Bacteriostasis of nisin against planktonic and biofilm bacteria: Its mechanism and application

Food safety incidents caused by bacterial contamination have always been one of the public safety issues of social concern. Planktonic cells, viable but non-culturable (VBNC) cells, and biofilm cells of bacteria can coexist in food or food processing, posing more serious challenges to public health and safety by increasing bacterial survival and difficulty in detection. As a non-toxic, no side effect, and highly effective bacteriostatic substance, nisin has received wide attention from researchers. In this review, we summarized the species and biosynthesis of nisin, the effects of nisin alone or in combination with other treatments on planktonic and biofilm cells, and its applications in the fields of food, feed, and medicine by consulting numerous studies. Meanwhile, the mechanism of nisin on planktonic and biofilm cells was proposed based on existing researches. Nisin not only has antibacterial activity against most G+ bacteria but also exhibits a bacteriostatic effect on G- bacteria when combined with other antibacterial treatments. In addition to planktonic cells, nisin also has significant effects on bacterial cells in biofilms by changing the thickness, density, and composition of biofilms. Based on the three action processes of nisin on biofilms, we summarized the changes of bacteria in biofilms, including the causes of bacterial death and the formation of the VBNC state. We consider that research on the relationship between nisin and VBNC state should be strengthened.

Nucleic acid strand displacement for indirect determination of foodborne bacteria by capillary electrophoresis and its application in antagonism and bacteriostasis studies

Foodborne bacteria threaten human's health. Capillary electrophoresis (CE) is a powerful separation means for the determination of bacteria. Direct separation of bacteria suffers from the shortages of low resolution, channel adsorption, and bacterial aggregation. In this work, a method of nucleic acid strand displacement was developed to indirect separate the bacteria by CE. DNA complexes, consisting of probes and aptamers, were mixed with the three bacteria Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The aptamers could specifically bond with bacteria and release the probes. Through the separation of the probes, the bacteria could be indirectly determined by CE. This method avoided the shortages of direct separation of bacteria. Under the optimized conditions, the three probes for the bacteria could be separated and detected within 2.5 min by high-speed CE with laser-induced fluorescence detection. The limits of detection for the bacteria were in the range 4.20 × 106 to 1.75 × 107  CFU/mL. Finally, the developed method was applied on the study of antagonism of the coexistent bacteria to reveal the relationship between them. Furthermore, the efficiency of bacteriostasis of three traditional Chinese medicines, Coptis chinensis, Schisandra chinensis, and honeysuckle, was also studied by this method.

Acetolactate Decarboxylase as an Important Regulator of Intracellular Acidification, Morphological Features, and Antagonism Properties in the Probiotic Lactobacillus reuteri

SCORE

This study identifies the coding gene (aldB) of acetolactate decarboxylase (ALDC) as an important regulatory gene of the intracellular pH in Lactobacillus reuteri (L. reuteri), uncovering the important role of ALDC in regulating intracellular pH, morphological features, and antagonism properties in the probiotic organism L. reuteri.

METHODS AND RESULTS

The aldB mutant (ΔaldB) of L. reuteri is established using the homologous recombination method. Compare to the wild-type (WT) strain, the ΔaldB strain shows a smaller body size, grows more slowly, and contains more acid in the cell cytoplasm. The survival rate of the ΔaldB strain is much lower in low pH and simulated gastric fluid (SGF) than that of the WT strain, but higher in simulated intestinal fluid (SIF). The antagonism test demonstrates the ΔaldB strain can inhibit Listeria monocytogenes (L. monocytogenes) and Salmonella more effectively than the WT strain. Additionally, there is a dramatic decrease in the adhesion rate of Salmonella to Caco-2 and HT-29 cells in the presence of the ΔaldB strain compared to the WT strain. Simultaneously analyze, the auto-aggregation, co-aggregation, cell surface hydrophobicity (CSH), hemolytic, temperature, NaCl, oxidative stress, and antibiotic susceptibility of the ΔaldB strain are consistent with the features of probiotics.

CONCLUSION

This study highlights that the aldB gene plays a significant role in the growth and antibacterial properties of L. reuteri.

Isolation of starch and protein degrading strain Bacillus subtilis FYZ1-3 from tobacco waste and genomic analysis of its tolerance to nicotine and inhibition of fungal growth

Aerobic fermentation is an effective technique for the large-scale processing of tobacco waste. However, the specificity of the structure and composition of tobacco-derived organic matter and the toxic alkaloids in the material make it currently difficult to directly use microbial agents. In this study, a functional strain FYZ1-3 was isolated and screened from thermophilic phase samples of tobacco waste composting. This strain could withstand temperatures as high as 80°C and grow normally at 0.6% nicotine content. Furthermore, it had a strong decomposition capacity of tobacco-derived starch and protein, with amylase activity of 122.3  U/mL and protease activity and 52.3  U/mL, respectively. To further understand the mechanism of the metabolic transformation of the target, whole genome sequencing was used and the secondary metabolite gene cluster was predicted. The inhibitory effect of the strain on common tobacco fungi was verified using the plate confrontation and agar column methods. The results showed that the strain FYZ1-3 was Bacillus subtilis, with a genome size of 4.17  Mb and GC content of 43.68%; 4,338 coding genes were predicted. The genome was annotated and analyzed using multiple databases to determine its ability to efficiently degrade starch proteins at the molecular level. Moreover, 14 functional genes related to nicotine metabolism were identified, primarily located on the distinct genomic island of FYZ1-3, giving a speculation for its nicotine tolerance capability on the molecular mechanism. By mining the secondary metabolite gene cluster prediction, we found potential synthetic bacteriocin, antimicrobial peptide, and other gene clusters on its chromosome, which may have certain antibacterial properties. Further experiments confirmed that the FYZ1-3 strain was a potent growth inhibitor of Penicillium chrysogenum, Aspergillus sydowii, A. fumigatus, and Talaromyces funiculosus. The creation and industrial use of the functional strains obtained in this study provide a theoretical basis for its industrial use, where it would be of great significance to improve the utilization rate of tobacco waste.

