The antimicrobial effects and synergistic antibacterial mechanism of the combination of ε-Polylysine and nisin against Bacillus subtilis

Preparation, characterization, and antibacterial and antioxidant activities of caffeic acid grafted ε-polylysine

The antioxidant activity of ε-polylysine (EPL) can be enhanced by grafting phenolic compound caffeic acid (CA) onto its amino groups. To enhance the antioxidant activity of EPL, this study synthesized caffeic acid-ε-polylysine conjugate (CA-EPL) by grafting CA onto EPL using carbodiimide coupling reaction. Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy confirmed the successful conjugation of caffeic acid and ε-polylysine. The ultraviolet-visible absorption spectra, grafting ratio, and Zeta potential data indicate that the molar ratio of CA to EPL has a significant impact on the grafting degree and Zeta potential of the conjugates. In particular, the highest grafting degree and the lowest Zeta potential were obtained when the molar ratio of carboxyl groups in CA to amino groups in EPL was 3:1. Furthermore, the antimicrobial and antioxidant activities of the conjugates were evaluated. The results of antimicrobial activity indicate that the conjugate CA-EPL still exhibits excellent antimicrobial properties. The results of antioxidant activity show a significant increase in the antioxidant activity of the conjugate CA-EPL, which was significantly higher than that of free EPL. In addition, the research results on the antimicrobial mechanism show that CA-EPL has a similar antimicrobial mechanism to EPL: by interacting with the bacterial cell membrane, it disrupts the cell membrane, causing leakage of cell contents, ultimately leading to bacterial death. These results indicate that CA-EPL, as a novel dual-functional active substance, has broad prospects in the food and pharmaceutical industries.

Broad Antibacterial Activity and Mechanism of Garlic (Allium sativum L. cv. Uiseong) Extracts against Cell Wall of Aeromonas hydrophila

Aeromonas hydrophila is a pathogenic bacterium known for its resistance to antibiotics and its ability to cause infections in aquatic environments. This has made disease management more complex, making the development of alternative antimicrobial agents necessary. Uiseong garlic is a superior variety from Republic of Korea, renowned for its high level of beneficial compounds, making it a promising candidate for natural antimicrobial application. Therefore, this study aimed to investigate the antibacterial activity and mechanism of Uiseong garlic extracts against the cell wall of A. hydrophila. Uiseong garlic extracts were prepared using water and ethanol at 22°C and 90°C, respectively. The antibacterial activities of Uiseong garlic extracts were evaluated for their yield, antibacterial dynamics, leakage of bacterial intracellular proteins, and changes in morphological characteristics. Uiseong garlic extracts at 22°C exhibited significant antibacterial activities against foodborne pathogens, particularly against 9 strains of A. hydrophila. In this study, the ethanol extract at 22°C demonstrated significantly higher antibacterial activity compared to the water extract at 22°C, with a similar pattern of antimicrobial dynamics with polymyxin B. The ethanol extract at 22°C caused a higher concentration of leaked bacterial proteins (92.87 ± 0.46 μg/ml), indicating cell membrane disruption. Additionally, transmission electron microscopy analysis further confirmed that both extracts induced plasmolysis, leading to notable damage to the bacterial cell membrane. Therefore, ethanol extract of Uiseong garlic was demonstrated as a promising alternative to antibiotics for controlling A. hydrophila.

Efficacy of Larimichthys crocea TASOR protein-derived peptide FAM286 against Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a major foodborne pathogen, could lead cause of intestinal infections in humans. Antimicrobial peptides, as emerging antimicrobial agents, are gradually replacing traditional agents due to their highly effective and safe antimicrobial activity. In this study, a novel peptide, designated as FAM286, was identified from TASOR protein of Larimichthys crocea, which had a strong antimicrobial activity against S. aureus with a minimum bactericidal concentration (MBC) of 3.9 μg/mL and completed bacteria killing by treatment for 1.5 h. The FAM286 could increase the permeability and disrupt the integrity of cell membranes. The cell showed aggregation phenomenon and entered the apoptosis stage. In addition, the non-bactericidal concentration of FAM286 could effectively inhibit the formation of biofilm and remove mature biofilm. Molecular docking experiments further verified the binding sites of FAM286 to S. aureus biofilm proteins SarA, AgrA, and Hld. FAM286 could also bind the bacterial DNA in an embedded manner, disrupting the structure of DNA and leading to the death of bacteria. This study comprehensively evaluated the antimicrobial mechanism of the FAM286 against S. aureus and provided a theoretical basis for the prevention and control of S. aureus.

Bacillus subtilis fermented shrimp waste isolated peptide, PVQ9, and its antimicrobial mechanism on four Gram-positive foodborne bacteria

Bacillus subtilis produces proteases that hydrolyze proteins to produce bioactive peptides. Given the mounting waste from processed shrimp, the antimicrobial potential of peptides isolated from B. subtilis fermented shrimp waste was explored. Among the five peptides screened using molecular docking prediction, PVQ9 (AVFPSIVGRPR) had strong antibacterial activity against four common foodborne Gram-positive bacteria, i.e., Staphylococcus aureus, Bacillus cereus, Mammaliicoccus sciuri, and Kurthia gibsonii. The minimum bactericidal concentrations (MBCs) were 62.5 μg/mL for S. aureus and B. cereus, and 31.3 μg/mL for both M. sciuri and K. gibsonii, with a time-kill of 3 h observed for all strains. Mechanistically, it was demonstrated that PVQ9 could destroy bacterial cell walls, change bacteria cell membrane permeability, bind to bacteria DNA, and cause cell apoptosis. Most importantly, peptide PVQ9 could inhibit the spoilage of bean curd or tofu contaminated with K. gibsonii. These findings suggest that PVQ9 could be a useful preservative in controlling foodborne pathogenic bacteria in soy products and other processed foods.

