Antibacterial activity and a membrane damage mechanism of Lachnum YM30 melanin against Vibrio parahaemolyticus and Staphylococcus aureus

The Effect of Nanoscale Modification of Nisin by Different Milk-Derived Proteins on Its Physicochemical Properties and Antibacterial Activity

Nisin is used as a natural food preservative because of its broad-spectrum antimicrobial activity against Gram-positive bacteria. However, free nisin is susceptible to various factors that reduce its antimicrobial activity. Milk protein, a protein derived from milk, has self-assembly properties and is a good carrier of bioactive substances. In this study, lactoferrin-nisin nanoparticles (L-N), bovine serum albumin-nisin nanoparticles (B-N), and casein-nisin nanoparticles (C-N) were successfully prepared by a self-assembly technique, and then their properties were investigated. The studies revealed that lactoferrin (LF) and nisin formed L-N mainly through hydrophobic interactions and hydrogen bonding, and L-N had the best performance. The small particle size (29.83 ± 2.42 nm), dense reticular structure, and good thermal stability, storage stability, and emulsification of L-N laid a certain foundation for its application in food. Further bacteriostatic studies showed that L-N enhanced the bacteriostatic activity of nisin, with prominent inhibitory properties against Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus, which mainly disrupted the cell membrane of the bacteria. The above results broaden our understanding of milk protein-nisin nanoparticles, while the excellent antibacterial activity of L-N makes it promising for application as a novel food preservative, which will help to improve the bioavailability of nisin in food systems.

Antibacterial efficacy of copper-based metal-organic frameworks against Escherichia coli and Lactobacillus

The widespread and excessive use of antimicrobial drugs has resulted in a concerning rise in bacterial resistance, leading to a risk of untreatable infections. The aim of this study was to formulate a robust and efficient antibacterial treatment to address this challenge. Previous work focused on the effectiveness of the Cu-BTC metal-organic framework (MOF; BTC stands for 1,3,5-benzenetricarboxylate) in combatting various bacterial strains. Herein, we compare the antibacterial properties of Cu-BTC with our newly designed Cu-GA MOF, consisting of copper ions bridged by deprotonated gallate ligands (H2gal2-), against Escherichia coli (E. coli) and Lactobacillus bacteria. Cu-GA was synthesized hydrothermally from copper salt and naturally derived gallic acid (H4gal) and characterized for antibacterial evaluation. The gradual breakdown of Cu(H2gal) resulted in a significant antibacterial effect that is due to the release of copper ions and gallate ligands from the framework. Both copper MOFs were nontoxic to bacteria at low concentrations and growth was completely inhibited at high concentrations when treated with Cu-BTC (1500 μg for E. coli and 1700 μg for Lactobacillus) and Cu-GA (2000 μg for both bacterial strains). Furthermore, our agarose gel electrophoresis results indicate that both MOFs could disrupt bacterial cell membranes, hindering the synthesis of DNA. These findings confirm the antibacterial properties of Cu-BTC and the successful internalization of Cu2+ ions and gallic acid by bacteria from the Cu-GA MOF framework, suggesting the potential for a sustained and effective therapeutic approach against pathogenic microorganisms.

Antibacterial and antibiofilm activities of iodinated hydrocarbons against Vibrio parahaemolyticus and Staphylococcus aureus

Food-related illnesses have become a growing public concern due to their considerable socioeconomic and medical impacts. Vibrio parahaemolyticus and Staphylococcus aureus have been implicated as causative organisms of food-related infections and poisoning, and both can form biofilms which confer antibiotic resistance. Hence, the need for continuous search for compounds with antibiofilm and antivirulence properties. In this study, 22 iodinated hydrocarbons were screened for their antibiofilm activity, and of these, iodopropynyl butylcarbamate (IPBC) was found to effectively control biofilm formation of both pathogens with a MIC of 50 µg/mL which was bactericidal to V. parahaemolyticus and S. aureus. Microscopic studies confirmed IPBC inhibits biofilm formation of both bacteria and also disrupted their mixed biofilm formation. Furthermore, IPBC suppressed virulence activities such as motility and hemolytic activity of V. parahaemolyticus and the cell surface hydrophobicity of S. aureus. It exhibited a preservative potential against both pathogens in a shrimp model. IPBC disrupted the cell membrane of S. aureus and V. parahaemolyticus and differentially affected gene expressions related to biofilm formation and virulence. Additionally, it displayed broad-spectrum antibiofilm activities against other clinically relevant pathogens. These findings indicate IPBC offers a potential means of controlling infections mediated by Vibrio and Staphylococcus biofilms.

Novel synergistic interactions between monolaurin, a mono-acyl glycerol and β lactam antibiotics against Staphylococcus aureus: an in vitro study

BACKGROUND

A major worldwide health issue is the rising frequency of resistance of bacteria.Drug combinations are a winning strategy in fighting resistant bacteria and might help in protecting the existing drugs.Monolaurin is natural compound extracted from coconut oil and has a promising antimicrobial activity against Staphylococcus.aureus. This study aims to examine the efficacy of monolaurin both individually and in combination with β-lactam antibiotics against Staphylococcus aureus isolates.

METHODS

Agar dilution method was used for determination of minimum inhibitory concentration (MIC) of monolaurin against S.aureus isolates. Scanning electron microscope (SEM) was used to detect morphological changes in S.aureus after treatment with monolaurin. Conventional and Real-time Polymerase chain reaction (RT-PCR) were performed to detect of beta-lactamase (blaZ) gene and its expressional levels after monolaurin treatment. Combination therapy of monolaurin and antibiotics was assessed through fractional inhibitory concentration and time-kill method.

RESULTS

The antibacterial activity of monolaurin was assessed on 115 S.aureus isolates, the MIC of monolaurin were 250 to 2000 µg/ml. SEM showed cell elongation and swelling in the outer membrane of S.aureus in the prescence of 1xMIC of monolaurin. blaZ gene was found in 73.9% of S.aureus isolates. RT-PCR shows a significant decrease in of blaZ gene expression at 250 and 500 µg/ml of monolaurin. Synergistic effects were detected through FIC method and time killing curve. Combination therapy established a significant reduction on the MIC value. The collective findings from the antibiotic combinations with monolaurin indicated synergism rates ranging from 83.3% to 100%.In time-kill studies, combination of monolaurin and β-lactam antibiotics produced a synergistic effect.

CONCLUSION

This study showed that monolaurin may be a natural antibacterial agent against S. aureus, and may be an outstanding modulator of β-lactam drugs. The concurrent application of monolaurin and β-lactam antibiotics, exhibiting synergistic effects against S. aureus in vitro, holds promise as potential candidates for the development of combination therapies that target particularly, patients with bacterial infections that are nearly incurable.