Preparation of pH sensitive bacteriostatic W/O/W emulsion microcapsules

This experiment was done to study the zeolite molecular sieve as a drug-binding effector, the non-antibiotic drug potassium diformate uniformly disperse in the internal aqueous phase of the 'egg box' structure formed by pectin-calcium ions. With oil phase as the intermediate phase and Xanthan gum Chitosan as the external water phase, the W/O/W type sustained release bacteriostatic microcapsules with pH response were prepared and characterized by Fourier transform infrared, thermogravimetric, SEM, and TEM. It can be obtained through characterization experiments that the inner water phase, oil phase, and outer water phase were formed by observation, and W/O/W emulsion microcapsules were obtained and the bacteriostasis effect of microcapsules was verified by bacteriostasis experiment. The permeance experiment showed that the molecular sieve was successfully coated in the microsphere. Studying on drug release mechanism and sustaining release performance of composite emulsion microcapsules. In vitro drug release study showed that the encapsulation efficiency and drug loading rate of microcapsules were improved by adding molecular sieve, reaching 12.31% and 61.55%, respectively. At the same time, we observed that the drug release rate slowed down during the simulated intestinal release process, and the drug release kinetics were in line with the first-order kinetic model and Ritger-Peppas model equation. Experiments had proven that the drug-loaded microcapsules exerted a significant bacteriostatic effect on Escherichia coli, Staphylococcus aureus, and Bacillus subtilis, with the highest antibacterial rates of 97.25%, 94.05%, and 95.93%, respectively. Therefore, the composite emulsion microcapsules can be used as a new controlled-release drug delivery system in vivo.

Advances in the application of functional nanomaterial and cold plasma for the fresh-keeping active packaging of meat

The most recent advancements in food science and technology include cold sterilization of food and fresh-keeping packaging. Active packaging technology has received much interest due to the photocatalytic activity (PCA) of functional nanoparticles, including titanium dioxide (TiO2) and ferric oxide (Fe2O3). However, there are still significant concerns about the toxicity and safety of these functional nanoparticles. This review emphasizes the bacteriostatic and fresh-keeping properties of functional nanoparticles as well as their packaging strategies using the ultraviolet photo-catalysis effect. High-voltage electric field cold plasma (HVEF-CP) is the most innovative method of cold-sterilizing food. HVEF-CP sterilizes by producing photoelectrons, ions, and active free radicals on food media, which come into contact with the bacteria's surface and destroy their cells. Next, this review also assesses the photocatalytic activity and bacteriostasis kinetics of nanosized TiO2 and Fe2O3 in poultry, beef, and lamb. In addition, this review also emphasizes the importance of exploiting the complex interaction processes between TiO2 and Fe2O3, along with dietary components and their utilization in the fresh meat industry.

Chestnut Shell Polyphenols Inhibit the Growth of Three Food-Spoilage Bacteria by Regulating Key Enzymes of Metabolism

The microbial contamination of food poses a threat to human health. Chestnut shells, which are byproducts of chestnut processing, contain polyphenols that exert various physiological effects, and thus have the potential to be used in food preservation. This study investigates the bacteriostatic effect and mechanism(s) of the action of chestnut shell polyphenols (CSPs) on three food-spoilage bacteria, namely Bacillus subtilis, Pseudomonas fragi, and Escherichia coli. To this end, the effect of CSPs on the ultrastructure of each bacterium was determined using scanning electron microscopy and transmission electron microscopy. Moreover, gene expression was analyzed using RT-qPCR. Subsequent molecular docking analysis was employed to elucidate the mechanism of action employed by CSPs via the inhibition of key enzymes. Ultrastructure analysis showed that CSPs damaged the bacterial cell wall and increased permeability. At 0.313 mg/mL, CSPs significantly increased the activity of alkaline phosphatase and lactate dehydrogenase, as well as protein leakage (p < 0.05), whereas the activity of the tricarboxylic acid (TCA) cycle enzymes, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, were inhibited (p < 0.05). The expression levels of the TCA-related genes gltA, icd, sucA, atpA, citA, odhA, IS178_RS16090, and IS178_RS16290 are also significantly downregulated by CSP treatment (p < 0.05). Moreover, CSPs inhibit respiration and energy metabolism, including ATPase activity and adenosine triphosphate (ATP) synthesis (p < 0.05). Molecular docking determined that proanthocyanidins B1 and C1, the main components of CSPs, are responsible for the antibacterial activity. Therefore, as natural antibacterial substances, CSPs have considerable potential for development and application as natural food preservatives.