Preparation, characterization and properties of chitosan-coated Epsilon-poly-lysine nanoliposomes in apple juice

Epsilon-poly-lysine (EPL) is widely used in food preservatives. However, EPL can react with components in food substrates, resulting in the formation of precipitates that reduce its antimicrobial properties. Nanoencapsulation is a promising technique and represents a novel approach to enhance EPL activity. In this study, EPL nanoliposomes (EPLLP) were prepared by the thin film hydration method, and chitosan-coated nanoliposomes (CS-EPLLP) were developed by modifying EPLLP with 0.5 mg/mL chitosan. The obtained CS-EPLLP exhibited a spherical morphology with a particle size range of 85.27-89.77 nm, a polydispersity index (PDI) of 0.293-0.301, and an encapsulation efficiency of 83.01 ± 4.00 %. After 30 days of storage, no significant difference in particle size was observed and the PDI was <0.30. The release rate of EPLLP was up to 40 % in 1 h, while that of CS-EPLLP was <20 %. The physical and thermal stability of EPLLP could be effectively improved by chitosan. Moreover, CS-EPLLP could effectively eradicate A. acidocaldarius and A. acidoterrestris in apple juice at concentrations of 2.5 and 0.625 mg/L, respectively. The cytotoxicity test showed that CS-EPLLP exhibited excellent biocompatibility. Therefore, this study has developed a novel nanoliposome material that provides new insights into the control of bacterial contamination in fruit juices.

The potential of glycinin basic peptide derived from soybean as a promising candidate for the natural food additive and preservative: A review

Glycinin basic peptide (GBP) is the basic polypeptide of soybean glycinin that is isolated using cheap and readily available raw materials (soybean meals). GBP can bear high-temperature processing and has good functional properties, such as emulsification and adhesion properties et al. GBP exhibits broad-spectrum antimicrobial activities against Gram-positive and Gram-negative bacteria as well as fungi. Beyond that, GBP shows enormous application potential to improve the quality and extend the shelf life of food products. This review will systematically provide information on the purification, physicochemical and functional properties of GBP. Moreover, the antimicrobial activities and multi-target antimicrobial mechanism of GBP as well as the applications of GBP in different food products are also reviewed and discussed in detail. This review aims to offer valuable insights for the applications of GBP in the food industry as a promising natural food additive and preservative.

Transcriptomic and Molecular Docking Analysis Reveal Virulence Gene Regulation-Mediated Antibacterial Effects of Benzyl Isothiocyanate Against Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a common pathogen that can cause many serious infections. Thus, efficient and practical techniques to fight S. aureus are required. In this study, transcriptomics was used to evaluate changes in S. aureus following treatment with benzyl isothiocyanate (BITC) to determine its antibacterial action. The results revealed that the BITC at subinhibitory concentrations (1/8th MIC) treated group had 94 differentially expressed genes compared to the control group, with 52 downregulated genes. Moreover, STRING analyses were used to reveal the protein interactions encoded by 36 genes. Then, we verified three significant virulence genes by qRT-PCR, including capsular polysaccharide synthesis enzyme (cp8F), capsular polysaccharide biosynthesis protein (cp5D), and thermonuclease (nuc). Furthermore, molecular docking analysis was performed to investigate the action site of BITC with the encoded proteins of cp8F, cp5D, and nuc. The results showed that the docking fraction of BITC with selected proteins ranged from - 6.00 to - 6.60 kcal/mol, predicting the stability of these complexes. BITC forms hydrophobic, hydrogen-bonded, π-π conjugated interactions with amino acids TRP (130), GLY (10), ILE (406), LYS (368), TYR (192), and ARG (114) of these proteins. These findings will aid future research into the antibacterial effects of BITC against S. aureus.

Synergistic effects of ε-poly-l-lysine and lysozyme against Pseudomonas aeruginosa and Listeria monocytogenes biofilms on beef and food contact surfaces

This study investigated the synergistic effects of ε-poly- L -lysine (ε-PL) and lysozyme against P. aeruginosa and L. monocytogenes biofilms. Single-culture biofilms of two bacteria were formed on silicone rubber (SR), stainless steel (SS), and beef surfaces and then treated with lysozyme (0.05-5 mg/mL) and ε-PL at minimum inhibitory concentrations (MICs) of 1 to 4 separately or in combination. On the SR surface, P. aeruginosa biofilm was reduced by 1.4 and 1.9 log CFU/cm2 within 2 h when treated with lysozyme (5 mg/mL) and ε-PL (4 MIC), respectively, but this reduction increased significantly to 4.1 log CFU/cm2 (P < 0.05) with the combined treatment. On beef surface, P. aeruginosa and L. monocytogenes biofilm was reduced by 4.2-5.0, and 3.3-4.2 log CFU/g when lysozyme was combined with 1, 2, and 4 MIC of ε-PL at 25 °C, respectively. Compared to 5 mg/mL lysozyme alone, the combined treatment with 1, 2, and 4 MIC of ε-PL on beef surface achieved additional reduction against P. aeruginosa biofilm of 0.5, 0.8, and 0.7 log CFU/g, respectively, at 25 °C. In addition, 0.25 mg/mL lysozyme and 0.5 MIC of ε-PL significantly (P < 0.05) suppressed the quorum-sensing (agrA) and virulence-associated (hlyA and prfA) genes of L. monocytogenes.