Effect of chlorogenic acid grafted chitosan on microbiological compositions of sea bass (Lateolabrax japonicus) fillets: Dominant spoilage bacteria, inhibition activity and membrane damage mechanisms

This study investigated the effect of chlorogenic acid grafted chitosan (CS-g-CA) on the microbiota composition of sea bass (Lateolabrax japonicus), isolated and identified the specific spoilage organisms (SSOs) in the late stage of refrigerated fillets and evaluation of their spoilage potential. Moreover, antibacterial activity and membrane damage mechanism of CS-g-CA against spoilage bacteria was also investigated. Illumina-MiSeq high throughput sequencing results showed that CS-g-CA retarded the growth of Pseudomonas spp., which largely contributed to delaying the quality degradation of sea bass during storage. Then nine spoilage bacteria were isolated and identified from the fillets at the end of storage and inoculated into sterile fish fillets to determine their spoilage capacity. Results showed that fish fillets inoculated with spoilage bacteria exhibited a significant increase in TVB-N, TBA and putrescine content and decreased sensory quality during storage. Subsequently, the inhibitory activity of CS-g-CA against spoilage bacteria was investigated and strains that were more sensitive to the CS-g-CA with a strong spoilage capacity were selected for the study of the inhibition mechanism. Results suggested that CS-g-CA had strong inhibitory activity and led to bacterial death through the mechanism of membrane damage. Overall, this study analyzed the effect of CS-g-CA on the preservation of fish fillets from a microbiological point of view to provide a reference for the anti-bacterial preservation of aquatic products.

A rationally engineered small antimicrobial peptide with potent antibacterial activity

Antimicrobial resistance (AMR) is a silent pandemic declared by the WHO that requires urgent attention in the post-COVID world. AMR is a critical public health concern worldwide, potentially affecting people at different stages of life, including the veterinary and agriculture industries. Notably, very few new-age antimicrobial agents are in the current developmental pipeline. Thus, the design, discovery, and development of new antimicrobial agents are required to address the menace of AMR. Antimicrobial peptides (AMPs) are an important class of antimicrobial agents for combating AMR due to their broad-spectrum activity and ability to evade AMR through a multimodal mechanism of action. However, molecular size, aggregability, proteolytic degradation, cytotoxicity, and hemolysis activity significantly limit the clinical application of natural AMPs. The de novo design and engineering of a short synthetic amphipathic AMP (≤16 aa, Mol. Wt. ≤ 2 kDa) with an unusual architecture comprised of coded and noncoded amino acids (NCAAs) is presented here, which demonstrates potent antibacterial activity against a few selected bacterial strains mentioned in the WHO priority list. The designer AMP is conformationally ordered in solution and effectively permeabilizes the outer and inner membranes, leading to bacterial growth inhibition and death. Additionally, the peptide is resistant to proteolysis and has negligible cytotoxicity and hemolysis activity up to 150 μM toward cultured human cell lines and erythrocytes. The designer AMP is unique and appears to be a potent therapeutic candidate, which can be subsequently subjected to preclinical studies to explicitly understand and address the menace of AMR.

Green One-Step Synthesis of Silver Nanoparticles Obtained from Schinus areira Leaf Extract: Characterization and Antibacterial Mechanism Analysis

The increased emergence of antibiotic-resistant bacteria is a serious health problem worldwide. In this sense, silver nanoparticles (AgNPs) have received increasing attention for their antimicrobial activity. In this context, the goal of this study was to produce AgNPs by a green synthesis protocol using an aqueous leaf extract of Schinus areira as biocomposite to later characterize their antimicrobial action. The nanomaterials obtained were characterized by UV‒vis spectroscopy, DLS, TEM, and Raman, confirming the presence of quasi-spherical AgNPs with a negative surface charge and diameter around 11 nm. Afterward, the minimum inhibitory and bactericidal concentration of the AgNPs against Staphylococcus aureus and Escherichia coli were obtained, showing high antibacterial activity. In both of the examined bacteria, the AgNPs were able to raise intracellular ROS levels. In E. coli, the AgNPs can harm the bacterial membrane as well. Overall, it can be concluded that it was possible to obtain AgNPs with colloidal stability and antibacterial activity against Gram-positive and Gram-negative bacteria. Our findings point to at least two separate mechanisms that can cause cell death, one of which involves bacterial membrane damage and the other of which involves intracellular ROS induction.

Bioproduction and optimization of newly characterized melanin pigment from Streptomyces djakartensis NSS-3 with its anticancer, antimicrobial, and radioprotective properties

BACKGROUND

Melanin is a natural pigment that is considered a promising biomaterial for numerous biotechnological applications across several industries. Melanin has biomedical applications as antimicrobial, anticancer, and antioxidant properties. Additionally, in the pharmaceutical and cosmetic industries, it is used in drug delivery and as a radioprotective agent. Also, melanin has environmental uses in the fields of bioremediation and the food industry. The biosynthesis of melanin pigment is an area of interest for researchers due to its multifunctionality, high compatibility, and biodegradability. Therefore, our present work is the first attempt to characterize and optimize the productivity of melanin pigment from Streptomyces djakartensis NSS-3 concerning its radioprotection and biological properties.

RESULTS

Forty isolates of soil actinobacteria were isolated from the Wadi Allaqui Biosphere Reserve, Egypt. Only one isolate, ACT3, produced a dark brown melanin pigment extracellularly. This isolate was identified according to phenotypic properties and molecular phylogenetic analysis as Streptomyces djakartensis NSS-3 with accession number OP912881. Plackett-Burman experimental design (PBD) and response surface methodology (RSM) using a Box-Behnken design (BBD) were performed for optimum medium and culturing conditions for maximum pigment production, resulting in a 4.19-fold improvement in melanin production (118.73 mg/10 mL). The extracted melanin pigment was purified and characterized as belonging to nitrogen-free pyomelanin based on ultraviolet-visible spectrophotometry (UV-VIS), Fourier transform infrared (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and NMR studies. Purified melanin demonstrated potent scavenging activity with IC50 values of 18.03 µg/mL and revealed high potency as sunscreens (in vitro SPF = 18.5). Moreover, it showed a nontoxic effect on a normal cell line (WI38), while it had a concentration-dependent anticancer effect on HCT116, HEPG, and MCF7 cell lines with IC50 = 108.9, 43.83, and 81.99 µg/mL, respectively. Also, purified melanin had a detrimental effect on the tested MDR bacterial strains, of which PA-09 and SA-04 were clearly more susceptible to melanin compared with other strains with MICs of 6.25 and 25 µg/mL, respectively.

CONCLUSION

Our results demonstrated that the newly characterized pyomelanin from Streptomyces djakartensis NSS-3 has valuable biological properties due to its potential photoprotective, antioxidant, anticancer, antimicrobial, and lack of cytotoxic activities, which open up new prospects for using this natural melanin pigment in various biotechnological applications and avoiding chemical-based drugs.

