on accurate identification of underlying resistance mechanisms. This review highlights the growing public health importance of Serratia spp. and underscores the need for improved surveillance, molecular diagnostics, antimicrobial stewardship, and the development of innovative therapeutic strategies in the context of the evolving antimicrobial resistance crisis. Full article

Cationic antimicrobial peptides (AMPs) that can target multidrug-resistant pathogenic bacteria via multiple mechanisms are considered promising alternatives to antibiotics. Small (~9 kDa) highly acidic acyl carrier proteins (ACPs), which are a well-known cofactor protein in bacterial fatty acid synthesis (FAS), are a potential intracellular target for AMPs. A previous study has demonstrated that the human AMP LL-37 can bind to ACP and thereby affect FAS and the bacterial membrane integrity. In this work, we have investigated the interactions of different classes of AMPs and antibiofilm peptides (ABPs) with the ACPs of two pathogens. We first studied the folding characteristics of the two ACPs and found that Pseudomonas aeruginosa ACP (PaACP) is fully folded at neutral pH in the absence of divalent cations. On the other hand, the homologous Francisella novicida ACP (FnACP) is unfolded at low ionic strength, but it adopts a fully folded conformation after the addition of divalent cations such as Ca²⁺ or Mg²⁺. These distinct characteristics were shown to be related to a unique His residue that is involved in a stabilizing cation–π interaction. Subsequent biophysical SPR and NMR interaction studies reveal that cationic AMPs and ABPs such as LL-37, melittin, tritrpticin, indolicidin, puroindoline A, lactoferricin B and IDR-1018, but not F5W-magainin 2, can bind to both apo- and holo-ACPs. Binding of Arg-rich peptides is preferred over their Lys-rich analogs. Interestingly, all the peptides bind to holo-ACP with higher affinity than to apo-ACP, which lacks the functionally important phosphopantothenate group. NMR peak intensity perturbation data reveal that helix II of ACP, which is known to be directly involved in complex formation with bacterial FAS enzymes, acts as a common and main recognition site for the peptides. We propose that binding of AMPs and ABPs to this region of bacterial ACPs can directly block fatty acid synthesis and interfere in other ACP-dependent biosynthetic and regulatory events, which in turn could contribute to killing the bacteria and could also intervene in biofilm formation. Full article

Background/Objectives: Antimicrobial conjugates have attracted considerable interest in addressing the threat of antimicrobial resistance by minimising the likelihood of resistance onset. Antimicrobial peptide mimic–antibiotic conjugates offer a unique strategy to revitalise current clinical agents through increased membrane permeabilisation, prolonging the longevity of traditional antibiotics while broadening the spectrum of activity of the AMP mimic. Methods: This study explored non-cleavable, enzyme-cleavable, and pH-cleavable linked conjugates between an anthranilamide-based peptide mimic and current clinically available antibiotics to assess the viability of conjugation in enhancing antimicrobial activity as measured through MIC assays. Cleavage studies were conducted to assess the stimulus susceptibility of relevant compounds. Results: Four amide-linked non-cleavable conjugates were synthesised. Of these, a primary amide-linked conjugate between ciprofloxacin and the peptidomimetic had the most significant activity with an MIC of 15.6 µM towards Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa, and an MIC of 7.8 µM towards Gram-negative Escherichia coli. A hydrazone-based pH-sensitive linker system was synthesised and had an MIC of 15.6 µM towards Gram-negative E. coli. Finally, an enzyme-cleavable cephalosporin conjugate system was investigated, which offered a unique method for the specific treatment of resistant bacterial strains. Cleavage studies of this conjugate suggested rapid degradation of the β-lactam ring and release of the subunit. Conclusions: This work presents conjugate systems between peptide mimics and antibiotics as a new, promising strategy to broaden the antimicrobial spectrum of novel antimicrobial agents. Full article

