Development of a novel hybrid antimicrobial peptide for enhancing antimicrobial spectrum and potency against food-borne pathogens.

AIMS: To address the increasingly serious challenge of the transmission of foodbrone pathogens in the food chain. METHODS AND RESULTS: In this study, we employed rational design strategies, including truncation, amino acid substitution, and heterozygosity, to generate seven engineered peptides with α-helical structure, cationic property, and amphipathic characteristics based on the original Abhisin template. Among them, as the hybird antimicrobial peptide (AMP), AM exhibits exceptional stability, minimal toxicity, as well as broad-spectrum and potent antimicrobial activity against foodborne pathogens. Besides, it was observed that the electrostatic incorporation demonstrates by AM results in its primary targeting and disruption of the cell wall and membrane of Escherichia coli O157: H7 (EHEC) and methicillin-resistant Staphylococcus aureus (MRSA), resulting in membrane perforation and enhanced permeability. Additionally, AM effectively counteracts the deleterious effects of lipopolysaccharide, eradicating biofilms and ultimately inducing the demise of both food spoilage and pathogenic microorganisms. CONCLUSIONS: The findings highlight the significant potential of AM as a highly promising candidate for a novel food preservative and its great importance in the design and optimization of AMP-related agents.

The inhibitory action of lactocin 63 on deterioration of seabass (Lateolabrax japonicus) during chilled storage.

BACKGROUND: The bacteriocins, particularly derived from lactic acid bacteria, currently exhibit potential as a promising food preservative owing to their low toxicity and potent antimicrobial activity. This study aimed to evaluate the efficacy of lactocin 63, produced by Lactobacillus coryniformis, in inhibiting the deterioration of Lateolabrax japonicas during chilled storage, while also investigating its underlying inhibitory mechanism. The measurement of total viable count, biogenic amines, and volatile organic compounds were conducted, along with high-throughput sequencing and sensory evaluation. RESULTS: The findings demonstrated that treatment with lactocin 63 resulted in a notable retardation of bacterial growth in L. japonicas fish fillet during refrigerated storage compared with the water-treated and nisin-treated groups. Moreover, lactocin 63 effectively maintained the microbial flora balance in the fish fillet and inhibited the proliferation and metabolic activity of specific spoilage microorganisms, particularly Shewanella, Pseudomonas, and Acinetobacter. Furthermore, the production of unacceptable volatile organic compounds (e.g. 1-octen-3-ol, hexanal, nonanal), as well as the biogenic amines derived from the bacterial metabolism, could be hindered, thus preventing the degradation in the quality of fish fillets and sustaining relatively high sensory quality. CONCLUSION: The results of this study provide valuable theoretical support for the development and application of lactocin 63, or other bacteriocins derived from lactic acid bacteria, as potential bio-preservatives in aquatic food. © 2024 Society of Chemical Industry.

Rational design of Abhisin-like peptides enables generation of potent antimicrobial activity against pathogens.

Infections caused by pathogens can be a significant challenge in wound healing, particularly when antimicrobial resistance is a factor. This can pose a serious threat to human health and well-being. In this scenario, it is imperative to explore novel antimicrobial agents to fight against multi-drug resistant (MDR) pathogenic bacteria. This study employed rational design strategies, including truncation, amino acid replacement, and heterozygosity, to obtain seven α-helical, cationic, and engineered peptides based on the original template of Abhisin. Among the analogs of Abhisin, AB7 displayed broad-spectrum and potent antimicrobial activity, superior targeting of membranes and DNA, and the ability to disrupt biofilms and anti-endotoxins in vitro. Additionally, we evaluated the anti-infection ability of AB7 using a murine skin wound model infected with methicillin-resistant Staphylococcus aureus (MRSA) and found that AB7 displayed negligible toxicity both in vitro and in vivo. Furthermore, AB7 exhibited desirable therapeutic efficacy by reducing bacterial burden and pro-inflammatory mediators, modulating cytokines, promoting wound healing, and enhancing angiogenesis. These results highlight the potential of AB7 as a promising candidate for a new antibiotic. KEY POINTS: • A α-helical, cationic, and engineered peptide AB7 was obtained based on Abhisin. • AB7 exhibited potent antimicrobial activity and multiple bactericidal actions. • AB7 effectively treated infected skin wounds in mice.