Anti-ultraviolet, antibacterial, and biofilm eradication activities against Cutibacterium acnes of melanins and melanin derivatives from Daedaleopsis tricolor and Fomes fomentarius

Fomes fomentarius and Daedaleopsis tricolor produced significant amounts of water-insoluble melanins, and our previous study successfully enhanced their water solubility by arginine modification. This research aimed to investigate the anti-ultraviolet, antibacterial, and biofilm eradication activities of both the melanins and arginine-modified melanin (melanin derivatives) from these two fungi against an acne-causing bacterium (Cutibacterium acnes). Apart from these, the cytotoxicity of the melanins and melanin derivatives on human skin cells was also evaluated. Melanin derivatives of both two fungi showed significantly higher antibacterial and biofilm eradication activities compared with their original forms. Specifically, the MIC50 values of the melanin derivatives (1,000 μg/mL) are the same as those of erythromycin. Regarding biofilm eradication capacity, the MBEC50 value of D. tricolor melanin derivative (250 μg/mL) was just half of both erythromycin and F. fomentarius melanin derivative. However, it required a 2-fold higher concentration of melanin derivatives than erythromycin to inhibit 90% of the bacterial population and eradicate 90% of their biofilm. Regarding anti-ultraviolet activity, blending melanins or melanin derivatives with a moisturizer/sunscreen enhanced their UV light absorption and the sun protection factor (SPF) values. In addition, melanins showed better effects than their derivatives, and those of D. tricolor were better than F. fomentarius. Remarkably, adding D. tricolor melanin (10%) to a Nivea pure cream could turn this cream into a broad-spectrum sunscreen, with its SPF value and critical wavelength increasing from 7.74 and 338.67 to 14.02 and 377.0, respectively. In addition, adding melanin or a melanin derivative of D. tricolor to an Olay sunscreen enhanced the SPF and the critical wavelength of the sunscreen from 17.25 and 371.67 to 23.82 and 374 and 23.38 and 372, respectively. Notably, melanins and melanin derivatives showed no toxicity in human fibroblasts. The obtained data suggest that arginine modification significantly enhanced the antibacterial and biofilm eradication activities of melanins from D. tricolor and F. fomentarius. However, this is not the case when it comes to their anti-ultraviolet activities. In addition, melanin and melanin derivatives from D. tricolor are potential candidates for anti-acne sunscreen products and are worth further investigation.

Antimicrobial Activity of Stilbenes from Bletilla striata against Cutibacterium acnes and Its Effect on Cell Membrane

The abnormal proliferation of Cutibacterium acnes is the main cause of acne vulgaris. Natural antibacterial plant extracts have gained great interest due to the efficacy and safety of their use in skin care products. Bletilla striata is a common externally used traditional Chinese medicine, and several of its isolated stilbenes were reported to exhibit good antibacterial activity. In this study, the antimicrobial activity of stilbenes from B. striata (BSS) against C. acnes and its potential effect on cell membrane were elucidated by determining the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), bacterial growth curve, adenosine triphosphate (ATP) levels, membrane potential (MP), and the expression of genes related to fatty acid biosynthesis in the cell membrane. In addition, the morphological changes in C. acnes by BSS were observed using transmission electron microscopy (TEM). Experimentally, we verified that BSS possessed significant antibacterial activity against C. acnes, with an MIC and MBC of 15.62 μg/mL and 62.5 μg/mL, respectively. The growth curve indicated that BSS at 2 MIC, MIC, 1/2 MIC, and 1/4 MIC concentrations inhibited the growth of C. acnes. TEM images demonstrated that BSS at an MIC concentration disrupted the morphological structure and cell membrane in C. acnes. Furthermore, the BSS at the 2 MIC, MIC, and 1/2 MIC concentrations caused a decrease in the intracellular ATP levels and the depolarization of the cell membrane as well as BSS at an MIC concentration inhibited the expression of fatty acid biosynthesis-associated genes. In conclusion, BSS could exert good antimicrobial activity by interfering with cell membrane in C. acnes, which have the potential to be developed as a natural antiacne additive.

Antibacterial potential of silver nanoparticles (SP-AgNPs) synthesized from Syzygium polyanthum (Wight) Walp. against selected foodborne pathogens

Foodborne diseases continue to pose a significant global health concern, causing a considerable number of deaths worldwide. In response to concerns surrounding bacterial resistance and the limitations of traditional antibiotics, there is a growing interest in exploring natural antibacterial agents as potential alternatives for addressing foodborne pathogens. Nowadays efforts are being made on exploring the potential of natural antibacterial agents against foodborne pathogens. In this study, the antibacterial efficacy of silver nanoparticles synthesized using S. polyanthum leaves extract (SP-AgNPs) against selected Gram-negative and Gram-positive foodborne pathogens was investigated by using multiple assays, including the well diffusion assay (WDA), minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assay. The well diffusion assay demonstrated the inhibitory potential of SP-AgNPs against all tested foodborne pathogens, with inhibition zones ranging from 10.16 + 1.25 to 13.16 + 1.52 mm. Furthermore, the MIC values ranged from 0.008 to 0.125 mg/mL, indicating the potent antibacterial activity of SP-AgNPs across a broad spectrum of foodborne pathogens. The MBC values, ranging from 0.008 to 0.250 mg/mL, further confirming the bactericidal ability of SP-AgNPs against these pathogens. In the time-kill experiment, most foodborne pathogens were entirely killed after 4 h of incubation at 4 × MIC concentration. However, only E. coli, K. pneumoniae, and S. Typhimurium showed a reduction in population to 3 Log10 CFU/mL, indicating a strong bactericidal effect of SP-AgNPs on most tested pathogens. In conclusion, this study provides compelling evidence that SP-AgNPs exhibit potent antibacterial activity against selected foodborne pathogens. The findings suggest that SP-AgNPs synthesized using S. polyanthum leaves extract hold great promise as a novel antibacterial agent for effectively controlling foodborne pathogens. These findings contribute to continuing efforts in developing alternative strategies to prevent foodborne diseases and enhance food safety.

Natural products acting against S. aureus through membrane and cell wall disruption

Covering: 2015 to 2022Staphylococcus aureus (S. aureus) is responsible for several community and hospital-acquired infections with life-threatening complications such as bacteraemia, endocarditis, meningitis, liver abscess, and spinal cord epidural abscess. In recent decades, the abuse and misuse of antibiotics in humans, animals, plants, and fungi and the treatment of nonmicrobial diseases have led to the rapid emergence of multidrug-resistant pathogens. The bacterial wall is a complex structure consisting of the cell membrane, peptidoglycan cell wall, and various associated polymers. The enzymes involved in bacterial cell wall synthesis are established antibiotic targets and continue to be a central focus for antibiotic development. Natural products play a vital role in drug discovery and development. Importantly, natural products provide a starting point for active/lead compounds that sometimes need modification based on structural and biological properties to meet the drug criteria. Notably, microorganisms and plant metabolites have contributed as antibiotics for noninfectious diseases. In this study, we have summarized the recent advances in understanding the activity of the drugs or agents of natural origin that directly inhibit the bacterial membrane, membrane components, and membrane biosynthetic enzymes by targeting membrane-embedded proteins. We also discussed the unique aspects of the active mechanisms of established antibiotics or new agents.