The growing threat of antimicrobial resistance necessitates alternative strategies to conventional antibiotics. Insects represent a promising source of antimicrobial peptides (AMPs) due to their potent innate immune responses. In this study, we investigated the hemolymph peptide extracts from Hermetia illucens larvae as a bioresource of infection-induced AMPs. Larvae were challenged with Gram-negative (Escherichia coli) and Gram-positive (Micrococcus flavus) bacteria, and hemolymph-derived peptides were extracted and fractionated by RP-HPLC. Peptide fractions were screened in vitro by agar diffusion assay against a panel of pathogenic strains. While extracts from uninfected larvae were essentially inactive, fractions 9–13 from infected larvae showed broad-spectrum antibacterial activity, including against multidrug-resistant clinical isolates such as carbapenem-resistant Klebsiella pneumoniae, suggesting an inducible immune response. Fractions were further analyzed by SDS-PAGE and LC-MS/MS to identify candidate AMPs, while shotgun proteomics on unfractionated extracts enabled quantitative comparison among conditions. Proteomics raw data are available via ProteomeXchange Consortium, with the dataset identifier PXD071144. In silico prediction using ProP 1.0, APD3, and CAMP_R4 supported the antimicrobial potential of candidate peptides. Overall, our integrative approach demonstrates that bacterial infection induces a diverse and bioactive immunopeptidome in H. illucens, supporting its potential as a sustainable platform for the discovery of novel antimicrobial agents. Full article

Fungal and bacterial pathogens significantly impact global crop yields, causing substantial economic losses and food insecurity. While chemical pesticides are effective, their excessive and improper use poses risks to the environment and human health. Antimicrobial peptides (AMPs)—components of innate immunity in plants and animals—are promising candidates for the development of novel, eco-friendly antimicrobials for agriculture and medicine. This study explores the antimicrobial activity of several γ-core peptides derived from defensins of Thinopyrum elongatum, a wild plant species known for its stress resistance. All peptides carried a net positive charge. 3D structural modeling indicated that most peptides adopted an α-helical conformation, with one predicted to form an anti-parallel β-hairpin structure. The conservation of the γ-core peptide sequences across Poaceae defensins was demonstrated, underscoring the importance of these peptide regions in biological functions of defensins. Antimicrobial assays demonstrated that all peptides exhibited broad-spectrum activity, with efficacy depending on the peptide’s amino acid sequence, 3D structure, and the pathogen tested. Notably, the peptide with the highest positive charge and β-hairpin structure showed the strongest pathogen inhibition. Additionally, synergistic interactions between some peptides against Fusarium oxysporum, which enhanced their antimicrobial effects, were shown. Our findings highlight the potential of wheatgrass γ-core peptides as templates for developing new peptide-based antimicrobials for agricultural and medical applications. Full article

Ascidians are a group of marine invertebrates, most of which are sessile and soft-bodied. Their lack of an adaptive immune system makes them rely on innate immune responses to detect and eliminate invading microbes. Antimicrobial peptides (AMPs) play an essential part in this process. In this paper, we present the isolation, structure elucidation, and bioactivities of two new cysteine-rich peptides (CRPs) from the Arctic marine ascidian Synoicum turgens. The sequences and structures of the peptides were determined by Edman degradation sequencing, mass spectrometry, and NMR analysis. This revealed two novel 2 kDa peptides, St-CRP-1 and St-CRP-2, with neutral net charge and C-terminal amidation. St-CRP-1 consisted of 18 amino acids and displayed selective and moderate growth inhibition of two Gram-positive bacterial strains (Bacillus subtilis and Corynebacterium glutamicum) at 24.6 µM, whereas St-CRP-2 consisted of 19 amino acids and inhibited the growth of B. subtilis at 49.2 µM. St-CRP-1 had no effect on two mammalian cell lines or the brine shrimp Artemia salina at the highest concentration tested. Structural analysis of the St-CRPs indicated a Cys1–Cys6, Cys2–Cys4, and Cys3–Cys5 disulfide connectivity, which is also found in alpha-defensins. The results from this study show that Arctic marine ascidians are a rich source of novel bioactive peptides. Full article