Injectable nanoparticle-crosslinked xyloglucan/ε-poly-l-lysine composite hydrogel with hemostatic, antimicrobial, and angiogenic properties for infected wound healing

Skin wounds are susceptible to infection, leading to severe inflammatory reactions that can progress to chronic wounds, ultimately causing significant physical and mental distress to the patient. In this study, we propose an injectable composite hydrogel achieved through one-pot gelation of oxidized xyloglucan (OXG), cationic polyamide ε-poly-l-lysine (EPL), and surface amino-rich silicon nanoparticles (SiNPs). OXG exhibits commendable anti-inflammatory properties and provides crosslinking sites. SiNPs serve as mechanically reinforced crosslinkers, facilitating the construction of a dynamic Schiff base network. SiNPs significantly reduced the gelation time to 3 s and tripled the storage modulus of the hydrogels. Additionally, the combination of EPL and SiNPs demonstrated synergistic antimicrobial activity against both S. aureus and E. coli. Notably, the hydrogel effectively halted liver bleeding within 30 s. The hydrogel demonstrated outstanding shear-thinning and self-healing properties, crucial considerations for the design of injectable hydrogels. Furthermore, its efficacy was evaluated as a wound dressing in a mouse model with S. aureus infection. The results indicated that, compared to commercial products, the hydrogel exhibited a shorter wound healing time, decreased inflammation, thinner epithelium, increased hair follicles, enhanced neovascularization, and more substantial collagen deposition. These findings strongly suggest the promising potential of the proposed hydrogel as an effective wound dressing for the treatment of infected wounds.

Biopolymer-based packaging films/edible coatings functionalized with ε-polylysine: New options for food preservation

In light of the commendable advantages inherent in natural polymers such as biocompatibility, biodegradability, and cost-effectiveness, researchers are actively engaged in the development of biopolymer-based biodegradable food packaging films (BFPF). However, a notable limitation is that most biopolymers lack intrinsic antimicrobial activity, thereby restricting their efficacy in food preservation. To address this challenge, various active substances with antibacterial properties have been explored as additives to BFPF. Among these, ε-polylysine has garnered significant attention in BFPF applications owing to its outstanding antibacterial properties. This study provides a brief overview of the synthesis method and chemical properties of ε-polylysine, and comprehensively examines its impact as an additive on the properties of BFPF derived from diverse biopolymers, including polysaccharides, proteins, aliphatic polyesters, etc. Furthermore, the practical applications of various BFPF functionalized with ε-polylysine in different food preservation scenarios are summarized. The findings underscore that ε-polylysine, functioning as an antibacterial agent, not only directly enhances the antimicrobial activity of BFPF but also serves as a cross-linking agent, interacting with biopolymer molecules to influence the physical and mechanical properties of BFPF, thereby enhancing their efficacy in food preservation.

Effect of Goji Berry extract on cell viability of Lactiplantibacillus plantarum M5 microcapsules during in vitro gastrointestinal digestion

Lactiplantibacillus plantarum M5 and Goji Berry extract were co-microencapsulated to maintain the activity of cells during gastrointestinal digestion, and the mechanism by which they could maintain high activity was investigated. The results showed that the microcapsules with 3% Goji Berry extract(A-GE-3) had the largest encapsulation efficiency(EE) of 92.41 ± 0.58%. SEM showed that the structure of A-GE-3 microcapsules were smoother and denser. Cell viability in A-GE-3 microcapsules remained at 7.17 log10 CFU/g after gastrointestinal digestion. Meanwhile, during the gastrointestinal digestion with 3% Goji Berry extract, cell membrane damage detected by fluorescent probes propidium iodide(PI) and 1.1-N-phenylnaphthylamine(NPN) was significantly reduced; the contents of arginine, glutamic acid and oleic acid in cell membrane were increased, which helped to maintain the dynamic balance of intracellular pH and regulated cell membrane fluidity in response to gastrointestinal environment. This study demonstrated the potential of Goji Berry extract as a probiotic protector in gastrointestinal digestion.

A rapid interactive chitosan-based medium with antioxidant and pro-vascularization properties for infected burn wound healing

Large-pore hydrogels are better suited to meet the management needs of nutrient transportation and gas exchange between infected burn wounds and normal tissues. However, better construction strategies are required to balance the pore size and mechanical strength of hydrogels to construct a faster substance/gas interaction medium between tissues. Herein, we developed spongy large pore size hydrogel (CS-TA@Lys) with good mechanical properties using a simple ice crystal-assisted method based on chitosan (CS), incorporating tannic acid (TA) and ε-polylysine (Lys). A large-pore and mechanically robust hydrogel medium was constructed based on hydrogen bonding between CS molecules. On this basis, a pro-restorative functional platform with antioxidation and pro-vascularization was constructed using TA and Lys. In vitro experiments displayed that the CS-TA@Lys hydrogel possessed favorable mechanical properties and fast interaction performances. In addition, the CS-TA@Lys hydrogel possessed the capacity to remove intra/extracellular reactive oxygen species (ROS) and possessed antimicrobial and pro-angiogenic properties. In vivo experiments displayed that the CS-TA@Lys hydrogel inhibited wound inflammation and promoted wound vascularization. In addition, the CS-TA@Lys hydrogel showed the potential for rapid hemostasis. This study provides a potential functional wound dressing with rapid interaction properties for skin wound repair.

Sustained release, antimicrobial, and antioxidant properties of modified porous starch-based biodegradable polylactic acid/polybutylene adipate-co-terephthalate/thermoplastic starch active packaging film

Porous starch (PS) is a modified starch with commendable biodegradable and adsorption properties. PS exhibits poor thermal stability, and the aqueous solution casting method is conventionally used for PS-activated packaging films. This approach limits the large-scale production of films and makes it difficult to play the functions of porous pores. In this study, PS was prepared by enzymatic digestion combined with freeze-drying and adsorbed with clove essential oil (CEO) after cross-linking with sodium trimetaphosphate. Subsequently, a novel PLA/PBAT/TPS/ScPS-CEO sustained release active packaging film was prepared by blending PLA, PBAT, TPS, and ScPS-CEO using industrial melt extrusion. Compared with PS, ScPS effectively slowed down the release of CEO from the film, with the maximum release of active substances at equilibrium increasing by approximately 100 %, which significantly enhanced the persistence of the antimicrobial and antioxidant properties. The polylactic acid/poly (butylene adipate-co-terephthalate)/thermoplastic starch/trimetaphosphate-crosslinked porous starch incorporated with clove essential oil (PLA/PBAT/TPS/ScPS-CEO) film could reduce the proteolysis, lipid oxidation and microbial growth of salmon, extending its shelf life by approximately 100 % at 4 °C. These results indicate that the ScPS can be used in fresh packaging material in practical applications.