Growth patterns of Pseudomonas aeruginosa in milk fortified with chitosan and selenium nanoparticles during refrigerated storage

Pseudomonas spp are considered a common milk-associated psychotropic bacteria, leading to milk deterioration during storage; therefore, our study aimed to study the distribution of Pseudomonas aeruginosa in raw milk and its associated products then studying the growth behavior of P. aeruginosa in milk after employing chitosan nanoparticles (CsNPs 50, 25, and 15 mg/100ml) and selenium nanoparticles (SeNPs 0.5, 0.3 and 0.1 mg/100ml) as a trial to control the bacterial growth in milk during five days of cooling storage. Our study relies on the ion gelation method and green synthesis for the conversion of chitosan and selenium to nanosized particles respectively, we subsequently confirmed their shape using SEM and TEM. We employing Pseudomonas selective agar medium for monitoring the bacterial growth along the cooling storage. Our findings reported that high prevalence of Pseudomonas spp count in raw milk and kareish cheese and high incidence percent of P. aeruginosa in ice cream and yogurt respectively. Both synthesized nanoparticles exhibited antibacterial activity in a dose-dependent manner. Moreover, CsNPs50 could inhibit the P. aeruginosa survival growth to a mean average of 2.62 ± 1.18 log10cfu/ml in the fifth day of milk cooling storage; also, it was noted that the hexagonal particles SeNPs0.5 could inhibit 2.49 ± 11 log10cfu/ml in comparison to the control P. aeruginosa milk group exhibited growth survival rate 7.24 ± 2.57 log10cfu/ml under the same conditions. In conclusion, we suggest employing chitosan and selenium nanoparticles to improve milk safety and recommend future studies for the fate of nanoparticles in milk.

Can Pyomelanin Produced by Pseudomonas aeruginosa Promote the Regeneration of Gastric Epithelial Cells and Enhance Helicobacter pylori Phagocytosis?

Helicobacter pylori (H. pylori) infection is the most common cause of chronic gastritis, peptic ulcers and gastric cancer. Successful colonization of the stomach by H. pylori is related to the complex interactions of these bacteria and its components with host cells. The growing antibiotic resistance of H. pylori and various mechanisms of evading the immune response have forced the search for new biologically active substances that exhibit antibacterial properties and limit the harmful effects of these bacteria on gastric epithelial cells and immune cells. In this study, the usefulness of pyomelanin (PyoM) produced by Pseudomonas aeruginosa for inhibiting the metabolic activity of H. pylori was evaluated using the resazurin reduction assay, as well as in vitro cell studies used to verify the cytoprotective, anti-apoptotic and pro-regenerative effects of PyoM in the H. pylori LPS environment. We have shown that both water-soluble (PyoMsol) and water-insoluble (PyoMinsol) PyoM exhibit similar antibacterial properties against selected reference and clinical strains of H. pylori. This study showed that PyoM at a 1 μg/mL concentration reduced H. pylori-driven apoptosis and reactive oxygen species (ROS) production in fibroblasts, monocytes or gastric epithelial cells. In addition, PyoM enhanced the phagocytosis of H. pylori. PyoMsol showed better pro-regenerative and immunomodulatory activities than PyoMinsol.

The Enigmatic World of Fungal Melanin: A Comprehensive Review

Synthetic dyes are generally not safe for human health or the environment, leading to the continuous search and growing demand for natural pigments that are considered safer, biodegrade more easily, and are environmentally beneficial. Among micro-organisms, fungi represent an emerging source of pigments due to their many benefits; therefore, they are readily viable on an industrial scale. Among all the bioactive pigments produced by fungi, melanin is an enigmatic, multifunctional pigment that has been studied for more than 150 years. This dark pigment, which is produced via the oxidative polymerization of phenolic compounds, has been investigated for its potential to protect life from all kingdoms, including fungi, from biotic and abiotic stresses. Over time, the research on fungal melanin has attracted a significant amount of scientific interest due to melanin's distinct biological activities and multifarious functionality, which is well-documented in the literature and could possibly be utilized. This review surveys the literature and summarizes the current discourse, presenting an up-to-date account of the research performed on fungal melanin that encompasses its types, the factors influencing its bioactivity, the optimization of fermentation conditions to enhance its sustainable production, its biosynthetic pathways, and its extraction, as well as biochemical characterization techniques and the potential uses of melanin in a wide range of applications in various industries. A massive scope of work remains to circumvent the obstacles to obtaining melanin from fungi and exploring its future prospects in a diverse range of applications.

Transcriptome Analysis Revealed That Hydrogen Peroxide-Regulated Oxidative Phosphorylation Plays an Important Role in the Formation of Pleurotus ostreatus Cap Color

Pleurotus ostreatus is widely cultivated in China. H2O2, as a signaling molecule, can regulate the formation of cap color, but its regulatory pathway is still unclear, severely inhibiting the breeding of dark-colored strains. In this study, 614 DEGs specifically regulated by H2O2 were identified by RNA-seq analysis. GO-enrichment analysis shows that DEGs can be significantly enriched in multiple pathways related to ATP synthesis, mainly including proton-transporting ATP synthesis complex, coupling factor F(o), ATP biosynthetic process, nucleoside triphosphate metabolic processes, ATP metabolic process, purine nucleoside triphosphate biosynthetic and metabolic processes, and purine ribonuclease triphosphate biosynthetic metabolic processes. Further KEGG analysis revealed that 23 DEGs were involved in cap color formation through the oxidative phosphorylation pathway. They were enriched in Complexes I, III, IV, and V in the respiratory chain. Further addition of exogenous uncoupling agents and ATP synthase inhibitors clarifies the important role of ATP synthesis in color formation. In summary, H2O2 may upregulate the expression of complex-encoding genes in the respiratory chain and promote ATP synthesis, thereby affecting the formation of cap color. The results of this study lay the foundation for the breeding of dark-colored strains of P. ostreatus and provide a basis for the color-formation mechanism of edible fungi.

Synthesis of biologically derived poly(pyrogallol) nanofibers for antibacterial applications

Herein, we present the facile synthesis of poly(pyrogallol) biopolymers and their application as antibacterial agents. Pyrogallol is a class of phenolic compounds that can be found in various plants. Polymerization was performed by the auto-oxidation of pyrogallol under a hydrated condition. The microscopic image of poly(pyrogallol) shows a highly homogenous nanofibrous structure with a diameter of 100.3 ± 16.3 nm. Spectroscopic analysis by FT-IR spectroscopy, Raman spectroscopy, and XPS corroborated the formation of ether (C-O-C) bonds between the hydroxyl group and adjacent carbons of pyrogallol during polymerization. The FT-IR and XPS spectra also revealed redox-active gallol functional groups on poly(pyrogallol) nanofibers, which can be used to release free electrons and protons during oxidation followed by the generation of reactive oxygen species (ROS). The generated ROS from poly(pyrogallol) was used to inhibit the growth of bacteria, Escherichia coli, at a inhibition rates of 56.3 ± 9.7% and 95.5 ± 2.0% within 0.5 and 2 h, respectively. This finding suggests that poly(pyrogallol) can be used as a naturally occurring antibacterial agent for various biomedical and environmental applications.

Antibacterial activity and mechanism of sanguinarine against Staphylococcus aureus by interfering with the permeability of the cell wall and membrane and inducing bacterial ROS production

Staphylococcus aureus (SA) is representative of gram-positive bacteria. Sanguinarine chloride hydrate (SGCH) is the hydrochloride form of sanguinarine (SG), one of the main extracts of Macleaya cordata (M. cordata). There are few reports on its antibacterial mechanism against SA. Therefore, in this study, we investigated the in vitro antibacterial activity and mechanism of SGCH against SA. The inhibitory zone, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) were measured, and the bactericidal activity curve was plotted. In addition, the micromorphology, alkaline phosphatase (AKP) activity, Na+K+, Ca2+Mg2+-adenosine triphosphate (ATP) activity, intracellular reactive oxygen species (ROS), and fluorescein diacetate (FDA) were observed and detected. The results showed that the inhibitory zone of SGCH against SA was judged as medium-sensitive; the MIC and MBC were 128 and 256 μg/mL, respectively; in the bactericidal activity curve, SGCH with 8 × MIC could completely kill SA within 24 h. SGCH was able to interfere with the integrity and permeability of the SA cell wall and membrane, as confirmed by the scanning electron microscopy (SEM) images, the increase in extracellular AKP and Na+ K+, Ca2+ Mg2+-ATP activities as well as the fluorescein diacetate (FDA) staining experiment results. Moreover, a high concentration of SGCH could induce SA to produce large amounts of ROS. In summary, these findings revealed that SGCH has a preferable antibacterial effect on SA, providing an experimental and theoretical basis for using SG as an antibiotic substitute in animal husbandry and for the clinical control and treatment of diseases caused by SA.