Analysis of the Antibacterial Properties of Compound Essential Oil and the Main Antibacterial Components of Unilateral Essential Oils

Plant essential oils are widely used in food, medicine, cosmetics, and other fields because of their bacteriostatic properties and natural sources. However, the bacteriostatic range of unilateral essential oils is limited, and compound essential oil has become an effective way to improve the antibacterial properties of unilateral essential oils. In this study, based on the analysis of the antibacterial properties of Chinese cinnamon bark oil and oregano oil, the proportion and concentration of the compound essential oil were optimized and designed, and the antibacterial activity of the compound essential oil was studied. The results showed that the antibacterial activity of Chinese cinnamon bark oil was higher than that of oregano oil. The compound essential oil prepared by a 1:1 ratio of Chinese cinnamon bark oil and oregano oil with a concentration of 156.25 ppm showed an excellent antibacterial activity against Escherichia coli and Staphylococcus aureus. The GC-MS results showed that cinnamaldehyde was the main antibacterial component of Chinese cinnamon bark essential oil, and carvacrol and thymol in oregano oil were the main antibacterial components.

Transcriptome Analysis of Glycerin Regulating Reuterin Production of Lactobacillus reuteri

Reuterin can be produced from glycerol dehydration catalyzed by glycerol dehydratase (GDHt) in Lactobacillus reuteri and has broad application prospects in industry, agriculture, food, and other fields as it is active against prokaryotic and eukaryotic organisms and is resistant to proteases and lipases. However, high concentrations of glycerin inhibit reuterin production, and the mechanism behind this phenomenon is not clear. To elucidate the inhibitory mechanism of glycerol on reuterin synthesis in L. reuteri and provide reference data for constructing an L. reuteri culture system for highly effective 3-hydroxypropionaldehyde synthesis, we used transcriptome-sequencing technology to compare the morphologies and transcriptomes of L. reuteri cultured in a medium with or without 600 mM of glycerol. Our results showed that after the addition of 600 mM of glycerol to the culture medium and incubation for 10 h at 37 °C, the culture medium of L. reuteri LR301 exhibited the best bacteriostatic effect, and the morphology of L. reuteri cells had significantly changed. The addition of 600 mM of glycerol to the culture medium significantly altered the transcriptome and significantly downregulated the transcription of genes involved in glycol metabolism, such as gldA, dhaT, glpK, plsX, and plsY, but significantly upregulated the transcription of genes related to D-glucose synthesis.

Functional modification of gelatin-based biodegradable composite films: a review

As one of the raw materials of biodegradable food packaging, gelatin is an environmentally friendly substitute for traditional plastic packaging. In this review both sources and extraction methods of gelatin are introduced, together with recent modification methods and applications of using plant sources instead of synthetic substances to endow gelatin film with functionality. Gelatin is extracted from mammals, marine organisms, and poultry. Different extraction methods (acid, alkali, enzyme treatment) can affect the molecular weight and amino acid composition of gelatin, thus affecting the molecular structure, physical properties, chemical and functional properties of gelatin. Gelatin serves as a good substrate, but its disadvantage is that it is very brittle. However, the addition of plasticizers can improve the flexibility of the film by reducing chain interactions during the dehydration process. Compared with other plasticizers, glycerol and sorbitol have better effects on adjusting the mechanical properties of gelatin films. Gelatin is combined with active substances such as essential oils, plant extracts, and nanoparticles to prepare gelatin based composite films with good mechanical properties and antibacterial and antioxidant properties. Gelatin-based composite films can effectively inhibit the growth and reproduction of microorganisms and lipid oxidation in food. Applying it to food packaging can improve the quality of fresh food and extend its shelf life.

Chromatin Accessibility and Transcriptional Landscape during Inhibition of Salmonella enterica by Lactobacillus reuteri in IPEC-J2 Cells

Lactobacillus reuteri is a probiotic with bacteriostatic effects, which can effectively inhibit the activity of pathogens. However, the molecular mechanism underlying the inhibition of pathogens by L. reuteri in intestinal cells remains unclear. Using the porcine intestinal cell line IPEC-J2 as a model, we combined RNA-seq and ATAC-seq methods to delineate the porcine genome-wide changes in biological processes and chromatin accessibility in IPEC-J2 cells stimulated by Salmonella enterica BNCC186354, as well as L. reuteri ATCC 53608. Overall, we found that many porcine transcripts were altered after S. enterica BNCC186354 treatment, while L. reuteri ATCC 53608 treatment partially restored this alteration, such as salmonella infection and PI3K/AKT and MAPK pathways. Combined analysis of these two datasets revealed that 26 genes with similar trends overlapped between gene expression and chromatin accessibility. In addition, we identified potential host functional transcription factors (TFs), such as GATA1, TAL1, TBP, RUNX1, Gmeb1, Gfi1b, RARA, and RXRG, in IPEC-J2 cells that might play a critical role and are targeted by L. reuteri ATCC 53608. Moreover, we verified that PI3K/AKT, MAPK, and apoptosis pathways are potentially regulated by S. enterica BNCC186354 but restored by L. reuteri ATCC 53608. The PI3K/AKT pathway was activated by L. reuteri ATCC 53608, thereby potentially inhibiting S. enterica BNCC186354 infection. In conclusion, our data provide new insights into the expression pattern of functional genes and the epigenetic alterations in IPEC-J2 cells underlying the bacteriostatic action of L. reuteri ATCC 53608.