Synthesis and Synergistic Antimicrobial Efficacy of Covalent Conjugates Composed of Epsilon-Poly-l-lysine and Beta-Lactam Antibiotics

The increasing severity of problems posed by drug-resistant pathogens has compelled researchers to explore innovative approaches for infection prevention. Among these strategies, conjugation methods stand out for their convenience and high efficacy. In this study, multiple covalent conjugates were synthesized, incorporating the natural antimicrobial peptide epsilon-poly-l-lysine (EPL) and two commonly used β-lactam antibiotics: penicillin G or ampicillin. Enhanced antimicrobial efficacy against typical Gram-negative pathogens, along with faster kill kinetics compared to combination approaches, was demonstrated by the EPL-Ampicillin covalent conjugates. Their antimicrobial mechanism was also substantiated through SEM and fluorescence tests in this work, confirming the inheritance of membrane-disrupting properties from EPL. Furthermore, the excellent biocompatibility of the raw materials was reserved in the covalent conjugates. This simplified conjugation method holds promise for the development of infection therapeutic drugs and potentially restores the sensitivity of conventional antibiotics to drug-resistant pathogens by introducing membrane-disrupting mechanisms.

Hyperbranched Polylysine Exhibits a Collaborative Enhancement of the Antibiotic Capacity to Kill Gram-Negative Pathogens

In recent years, traditional antibiotic efficacy outcomes have rapidly diminished due to the advent of drug resistance, and the dose limitation value has increased due to the severe side effect of globalized healthcare. Therefore, novel strategies are required to resensitize resistant pathogens to antibiotics existing in the field and prevent the emergence of drug resistance. In this study, cationic hyperbranched polylysine (HBPL-6) was synthesized using the one-pot polymerization method. HBPL-6 exhibited excellent non-cytotoxicity and bio-solubility properties. The present study also showed that HBPL-6 altered the outer membrane (OM) integrity of Escherichia coli O157:H7, Salmonella typhimurium, and Pseudomonas aeruginosa PAO1 by improving their permeability levels. When administered at a safe dosage, HBPL-6 enhanced the accumulation of rifampicin (RIF) and erythromycin (ERY) in bacteria to restore the efficacy of the antibiotics used. Moreover, the combination of HBPL-6 with colistin (COL) reduced the antibiotic dosage, which was helpful in preventing further drug-resistance outcomes. Therefore, this research provides a new strategy for reducing the dosage of drugs used to combat Gram-negative (G-) bacteria through their synergistic effects.

Nisin and ε-polylysine combined treatment enhances quality of fresh-cut jackfruit at refrigerated storage

This study investigated the effects of nisin combined with ε-polylysine on microorganisms and the refrigerated quality of fresh-cut jackfruit. After being treated with distilled water (control), nisin (0.5 g/L), ε-polylysine (0.5 g/L), and the combination of nisin (0.1 g/L) and ε-polylysine (0.4 g/L), microporous modified atmosphere packaging (MMAP) was carried out and stored at 10 ± 1°C for 8 days. The microorganisms and physicochemical indexes were measured every 2 days during storage. The results indicated that combined treatment (0.1 g/L nisin, 0.4 g/L ε-polylysine) had the best preservation on fresh-cut jackfruit. Compared with the control, combined treatment inhibited microbial growth (total bacterial count, mold and yeast), reduced the weight loss rate, respiratory intensity, polyphenol oxidase and peroxidase activities, and maintained higher sugar acid content, firmness, and color. Furthermore, it preserved higher levels of antioxidant compounds, reduced the accumulation of malondialdehyde and hydrogen peroxide, thereby reducing oxidative damage and maintaining high nutritional and sensory qualities. As a safe application of natural preservatives, nisin combined with ε-polylysine treatment has great application potential in the fresh-cut jackfruit industry.

Studies on the Inhibition Mechanism of Linalyl Alcohol against the Spoilage Microorganism Brochothrix thermosphacta

The aim of this study was to investigate the bacterial inhibitory ability and mechanism of action of linalyl alcohol against B. thermosphacta. Linalyl alcohol causes the leakage of intracellular material by disrupting the cell wall and exposing the hydrophobic phospholipid bilayer, which binds to bacterial membrane proteins and alters their structure. In addition, linalyl alcohol causes cell membrane damage by affecting fatty acids and proteins in the cell membrane. By inhibiting the synthesis of macromolecular proteins, the normal physiological functions of the bacteria are altered. Linalyl alcohol binds to DNA in both grooved and embedded modes, affecting the normal functioning of B. thermosphacta, as demonstrated through a DNA interaction analysis.

Antimicrobial activity enabled by chitosan-ε-polylysine-natamycin and its effect on microbial diversity of tomato scrambled egg paste

For a long time, food spoilage posed a severe impairment on food safety and public health. Although chemical preservatives are commonly used to inhibit spoilage/ pathogenic microbial growth, the disadvantages of a single target, potential toxicity and high dose of use limit the better use of preservatives. In this research, the combination of natural preservatives: Natamycin (Nat), ε-polylysine (ε-PL), and Chitosan (CS) could achieve an excellent antimicrobial effect including bacteria and fungi, and reduce the usage of a single preservative. Compound preservatives could destroy microbial morphology and damage the integrity of the cell wall/membrane by leakage of protein and alkaline phosphatase (AKP). Besides, high-throughput sequencing revealed that compound preservatives could decrease microbial diversity and richness, especially, Pseudomonas, Acinetobacter, Fusarium, and Aspergillus. Therefore, the combination of 1/8 × MIC CS, 1/4 × MIC ε-PL, and 1/2 × MIC Nat can achieve an excellent antibacterial effect, providing new ideas for food preservation.