Characterization of an EPS-producing bifidobacterial strain based on integration of phenotypic and complete genome sequencing data.

Bifidobacterium and Lactobacillus are known to be common members of the human intestinal microbiota, which play important roles in maintaining the homeostasis of host gut microenvironment. Several bifidobacterial and lactobacilli strains have been used as probiotics for health benefits. The exopolysaccharides (EPSs) produced by strains from Bifidobacterium and Lactobacillus are considered as beneficial traits mediating these beneficial effects. In this study, 21 strains belonging to Bifidobacterium and Lactobacillus were isolated from healthy infants' stool and were screened for EPS-producing ability. Among these strains, Bifidobacterium longum XZM1 showed the highest EPS productivity, which was further confirmed and characterized. The complete genome of strain XZM1 was sequenced, which revealed the presence of a gene cluster for EPS production. Furthermore, comparative genome analysis was performed among XZM1 and other strains from B. longum species. Following purification, the molecular weight (Mw) of EPS from XZM1 was determined as 4023 Da (Mw) through gel permeation chromatography. Analysis of the EPS hydrolysates revealed that the EPS was composed of mannose, glucose, galactose, arabinose, and fucose. Additionally, the EPS exhibited higher scavenging abilities toward hydroxyl than 1,1-diphenyl-2-picrylhydrazyl free radical. Overall, these results suggest that XZM1 from B. longum species may be a promising probiotic candidate.

A Murine Commensal Protozoan Influences Host Glucose Homeostasis by Facilitating Free Choline Generation.

Recent progress indicates that the gut microbiota plays important role in regulating the host's glucose homeostasis. However, the mechanisms remain unclear. Here, we reported that one integral member of the murine gut microbiota, the protozoan Tritrichomonas musculis could drive the host's glucose metabolic imbalance. Using metabolomics analysis and in vivo assays, we found that mechanistically this protozoan influences the host glucose metabolism by facilitating the production of a significant amount of free choline. Free choline could be converted sequentially by choline-utilizing bacteria and then the host to a final product trimethylamine N-oxide, which promoted hepatic gluconeogenesis. Together, our data reveal a previously underappreciated gut eukaryotic microorganism by working together with other members of microbiota to influence the host's metabolism. Our study underscores the importance and prevalence of metabolic interactions between the gut microbiota and the host in modulating the host's metabolic health. IMPORTANCE Blood glucose levels are important for human health and can be influenced by gut microbes. However, its mechanism of action was previously unknown. In this study, researchers identify a unique member of the gut microbes in mice that can influence glucose metabolism by promoting the host's ability to synthesis glucose by using nonglucose materials. This is because of its ability to generate the essential nutrient choline, and choline, aided by other gut bacteria and the host, is converted to trimethylamine N-oxide, which promotes glucose production. These studies show how gut microbes promote metabolic dysfunction and suggest novel approaches for treating patients with blood glucose abnormality.

Purification, molecular characterization of Lactocin 63 produced by Lactobacillus coryniformis FZU63 and its antimicrobial mode of action against Shewanella putrefaciens.