A Unified Therapeutic-Prophylactic Tissue-Engineering Scaffold Demonstrated to Prevent Tumor Recurrence and Overcoming Infection toward Bone Remodeling

Osteosarcoma occurs in children and adolescents frequently and leads to a high fatality rate. Although surgical resection is the most common methods in clinic, patients always suffer from tumor metastasis and recurrence and it is difficult for them to self-repair large bone defects. Furthermore, the postoperative infection from bacteria triggers an inflammatory response and hinders the bone-repair process. This work demonstrates a gadolinium (Gd)-complex and molybdenum sulfide (MoS₂ ) co-doped N-acryloyl glycinamide (NAGA)/gelatin methacrylate (Gel-MA) multifunctional hydrogel (GMNG). The combination between NAGA and Gel-MA endows the GMNG with attractive mechanical properties and controllable degradation ability. The MoS₂ improves the hydrogel system, which has excellent photothermal ability to kill tumor cells and inhibit bacterial infection both in vitro and in vivo. Based on the Gd-complex, the magnetic resonance imaging (MRI) effect can be used to monitor the position and degradation situation of the hydrogel. Notably, accompanied by the degradation of GMNG hydrogel, the gradually released Gd³⁺ from the hydrogel exhibits osteogenic property and could promote new bone formation efficiently in vivo. Therefore, this strategy supplies a method to prepare multifunctional bone-defect-repair materials and is expected to represent a significant guidance and reference to the development of biomaterials for bone tissue engineering.

Functional chitosan gel coating enhances antimicrobial properties and osteogenesis of titanium alloy under persistent chronic inflammation

Titanium is widely used as surgical bone implants due to its excellent mechanical properties, corrosion resistance, and good biocompatibility. However, due to chronic inflammation and bacterial infections caused by titanium implants, they are still at risk of failure in interfacial integration of bone implants, severely limiting their broad clinical application. In this work, chitosan gels crosslinked with glutaraldehyde were prepared and successfully loaded with silver nanoparticles (nAg) and catalase nanocapsules (n (CAT)) to achieve functionalized coating on the surface of titanium alloy steel plates. Under chronic inflammatory conditions, n (CAT) significantly reduced the expression of macrophage tumor necrosis factor (TNF-α), increased the expression of osteoblast alkaline phosphatase (ALP) and osteopontin (OPN), and enhanced osteogenesis. At the same time, nAg inhibited the growth of S. aureus and E. coli. This work provides a general approach to functional coating of titanium alloy implants and other scaffolding materials.

Phillygenin Inhibits Helicobacter pylori by Preventing Biofilm Formation and Inducing ATP Leakage

With the widespread use and abuse of antibiotics, Helicobacter pylori (H. pylori) has become seriously drug resistant. The development of new antibiotics is an important way to solve H. pylori's drug resistance. Screening antibacterial ingredients from natural products is a convenient way to develop new antibiotics. Phillygenin, an effective antibacterial component, was selected from the natural product, forsythia, in this study. Its minimal inhibitory concentration (MIC) for 18 H. pylori strains was 16-32 μg/ml. The minimum bactericidal concentration (MBC) of H. pylori G27 was 128 μg/ml; the higher the drug concentration and the longer the time, the better the sterilization effect. It was non-toxic to gastric epithelial cell (GES)-1 and BGC823 cells at the concentration of 100 μg/ml. It presented a better antibacterial effect on H. pylori in an acidic environment, and after 24 days of induction on H. pylori with 1/4 MIC of phillygenin, no change was found in the MIC of H. pylori. In the mechanism of action, phillygenin could cause ATP leakage and inhibit the biofilm formation; the latter was associated with the regulation of spoT and Hp1174 genes. In addition, phillygenin could regulate the genes of Nhac, caggamma, MATE, MdoB, flagellinA, and lptB, leading to the weakening of H. pylori's acid resistance and virulence, the diminishing of H. pylori's capacity for drug efflux, H. pylori's DNA methylation, the initiation of human immune response, and the ATP leakage of H. pylori, thus accelerating the death of H. pylori. In conclusion, phillygenin was a main ingredient inhibiting H. pylori in Forsythia suspensa, with a good antibacterial activity, high safety, strong specificity, better antibacterial effect under acidic conditions, and low risk of resistance development by H. pylori. Its mechanism of action was mainly associated with inhibiting the biofilm formation and resulting in ATP leakage. In addition, phillygenin was shown to be able to reduce the acid resistance and virulence of H. pylori.