Multiple potential strategies for the application of nisin and derivatives

Nisin is a naturally occurring bioactive small peptide produced by Lactococcus lactis subsp. lactis and belongs to the Type A (I) lantibiotics. Due to its potent antimicrobial activity, it has been broadly employed to preserve various food materials as well as to combat a variety of microbial pathogens. The present review discusses the antimicrobial properties of nisin and different types of their derivatives employed to treat microbial pathogens with a detailed underlying mechanism of action. Several alternative strategies such as combination, conjugation, and nanoformulations have been discussed in order to address several issues such as rapid degradation, instability, and reduced activity due to the various environmental factors that arise in the applications of nisin. Furthermore, the evolutionary relationship of many nisin genes from different nisin-producing bacterial species has been investigated. A detailed description of the natural and bioengineered nisin variants, as well as the underlying action mechanisms, has also been provided. The chemistry used to apply nisin in conjugation with natural or synthetic compounds as a synergetic mode of antimicrobial action has also been thoroughly discussed. The current review will be useful in learning about recent and past research that has been performed on nisin and its derivatives as antimicrobial agents.

Laponite stabilized endogenous antibacterial hydrogel as wet-tissue adhesive

Clinical adhesives for suture-less wound closure remain the problem of poor biocompatibility, weak adhesive strength, and no endogenous antibacterial ability. Here, we designed a novel antibacterial hydrogel (CP-Lap hydrogel) consisting of chitosan and ε-polylysine after being modified with gallic acid (pyrogallol structure). The hydrogel was crosslinked by glutaraldehyde and Laponite via Schiff base and dynamic Laponite-pyrogallol interaction, free from heavy metal and oxidants. Given its dual crosslinking feature, the CP-Lap hydrogel exhibited adequate mechanical strength (150-240 kPa) and demonstrated swelling and degradation resistance. For a typical lap shear test with pigskin, the apparent adhesion strength of the CP-Lap hydrogel could be enhanced to ∼30 kPa benefiting from the O2 blocking effect provided by nanoconfinement space between Laponite. In addition, the hydrogel showed effective antibacterial properties and excellent biocompatibility. The results indicated that this hydrogel has great potential for wound-closing bioadhesives to avoid chronic infections and further harm.

Potential Impact of Combined Inhibition by Bacteriocins and Chemical Substances of Foodborne Pathogenic and Spoilage Bacteria: A Review

In recent years, food safety caused by foodborne pathogens and spoilage bacteria has become a major public health problem worldwide. Bacteriocins are a kind of antibacterial peptide synthesized by microbial ribosomes, and are widely used as food preservatives. However, when used individually bacteriocins may have limitations such as high cost of isolation and purification, narrow inhibitory spectrum, easy degradation by enzymes, and vulnerability to complex food environments. Numerous studies have demonstrated that co-treatment with bacteriocins and a variety of chemical substances can have synergistic antibacterial effects on spoilage microorganisms and foodborne pathogens, effectively prolonging the shelf life of food and ensuring food safety. Therefore, this paper systematically summarizes the synergistic bacteriostatic strategies of bacteriocins in combination with chemical substances such as essential oils, plant extracts, and organic acids. The impacts of bacteriocins when used individually and in combination with other chemical substances on different food substrates are clarified, and bacteriocin-chemical substance compositions that enhance antibacterial effectiveness and reduce the potential negative effects of chemical preservatives are highlighted and discussed. Combined treatments involving bacteriocins and different kinds of chemical substances are expected to be a promising new antibacterial method and to become widely used in both the food industry and biological medicine.

Brij-58 supplementation enhances menaquinone-7 biosynthesis and secretion in Bacillus natto

Menaquinone-7 is a form of vitamin K2 that has been shown to have numerous healthy benefits. In this study, several surfactants were investigated to enhance the production of menaquinone-7 in Bacillus natto. Results showed that Brij-58 supplementation influenced the cell membrane via adsorption, and changed the interfacial tension of fermentation broth, while the changes in the state and the composition of the cell membrane enhanced the secretion and biosynthesis of menaquinone-7. The total production and secretion rate of menaquinone-7 increased by 48.0% and 56.2% respectively. During fermentation, the integrity of the cell membrane decreased by 82.9% while the permeability increased by 158% when the maximum secretory rate was reached. Furthermore, Brij-58 supplementation induced the stress response in bacteria, resulting in hyperpolarization of the membrane, and increased membrane ATPase activity. Finally, changes in fatty acid composition increased membrane fluidity by 30.1%. This study provided an effective strategy to enhance menaquinone-7 yield in Bacillus natto and revealed the mechanism of Brij-58 supplementation in menaquinone-7 production. KEY POINTS: • MK-7 yield in Bacillus natto was significantly increased by Brij-58 supplementation. • Brij-58 could be adsorbed on cell surface and change fermentation environment. • Brij-58 supplementation could affect the state and composition of the cell membrane.

Metagenomic Sequencing to Analyze Composition and Function of Top-Gray Chalky Grain Microorganisms from Hybrid Rice Seeds

The top-gray chalkiness of hybrid rice (Oryza sativa L.) seeds is a typical phenomenon in hybrid rice seeds. The chalky part of the grain is infected and is the inoculum to infect the normal seeds during storage and soaking. These seed-associated microorganisms were cultivated and sequenced using metagenomics shotgun sequencing to obtain more comprehensive information on the seed-associated microorganisms in this experiment. The results showed that fungi could grow well on the rice flour medium, similar to the ingredients of rice seed endosperms. After the assembly of metagenomic data, a gene catalog was established, comprising 250,918 genes. Function analysis showed that glycoside hydrolases were the dominant enzymes, and the genus Rhizopus accounted for the dominant microorganisms. The fungal species R. microspores, R. delemar, and R. oryzae were likely to be the candidate pathogens in the top-gray chalky grains of hybrid rice seeds. These results will provide a reference for improving hybrid rice processing after harvest.