Cystic fibrosis (CF)-associated lung infections caused by Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) remain difficult to treat due to multidrug resistance and the redox instability of the pulmonary environment, which can impair antibiotic efficacy. In this study, we investigated alvinellacin (ALV), a disulfide-stabilized β-hairpin antimicrobial peptide (AMP) derived from the deep-sea polychaete Alvinella pompejana (A. pompejana), as a potential therapeutic agent naturally adapted to redox-fluctuating conditions. The antibacterial and antibiofilm activities of ALV were evaluated against multidrug-resistant (MDR) clinical isolates under CF-like reducing conditions (6 mM dithiothreitol (DTT)). Circular dichroism (CD) analysis showed that DTT did not alter the β-hairpin secondary structure of ALV, supporting its structural stability in CF-like environments. Mechanistic analyses included pore-forming assay, membrane interaction studies, scanning electron microscopy (SEM), lipid-binding assays, cytotoxicity testing, and resistance induction assays, while in vivo efficacy was assessed using the Galleria mellonella infection model. ALV demonstrated strong bactericidal activity that was maintained in the presence of NaCl or human serum. ALV did not induce bacterial resistance and effectively inhibited early-stage biofilm formation and disrupted preformed biofilms, including those of the clinical isolate, even under reducing conditions. The peptide showed selective permeabilization of bacterial membranes linked to its stronger affinity for bacterial membrane lipids and negligible interaction with host-like membranes, with no observed cytotoxicity. In vivo, ALV significantly improved survival in infected larvae. These findings highlight ALV as a promising redox-resilient antimicrobial candidate for treating MDR CF lung infections. Full article

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a major cause of morbidity and mortality worldwide, particularly due to the emergence of drug-resistant strains. Membrane-active antimicrobial peptides (AMPs) represent attractive therapeutic candidates because they target bacterial envelope integrity and disrupt essential cellular processes. We evaluated two rationally designed LL-37-derived peptides: a truncated C-terminally amidated analog (LL37-1) and a modified variant incorporating N-terminal acetylation and a single D-amino acid substitution (D-LL37). Dose–response analysis demonstrated that D-LL37 exhibited greater antimycobacterial potency, with lower inhibitory concentrations of 90% (IC₉₀) and 50% (IC₅₀) values (18.40 ± 0.39 μM and 10.11 ± 0.60 μM, respectively) compared with LL37-1 (25.44 ± 0.36 μM and 15.45 ± 1.40 μM). Fluorescence-based permeability assays revealed partial membrane disruption (36% and 44% at IC₉₀ for LL37-1 and D-LL37, respectively), which was supported by ultrastructural alterations observed by scanning electron microscopy, including bacillary shortening, rough surface formation, cell clusters, and the presence of cellular debris, all of which are consistent with membrane damage. RT-qPCR analysis demonstrated significant upregulation of the P-type ATPase genes ctpF, ctpA, and ctpH following D-LL37 exposure. Collectively, these findings indicate that optimized LL-37-derived peptides exert antitubercular activity associated with envelope perturbation and coordinated activation of ion transport-related stress responses. Full article

Background/Objectives: Leprosy is a chronic infection caused by Mycobacterium leprae that, in addition to Schwann cells, macrophages, and adipocytes, also infects human peripheral blood monocytes and subverts their metabolism in its favor. Infection is marked by cholesterol and fatty acid accumulation in lipid droplets (LDs), and a reduction in mitochondrial membrane potential (Δψm). Previous studies showed that M. leprae downregulates adenosine receptor A_2A (A_2AR) expression in Schwann cells, while activation reduces LD accumulation and bacterial viability. Since A_2AR controls immunometabolic response, we investigated whether A_2AR signaling restrains M. leprae-driven reprogramming in monocytes. Methods: Peripheral blood mononuclear cells from healthy donors were enriched for monocytes and infected with M. leprae in the presence or absence of adenosinergic modulators (5′AMP, adenosine (ADO), A_2AR agonist CGS21680, the antagonist ZM241385, or A_2BR antagonist, MRS1754). We used flow cytometry, fluorescence microscopy, and RT-qPCR to evaluate purinergic components expression and bacillary viability. LDs and Δψm were measured by fluorescence microscopy, and extracellular levels of inosine (INO) and hypoxanthine (HPX) by LC-MS/MS. Results: The results show that infection increased CD39, ADA, A_2AR and A₃R expression, decreased ENT1, A₁R and A_2BR, and raised extracellular INO and HPX. In addition, 5′AMP, ADO and CGS21680 reversed infection-induced LD accumulation. CGS21680 also restored Δψm and decreased intracellular M. leprae viability. Conclusions: Our data suggest that M. leprae suppresses A_2AR signaling to favor its survival in monocytes, indicating that the extracellular ADO–A_2AR pathway may be a potential target to limit early M. leprae infection. Full article