Preservative effects of a novel bacteriocin from Lactobacillus panis C-M2 combined with dielectric barrier discharged cold plasma (DBD-CP) on acquatic foods

In this study, a novel bacteriocin Lactocin C-M2 produced by Lactobacillus panis C-M2, combined with dielectric barrier discharged cold plasma (DBD-CP), was used to evaluate the antibacterial effect on aquatic foods. After the purification procedures of ethyl acetate extraction, cation exchange chromatography and semi-preparative liquid phase, the stability of Lactocin C-M2 under DBD-CP environment was determined, and the preservation effect of these two joint treatments was investigated on fresh white fish samples. As revealed by LC-MS/MS and BLAST analysis, Lactocin C-M2 is a new type of class Ⅱ bacteriocin, with a molecular weight of 863.52 Da and the N-terminal sequence MVKKTSAV. Application of Lactocin C-M2 showed significantly stronger inhibitory effect on bacteria than on yeasts and mold. All the tested 10 Gram positive bacteria and 3 Gram-negative bacteria, including Staphylococcus aureus, Shigella flexneri, Bacillus spp, Lactobacillus spp, Escherichia coli, Pseudomonas aeruginosa, and so on, were inhibited. Lactocin C-M2 also presented stable antibacterial activity after exposure to DBD-CP, with the 95% residual activity against Staphylococcus aureus under the 40∼80 kV voltage for 30∼180 s, indicating the possibility of synergistic application. Combined with addition of 0.9 mg/g Lactocin C-M2, the treatment of DBD-CP with voltage at 60 kV for 90 s on fresh white fish (Culter alburnus) could significantly inhibit the microbial growth, the accumulation of volatile nitrogen and histamine during the storage. Therefore, the Lactocin C-M2, used together with the DBD-CP, is effective in food preservation.

Bismuth Vanadium Oxide Can Promote Growth and Activity in Arabidopsis thaliana

The excellent properties of nanomaterials have been confirmed in many fields, but their effects on plants are still unclear. In this study, different concentrations of bismuth vanadate (BV) were added to the growth medium to analyze the growth of seedlings, including taproots, lateral roots, leaf stomata, root activity, and superoxide anion O₂^.- generation. Gene expression levels related to root growth were determined by quantitative PCR in Arabidopsis thaliana. The results showed that BV promoted the growth of taproots and the development of lateral roots, enhanced the length of the extension zone in roots, increased the number and size of leaf stomata and root activity, reduced the accumulation of ROS in seedlings, and changed the expression levels of genes related to polyamines or hormones. At the same time, we investigated the antibacterial activity of BV against a variety of common pathogens causing crop diseases. The results showed that BV could effectively inhibit the growth of Fusarium wilt of cotton and rice sheath blight. These results provide a new prospect for the development of nanomaterial-assisted plants, which is expected to become one of the ways to solve the problem of controlling and promoting the development of plants. At the same time, it also provides a reference for the study of the effect of BV on plants.

Bioactive Peptides: A Promising Alternative to Chemical Preservatives for Food Preservation

Bioactive peptides used for food preservation can prolong the shelf life through bacteriostasis and antioxidation. On the one hand, bioactive peptides can inhibit lipid oxidation by scavenging free radicals, interacting with metal ions, and inhibiting lipid peroxidation. On the other hand, bioactive peptides can fundamentally inhibit the growth and reproduction of microorganisms by destroying their cell membranes or targeting intracellular components. Besides, bioactive peptides are biocompatible and biodegradable in vivo. Therefore, they are regarded as a promising alternative to chemical preservatives. However, bioactive peptides are easily affected by the external environment in practical application, which hinders their commercialization. Currently, the studies to overcome the weakness focus on encapsulation and chemical synthesis. Bioactive peptides have been applied to the preservation of various foods in experimental research, with good results. In the future, with the deepening understanding of their safety and structure-activity relationship, there may be more bioactive peptides as food preservatives.

Optimization of extraction and bioactivity detection of celery leaf flavonoids using BP neural network combined with genetic algorithm and response

In the present study, ultrasound-assisted extraction was employed to extract the general flavone from celery leaves using response surface methodology and BP neural network model with a genetic algorithm (GA). The effects of temperature, time, solid-liquid ratio, and ethanol concentration on the extraction results were assessed by Box-Behnken design. Further optimization of the process was performed by GA-BP. Our results showed that the optimal conditions were an ethanol concentration of 70.31%, a temperature of 67.2 °C and an extraction time of 26.6 min. In addition, significant antioxidant activity and in vitro bacteriostasis were observed. We found that the total flavonoids of the celery leaves exerted a strong inhibitory effect on Escherichia coli, Staphylococcus aureus, and Bacillus subtilis. Additionally, considerable DPPH· and ·OH scavenging effects were exerted by flavonoids. Therefore, flavonoids from celery leaves can be considered natural antioxidants and bacterial inhibitors.

[Structure prediction and biological activity analysis of dybowskin-1ST antimicrobial peptide in Rana dybowskii]

