Melittin and its potential in the destruction and inhibition of the biofilm formation by Staphylococcus aureus , Escherichia coli and Pseudomonas aeruginosa isolated from bovine milk

Green synthesis of antimicrobial nanotechnology using flavonoids: a systematic review

Antimicrobial resistance (AMR) is a critical public health concern that arises when microorganisms evolve mechanisms to evade the effects of antibiotics, thereby rendering conventional treatments ineffective. This growing challenge underscores the urgent need for novel therapeutic approaches. Nanotechnology, particularly when combined with environmentally sustainable practices such as green synthesis, reduces the use of toxic substances and minimises waste, offering a promising solution. This review explores the green synthesis of antimicrobial nanoparticles using flavonoids-natural compounds with substantial biological activity-as reducing and stabilising agents. By systematically analysing articles from PubMed, Scopus, Web of Science, and Embase, 10 key studies were identified. The primary nanoparticles examined were metallic, including silver, gold, copper, and metallic, which demonstrated notable efficacy against pathogens such as S. aureus, E. coli, and P. aeruginosa. The results support that green-synthesised nanoparticles represent a viable strategy to combat AMR, offering an effective and eco-friendly alternative for developing antimicrobial agents.

Antimicrobial Properties of Hive Products and Their Potential Applications in Human and Veterinary Medicine

Hive products, encompassing honey, propolis, bee venom, royal jelly, and pollen, are recognized for their antimicrobial and therapeutic properties. This review examines their chemical composition, explores their mechanisms of action, and discusses their potential applications in both human and veterinary medicine, particularly in addressing the challenge of antimicrobial resistance. This study utilized a comprehensive literature search strategy, gathering data from Google Scholar, MEDLINE PubMed, SciELO, and SCOPUS databases. Relevant search terms were employed to ensure a thorough retrieval of the pertinent literature. Honey, rich in bioactive compounds such as hydrogen peroxide and methylglyoxal, effectively disrupts biofilms and combats multi-drug-resistant pathogens, showing promise in treating a range of infections. Propolis, with its flavonoids and phenolic acids, demonstrates synergistic effects when used in conjunction with antibiotics. Bee venom, particularly its component melittin, exhibits antibacterial and immunomodulatory properties, although further research is needed to address toxicity concerns. Pollen and royal jelly demonstrate broad-spectrum antimicrobial activity, which is particularly relevant to animal health. Existing pre-clinical and clinical data support the therapeutic potential of these hive products. Hive products represent a vast and largely untapped natural resource for combating antimicrobial resistance and developing sustainable therapies, particularly in the field of veterinary medicine. However, challenges remain due to the inherent variability in their composition and the lack of standardized protocols for their preparation and application. Further research is essential to fully elucidate their mechanisms of action, optimize formulations for enhanced efficacy, and establish standardized protocols to ensure their safe and effective clinical use.

Detection and Treatment with Peptide Power: A New Weapon Against Bacterial Biofilms

Bacterial biofilms, complex microbial communities encased in a protective extracellular matrix, pose a significant threat to public health due to their inherent antibiotic resistance. This review explores the potential of peptides, particularly antimicrobial peptides (AMPs), as innovative tools to combat biofilm-related infections. AMPs, characterized by their potent antimicrobial activity and tissue permeability, offer a promising approach to overcome the challenges posed by biofilms. By disrupting biofilm architecture, inhibiting bacterial growth, and enhancing biofilm detection through nuclear-based, fluorescence-based, and nanobased techniques, AMPs provide a multifaceted strategy. This review highlights recent advancements, approaches, and strategies in peptide research, examining their potential as both diagnostic and therapeutic agents. It also addresses key challenges and outlines future directions for optimizing peptide-based detection and therapies. By overcoming these challenges and refining peptide design, we can unlock the full potential of AMPs in combating bacterial biofilm infections, paving the way for the development of innovative solutions to tackle biofilm-related diseases and improve global health.