A microfluidic chip-based multivalent DNA walker amplification biosensor for the simultaneous detection of multiple food-borne pathogens

The rapid, simultaneous, sensitive detection of the targets has important application prospects for disease diagnosis and biomedical studies. However, in practical applications, the content of the targets is usually very low, and signal amplification strategies are often needed to improve the detection sensitivity. DNAzyme-driven DNA walkers are an excellent signal amplification strategy due to their outstanding specificity and sensitivity. Food-borne pathogens have always been a foremost threat to human health, and it is an urgent demand to develop a simple, rapid, sensitive, and portable detection method for food-borne pathogens. In addition, there are various species of pathogens, and it is difficult to simultaneously detect multiple pathogens by a single DNA walker. For this reason, a substrate strand with three rA cleavage sites was cleverly designed, and a multivalent DNA walker sensor combined with the microfluidic chip technology was proposed for the simultaneous, rapid, sensitive analysis of Vibrio parahaemolyticus, Salmonella typhimurium, and Staphylococcus aureus. The developed sensor could be used to detect pathogens simultaneously and efficiently with low detection limits and wide detection ranges. Moreover, the combination of gold stirring rod enrichment and DNA walker achieved double amplification, which greatly improved the detection sensitivity. More importantly, by changing the design of the substrate chain, the sensor was expected to be used to detect other targets, thus broadening the scope of practical applications. Therefore, the sensor can build novel detection tool platforms in the field of biosensing.

Recent Advances and Progress on Melanin: From Source to Application

Melanin is a biological pigment formed by indoles and phenolic compounds. It is widely found in living organisms and has a variety of unique properties. Due to its diverse characteristics and good biocompatibility, melanin has become the focus in the fields of biomedicine, agriculture, the food industry, etc. However, due to the wide range of melanin sources, complex polymerization properties, and low solubility of specific solvents, the specific macromolecular structure and polymerization mechanism of melanin remain unclear, which significantly limits the further study and application of melanin. Its synthesis and degradation pathways are also controversial. In addition, new properties and applications of melanin are constantly being discovered. In this review, we focus on the recent advances in the research of melanin in all aspects. Firstly, the classification, source, and degradation of melanin are summarized. Secondly, a detailed description of the structure, characterization, and properties of melanin is followed. The novel biological activity of melanin and its application is described at the end.

Alkyl ferulic acid esters: Evaluating their structure and antibacterial properties

Ferulic acid (FA) is a natural antibacterial agent rich in plants, FA has excellent antioxidant and antibacterial properties. However, because of its short alkane chain and large polarity, FA is difficult to penetrate the soluble lipid bilayer in the biofilm to enter the cell to play an inhibitory role, limiting its biological activity. To improve the antibacterial activity of FA, with the catalytic condition of Novozym 435, four alkyl ferulic acid esters (FCs) with different alkyl chain lengths were obtained by fatty alcohols (including 1-propanol (C3), 1-hexanol (C6), nonanol (C9), and lauryl alcohol (C12)) modification. The effect of FCs on P. aeruginosa was determined by Minimum inhibitory concentrations (MIC), minimum bactericidal concentrations (MBC), Growth curves, alkaline phosphatase (AKP) activity, crystal violet method, scanning electron microscopy (SEM), membrane potential, PI, cell contents leakage. Results showed that the antibacterial activity of FCs increased after esterification, and the antibacterial activity significantly increased and then decreased with the extension of the alkyl chain of the FCs. Hexyl ferulate (FC6) showed the best antibacterial activities against E. coli and P. aeruginosa (MIC for E. coli was 0.5 mg/ml, MIC for P. aeruginosa was 0.4 mg/ml). And Propyl ferulate (FC3) and FC6 showed the best antibacterial activities S. aureus and B. subtilis (MIC for S. aureus was 0.4 mg/ml, The MIC of B. subtilis was 1.1 mg/ml). In addition, the growth, AKP activity, bacterial biofilm, bacterial cell morphology, membrane potential and cell contents leakage of P. aeruginosa after different FCs were investigated, which found that FCs could damage the cell wall of P. aeruginosa and showed different effects on the P. aeruginosa cell biofilm. FC6 showed the best inhibition on the biofilm formation of P. aeruginosa cells, which caused the surface of P. aeruginosa cells to be rough and wrinkled. Some P. aeruginosa cells showed aggregation and adhesion, even rupture. The membrane hyperpolarization was obvious, which appeared as holes, leading to cell contents leakage (protein and nucleic acid). All these results concluded that the antibacterial activities FCs against foodborne pathogens depended on different fatty alcohol esterification of FA. FC6 showed the best inhibition on P. aeruginosa due to its effect on P. aeruginosa cell walls and biofilms and the leak of the cell contents. This study provides more practical methods and a theoretical basis for giving full play to the bacteriostatic effect of plant FA.

Melanin of fungi: from classification to application

Melanin is a secondary metabolite composed of complex heterogeneous polymers. Fungal melanin is considered to be a sustainable and biodegradable natural pigment and has a variety of functional properties and biological activities. On one hand, due to its own specific properties it can play the role of antioxidant, anti-radiation, adsorption, and photoprotection. On the other hand, it has good biological activities such as hepatoprotective effect, hypolipidemic effect and anti-cancer. Therefore, it is widely used in various fields of daily life, including dyeing, food, biomedical and commercial industry. It is conducive to environmental protection and human health. However, the insolubility of fungal melanin in water, acids and organic solvents has been an obstacle to its commercial applications. Thus, the chemical modification methods of fungal melanin are summarized to increase its solubility and expand the application fields. Although fungal melanin has been used in many industries, as the structure and function of fungal melanin and modified melanin are further studied, more functional properties and bioactivities are expected to be discovered for a wide range of applications in the future.