The evolution, structure and antigenic epitopes prediction of Rana dybowskii antimicrobial peptide dybowskin-1ST were carried out using bioinformatics software available online. Its antibacterial mechanism and structural properties were analyzed, and its activity was verified by applying wound healing assay in mice and bacteriostatic assay in vitro. This provides the theoretical basis for the improvement of parental peptide and the development of novel derivative peptides. The software MEGA_X were used to conduct homology alignment and to construct a phylogenetic tree. The online software ProtParam, ProtScale, PeptideCutter, signal, TMHMM Server were respectively used to predict the physicochemical parameters, hydrophilia/hydrophobicity, shear sites, signal peptides, and transmembrane domains of dybowskin-1ST. The online software SOPMA, Jpred4, DNAstar Protean were used to predict the secondary structure of dybowskin-1ST, and SWISS-MODEL, I-TASSER were used to predict the tertiary structure. ABCpred and SYFPEITHI were respectively used to predict its B-and T-cell epitopes. The effect of dybowskin-1ST on the wound healing was observed on experimental mice. Kirby-Bauer method and dilution method were used to determine the bacteriostatic activity of dybowskin-1ST. The dybowskin-1ST consists of 59 amino acid residues, of which leucine accounts for 16.9%, with a molecular formula of C₃₁₈H₅₁₀N₈₀O₉₃S₂. Its theoretical isoelectric point is 5.10 and the charge is -2. The dybowskin-1ST and dybowskin-1CDYa are closely related phylogenetically. The secondary structure of dybowskin-1ST predicted by the three methods were similar, which consisted of α-helix (44.07%), extended strand (16.95%), β-turns (3.39%), and random coil (35.39%). The prediction of tertiary structure showed that dybowskin-1ST was mainly composed of α-helix, and it was regarded as a hydrophilic protein with signal peptide sequence. Subcellular localization analysis showed that the probability of secreting the mitochondrial targeted peptides was 0.944. Dybowskin-1ST is an extracellular protein with no transmembrane structure region, but contains seven phosphorylation sites, three T-cell epitopes and eight B-cell epitopes. The dybowskin-1ST promoted wound healing and effectively inhibited the growth of Escherichia coli and Staphylococcus aureus. However, it had limited antibacterial activity against fungi and drug-resistant bacteria. Although the structure of dybowskin-1ST is rich in α-helix, the verification experiments showed that its antibacterial ability needs to be enhanced. The reason may be that it is a negatively charged and hydrophilic protein, and amino acid modification with the aim of increasing the number of positive charges and changing the hydrophobicity may be used to obtain derived peptides with enhanced activity.

Bacteriostatic Potential of Melatonin: Therapeutic Standing and Mechanistic Insights

Diseases caused by pathogenic bacteria in animals (e.g., bacterial pneumonia, meningitis and sepsis) and plants (e.g., bacterial wilt, angular spot and canker) lead to high prevalence and mortality, and decomposition of plant leaves, respectively. Melatonin, an endogenous molecule, is highly pleiotropic, and accumulating evidence supports the notion that melatonin's actions in bacterial infection deserve particular attention. Here, we summarize the antibacterial effects of melatonin in vitro, in animals as well as plants, and discuss the potential mechanisms. Melatonin exerts antibacterial activities not only on classic gram-negative and -positive bacteria, but also on members of other bacterial groups, such as Mycobacterium tuberculosis. Protective actions against bacterial infections can occur at different levels. Direct actions of melatonin may occur only at very high concentrations, which is at the borderline of practical applicability. However, various indirect functions comprise activation of hosts' defense mechanisms or, in sepsis, attenuation of bacterially induced inflammation. In plants, its antibacterial functions involve the mitogen-activated protein kinase (MAPK) pathway; in animals, protection by melatonin against bacterially induced damage is associated with inhibition or activation of various signaling pathways, including key regulators such as NF-κB, STAT-1, Nrf2, NLRP3 inflammasome, MAPK and TLR-2/4. Moreover, melatonin can reduce formation of reactive oxygen and nitrogen species (ROS, RNS), promote detoxification and protect mitochondrial damage. Altogether, we propose that melatonin could be an effective approach against various pathogenic bacterial infections.

Anti-Bacterial Properties of Cannabigerol Toward Streptococcus mutans

Streptococcus mutans (S. mutans) is a gram-positive facultatively anaerobic bacterium and the most common pathogen associated with tooth caries. The organism is acid tolerant and can undergo physiological adaptation to function effectively in acid environments such as carious dental plaque. Some cannabinoids have been found to have potent anti-microbial activity against gram-positive bacteria. One of these is the non-psychoactive, minor phytocannabinoid Cannabigerol (CBG). Here we show that CBG exhibits anti-bacterial activities against S. mutans. CBG halts the proliferation of planktonic growing S. mutans, which is affected by the initial cell density. High-resolution scanning electron microscopy showed that the CBG-treated bacteria become swollen with altered membrane structures. Transmission electron microscopy provided data showing that CBG treatment leads to intracellular accumulation of membrane structures. Nile red, DiOC2(3) and laurdan staining demonstrated that CBG alters the membrane properties, induces membrane hyperpolarization, and decreases the membrane fluidity. CBG-treated bacteria showed increased propidium iodide uptake and reduced calcein AM staining, suggesting that CBG increases the membrane permeability and reduces the metabolic activity. Furthermore, CBG prevented the drop in pH caused by the bacteria. In summary, we present here data showing the mechanisms by which CBG exerts its anti-bacterial effect against S. mutans.

Research Progress of the Biosynthesis of Natural Bio-Antibacterial Agent Pulcherriminic Acid in Bacillus

Pulcherriminic acid is a cyclic dipeptide found mainly in Bacillus and yeast. Due to the ability of pulcherriminic acid to chelate Fe3+ to produce reddish brown pulcherrimin, microorganisms capable of synthesizing pulcherriminic acid compete with other microorganisms for environmental iron ions to achieve bacteriostatic effects. Therefore, studying the biosynthetic pathway and their enzymatic catalysis, gene regulation in the process of synthesis of pulcherriminic acid in Bacillus can facilitate the industrial production, and promote the wide application in food, agriculture and medicine industries. After initially discussing, this review summarizes current research on the synthesis of pulcherriminic acid by Bacillus, which includes the crystallization of key enzymes, molecular catalytic mechanisms, regulation of synthetic pathways, and methods to improve efficiency in synthesizing pulcherriminic acid and its precursors. Finally, possible applications of pulcherriminic acid in the fermented food, such as Chinese Baijiu, applying combinatorial biosynthesis will be summarized.