Bacteriocins derived from lactic acid bacteria (LAB) are well recognized as promising food preservative due to high safety and potent antibacterial activity against foodborne pathogens and spoilage bacteria. In this study, an antimicrobial agent-producing strain FZU63 from Chinese sauerkraut was identified as Lactobacillus coryniformis based on physio-biochemical characterization and 16S rDNA sequence analysis. In addition, a bacteriocin was purified from the culture supernatant of L. coryniformis FZU63, and its molecular mass was determined as 1493.709 Da. Moreover, the amino acid sequence of the bacteriocin was predicted to be RQQPMTLDYRW-NH2 using nanoliter/microliter liquid chromatography combined with triple quadrupole-linear ion trap tandem mass spectrometry and was named as Lactocin 63. Furthermore, Lactocin 63 displays potent antimicrobial activity against the tested Gram-positive and negative bacteria based on the results of determining MICs. Subsequently, the action mode of Lactocin 63 against Shewanella putrefaciens was investigated. The results demonstrated that Lactocin 63 targets and is adsorbed onto the bacterial cell wall and membrane and then disrupts cytoplasmic membrane, which is leading to leakage of cytoplasm according to the results of flow cytometry analysis and the observation of cellular ultra-structure using confocal laser microscopy and atomic force microscopy. Collectively, these results are helpful and providing the theoretical base for developing and applying LAB-derived bacteriocins as promising bio-preservatives to combat foodborne pathogens and spoilage bacteria in seafood industries.Key points• A bacteriocin-producing strain Lactobacillus coryniformis was isolated.• A novel bacteriocin produced by Lactobacillus coryniformis FZU63 was characterized.• Action mechanism of the bacteriocin against S. putrefaciens was elucidated in vitro.

Antibacterial Activity and Mechanism of Ginger Essential Oil against Escherichia coli and Staphylococcus aureus.

Though essential oils exhibit antibacterial activity against food pathogens, their underlying mechanism is understudied. We extracted ginger essential oil (GEO) using supercritical CO2 and steam distillation. A chemical composition comparison by GC-MS showed that the main components of the extracted GEOs were zingiberene and α-curcumene. Their antibacterial activity and associated mechanism against Staphylococcus aureus and Escherichia coli were investigated. The diameter of inhibition zone (DIZ) of GEO against S. aureus was 17.1 mm, with a minimum inhibition concentration (MIC) of 1.0 mg/mL, and minimum bactericide concentration (MBC) of 2.0 mg/mL. For E. coli, the DIZ was 12.3 mm with MIC and MBC values of 2.0 mg/mL and 4.0 mg/mL, respectively. The SDS-PAGE analysis revealed that some of the electrophoretic bacterial cell proteins bands disappeared with the increase in GEO concentration. Consequently, the nucleic acids content of bacterial suspension was raised significantly and the metabolic activity of bacteria was markedly decreased. GEO could thus inhibit the expression of some genes linked to bacterial energy metabolism, tricarboxylic acid cycle, cell membrane-related proteins, and DNA metabolism. Our findings speculate the bactericidal effects of GEO primarily through disruption of the bacterial cell membrane indicating its suitability in food perseveration.

The antibacterial activity of LI-F type peptide against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and inhibition of infections in murine scalded epidermis.

LI-F type peptides are a family of cyclic lipodepsipeptide antibiotics isolated from Paenibacillus polymyxa and display potent activities against positive bacteria including methicillin-resistant S. aureus (MRSA). In this study, we investigated the mechanism of action of LI-F type peptide AMP-jsa9 against a MRSA (S. aureus CICC10790), which is resistant to ciprofloxacin, gentamicin, kanamycin, chloramphenicol, methicillin, and tetracycline. It was found that AMP-jsa9 mainly targets the cell membrane of MRSA and is able to inhibit biofilm formation through killing planktonic bacteria cells. Moreover, AMP-jsa9 can bind to DNA in vitro, which represents another pathway for the action on MRSA. Furthermore, in vivo treatment of scalded mice with AMP-jsa9 resulted in inhibiting MRSA infections and healing of the scalded wound. In addition, it was demonstrated that AMP-jsa9 can effectively inhibit MRSA infections in scalded murine epidermis and that inflammatory cytokines including IL-8, IL-6, tumor necrosis factor alpha (TNF-α), and monocyte chemotactic factor-1 (MCP-1) were reduced; moreover, both protein and gene expression levels of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (e-NOS) were enhanced, which promote neovascularization and proliferation of new granulation tissue.