Antimicrobial and antibiofilm potential of α-MSH derived cationic and hydrophobic peptides against Escherichia coli: Mechanistic insight through peptide-lipopolysaccharide interactions

The prevalence of infections caused by various Gram-negative pathogens specifically Escherichia coli continuously poses a significant challenge in health care as well as community settings owing to their ability to form biofilm and escalating tolerance towards available antibiotics. While most treatment regimes are targeted at eliminating the E. coli cells, the pathogenicity factors called endotoxin (lipopolysaccharides), associated with the sepsis initiation and the leading cause of death in intensive care units globally, are often ignored. In this study, the potency of alpha-melanocyte stimulating hormone based-peptides, particularly Ana-9 and Ana-10 against E. coli was investigated through microbiological, biophysical, and microscopic assays. Both Ana-9 and Ana-10 demonstrated enhanced activity against planktonic E. coli cells, and retained their activity against biofilm, which was supported by confocal microscopy. From the mechanistic perspective, spectroscopic studies indicated that the binding of peptides with LPS led to structural alteration of peptides due to their insertion into the hydrophobic environment of LPS. The electrostatic interaction of the peptide with LPS leads to outer membrane disorganization, allowing the peptide to access the inner membrane, depolarize it and ultimately inhibit the bacterial cells within the biofilm. These observations were further confirmed by atomic force and scanning electron microscopy. Thus, this study deepens our understanding of the structural characteristics of peptides attached to LPS, which could lead to the gradual improvement in developing more potent, broad-spectrum endotoxin neutralizers.

ProT-Diff: A Modularized and Efficient Strategy for De Novo Generation of Antimicrobial Peptide Sequences by Integrating Protein Language and Diffusion Models

Antimicrobial peptides (AMPs) are a promising solution for treating antibiotic-resistant pathogens. However, efficient generation of diverse AMPs without prior knowledge of peptide structures or sequence alignments remains a challenge. Here, ProT-Diff is introduced, a modularized deep generative approach that combines a pretrained protein language model with a diffusion model for the de novo generation of AMPs sequences. ProT-Diff generates thousands of AMPs with diverse lengths and structures within a few hours. After silico physicochemical screening, 45 peptides are selected for experimental validation. Forty-four peptides showed antimicrobial activity against both gram-positive or gram-negative bacteria. Among broad-spectrum peptides, AMP_2 exhibited potent antimicrobial activity, low hemolysis, and minimal cytotoxicity. An in vivo assessment demonstrated its effectiveness against a drug-resistant E. coli strain in acute peritonitis. This study not only introduces a viable and user-friendly strategy for de novo generation of antimicrobial peptides, but also provides potential antimicrobial drug candidates with excellent activity. It is believed that this study will facilitate the development of other peptide-based drug candidates in the future, as well as proteins with tailored characteristics.

Peptide-based strategies for overcoming biofilm-associated infections: a comprehensive review

Biofilms represent resilient microbial communities responsible for inducing chronic infections in human subjects. Given the escalating challenges associated with antibiotic therapy failures in clinical infections linked to biofilm formation, a peptide-based approach emerges as a promising alternative to effectively combat these notoriously resistant biofilms. Contrary to conventional antimicrobial peptides, which predominantly target cellular membranes, antibiofilm peptides necessitate a multifaceted approach, addressing various "biofilm-specific factors." These factors encompass Extracellular Polymeric Substance (EPS) degradation, membrane targeting, cell signaling, and regulatory mechanisms. Recent research endeavors have been directed toward assessing the potential of peptides as potent antibiofilm agents. However, to translate these peptides into viable clinical applications, several critical considerations must be meticulously evaluated during the peptide design process. This review serves to furnish an all-encompassing summary of the pivotal factors and parameters that necessitate contemplation for the successful development of an efficacious antibiofilm peptide.

Biocompatible plasma-treated liquids: A sustainable approach for decontaminating gastrointestinal-infection causing pathogens

Nosocomial infections are a serious threat and difficult to cure due to rising antibiotic resistance in pathogens and biofilms. Direct exposure to cold atmospheric plasma (CAP) has been widely employed in numerous biological research endeavors. Nonetheless, plasma-treated liquids (PTLs) formulated with physiological solutions may offer additional benefits such as enhanced portability, and biocompatibility. Additionally, CAP-infused long-lived reactive oxygen and nitrogen species (RONS) such as nitrite (NO2-), nitrate (NO3-), and hydrogen peroxide (H2O2) can synergistically induce their antibacterial activity. Herein, we investigated those argon-plasma jet-treated liquids, including Ringer's lactate (RL), phosphate-buffered saline (PBS), and physiological saline, have significant antibacterial activity against nosocomial/gastrointestinal-causing pathogens, which might be due to ROS-mediated lipid peroxidation. Combining the conventional culture-based method with propidium iodide monoazide quantitative PCR (PMAxx™-qPCR) indicated that PTLs induce a minimal viable but non-culturable (VBNC) state and moderately affect culturable counts. Specifically, the PTL exposure resulted in pathogenicity dysfunction via controlling T3SS-related effector genes of S. enterica. Overall, this study provides insights into the effectiveness of PTLs for inducing ROS-mediated damage, controlling the virulence of diarrheagenic bacteria, and modulating homeostatic genes.