Impact of the calcium concentration on the efficacy of phage phiIPLA-RODI, LysRODIΔAmi and nisin for the elimination of Staphylococcus aureus during lab-scale cheese production

Staphylococcus aureus is a Gram-positive human opportunistic pathogen that may also cause food poisoning because of the ability of some strains to produce heat stable enterotoxins that can persist in food even after the pathogen is successfully eliminated. In this context, biopreservation may be a forward-looking strategy to help eliminate staphylococcal contamination in dairy products by using natural compounds. However, these antimicrobials exhibit individual limitations that may be overcome by combining them. This work investigates the combination of a virulent bacteriophage, phiIPLA-RODI, a phage-derived engineered lytic protein, LysRODIΔAmi, and the bacteriocin nisin for the elimination of S. aureus during lab-scale cheese production at two CaCl₂ concentrations (0.2 % and 0.02 %), and subsequent storage at two different temperatures (4 °C and 12 °C). In most of the assayed conditions, our results demonstrate that the combined action of the antimicrobials led to a greater reduction of the pathogen population than the compounds individually, albeit this effect was additive and not synergistic. However, our results did show synergy between the three antimicrobials for reducing the bacterial load after 14 days of storage at 12 °C, temperature at which there is growth of the S. aureus population. Additionally, we tested the impact of the calcium concentration on the activity of the combination treatment and observed that higher CaCl₂ levels led to a notable increase in endolysin activity that allowed the utilization of approximately 10-times less protein to attain the same efficacy. Overall, our data show that the combination of LysRODIΔAmi with nisin and/or phage phiIPLA-RODI, and an increase in the calcium concentration are successful strategies to decrease the amount of protein required for the control of S. aureus contamination in the dairy sector with a low potential for resistance selection, thereby reducing costs.

Preparation and antimicrobial mechanism of Maillard reaction products derived from ε-polylysine and chitooligosaccharides

Chitooligosaccharides can be combined with amino acids or polypeptide to form Maillard reaction products (MRPs) with the antibacterial characteristics through Maillard reaction. This research aims to clarify the structure, antimicrobial effect and mechanism against Shewanella putrefaciens (S. putrefaciens) of ε-polylysine and chitooligosaccharides Maillard reaction products (LC-MRPs). The results of intrinsic fluorescence (IF) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, proton nuclear magnetic resonance (¹H NMR) spectra and scanning electron microscope (SEM) indicated Maillard reaction occurred between ε-polylysine and chitooligosaccharides. The observation of confocal laser scanning microscopy (CLSM), SEM and growth curves of S. putrefaciens evidenced that LC-MRPs have the strongest antibacterial effects. The leakage of alkaline phosphatase (AKP) and lactate dehydrogenase (LDH) implied that LC-MRPs sabotaged bacterial barrier (cell wall and cell membrane). The changes in content of nucleic acids, reactive oxygen species (ROS) level, lipid peroxidation content (LPO), succinate dehydrogenase (SDH) activity and adenosine triphosphate (ATP) content showed LC-MRPs will affect bacterial genetic gene transcription, material and energy metabolism. Therefore, the LC-MRPs were effective antibacterial agents to inhibit S. putrefaciens, which will help to preserve food with S. putrefaciens as the main spoilage bacteria.

A Hydrotalcite-Based PET Composites with Enhanced Properties for Liquid Milk Packaging Applications

In the present work, the two-phase mixture (HTLc) of hydrotalcite and its oxide were used to improve the barrier properties, UV resistance and antimicrobial activity of Poly(ethylene terephthalate) (PET) for their application in liquid milk packaging. Firstly, CaZnAl-CO₃-LDHs with a two-dimensional layered structure were synthesized by hydrothermal method. CaZnAl-CO₃-LDHs precursors were characterized by XRD, TEM, ICP and dynamic light scattering. A series of PET/HTLc composite films were then prepared, characterized by XRD, FTIR and SEM, and a possible mechanism of the composite films with hydrotalcite was proposed. Barrier properties to water vapor and oxygen have been studied in PET nanocomposites, as well as their antibacterial efficacy by the colony technique and their mechanical properties after exposure to UV irradiation for 24 h. By the presence of 1.5 wt% HTLc in the PET composite film, the oxygen transmission rate (OTR) was reduced by 95.27%, the water vapor transmission rate was reduced by 72.58% and the inhibition against Staphylococcus aureus and Escherichia coli was 83.19% and 52.75%. Moreover, a simulation of the migration process in dairy products was used to prove the relative safety. This research first proposes a safe technique for fabricating hydrotalcite-based polymer composites with a high gas barrier, UV resistance and effective antibacterial activity.

Cyclodextrins and Their Polymers Affect the Lipid Membrane Permeability and Increase Levofloxacin’s Antibacterial Activity In Vitro

Cyclodextrins (CDs) are promising drug carriers that are used in medicine. We chose CDs with different substituents (polar/apolar, charged/neutral) to obtain polymers (CDpols) with different properties. CDpols are urethanes with average Mw of ~120 kDa; they form nanoparticles 100–150 nm in diameter with variable ζ-potential. We studied the interaction of CD and CDpols with model (liposomal) and bacterial membranes. Both types of CD carriers cause an increase in the liposomal membrane permeability, and for polymers, this effect was almost two times stronger. The formation of CD/CDpols complexes with levofloxacin (LV) enhances LV’s antibacterial action 2-fold in vitro on five bacterial strains. The most pronounced effect was determined for LV-CD complexes. LV-CDs and LV-CDpols adsorb on bacteria, and cell morphology influences this process dramatically. According to TEM studies, the rough surface and proteinaceous fimbria of Gram-negative E. coli facilitate the adsorption of CD particles, whereas the smooth surface of Gram-positive bacteria impedes it. In comparison with LV-CDs, LV-CDpols are adsorbed 15% more effectively by E. coli, 2.3-fold better by lactobacilli and 5-fold better in the case of B. subtilis. CDs and CDpols are not toxic for bacterial cells, but may cause mild defects that, in addition to LV-CD carrier adsorption, improve LV’s antibacterial properties.