Use of Nanoparticles to Prevent Resistance to Antibiotics-Synthesis and Characterization of Gold Nanosystems Based on Tetracycline

Antimicrobial resistance (AMR) is a serious public health problem worldwide which, according to the World Health Organization (WHO), requires research into new and more effective drugs. In this work, both gold nanoparticles covered with 16-3-16 cationic gemini surfactant (Au@16-3-16) and DNA/tetracycline (DNA/TC) intercalated complexes were prepared to effectively transport tetracycline (TC). Synthesis of the Au@16-3-16 precursor was carried out by using trihydrated gold, adding sodium borohydride as a reducing agent and the gemini surfactant 16-3-16 as stabilizing agent. Circular dichroism and atomic force microscopy techniques were then used to ascertain the optimal R range of the relationship between the concentrations of Au@16-3-16 and the DNA/TC complex (R = CAu@16-3-16/CDNA) that allow the obtainment of stable and compact nanosystems, these characteristics being fundamental for their use as antibiotic transporters. Stability studies over time were carried out for distinct selected Au@16-3-16 and Au@16-3-16/DNA-TC nanoformulations using the ultraviolet−visible spectrophotometry technique, checking their stability for at least one month. In addition, in order to know the charge and size distribution of the nanocomplexes, DLS and zeta potential measurements were performed in the solution. The results showed that the characterized nanosystems were highly charged, stable and of a reduced size (<100 nm) that allows them to cross bacterial membranes effectively (>1 μm). Once the different physicochemical characteristics of the gold nanosystems were measured, Au@16-3-16 and Au@16-3-16/DNA-TC were tested on Escherichia coli and Staphylococcus aureus to study their antibacterial properties and internalization capacity in microbes. Differences in the interaction of the precursors and the compacted nanosystems generated were observed in Gram-positive and Gram-negative bacteria, possibly due to membrane damage or electrostatic interaction with internalization by endocytosis. In the internalization experiments, depending on the treatment application time, the greatest bacterial destruction was observed for all nanoformulations explored at 18 h of incubation. Importantly, the results obtained demonstrate that both new nanosystems based on TC and Au@16-3-16 precursors have optimal antimicrobial properties and would be beneficial for use in patients, avoiding possible side effects.

Antimicrobial and anti-biofilm activities of chlorogenic acid grafted chitosan against Staphylococcus aureus

In this work, Chitosan-grafted-chlorogenic acid (CS-g-CA) was prepared by the carbodiimide method. The purpose of this study was to investigate the antibacterial and anti-biofilm activity of CS-g-CA against Staphylococcus aureus (S. aureus). The minimum inhibitory concentration (MIC) of CS-g-CA against S. aureus was identified as 0.625 mg/mL. S. aureus treated with 1/2×MIC of CS-g-CA had a longer logarithmic growth phase than that of the CK group, while 1×MIC and 2×MIC inhibited the growth of bacteria. The damaging effect of CS-g-CA on bacterial cells was analyzed by measuring the activity of cellular antioxidant enzymes (Catalase (CAT) and Glutathione peroxidase (GSH-Px)) and intracellular enzymes (alkaline phosphatase (AKPase) and adenosine triphosphatase (ATPase)). The results of DNA gel electrophoresis illustrated that CS-g-CA disrupted the normal metabolism of bacteria. Scanning electron microscopy (SEM) results showed that S. aureus shrank and died under CS-g-CA treatment. 1×MIC of CS-g-CA can significantly inhibit the formation of biofilms, and 1/2×MIC of CS-g-CA control the swimming speed of S. aureus. In addition, 77.53% mature biofilm and 60.62% extracellular polysaccharide (EPS) in the mature biofilm of S. aureus were eradicated by CS-g-CA at 2×MIC. Confocal laser scanning microscopy (CLSM) observation further confirmed these results. Therefore, CS-g-CA was an antimicrobial and antibiofilm agent to control S. aureus, which can effectively controlling the growth of S. aureus in food, thereby preventing the occurrence of food-borne diseases.

Antibacterial Activity of Coffea robusta Leaf Extract against Foodborne Pathogens

The purpose of this study was to examine the phytochemical compounds and antibacterial activity of Coffea robusta leaf extract (RLE). The results indicated that chlorogenic acid (CGA) is a major component of RLE. The minimum inhibitory concentrations (MICs) of RLE against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella Typhimurium were 6.25, 12.5, 12.5, and 12.5 mg/ml, respectively. RLE effectively damages the bacterial cell membrane integrity, as indicated by the high amounts of proteins and nucleic acids released from the bacteria, and disrupts bacterial cell membrane potential and permeability, as revealed via fluorescence analysis. Cytotoxicity testing showed that RLE is slightly toxic toward HepG2 cells at high concentration but exhibited no toxicity toward Caco2 cells. The results from the present study suggest that RLE has excellent potential applicability as an antimicrobial in the food industry.

Effects of Natural Rheum tanguticum on the Cell Wall Integrity of Resistant Phytopathogenic Pectobacterium carotovorum subsp. Carotovorum

The abuse of agricultural antibiotics has led to the emergence of drug-resistant phytopathogens. Rifampicin and streptomycin and streptomycin resistance Pectobacterium carotovorum subsp. carotovorum (PccS1) was obtained from pathological plants in a previous experiment. Rheum tanguticum, derived from the Chinese plateau area, exhibits excellent antibacterial activity against PccS1, yet the action mode has not been fully understood. In present text, the cell wall integrity of the PccS1 was tested by the variation of the cellular proteins, SDS polyacrylamide gel electrophoresis (SDS-PAGE), scanning electron microscopy (SEM) and Fourier transform infrared spectrophotometer (FTIR) characteristics. Label-free quantitative proteomics was further used to identify the DEPs in the pathogen response to treatment with Rheum tanguticum Maxim. ex Balf. extract (abbreviated as RTMBE). Based on the bioinformatics analysis of these different expressed proteins (DEPs), RTMBE mainly inhibited some key protein expressions of beta-Lactam resistance, a two-component system and phosphotransferase system. Most of these membrane proteins were extraordinarily suppressed, which was also consistent with the morphological tests. In addition, from the downregulated flagellar motility related proteins, it was also speculated that RTMBE played an essential antibacterial role by affecting the swimming motility of the cells. The results indicated that Rheum tanguticum can be used to attenuate the virulence of the drug-resistant phytopathogenic bacteria.

The antimicrobial and bioactive properties of lactobionic acid

Lactobionic acid (LBA) is a bioactive molecule that has generated keen interest in different industries. However, its future application in the food area is one of the most promising. Chemically, it is a polyhydroxy acid formed by the union of two molecules (galactose and gluconic acid) linked by an ether-bond, showing many interesting and unusual properties due to its structure and composition, although it is traditionally known in the food industry for its chelating, moisturizing, gelling, and antioxidant properties. There has been much research into the production of LBA, either by microbial fermentation or biocatalytic approaches such as enzymatic synthesis, but its use in foodstuffs, to produce new functional products and to evaluate its antimicrobial activity against food-borne pathogens, is a relatively new topic that has attracted the interest of the international research community recently. Furthermore, in spite of the potential of LBA, it has been approved only by the US Food and Drug Administration, and for its use as the salt form, but the publication of new comprehensive studies, able to agglutinate all the new food-related LBA research results, could disseminate knowledge about this compound and have an influence on its current regulation status. The aim of the present review is to describe the most recent advances and research on its antimicrobial potential, as well as summarizing the significant aspects that make LBA a promising bioactive compound for the food sector. © 2022 Society of Chemical Industry.