Investigating the Effect of Melittin Peptide in Preventing Biofilm Formation, Adhesion and Expression of Virulence Genes in Listeria monocytogenes

Listeria monocytogenes is a notable food-borne pathogen that has the ability to create biofilms on different food processing surfaces, making it more resilient to disinfectants and posing a greater risk to human health. This study assessed melittin peptide's anti-biofilm and anti-pathogenicity effects on L. monocytogenes ATCC 19115. Melittin showed minimum inhibitory concenteration (MIC) of 100 μg/mL against this strain and scanning electron microscopy images confirmed its antimicrobial efficacy. The OD measurement demonstrated that melittin exhibited a strong proficiency in inhibiting biofilms and disrupting pre-formed biofilms at concentrations ranging from 1/8MIC to 2MIC and this amount was 92.59 ± 1.01% to 7.17 ± 0.31% and 100% to 11.50 ± 0.53%, respectively. Peptide also reduced hydrophobicity and self-aggregation of L. monocytogenes by 35.25% and 14.38% at MIC. Melittin also significantly reduced adhesion to HT-29 and Caco-2 cells by 61.33% and 59%, and inhibited invasion of HT-29 and Caco-2 cells by 49.33% and 40.66% for L. monocytogenes at the MIC value. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) revealed melittin's impact on gene expression, notably decreasing inlB (44%) and agrA (45%) gene expression in L. monocytogenes. flaA and hly genes also exhibited reduced expression. Also, significant changes were observed in sigB and prfA gene expression. These results underscore melittin's potential in combating bacterial infections and biofilm-related challenges in the food industry.

Homologous polydopamine ameliorates haemolysis of melittin for enhancing its anticancer efficacy

Despite exhibiting potent anticancer activity, the strong hemolytic properties of melittin (MEL) significantly restrict its delivery efficiency and clinical applications. To address this issue, we have devised a strategy wherein homologous dopamine (DA), an essential component of bee venom, is harnessed as a vehicle for the synthesis of MEL-polydopamine (PDA) nanoparticles (MP NPs). The ingenious approach lies in the fact that MEL is a basic polypeptide, and the polymerization of DA is also conducted under alkaline conditions, indicating the distinctive advantages of PDA in MEL encapsulation. Furthermore, MP NPs are modified with folic acid to fabricate tumor-targeted nanomedicine (MPF NPs). MPF NPs can ameliorate the hemolysis of MEL in drug delivery and undergo degradation triggered by high levels of reactive oxygen species (ROS) within solid tumors, thereby facilitating MEL release and subsequent restoration of anticancer activity. After cellular uptake, MPF NPs induce cell apoptosis through the PI3K/Akt-mediated p53 signaling pathway. The tumor growth inhibitory rate of MPF NPs in FA receptor-positive 4T1 and CT26 xenograft mice reached 78.04% and 81.66%, which was significantly higher compared to that in FA receptor-negative HepG2 xenograft mice (45.79%). Homologous vehicles provide a new perspective for nanomedicine design.

Hybrid bio-nanoporous peptide loaded-polymer platforms with anticancer and antibacterial activities