Mechanism of action of AMP-jsa9, a LI-F-type antimicrobial peptide produced by Paenibacillus polymyxa JSa-9, against Fusarium moniliforme.

LI-F type peptides (AMP-jsa9) are a group of cyclic lipodepsipeptides that exhibit broad antimicrobial spectrum against Gram-positive bacteria and filamentous fungi. We sought to assess the toxicity of AMP-jsa9 and the mechanism of AMP-jsa9 action against Fusarium moniliforme. AMP-jsa9 exhibited weak hemolytic activity and weak cytotoxicity at antimicrobial concentrations (32µg/ml). Confocal laser microscopy, SEM, and TEM indicated that AMP-jsa9 primarily targets the cell wall, plasma membrane, and cytoskeleton, increases membranepermeability, and enhances cytoplasm leakage (e.g., K+, protein). Quantitative proteomic analysis using isobaric tags for relative and absolute quantitation (iTRAQ) detected a total of 162 differentially expressed proteins (59 up-regulated and 103 down-regulated) following treatment of F. moniliforme with AMP-jsa9. AMP-jsa9 treatment also led to reductions in chitin, ergosterol, NADH, NADPH, and ATP levels. Moreover, fumonisin B1 expression and biosynthesis was suppressed in AMP-jsa9-treated F. moniliforme. Our results provide a theoretical basis for the application of AMP-jsa9 as a natural and effective antifungal agent in the agricultural, food, and animal feed industries.

Plipastatin and surfactin coproduction by Bacillus subtilis pB2-L and their effects on microorganisms.

To convert the lipopeptide non-producer strain Bacillus subtilis pB2 into a plipastatin and surfactin coproducer, a gene expression cassette composed of a constitutive promoter (P43), functional gene sfp, and pleiotropic regulatory gene degQ was integrated into the chromosomal amyE locus of strain B. subtilis pB2 by homologous recombination, which generated a plipastatin and surfactin co-producer. Thirteen plipastatins and fifteen surfactins were identified in lipopeptide extracts using analytical techniques, and their effects on microorganisms were described by microscopic, cytoskeleton analysis and flow-cytometry, respectively. Plipastatins isolated from the engineered strain pB2-L exhibited strong antifungal activity (MIC 16 µg ml-1) by disrupting the cell walls, membranes and cytoskeleton of Fusarium oxysporum f. sp. cucumerinum hyphae. Surfactins affected the cell membrane of Staphylococcus aureus (MIC 20 µg ml-1), resulting in nucleic acid leakage and ultimately, cell death. Based on the convenience of genetic manipulation in the engineering strain, this work could be useful for the rational design of lipopeptide synthetases via the recombination of gene fragments to generate arrays of peptide derivatives and thus expand the diversity of microbial-produced lipopeptides.

Optimizing the Maximum Recovery of Dihydromyricetin from Chinese Vine Tea, Ampelopsis grossedentata, Using Response Surface Methodology.

This work provides an optimized extraction approach intended to maximize the recovery of dihydromyricetin (DHM) from Chinese vine tea (Ampelopsis grossedentata) leaves. The presented work adopts a Box-Behnken design as a response surface methodology to understand the role and influence of specific extraction parameters including: time, temperature, and solvent composition/ethanol (%) on DHM final yields. Initially, single factor experiments were used to delineate the role of above factors (temperature, time, and solvent composition) before proceeding with three factors-three levels Box-Behnken design with 17 separate runs to assess the effect of multifactorial treatments on DHM recovery rates. The collected data shows that independent variables (solvent composition, time, and temperature) can significantly affect DHM recovery rates with maximum yields resulting from a combined 60 °C, 60% aqueous ethanol, and 180 min treatment. From the empirical point of view, the above optimized extraction protocol can substantially enhance processing and profitability margins with a minimum need of interventions or associated costs.

Fam96a is essential for the host control of Toxoplasma gondii infection by fine-tuning macrophage polarization via an iron-dependent mechanism.