Antibacterial Activity and Mechanism of Polygonum orientale L. Essential Oil against Pectobacterium carotovorum subsp. carotovorum

Infected by Pectobacterium carotovorum subsp. carotovorum (Pcc), the quality of Chinese cabbage could severely decline. Using chemical bactericides to control Pcc could cause food safety problems. Thus, we investigated the optimum extraction conditions, antibacterial activity, chemical compounds and antibacterial mechanism of Polygonum orientale L. essential oil (POEO) against Pcc in order to search a new way to control Pcc. The optimum extraction conditions of POEO (soaking time 2.6 h, extraction time 7.7 h and ratio of liquid to solid 10.3 mL/g) were optimized by response surface methodology. The minimum inhibitory concentration (MIC) of POEO against Pcc was 0.625 mg/mL. The control efficiency of protective activity of POEO against Pcc was 74.67~92.67%, and its curative activity was 76.00~93.00%. Then, 29 compounds were obtained by GC-MS; the prime compounds of POEO were phytol, phytone, n-pentacosane, 1-octen-3-ol and β-ionone. It was verified that, compared with control samples, POEO destroyed cell morphology. It increased surface potential, increased hydrophobicity, damaged cell walls, destroyed the integrity and permeability of cell membrane, reduced membrane potential (MP), and changed membrane protein conformation. It inhibited the activities of pyruvate kinase (PK), succinate dehydrogenase (SDH) and adenosine triphosphatase (ATPase). Briefly, the results of this study demonstrate that POEO showed effective inhibitory activity against Pcc, thus POEO could have potential application in controlling Pcc.

Antibacterial Activity of Chinese Red Propolis against Staphylococcus aureus and MRSA

The antibacterial activity of propolis has long been of great interest, and the chemical composition of propolis is directly dependent on its source. We recently obtained a type of propolis from China with a red color. Firstly, the antibacterial properties of this unusual propolis were determined against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA). Studies on its composition identified and quantified 14 main polyphenols of Chinese red propolis extracts (RPE); quantification was carried out using liquid chromatography triple quadrupole tandem mass spectrometry (LC-QQQ-MS/MS) and RPE was found to be rich in pinobanksin, pinobanksin-3-acetate, and chrysin. In vitro investigations of its antibacterial activity revealed that its activity against S. aureus and MRSA is due to disruption of the cell wall and cell membrane, which then inhibits bacterial growth. Despite its similar antibacterial activities against S. aureus and MRSA, metabolomic analysis further revealed the effects of RPE on bacteria metabolism were different. The untargeted metabolomic results showed that a total of 7 metabolites in 12 metabolic pathways had significant changes (Fold change > 2, p < 0.05 *) after RPE treatment in S. aureus, while 11 metabolites in 9 metabolic pathways had significant changes (Fold change > 2, p < 0.05 *) after RPE treated on MRSA. Furthermore, RPE downregulated several specific genes related to bacterial biofilm formation, autolysis, cell wall synthesis, and bacterial virulence in MRSA. In conclusion, the data obtained indicate that RPE may be a promising therapeutic agent against S. aureus and MRSA.

Antimicrobial Effects of Novel H2O2-Ag+ Complex on Membrane Damage to Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella Typhimurium

ABSTRACT

Diseases caused by harmful microorganisms pose a serious threat to human health. Safe and environmentally friendly disinfectants are, therefore, essential in preventing and controlling such pathogens. This study aimed to investigate the antimicrobial activity and mechanism of a novel hydrogen peroxide and silver (H2O2-Ag+) complex (HSC) in combatting Staphylococcus aureus ATCC 29213, Escherichia coli O157:H7 NCTC 12900, and Salmonella Typhimurium SL 1344. The MICs and MBCs against S. aureus were found to be 0.014% H2O2-3.125 mg/L Ag+, and for both E. coli O157:H7 and Salmonella Typhimurium they were 0.028% H2O2-6.25 mg/L Ag+. Results of the time-kill trial suggest that HSC could inhibit the growth of the tested bacteria, because 99.9% of viable cells were killed following treatment at 1 MIC for 3 h. The mechanism of antibacterial action of HSC was found to include the disruption of the bacterial cell membrane, followed by reduction of intracellular ATP concentration and inhibition of the activity of antioxidases, superoxide dismutase, and catalase. The enhanced bactericidal effect of hydrogen peroxide combined with silver indicates a potential for its application in environmental disinfection, particularly in the food industry.

HIGHLIGHTS

Bacitracin-Ag Nanoclusters as a Novel Antibacterial Agent Combats Shigella flexneri by Disrupting Cell Membrane and Inhibiting Biofilm Formation

A novel nanomaterial Bacitracin-Ag Nanoclusters (Bacitracin-AgNCs) was formed to achieve a better antibacterial effect on Shigella flexneri which poses a serious threat to human health. In the current study, X-ray photoelectron spectrometer (XPS), Fourier transform infrared (FTIR), field-emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HR-TEM) and thermal gravimetric analysis (TGA) were used to characterize the properties of composited Bacitracin-AgNCs. Furthermore, the inhibitory effects of Bacitracin-AgNCs against S. flexneri were explored, and the inhibition mechanism was discussed in terms of its aspects of cell membrane ravage, ATPase activity decline and biofilm inhibition. The results reveal that the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Bacitracin-AgNCs against S. flexneri were 0.03 mg/mL and 4 mg/mL. Bacitracin-AgNCs may cause irreversible impairment to cells and greatly change the cell morphology. The cell membrane integrity of S. flexneri was destroyed with changes in the characteristics of membrane permeability and intracellular substances leakage. Moreover, our study further proved that Bacitracin-AgNCs significantly inhibited the formation of S. flexneri biofilms and reduced the number of viable bacteria in biofilm. These findings provide a potential method for the exploitation of organic composite nanomaterials as a novel antimicrobial agent and its application in the food industry.

An Engineered Pseudo-Macrophage for Rapid Treatment of Bacteria-Infected Osteomyelitis via Microwave-Excited Anti-Infection and Immunoregulation

Preventing deep bacterial infection and simultaneously enhancing osteogenic differentiation are in great demand for osteomyelitis. Microwave (MW) dynamic therapy is attracting attention due to its excellent penetration ability, but the mechanism of MW-induced reactive oxygen species (ROS) is still unknown. Herein, MW-responsive engineered pseudo-macrophages (M-Fe₃ O₄ /Au nanoparticles (NPs)) are fabricated to clear Staphylococcus aureus infections and induce M2 polarization of macrophages to improve osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) under MW irradiation. Fe₃ O₄ /Au NPs can generate ·O₂ ^- and heat under MW irradiation in a saline solution, and the mechanism is put forward via finite element modeling and density functional theory calculations. Due to the gap plasmon, electromagnetic hotspots are produced at Fe₃ O₄ -Au interface at 2.45 GHz. Because of these induced electromagnetic hotspots, the sodium species is field-ionized and subsequently reacts with oxygen to produce ·O₂ ^- . Meanwhile, the Fe₃ O₄ /Au NPs have a stronger ability than Fe₃ O₄ NPs to fix oxygen, favoring the production of ROS. Additionally, MW-treated macrophages diminish to secrete inflammatory cytokines, resulting in the decrease of ROS production in MSCs and thus enhancing their osteogenic differentiation. These engineered pseudo-macrophages will be promising for effectively treating bacterial infections and promoting osteoblast differentiation simultaneously in deep tissues under MW irradiation.