In this study, hybrid bio-nanoporous peptides loaded onto poly(N-isopropylacrylamide-co-butylacrylate) (pNIPAM-co-BA) coatings were designed and obtained via matrix-assisted pulsed laser evaporation (MAPLE) technique. The incorporation of cationic peptides magainin (MG) and melittin (Mel) and their combination was tailored to target synergistic anticancer and antibacterial activities with low toxicity on normal mammalian cells. Atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy as well as contact angle and surface energy measurements revealed the successful and functional incorporation of both the peptides within porous polymeric nanolayers as well as surface modifications (i.e. variation in the pore size diameter, surface roughness, and wettability) after Mel, MG or Mel-MG incorporation compared to pNIPAM-co-BA. In vitro testing revealed the impairment of biofilm formation on all the hybrid coatings while testing with S. aureus, E. coli and P. aeruginosa. Moreover, MG was shown to modulate the effect of Mel in the combined Mel-MG extract formulation released via pNIPAM-platforms, thus significantly reducing cancer cell proliferation through apoptosis/necrosis as revealed by flow cytometry analysis performed in vitro on HEK293T, A375, B16F1 and B16F10 cells. To the best of our knowledge, Mel-MG combination entrapped in the pNIPAM-co-BA copolymer has not yet been reported as a new promising candidate with anticancer and antibacterial properties for improved utility in the biomedical field. Mel-MG incorporation compared to pNIPAM-co-BA in in vitro testing revealed the impairment of biofilm formation in all the hybrid formulations.

Anti-Staphylococcus aureus effects of natural antimicrobial peptides and the underlying mechanisms

Staphylococcus aureus can cause localized infections such as abscesses and pneumonia, as well as systemic infections such as bacteremia and sepsis. Especially, methicillin-resistant S. aureus often presents multidrug resistance, which becomes a major clinical challenge. One of the most common reasons for methicillin-resistant S. aureus antibiotic resistance is the presence of biofilms. Natural antimicrobial peptides derived from different species have shown effectiveness in combating S. aureus biofilms. In this review, we summarize the inhibitory activity of antimicrobial peptides against S. aureus planktonic cells and biofilms. We also summarize the possible inhibitory mechanisms, involving cell adhesion inhibition, membrane fracture, biofilm disruption and DNA disruption. We believe this can provide the basis for further research against S. aureus biofilm-associated infections.

Bifunctional peptides as alternatives to copper-based formulations to control citrus canker

Citrus canker is an infectious bacterial disease and one of the major threats to the orange juice industry, a multibillion-dollar market that generates hundreds of thousands of jobs worldwide. This disease is caused by the Gram-negative bacterium Xanthomonas citri subsp. citri. In Brazil, the largest producer and exporter of concentrate orange juice, the control of citrus canker is exerted by integrated management practices, in which cupric solutions are intensively used in the orchards to refrain bacterial spreading. Copper ions accumulate and are as heavy metals toxic to the environment. Therefore, the aim of the present work was to evaluate bifunctional fusion proteins (BiFuProts) as novel and bio-/peptide-based alternatives to copper formulations to control citrus canker. BiFuProts are composed of an anchor peptide able to bind to citrus leaves, and an antimicrobial "killer" peptide to protect against bacterial infections of plants. The selected BiFuProt (Mel-CgDEF) was bactericidal against X. citri at 125 μg mL-1, targeting the bacterial cytoplasmic membrane within the first minutes of contact. The results in the greenhouse assays proved that Mel-CgDEF at 250 μg mL-1 provided protection against X. citri infection on the leaves, significantly reducing the number of lesions by area when compared with the controls. Overall, the present work showed that the BiFuProt Mel-CgDEF is a biobased and biodegradable possible alternative for substitute cupric formulations. KEY POINTS: • The bifunctional fusion protein Mel-CgDEF was effective against Xanthomonas citri. • Mel-CgDEF action mechanism was the disruption of the cytoplasmic membrane. • Mel-CgDEF protected citrus leaves against citrus canker disease.

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.

Discovery of Melittin as Triple-Action Agent: Broad-Spectrum Antibacterial, Anti-Biofilm, and Potential Anti-Quorum Sensing Activities

The development of antibiotic-resistant microorganisms is a major global health concern. Recently, there has been an increasing interest in antimicrobial peptides as a therapeutic option. This study aimed to evaluate the triple-action (broad-spectrum antibacterial, anti-biofilm, and anti-quorum sensing activities) of melittin, a membrane-active peptide present in bee venom. The minimum inhibitory concentration and minimum bactericidal concentration of the melittin were determined using the microdilution method and agar plate counting. Growth curve analysis revealed that melittin showed a concentration-dependent antibacterial activity. Scanning electron microscope analysis revealed that melittin treatment altered the morphology. Confocal laser scanning microscope revealed that melittin increased the membrane permeability and intracellular ROS generation in bacteria, all of which contribute to bacterial cell death. In addition, the crystal violet (CV) assay was used to test the anti-biofilm activity. The CV assay demonstrated that melittin inhibited biofilm formation and eradicated mature biofilms. Biofilm formation mediated by quorum sensing (QS) plays a major role in this regard, so molecular docking and molecular dynamics analysis confirmed that melittin interacts with LasR receptors through hydrogen bonds, and further evaluates the anti-QS activity of melittin through the production of virulence factors (pyocyanin, elastase, and rhamnolipid), exopolysaccharides secretion, and bacterial motility, that may be the key to inhibiting the biofilm formation mechanism. The present findings highlight the promising role of melittin as a broad-spectrum antibacterial, anti-biofilm agent, and potential QS inhibitor, providing a new perspective and theoretical basis for the development of alternative antibiotics.