BACKGROUND: Toxoplasmosis affects a quarter of the world's population. Toxoplasma gondii (T.gondii) is an intracellular parasitic protozoa. Macrophages are necessary for proliferation and spread of T.gondii by regulating immunity and metabolism. Family with sequence similarity 96A (Fam96a; formally named Ciao2a) is an evolutionarily conserved protein that is highly expressed in macrophages, but whether it play a role in control of T. gondii infection is unknown. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we utilized myeloid cell-specific knockout mice to test its role in anti-T. gondii immunity. The results showed that myeloid cell-specific deletion of Fam96a led to exacerbate both acute and chronic toxoplasmosis after exposure to T. gondii. This was related to a defectively reprogrammed polarization in Fam96a-deficient macrophages inhibited the induction of immune effector molecules, including iNOS, by suppressing interferon/STAT1 signaling. Fam96a regulated macrophage polarization process was in part dependent on its ability to fine-tuning intracellular iron (Fe) homeostasis in response to inflammatory stimuli. In addition, Fam96a regulated the mitochondrial oxidative phosphorylation or related events that involved in control of T. gondii. CONCLUSIONS/SIGNIFICANCE: All these findings suggest that Fam96a ablation in macrophages disrupts iron homeostasis and inhibits immune effector molecules, which may aggravate both acute and chronic toxoplasmosis. It highlights that Fam96a may autonomously act as a critical gatekeeper of T. gondii control in macrophages.

Rational Design and Antimicrobial Potency Assessment of Abaecin Analogues.

The widespread and escalating emergence of multidrug resistance is now recognized as one of the most severe global threats to human health. To address the urgent issue of drug-resistant bacteria and the limitation of effective clinical treatments, antimicrobial peptides (AMPs) have been developed as promising substituents of conventional antibiotics. In this study, rational design strategies were employed to acquire seven cationic and α-helical engineered peptides based on the original template of Abaecin. After investigation, we found that AC7 (LLRRWKKLFKKIIRWPRPLPNPGH) demonstrated potent and broad-spectrum antimicrobial activity. Additionally, it demonstrated low cytotoxicity and hemolysis while maintaining good stability. Notably, AC7 displays the antibacterial mechanism with superior abilities in cell membrane disruption and potential DNA binding in vitro, as well as effectively disrupting biofilms. Moreover, the murine skin wound model infected with drug-resistant Pseudomonas aeruginosa was employed to evaluate the anti-infective efficacy and therapeutic potential of AC7. It was observed that AC7 displays a remarkable capacity to inhibit wound colonization, reduce levels of inflammatory cytokines (TNF-α) and inflammatory cells (white blood cells (WBC), monocytes (MONO), lymphocytes (LYMPH), neutrophils (GRAN)), promote the levels of IL-10 and VEGF, and enhance wound healing. Overall, these findings demonstrate the potential of AC7 as a viable alternative to traditional antibiotics.

Antimicrobial peptides: Sustainable application informed by evolutionary constraints.

The proliferation and global expansion of multidrug-resistant (MDR) bacteria have deepened the need to develop novel antimicrobials. Antimicrobial peptides (AMPs) are regarded as promising antibacterial agents because of their broad-spectrum antibacterial activity and multifaceted mechanisms of action with non-specific targets. However, if AMPs are to be applied sustainably, knowledge of how they induce resistance in pathogenic bacteria must be mastered to avoid repeating the traditional antibiotic resistance mistakes currently faced. Furthermore, the evolutionary constraints on the acquisition of AMP resistance by microorganisms in the natural environment, such as functional compatibility and fitness trade-offs, inform the translational application of AMPs. Consequently, the shortcut to achieve sustainable utilization of AMPs is to uncover the evolutionary constraints of bacteria on AMP resistance in nature and find the tricks to exploit these constraints, such as applying AMP cocktails to minimize the efficacy of selection for resistance or combining nanomaterials to maximize the costs of AMP resistance. Altogether, this review dissects the benefits, challenges, and opportunities of utilizing AMPs against disease-causing bacteria, and highlights the use of AMP cocktails or nanomaterials to proactively address potential AMP resistance crises in the future.

pH-Switchable Antimicrobial Supramolecular Hydrogels for Synergistically Eliminating Biofilm and Promoting Wound Healing.