Antibacterial Regularity Mining Beneath the Systematic Activity Database of Lipopeptides Brevilaterins: An Instructive Activity Handbook for Its Food Application

Bacterial contamination is a primary threat to food safety. Therefore, the persistent development of natural antibacterial agents has become essential work. The present essay attempts to establish a systematic antibacterial activity database to instruct the food application of brevilaterins, promising antibacterial lipopeptides from Brevibacillus laterosporus S62-9. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were systematically collected from 43 species of standard bacteria and 140 strains of isolated bacteria (food spoilage bacteria and antibiotic-resistant bacteria) using a broth dilution method. The results showed that brevilaterins performed a broad-spectrum inhibitory (0.5~128 μg/mL) and bactericidal activity (1~256 μg/mL), especially efficient against Gram-positive bacteria and spoilage bacteria from grain products. Moreover, brevilaterins not only inhibit and kill multiple antibiotic-resistant bacteria but do not readily develop resistance, with a small specific value of MBC/MIC (1~8). Furthermore, brevilaterins would interact with negatively charged sodium dodecyl sulfate and bind amphipathic soybean phospholipid with an affinity constant of K_D = 4.70 × 10⁻⁴ M. No significant activity difference was found between brevilaterin B and brevilaterin C. Collectively, this work contributed rich antibacterial data of brevilaterins and revealed the antibacterial regularity beneath these data, which can be used as an activity handbook to instruct their application in food safety.

Antibacterial Activity and Mechanism of Action of Whey Protein-ε-Polylysine Complexes against Staphylococcus aureus and Bacillus subtilis

ε-Polylysine (ε-PL) is a cationic antimicrobial peptide, which easily forms complexes with food polyanions to weaken its antibacterial activity. A whey protein-ε-PL complex delivery system was found to be able to solve this problem. This study investigated the antimicrobial activity of the complexes and their mechanism against Gram-positive bacteria. The minimal inhibitory concentration of the complexes with different ε-PL contents against Staphylococcus aureus and Bacillus subtilis were 19.53–31.26 and 3.90–7.81 μg/mL, respectively, which were similar to free ε-PL. Furthermore, the whey protein-ε-PL complexes had a strong bactericidal effect on Bacillus subtilis. The inhibition zone diameters of the complexes against Staphylococcus aureus and Bacillus subtilis containing 5000 μg/mL of ε-PL were 14.14 and 16.69 mm, respectively. The results of scanning electron microscopy showed that the complexes could destroy the cell membrane structure in Bacillussubtilis, resulting in holes on the surface, but not in Staphylococcus aureus. The results of molecular dynamics simulation showed that under electrostatic interaction, the complexes captured the phospholipid molecules of the bacterial membrane through the hydrogen bonds. Parts of the ε-PL molecules of the complexes were embedded in the bilayer membrane, and parts of the ε-PL molecules could penetrate the bilayer membrane and enter the bacterial internal environment, forming holes on the surface of the bacteria. The antibacterial results in fresh meat showed that the whey protein-ε-PL complexes could reduce the total mesophilic and Staphylococcus aureus counts. This study on the antibacterial activity mechanism of whey protein-ε-PL complexes could provide a reference for the application of ε-PL in protein food matrices.

Study of the mechanism of ε-poly-l-lysine as an antifungal on Candida albicans and Saccharomyces cerevisiae

The antimicrobial activity of ε-poly-l-lysine (EPL) has been documented, but its antifungal activity on yeast is not well defined and its mechanism of action has been vaguely explained. Our studies revealed that on both, Candida albicans and Saccharomyces cerevisiae, the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC) were 250 μg·mL^-1; EPL produced a K⁺ and Ca²⁺ efflux, and at higher concentrations also an efflux of material absorbing at 260 nm, small peptides, and phosphate is produced, along with the inhibition of fermentation and extracellular acidification and respiration. Moreover, growth was inhibited, reactive oxygen species (ROS) production increased, and cell viability decreased. The polycation also produced plasma membrane potential hyperpolarization. The effects were dependent both on the cell quantity and polycation concentration, as well as the media used. The plasma membrane disruption was confirmed by TEM and PI staining.

Preparation and Properties of Pea Starch/ε-Polylysine Composite Films

The composite films comprising pea starch (St) and ε-polylysine (PL) as the matrix and glycerol and sodium alginate as the plasticizers were investigated. The rheological properties, mechanical properties, Fourier transformed infrared spectroscopy, water vapor permeability (WVP), oil permeability, microstructure, thermogravimetry (TGA), and antimicrobial properties of the composite films were analyzed. The properties of the composite films with different mass ratios of St/PL varied significantly. First, the five film solutions were different pseudoplastic fluids. Additionally, as the mass ratio of PL increased, the tensile strength of the blends decreased from 9.49 to 0.14 MPa, the fracture elongation increased from 38.41 to 174.03%, the WVP increased, and the oil resistance decreased substantially. The films with a broad range of St/PL ratios were highly soluble; however, the solubility of the film with a St/PL ratio of 2:8 was reduced. Lastly, the inhibition of E. coli, B.subtilis, and yeast by the films increased with increasing mass ratios of PL, and the inhibition of B.subtilis was the strongest.