Surface functionalization of PEEK with silicon nitride

Surface roughness, bioactivity, and antibacterial properties are desirable in skeletal implants. We hot-pressed a mix of particulate sodium chloride (NaCl) salt and silicon nitride (β-Si3N4) onto the surface of bulk PEEK. NaCl grains were removed by leaching in water, resulting in a porous PEEK surface embedded with ~15 vol.% β-Si3N4 particles. This functionalized surface showed the osteogenic and antibacterial properties previously reported in bulk silicon nitride implants. Surface enhancement of PEEK with β-Si3N4 could improve the performance of spinal fusion cages, by facilitating arthrodesis and resisting bacteria.

Additive Manufactured Graphene Coating with Synergistic Photothermal and Superhydrophobic Effects for Bactericidal Applications

Drug-resistant bacterial infection is a global threat to public health due to the high mobility of the population. Novel therapy methods have been intensively studied for the eradication of antibiotic-resistant bacteria, including photothermal treatment, which has established outstanding bacterial killing efficiencies under laser radiation, and superhydrophobic surfaces have exhibited excellent antifouling properties. However, an effective, scalable, and affordable bactericidal coating for eliminating drug-resistant bacteria is lacking. Herein, a novel graphene coating using one-step laser-induced graphene and simultaneous laser-induced forward transfer is introduced. The graphene coating shows high photothermal conversion and superhydrophobic performance, and these synergistic effects can make the bacteria number decrease with over 99.99% proportions under one sun illumination. The superhydrophobic properties can also reduce 99.87% of bacteria compared to the control sample when the solar energy is not available. This additive and scalable method can quickly coat functional graphene onto various substrates, with bacterial applications in many areas, such as water pipeline robots.

Simonkolleite Coating on Poly(Amino Acids) to Improve Osteogenesis and Suppress Osteoclast Formation in Vitro

Zinc can enhance osteoblastic bone formation and stimulate osteogenic differentiation, suppress the differentiation of osteoclast precursor cells into osteoclasts, and inhibit pathogenic bacterial growth in a dose-dependent manner. In this study, simonkolleite, as a novel zinc resource, was coated on poly (amino acids) (PAA) via suspending PAA powder in different concentrations of zinc chloride (ZnCl₂) solution, and the simonkolleite-coated PAA (Zn–PAA) was characterized by SEM, XRD, FT-IR and XPS. Zinc ions were continuously released from the coating, and the release behavior was dependent on both the concentration of the ZnCl₂ immersing solution and the type of soak solutions (SBF, PBS and DMEM). The Zn–PAA was cultured with mouse bone marrow stem cells (BMSCs) through Transwell^TM plates, and the results indicated that the relative cell viability, alkaline phosphatase (ALP) activity and mineralization of BMSCs were significantly higher with Zn–PAA as compared to PAA. Moreover, the Zn–PAA was cultured with RAW264.7 cells, and the results suggested an inhibiting effect of Zn–PAA on the cell differentiation into osteoclasts. In addition, Zn–PAA exhibited an antibacterial activity against both S. aureus and E. coli. These findings suggest that simonkolleite coating with certain contents could promote osteogenesis, suppress osteoclast formation and inhibit bacteria, indicating a novel way of enhancing the functionality of synthetic bone graft material and identifying the underline principles for designing zinc-containing bone grafts.

[Purification and bacteriostatic identification of CpxP protein from Pectobacterium carotovorum subsp. carotovorum]

Pectobacterium carotovorum subsp. carotovorum is one of the world's top ten plant pathogens, mainly infecting cruciferous economic crops and ornamental flowers. In this study, an antibacterial gene cpxP (Gene ID: 29704421) was cloned from the genome of Pectobacterium carotovorum subsp. carotovorum, and constructed on the prokaryotic expression plasmid pET-15b, and the recombinant plasmid was transformed into Escherichia coli BL21 (DE3), then stability and bacteriostatic experiments of the purified CpxP protein were performed. The final concentration of IPTG was 1 mmol/L, obtaining high-efficiency exogenous expression of the CpxP protein. There was no other protein after purification, and the destined protein exhibited good thermal stability and pH stability. The antibacterial test results showed that the inhibition rate of the CpxP protein on carrot slice was 44.89% while the inhibition rate on potato slice was 59.41%. To further explain its antibacterial mechanism, studying the spatial structure of this protein can provide new ideas for the control of soft rot and new protein pesticide targets.