The rise in antimicrobial resistance represents a significant challenge to global health. The reason partially lies in an inappropriate use of conventional antibiotics and the subsequent rapid spread of multidrug-resistant pathogen strains. This emergency requires an urgent search for conceptually new antimicrobial agents. A viable alternative to conventional antibiotics is antimicrobial peptides (AMPs), which are ribosomally synthesized molecules with considerable potential as next-generation anti-infectious therapeutics. Previously, we have reported on the β-hairpin peptide Ap9, an analog of abarenicin from the marine polychaeta Abarenicola pacifica, with potent activity against key Gram-negative pathogens. Here, it is shown that Ap9 acts in a manner resembling polymyxin B, namely via interaction with lipopolysaccharide (LPS), and retains its activity against polymyxin-resistant isolates without observed cross-resistance, and causes insignificant damage in cytoplasmic membrane at bactericidal concentrations. NMR spectroscopy reveals that LPS binding induces a conformational rearrangement of Ap9, its dimer formation, and local structural remodeling of the peptide region (residues 8–12) into 3₁₀-helix. Bacterial resistance to Ap9 was found to be relatively low with a reduced susceptibility associated with infrequent genetic alterations, such as the mutation in lptD or the deletion in mlaA. Furthermore, Ap9 demonstrates a favorable tolerability, a wider therapeutic window than that of polymyxin B, and a sufficiently long half-life through the systemic use, as well as in vivo efficacy in murine models of Gram-negative infections, including sepsis caused by the mcr-1-harboring Escherichia coli strain. The obtained results point to Ap9 as a promising candidate for further preclinical studies aimed at development of an alternative to polymyxins. Full article

Vibrio alginolyticus is a common pathogenic bacterium and can cause diseases in aquaculture animals. Lysine lactylation (Kla) is a novel post-translational modification (PTM) that has been confirmed to play critical roles in key biological processes. However, the modification landscape and functions of Kla in V. alginolyticus remain unclear. In this study, lactylation modification profiles of the bacterial pathogen V. alginolyticus were first systematically characterized; a total of 9308 lactylation sites on 2155 proteins were successfully identified. The lactylation of cAMP receptor protein (CRP) and triosephosphate isomerase (TPI) was verified by Co-immunoprecipitation (Co-IP) and Western blot to validate the lactylome data. Bioinformatic analysis of the Kla sites revealed 32 conserved sequence motifs surrounding the modified residues. Kla proteins were mainly involved in central metabolic pathways, including glycolysis/gluconeogenesis and ribosome biogen regulators were found to contain Kla modification sites. To investigate crosstalk among lysine acylations in V. alginolyticus, we integrated Kla, lysine acetylation (Kac), and lysine succinylation (Ksuc) profiles and identified 337 co-modified proteins and 5 co-modified sites. Additionally, phylogenetic analysis of Vibrio alginolyticus CobQ based on protein sequence alignment revealed no homology to the known delactylase CobB. Combined in vitro and in vivo functional validation identified VaCobQ as a candidate delactylase with potential NAD⁺-independent activity. This study establishes a lysine lactylation landscape in V. alginolyticus, providing a resource for exploring Kla functions in bacterial metabolism and its possible connections to virulence. Full article

The rapid global spread of antimicrobial resistance among pathogenic microorganisms poses a serious challenge to both human and animal health, underscoring the urgent need for new strategies to combat resistance. Antimicrobial peptides (AMPs), key components of the innate immune system, are promising candidates because they disrupt the membranes of bacteria, fungi, and viruses, thereby reducing the risk of resistance development. Lactoferrin (LF), a multifunctional iron-binding glycoprotein abundant in mammalian milk, is a rich source of AMPs. Cationic peptide fragments such as lactoferricin and lactoferrampin exhibit more potent direct antimicrobial activity than the intact protein. Our previous studies have shown that peptides derived from Equine milk lactoferrin exhibit antihypertensive, anti-inflammatory, and anti-oncogenic activity in silico, highlighting their multifunctional bioactive potential. Building on these results, the present study aims to investigate the antimicrobial properties of these peptides. We used an integrated approach combining computer modeling and in vitro studies to identify and validate novel antimicrobial peptides from equine milk lactoferrin. Bioinformatics tools, including AMPScanner and CAMP, were used to predict antimicrobial domains, followed by experimental testing against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. The results showed that equine milk lactoferrin peptides possess potent and selective antimicrobial activity, with efficacy varying across bacterial species. These data expand the functional profile of lactoferrin-derived peptides, demonstrating their multifunctionality, and suggest that equine milk lactoferrin represents a promising natural source of antimicrobial agents, supporting alternative strategies to reduce antibiotic use in human and veterinary medicine. Full article