Biofilm infection will cause chronic inflammation and hinder the normal healing process of wound. Here, based on the self-assembly of three designed amphiphilic pentapeptides named EK, GG, and DR, pH-switchable antibacterial hydrogels with amphiphilic fiber network are used for the eradication of biofilms and the rescue of delayed healing in infected wounds. These pentapeptides-based hydrogels exhibit an acidic pH-switchable antimicrobial effect and are biocompatible at neutral pH. Additionally, supramolecular nanofiber networks with physical cross-linking with thermosensitive polymers (PNIPAm) and loaded antibacterial oregano oil are further developed. In vitro experiments indicate that the antimicrobial activity of hydrogels comes from the disassembly of acidic pH-dependent nanofiber network and activated release of pentapeptides and oregano oil, which achieves synergistic biofilm eradication. Remarkably, DR-based supramolecular hydrogel improves the healing efficiency of the full-thickness wound of skin in vivo, which is manifested by increased wound closure rate, reduced inflammatory response, faster angiogenesis, and collagen deposition in the wound, exhibiting great potential as wound dressing. The proposed synergistic strategy of inhibiting biofilm formation and activating healing may provide an efficient method for the treatment of clinically infected wounds.

Translocation of subunit PPSE in plipastatin synthase and synthesis of novel lipopeptides.

Nonribosomal peptide synthase (NRPS) is a unique molecular assembly mechanism with high hybridity. Its recombination is conducive to the development of novel lipopeptides. However, there are few reports on NRPS subunit recombination of plipastatin at present. In this paper, plipastatin synthase was modified by the forward movement of subunit PPSE and the replacement of the communication-mediating (COM) domain. The results showed that ppsABE, a new assembly line, could synthesize novel lipopeptides such as cycle pentapeptide (C16-18ß-OHFA-E-O-cyclo(Y-T-I), and its antimicrobial activity against Rhizopus stolonifer and Staphylococcus aureus was better than that of plipastatin. However, the reactivity of ppsABCE disappeared, but the substitution of COMD ppsC/COMA ppsD or COMD ppsD/COMA ppsE for COMD ppsC/COMA ppsE could restore its activity and conduct the biosynthesis of linear hexapeptide (C16-17ß-OHFA-E-O-Y-T-E-A/V) and heptapeptide (C17-18ß-OHFA-E-O-Y-T-E-A-I). Collectively, these findings indicated that the COM donor domain at the C-terminus of PPSB could communicate with the COM acceptor domain at the N-terminus of PPSE and that the compatible COM domain is an important tool for communication between nonpartner subunits. Moreover, the integrity and selective compatibility of the COM acceptor domain of subunit PPSE are essential to promote the interaction between PPSE and other subunits. This work further complemented the rules of NRPS subunit recombination and provided a theoretical basis for the development of novel high-efficiency lipopeptides.

Chlorine dioxide oxidation of hemicellulose from alkaline hydrolysate bagasse to remove lignin unit in lignin-carbohydrate complex.

Owing to the existence of lignin-carbohydrate complex (LCC) linkages, the extracted hemicellulose contains lignin, which is difficult to remove. Chlorine dioxide selectively oxidizes lignin without reacting with carbohydrates. In this study, chlorine dioxide was used to remove lignin from the hemicellulose sample. Ion chromatography and 2D-HSQC NMR were used to observe the changes in the LCC. After chlorine dioxide treatment, acid-insoluble lignin was largely degraded, with a removal rate reaching 68%. Furthermore, the 2D-HSQC NMR spectrum showed that guaiacyl (G) lignin underwent dramatic degradation and degradation of syringyl (S) lignin was also obvious. Phenyl glycoside-type LC linkages were also largely degraded. Moreover, the sugar composition and structure of the hemicellulose did not change significantly. This suggests that it is feasible to remove lignin from LCCs through oxidation of hemicellulose using chlorine dioxide. Meanwhile, hemicellulose with high molecular weight and high purity can be obtained by this method.