The current landscape of the antimicrobial peptide melittin and its therapeutic potential

Melittin, a main component of bee venom, is a cationic amphiphilic peptide with a linear α-helix structure. It has been reported that melittin can exert pharmacological effects, such as antitumor, antiviral and anti-inflammatory effects in vitro and in vivo. In particular, melittin may be beneficial for the treatment of diseases for which no specific clinical therapeutic agents exist. Melittin can effectively enhance the therapeutic properties of some first-line drugs. Elucidating the mechanism underlying melittin-mediated biological function can provide valuable insights for the application of melittin in disease intervention. However, in melittin, the positively charged amino acids enables it to directly punching holes in cell membranes. The hemolysis in red cells and the cytotoxicity triggered by melittin limit its applications. Melittin-based nanomodification, immuno-conjugation, structural regulation and gene technology strategies have been demonstrated to enhance the specificity, reduce the cytotoxicity and limit the off-target cytolysis of melittin, which suggests the potential of melittin to be used clinically. This article summarizes research progress on antiviral, antitumor and anti-inflammatory properties of melittin, and discusses the strategies of melittin-modification for its future potential clinical applications in preventing drug resistance, enhancing the selectivity to target cells and alleviating cytotoxic effects to normal cells.

Gallium-based metal-organic frameworks loaded with antimicrobial peptides for synergistic killing of drug-resistant bacteria

Increased antibiotic resistance has made bacterial infections a global concern, which requires novel non-antibiotic-dependent antibacterial strategies to address the menace. Antimicrobial peptides (AMPs) are a promising antibiotic alternative, whose antibacterial mechanism is mainly to destroy the membrane of bacteria. Gallium ions exhibit an antibacterial effect by interfering with the iron metabolism of bacteria. With the rapid development of nanotechnology, it is worth studying the potential of gallium-AMP-based nanocomposites for treating bacterial infections. Herein, novel gallium-based metal-organic frameworks (MOFs) were synthesized at room temperature, followed by in situ loading of the model AMP melittin. The obtained nanocomposites exhibited stronger antibacterial activity than pure MEL and gallium ions, achieving the effects of "one plus one is greater than two". Moreover, the nanocomposites showed favorable biocompatibility and accelerated healing of a wound infected by methicillin-resistant Staphylococcus aureus by down-regulation of inflammatory cytokines IL-6 and TNF-α. This work presents an innovative antibacterial strategy to overcome the antibiotic resistance crisis and expand the application of AMPs.

Class-Driven Synergy and Antagonism between a Pseudomonas Phage and Antibiotics

The ubiquitous bacterial pathogen Pseudomonas aeruginosa is responsible for severe infections in patients with burns, cystic fibrosis, and neutropenia. Biofilm formation gives physical refuge and a protected microenvironment for sessile cells, rendering cure by antibiotics a challenge. Bacteriophages have evolved to prey on these biofilms over millions of years, using hydrolases and depolymerases to penetrate biofilms and reach cellular targets. Here, we assessed how a newly discovered KMV-like phage (ΦJB10) interacts with antibiotics to treat P. aeruginosa more effectively in both planktonic and biofilm forms. By testing representatives of four classes of antibiotics (cephalosporins, aminoglycosides, fluoroquinolones, and carbapenems), we demonstrated class-dependent interactions between ΦJB10 and antibiotics in both biofilm clearance and P. aeruginosa killing. Despite identifying antagonism between some antibiotic classes and ΦJB10 at early time points, all classes showed neutral to favorable interactions with the phage at later time points. In one notable example where the antibiotic alone had poor activity against both biofilm and high-density planktonic cells, we found that addition of ΦJB10 demonstrated synergy and resulted in effective treatment of both. Further, ΦJB10 seemed to act as an adjuvant to several antibiotics, reducing the concentration of antibiotics required to ablate the biofilm. This report shows that phages such as ΦJB10 may be valuable additions to the armamentarium against difficult-to-treat biofilm-based infections.