Nanoparticle-stabilized encapsulation of borneol and citral: Physicochemical characteristics, storage stability, and enhanced antibacterial activities

Combinations of phytochemical(s) and engineered nanoparticles have attracted immense research interest due to their superior antimicrobial effects against contaminations. Herein, a Pickering emulsion is developed with capsulized phytochemicals including borneol and citral (BC-Cap) stabilized by hydrophilic amine-functionalized silica nanoparticles (SiO₂ ─NH₂ NPs). The droplet sizes of Pickering emulsion were 5.2 ± 1.4 µm under the condition that the concentrations of SiO₂ ─NH₂ NPs ranged from 0.6 to 1.2 wt.%, and the emulsion showed desirable stability during storage at 40°C for 365 days. In addition, the antibacterial and antibiofilm activities of the Pickering emulsion were investigated. The antibacterial effect of BC-Cap increased by two- to fourfold compared with citral or borneol alone. Treatment of BC/BC-Cap for 4 h eliminated the formation of biofilms generated by Listeria monocytogenes (at 5/1.25 mg/ml; 2 × MIC concentration) and Pseudomonas aeruginosa (at 5/2.5 mg/ml; 2 × MIC concentration). Further mechanistic studies revealed that the antibiofilm effects of BC-Cap were attributed to its ability to increase the porosity and lytic effects on the cell membrane of bacteria. Findings from the current study support the antibacterial and antibiofilm effects of BC-Cap Pickering emulsion as a promising food additive. PRACTICAL APPLICATION: The Pickering emulsion has potential applications as bacteriostatic agent in packaging materials and general surface disinfectant. The combination of borneol and citral is stabilized by hydrophilic amine-functionalized silica nanoparticles (SiO₂ ─NH₂ NPs). With the synergistic effects of borneol and citral, the Pickering emulsion shows a promising elimination effect against the formation of biofilms produced by Listeria monocytogenes and Pseudomonas aeruginosa.

Antibacterial effect of Blumea balsamifera (L.) DC. essential oil against Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a common pathogenic bacteria in clinical environment, which can cause various diseases. Blumea balsamifera (L.) DC. as a traditional Chinese herb, its essential oil shows excellent bacteriostatic effect against S. aureus. To study the antibacterial effect of B. balsamifera (L.) DC. essential oil (BBO) against S. aureus, this study evaluated the effect of BBO on the permeability and integrity of cell membranes and on the total protein and nucleic acid content in S. aureus. Furthermore, proteomics was used to study the effect of BBO on the proteome of S. aureus. The results showed that BBO can destroy the permeability of the cell membrane, and inhibit the synthesis of bacterial nucleic acid and protein. Proteomics shows that BBO affects disorder of amino acid metabolism and affects the activity of various enzymes and the transport of substances. Taken together, these results indicated a substantial antibacterial effect of BBO on S. aureus.

Microbial melanin: Recent advances in biosynthesis, extraction, characterization, and applications

Melanin is a common name for a group of biopolymers with the dominance of potential applications in medical sciences, cosmeceutical, bioremediation, and bioelectronic applications. The broad distribution of these pigments suggests their role to combat abiotic and biotic stresses in diverse life forms. Biosynthesis of melanin in fungi and bacteria occurs by oxidative polymerization of phenolic compounds predominantly by two pathways, 1,8-dihydroxynaphthalene [DHN] or 3,4-dihydroxyphenylalanine [DOPA], resulting in different kinds of melanin, i.e., eumelanin, pheomelanin, allomelanin, pyomelanin, and neuromelanin. The enzymes responsible for melanin synthesis belong mainly to tyrosinase, laccase, and polyketide synthase families. Studies have shown that manipulating culture parameters, combined with recombinant technology, can increase melanin yield for large-scale production. Despite significant efforts, its low solubility has limited the development of extraction procedures, and heterogeneous structural complexity has impaired structural elucidation, restricting effective exploitation of their biotechnological potential. Innumerable studies have been performed on melanin pigments from different taxa of life in order to advance the knowledge about melanin pigments for their efficient utilization in diverse applications. These studies prompted an urgent need for a comprehensive review on melanin pigments isolated from microorganisms, so that such review encompassing biosynthesis, bioproduction, characterization, and potential applications would help researchers from diverse background to understand the importance of microbial melanins and to utilize the information from the review for planning studies on melanin. With this aim in mind, the present report compares conventional and modern ideas for environment-friendly extraction procedures for melanin. Furthermore, the characteristic parameters to differentiate between eumelanin and pheomelanin are also mentioned, followed by their biotechnological applications forming the basis of industrial utilization. There lies a massive scope of work to circumvent the bottlenecks in their isolation and structural elucidation methodologies.

Bacterial Mediated Rapid and Facile Synthesis of Silver Nanoparticles and Their Antimicrobial Efficacy against Pathogenic Microorganisms

In the present study, silver nanoparticles (AgNPs), biosynthesized using culture supernatant of bacterial strain Paenarthrobacter nicotinovorans MAHUQ-43, were characterized and their antimicrobial activity was investigated against both Gram-positive Bacillus cereus and Gram-negative bacteria Pseudomonas aeruginosa. Bacterial-mediated synthesized AgNPs were characterized by UV-Visible (UV-Vis) spectrophotometer, field emission-transmission electron microscopy (FE-TEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS) analysis. The UV-Vis spectral analysis showed the absorption maxima at 466 nm which assured the synthesis of AgNPs. The FE-TEM analysis revealed the spherical shape of nanoparticles with the size range from 13 to 27 nm. The EDX and XRD analysis ensured the crystalline nature of biosynthesized AgNPs. The FTIR analysis revealed the involvement of different biomolecules for the synthesis of AgNPs as reducing and capping agents. The bacterial-mediated synthesized AgNPs inhibited the growth of pathogenic strains B. cereus and P. aeruginosa and developed a clear zone of inhibition (ZOI). The MIC and MBC for both pathogens were 12.5 µg/mL and 25 µg/mL, respectively. Moreover, field emission scanning electron microscopy analysis revealed that the synthesized AgNPs can destroy the outer membrane and alter the cell morphology of treated pathogens, leading to the death of cells. This study concludes the eco-friendly, facile and rapid synthesis of AgNPs using P. nicotinovorans MAHUQ-43 and synthesized AgNPs showed excellent antimicrobial activity against both Gram-positive and Gram-negative pathogens.

New insight into melanin for food packaging and biotechnology applications

Melanin is a dark brown to black biomacromolecule with biologically active multifunctional properties that do not have a precise chemical structure, but its structure mainly depends on the polymerization conditions during the synthesis process. Natural melanin can be isolated from various animal, plant, and microbial sources, while synthetic melanin-like compounds can be synthesized by simple polymerization of dopamine. Melanin is widely used in various areas due to its functional properties such as photosensitivity, light barrier property, free radical scavenging ability, antioxidant activity, etc. It also has an excellent ability to act as a reducing agent and capping agent to synthesize various metal nanoparticles. Melanin nanoparticles (MNP) or melanin-like nanoparticles (MLNP) have the unique potential to act as functional materials to improve nanocomposite films' physical and functional properties. Various food packaging and biomedical applications have been made alone or by mixing melanin or MLNP. In this review, the general aspects of melanin that highlight biological activity, along with a description of MNP and the use as nanofillers in packaging films as well as reducing and capping agents and biomedical applications, were comprehensively reviewed.