Baicalin promotes the bacteriostatic activity of lysozyme on S. aureus in mammary glands and neutrophilic granulocytes in mice

Staphylococcus aureus causes mastitis as a result of community-acquired or nosocomial infections. Lysozyme (LYSO) is an enzyme that is upregulated in many organisms during the innate immune response against infection by bacterial pathogens. Baicalin is a bioactive flavonoid that can bind to enzymes, often to potentiate their effect. Here we tested the effects of baicalin on the activity of LYSO using the S. aureus mastitis mouse model and neutrophilic granulocyte model of S. aureus infection. In our experiments, S. aureus counts decreased with increasing baicalin concentration. Furthermore, qPCR and western blot analyses showed that LYSO expression was unaffected by baicalin, while fluorescence quenching and UV fluorescence spectral analyses showed that baicalin binds to LYSO. To test whether this binding increased LYSO activity, we assessed LYSO-induced bacteriostasis in the presence of baicalin. Our results showed that LYSO-induced S. aureus bacteriostasis increased with increasing concentrations of baicalin, and that baicalin binding to LYSO synergistically increased the antibacterial activity of LYSO. These results demonstrate that baicalin enhances LYSO-induced bacteriostasis during the innate immune response to S. aureus. They suggest baicalin is a potentially useful therapeutic agent for the treatment of bacterial infections.

Enhanced Bioactivity and Bacteriostasis of Surface Fluorinated Polyetheretherketone

Although polyetheretherketone (PEEK) has been considered as a potential orthopedic and dental application material due to its similar elastic modulus as bones, inferior osseointegration and bacteriostasis of PEEK hampers its clinical application. In this work, fluorinated PEEK was constructed via plasma immersion ion implantation (PIII) followed by hydrofluoric acid treatment to ameliorate the osseointegration and antibacterial properties of PEEK. The surface microstructure, composition, and hydrophilicity of all samples were investigated. Rat bone mesenchymal stem cells (rBMSCs) were cultured on their surfaces to estimate bioactivity. The fluorinated PEEK can enhance the cell adhesion, cell spreading, proliferation, and alkaline phosphatase (ALP) activity compared to pristine PEEK. Furthermore, the fluorinated PEEK surface exhibits good bacteriostatic effect against Porphyromonas gingivalis, which is one of the major periodontal pathogens. In summary, we provide an effective route to introduce fluorine and the results reveal that the fluorinated PEEK can enhance the osseointegration and bacteriostasis, which provides a potential candidate for dental implants.

The Chromosomal parDE2 Toxin-Antitoxin System of Mycobacterium tuberculosis H37Rv: Genetic and Functional Characterization

Mycobacterium tuberculosis H37Rv escapes host-generated stresses by entering a dormant persistent state. Activation of toxin-antitoxin modules is one of the mechanisms known to trigger such a state with low metabolic activity. M. tuberculosis harbors a large number of TA systems mostly located within discernible genomic islands. We have investigated the parDE2 operon of M. tuberculosis H37Rv encoding MParE2 toxin and MParD2 antitoxin proteins. The parDE2 locus was transcriptionally active from growth phase till late stationary phase in M. tuberculosis. A functional promoter located upstream of parD2 GTG start-site was identified by 5'-RACE and lacZ reporter assay. The MParD2 protein transcriptionally regulated the P parDE2 promoter by interacting through Arg16 and Ser15 residues located in the N-terminus. In Escherichia coli, ectopic expression of MParE2 inhibited growth in early stages, with a drastic reduction in colony forming units. Live-dead analysis revealed that the reduction was not due to cell death alone but due to formation of viable but non-culturable cells (VBNCs) also. The toxic activity of the protein, identified in the C-terminal residues Glu98 and Arg102, was neutralized by the antitoxin MParD2, both in vivo and in vitro. MParE2 inhibited mycobacterial DNA gyrase and interacted with the GyrB subunit without affecting its ATPase activity. Introduction of parE2 gene in the heterologous M. smegmatis host prevented growth and colony formation by the transformed cells. An M. smegmatis strain containing the parDE2 operon also switched to a non-culturable phenotype in response to oxidative stress. Loss in colony-forming ability of a major part of the MParE2 expressing cells suggests its potential role in dormancy, a cellular strategy for adaptation to environmental stresses. Our study has laid the foundation for future investigations to explore the physiological significance of parDE2 operon in mycobacterial pathogenesis.

In situ fabrication of silver nanoparticle-filled hydrogen titanate nanotube layer on metallic titanium surface for bacteriostatic and biocompatible implantation

A silver nanoparticle (AgNP)-filled hydrogen titanate nanotube layer was synthesized in situ on a metallic titanium substrate. In the synthesis approach, a layer of sodium titanate nanotubes is first prepared on the titanium surface by using a hydrothermal method. Silver nitrate solution is absorbed into the nanotube channels by immersing a dried nanotube layer in silver nitrate solution. Finally, silver ions are reduced by glucose, leading to the in situ growth of AgNPs in the hydrogen titanate nanotube channels. Long-term silver release and bactericidal experiments demonstrated that the effective silver release and effective antibacterial period of the titanium foil with a AgNP-filled hydrogen titanate nanotube layer on the surface can extend to more than 15 days. This steady and prolonged release characteristic is helpful to promote a long-lasting antibacterial capability for the prevention of severe infection after surgery. A series of antimicrobial and biocompatible tests have shown that the sandwich nanostructure with a low level of silver loading exhibits a bacteriostatic rate as high as 99.99%, while retaining low toxicity for cells and possessing high osteogenic potential. Titanium foil with a AgNP-filled hydrogen titanate nanotube layer on the surface that is fabricated with low-cost surface modification methods is a promising implantable material that will find applications in artificial bones, joints, and dental implants.