Physical properties and pharmacological applications of Co3O4, CuO, NiO and ZnO nanoparticles

Nano materials have found developing interest in biogenic approaches in the present times. In this study, metal oxide nanoparticles (NPs) such as cobalt oxide (Co₃O₄), copper oxide (CuO), nickel oxide (NiO) and zinc oxide (ZnO), were synthesized using a convenient and rapid method. The structural features of synthesized metal oxide NPs were studied using various microscopic and spectroscopic techniques like SEM, TEM, XRD, FTIR and EDX. The characterization results confirmed that the prepared NPs possess highly pure, unique and crystalline geometry with size ranging between 10 and 20 nm. The synthesized nanoparticles were successfully employed for pharmacological applications. Enzyme inhibition potential of NPs was evaluated against the urease and tyrosinase enzymes. The percent inhibition for the urease enzyme was observed as 80 to 90% by using Co₃O₄, CuO, NiO and ZnO NPs while ZnO NPs were found to have best anti-urease and anti-tyrosinase activities. Moreover, effective inhibition was observed in the case of ZnO NPs at IC₅₀ values of 0.0833 and 0.1732 for urease and tyrosinase enzymes which were comparable to reference drugs thiourea and kojic acid. The lower the IC₅₀ value, higher the free radical scavenging power. Antioxidant activity by DPPH free radical scavenging method was found moderately high for the synthesized metal oxide NPs while best results were obtained for Co₃O₄ and ZnO NPs as compared to the standard ascorbic acid. Antimicrobial potential was also evaluated via the disc diffusion and well diffusion methods. CuO NPs show a better zone of inhibition at 20 and 27 mm by using both methods. This study proves that the novel metal oxide NPs can compete with the standard materials used in the pharmacological studies nowadays.

In vitro and in vivo antimicrobial activity of self-assembled melittin nanoparticles: A comparative study with melittin peptide

The aim of the present study was to analyse the efficacy of self-assembled melittin nanoparticles (MelNP) and compare with native melittin peptide (Mel). Self-assembly formation of the melittin was promoted by heating at 90 °C for 50 min followed by cooling at room temperature. SEM micrographs revealed the formation of nanovesicles. MIC of MelNP against E. coli, S. aureus and P. aeruginosa was found to be 4, 2, and 2 μM, respectively while it was 8, 8 and 4 μM for Mel peptide. Markedly, MelNP showed 12.6 % hemolysis at 8 μM whereas with Mel it was about 71.63 %. The lytic activity of MelNP was also higher in the presence of trypsin/serum than Mel. Both MelNP and Mel exhibited membranolytic activity with cellular disintegration. Further, toxicity analysis studied up to 72 h showed that MelNP was non-toxic to zebrafish embryos up to 6 μM; however, with Mel exposed embryos showed up 30 dead embryos. Bacterial load was markedly reduced in MelNP and Mel exposed infected embryos than compared to the infected one. Moreover, the peptides were also responsible for reducing the infection and prolonging the survivability in infected embryos. Thus, MelNP could be considered an efficient and safer therapeutic molecule that Mel and wherein further experiments are warranted to affirm the broad spectrum efficiency.

Differentiating interactions of antimicrobials with Gram-negative and Gram-positive bacterial cell walls using molecular dynamics simulations