Synergistic antibacterial activity and mechanism of action of nisin/carvacrol combination against Staphylococcus aureus and their application in the infecting pasteurized milk.

Synergistic antibacterial effect is a promising way to overcome the challenge of microbial contamination in food. In this study, we detected the synergistic interactions of nisin and carvacrol. The MIC of nisin and carvacrol against S. aureus were 60 and 125 µg/mL, respectively. The FICI and FBCI were 0.28125 and 0.09375, which suggested that the nisin/carvacrol combination presented synergistic antibacterial effect against S. aureus. The antibacterial activity of nisin/carvacrol combination was much higher than their individuals and the dose of antibacterials was obviously reduced. The combination could completely kill S. aureus within 8 h, accelerate the destruction of cell membrane, and inhibit formation of biofilm. Under the intervention of nisin, more CAR could enter cell to hunt intracellular targets, leading to an increase in intracellular antibacterial level. Besides, in the storage of pasteurized milk, the combinational treatment successfully inhibited microbial reproduction at 25 °C and 4 °C. Thus, the combination of nisin and carvacrol was a potential synergistic strategy for food preservation.

An injectable double network hydrogel with hemostasis and antibacterial activity for promoting multidrug-resistant bacteria infected wound healing.

Multidrug-resistant bacteria infections frequently occur in wound care due to the excessive use of antibiotics. It can cause scar formation, wound closure delay, multiple organ failure, and high mortality. Here, a double network hydrogel with injectability, hemostasis, and antibacterial activity was developed to prompt multidrug-resistant bacteria infected wound healing. The double network hydrogel is composed of gelatin methacryloyl (GelMA), oxidized dextran (ODex), ε-polylysine (EPL), and bacitracin, and formed through the Schiff-base and UV-initiated crosslinking reaction. The injectable hydrogel with an adhesion effect could adapt to the irregular shape of the wound and possesses good hemostatic ability. The hydrogel presents good flexibility and rapid resilience due to its double network structure, and it can prompt cell proliferation and migration. In particular, the hydrogel has broad-spectrum in vitro antimicrobial activities against S. aureus, E. coli, and methicillin-resistant S. aureus (MRSA), and disrupts E. coli and MRSA biofilms. In vivo results demonstrated that the hydrogel can completely heal MRSA-infected wound in rats within 15 days, through inhibiting the growth of bacteria, accelerating skin tissue reepithelialization, collagen deposition, and angiogenesis, as well as adjusting the expression of CD31, α-SMA, and TNF-α. The findings of this study suggest that the presented hydrogel could enhance multidrug-resistant bacteria infected wound healing and mitigate antimicrobial resistance.

Structural evolution of lignin after selective oxidation of lignin-carbohydrate complex by chlorine dioxide.

Lignin-carbohydrate complexes (LCCs) are important from the perspective of the anti-depolymerization barrier of lignocellulosic biomass, as it limits the high-value utilization of lignocellulosic biomass resources. In this study, the unit structure of lignin in the LCC has been investigated in depth. Oxidation of a selective lignin unit by chlorine dioxide revealed that the LCC structures are enriched with xylanase-macroporous resins, and the structure that was not oxidized in LCC was also identified. At a chlorine dioxide concentration of 90.93 mg/L, 1 g of LCC lignin is oxidized by 0.7 g chlorine dioxide. The purified residual hemicellulose lignin was mainly H-type. The ß-O-4' signal was the strongest for the bond between lignin and carbohydrates. Therefore, it is speculated that most of the residual lignin in bamboo-alkali hemicellulose exists in the form of non-phenolic structural units. This study provides a reference for further studies on the specific structures of LCC.