Chitosan-grafted-phenolic acid copolymers against Shewanella putrefaciens by disrupting the permeability of cell membrane

Chitosan (CS) is a kind of high molecular polymer with antibacterial properties. A copolymer with high bacteriostatic activity can be formed by grafting phenolic acid compounds into the chitosan molecular chain, which can inhibit the growth of dominant spoilage bacteria in aquatic products. The study aimed to investigate the antibacterial effect and mechanism of chitosan-grafted-phenolic acid copolymers on Shewanella putrefaciens (S. putrefaciens). CS-grafted-protocatechuic acid (CS-g-PA) and CS-grafted-gallic acid (CS-g-GA) were attained by EDC/NHS coupling reaction. The antibacterial tests indicated that CS-g-PA and CS-g-GA had the same minimum inhibitory concentration (MIC) (1.25 mg/mL) and minimum bactericidal concentration (MBC) (5.0 mg/mL) against S. putrefaciens. According to the change trend of growth curve, the growth of S. putrefaciens was significantly restrained under 2MIC graft copolymers (P < 0.05). Moreover, the increment of alkaline phosphatase (AKPase) activity and electrical conductivity demonstrated that the cell wall and membrane permeability of S. putrefaciens were damaged respectively. In addition, the increase of lactate dehydrogenase (LDHase) activity, protein and nucleic acid absorbance and the decrease of adenosine triphosphatase (ATPase) activity suggested that the cell membrane was incomplete and poor fluidity. The irregular shape of bacteria and the outflow of intercellular contents were also observed from scanning electron microscope (SEM). The above results manifested a great potential of CS-g-PA and CS-g-GA for use as food preservatives to aquatic products.

Comparative Study of ɛ-Polylysine or Nisin Inhibition Kinetics of Lactococcus lactis and Spoilage Microorganisms in Fresh Flammulina velutipes Fruiting Bodies

Flammulina velutipes is one of the most important edible mushrooms, which quickly decays with a short shelf life. However, little is known about the effect of ɛ-polylysine (ɛ-PL) or nisin on the survival of Lactococcus lactis (L. lactis) during the storage at constant temperatures. The objective of this study was to investigate the effect of ɛ-PL or nisin on the growth of L. lactis and background (BK) microorganisms in fresh Flammulina velutipes fruiting bodies (FVFB) and develop mathematical models to predict their growth behavior. The effect of ɛ-PL (0.15 and 0.30 g/kg) or nisin (0.10 and 0.20 g/kg) on the growth of L. lactis and BK microorganisms in FVFB was analyzed at 4, 16, and 20°C. The lag phase of L. lactis was extended, and the specific growth rate was decreased by increasing concentrations of ɛ-PL or nisin and lowering the temperature. The results showed that ɛ-PL or nisin could control the growth of L. lactis in FVFB. However, the growth of BK microorganisms was not affected by ɛ-PL or nisin. The growth of L. lactis and BK microorganisms could be successfully described by the reparameterized Gompertz and no lag phase models, respectively. Additionally, ɛ-PL or nisin could maintain the quality of FVFB by preventing weight loss, color-changing, and decreasing soluble solid content in FVFB at 4°C. These results suggest that ɛ-PL or nisin in combination with low temperature may inhibit the growth of L. lactis in FVFB and prevent the decrease in the quality of FVFB.

Low temperature extrusion blown ε-polylysine hydrochloride-loaded starch/gelatin edible antimicrobial films

Edible antimicrobial films made from starch/gelatin (S/G) incorporated with different ε-polylysine hydrochloride (ε-PL) contents were developed by low-temperature extrusion blowing process. ε-PL addition reduced the complex viscosity and storage modulus of blends, while promoted the formation of hydrogen bonding among film components. The control film had an A-type crystalline structure, while increasing the ε-PL content promoted its transformation to B-shaped structure. Without ε-PL and under the processing temperature used, the starch granules were not sufficiently gelatinized. However, ε-PL addition significantly enhanced the gelatinization degree. Increasing ε-PL content in S/G films increased film flexibility, water contact angle value, swelling degree, antimicrobial effect, and storage period of fresh bread, but decreased water vapor permeability and tensile strength. S/G film with 4 wt% ε-PL had the highest water contact angle (94°) and elongation at break (149%). This research demonstrates the plasticizing effects of ε-PL and potential of S/G films containing ε-PL for food preservation/packaging.

Synergistic antimicrobial interactions of nisin A with biopolymers and solubilising agents for oral drug delivery

In order to develop bacteriocins, like the lantibiotic nisin A, into effective alternatives to existing antibiotics, their biophysical and physicochemical properties must first be assessed, from solubility, to susceptibility and absorption. It has been well established that formulation strategies at early drug development stages can be crucial for successful outcomes during preclinical and clinical phases of development, particularly for molecules with challenging physicochemical properties. This work elucidates the physicochemical challenges of nisin A in terms of its susceptibility to digestive enzymes like pepsin, pancreatin and proteinase K and its poor solubility at physiological pHs. Low solution concentrations, below the minimum inhibitory concentration against Staphylococcus aureus, were obtained in phosphate buffered saline (PBS, pH 7.4) and in fasted state simulated intestinal fluid (FaSSIF, pH 6.5), while higher solubilities at more acidic pH's such as in a KCl/HCl buffer (pH 2) and in fasted state simulated gastric fluid (FaSSGF, pH 1.6) are observed. Tween® 80 (0.01% v/v) significantly increased the solution concentration of nisin A in PBS (pH 7.4, 24 hr). Pancreatin doubled nisin A's solution concentration at pH 7.4 (PBS) but reduced its' inhibitory activity to ∼ 20%, and pepsin almost completely degraded nisin (after 24 hr), but retained activity at biologically relevant exposure times (∼ 15 min). Harnessing synergism between nisin A and either glycol chitosan or ε-poly lysine, combined with the solubilizing effect of Tween®, increased the antimicrobial activity of nisin A six fold in an in vitro oral administration model.