Developing molecular models to capture the complex physicochemical architecture of the bacterial cell wall and to study the interaction with antibacterial molecules is an important aspect of assessing and developing novel antimicrobial molecules. We carried out molecular dynamics simulations using an atomistic model of peptidoglycan to represent the architecture for Gram-positive S. aureus. The model is developed to capture various structural features of the Staphylococcal cell wall, such as the peptide orientation, area per disaccharide, glycan length distribution, cross-linking, and pore size. A comparison of the cell wall density and electrostatic potentials is made with a previously developed cell wall model of Gram-negative bacteria, E. coli, and properties for both single and multilayered structures of the Staphylococcal cell wall are studied. We investigated the interactions of the antimicrobial peptide melittin with peptidoglycan structures. The depth of melittin binding to peptidoglycan is more pronounced in E. coli than in S. aureus, and consequently, melittin has greater contacts with glycan units of E. coli. Contacts of melittin with the amino acids of peptidoglycan are comparable across both the strains, and the D-Ala residues, which are sites for transpeptidation, show enhanced interactions with melittin. A low energetic barrier is observed for translocation of a naturally occurring antimicrobial thymol with the four-layered peptidoglycan model. The molecular model developed for Gram-positive peptidoglycan allows us to compare and contrast the cell wall penetrating properties with Gram-negative strains and assess for the first time binding and translocation of antimicrobial molecules for Gram-positive cell walls.

Efficacy of natural antimicrobial peptides versus peptidomimetic analogues: a systematic review

Aims: This systematic review was carried out to determine whether synthetic peptidomimetics exhibit significant advantages over antimicrobial peptides in terms of in vitro potency. Structural features - molecular weight, charge and length - were examined for correlations with activity. Methods: Original research articles reporting minimum inhibitory concentration  values against Escherichia coli, indexed until 31 December 2020, were searched in PubMed/ScienceDirect/Google Scholar and evaluated using mixed-effects models. Results: In vitro antimicrobial activity of peptidomimetics resembled that of antimicrobial peptides. Net charge significantly affected minimum inhibitory concentration values (p < 0.001) with a trend of 4.6% decrease for increments in charge by +1. Conclusion: AMPs and antibacterial peptidomimetics exhibit similar potencies, providing an opportunity to exploit the advantageous stability and bioavailability typically associated with peptidomimetics.

Improvement of the Antibacterial Activity of Phage Lysin-Derived Peptide P87 through Maximization of Physicochemical Properties and Assessment of Its Therapeutic Potential

Phage lysins are a promising alternative to common antibiotic chemotherapy. However, they have been regarded as less effective against Gram-negative pathogens unless engineered, e.g., by fusing them to antimicrobial peptides (AMPs). AMPs themselves pose an alternative to antibiotics. In this work, AMP P87, previously derived from a phage lysin (Pae87) with a presumed nonenzymatic mode-of-action, was investigated to improve its antibacterial activity. Five modifications were designed to maximize the hydrophobic moment and net charge, producing the modified peptide P88, which was evaluated in terms of bactericidal activity, cytotoxicity, MICs or synergy with antibiotics. P88 had a better bactericidal performance than P87 (an average of 6.0 vs. 1.5 log-killing activity on Pseudomonas aeruginosa strains treated with 10 µM). This did not correlate with a dramatic increase in cytotoxicity as assayed on A549 cell cultures. P88 was active against a range of P. aeruginosa isolates, with no intrinsic resistance factors identified. Synergy with some antibiotics was observed in vitro, in complex media, and in a respiratory infection mouse model. Therefore, P88 can be a new addition to the therapeutic toolbox of alternative antimicrobials against Gram-negative pathogens as a sole therapeutic, a complement to antibiotics, or a part to engineer proteinaceous antimicrobials.

Conjugation of a Cationic Cell-Penetrating Peptide with a Novel Kunitzin-like Trypsin Inhibitor: New Insights for Enhancement of Peptide Bioactivities

Cationic cell-penetrating peptides (CPPs), such as transactivator of transcription (TAT) peptide, have been proposed as effective drug carriers to improve intracellular delivery of biological macromolecules. Amphibian skin-derived Kunitz-type trypsin inhibitors (KTIs), short counterparts of KTIs from plant sources, were found to possess potent serine protease inhibitory activity. However, poor transmembrane permeability of these molecules has largely hindered the study of the full spectrum of their biological actions. As a result, this study aimed to extend the biological activities of amphibian KTIs by their conjugation to cationic CPPs. Herein, a novel peptide (kunitzin-OV2) and its phenylalanine-substituted analogue F9-kunitzin-OV2 (F9-KOV2) were evaluated for inhibition of trypsin/chymotrypsin and showed weak antibacterial activity against Escherichia coli (E. coli). As expected, the conjugation to TAT peptide did not increase membrane lysis compared with the original kunitzin-OV2, but effectively assisted this complex to enter cells. TAT-kunitzin-OV2 (TAT-KOV2) exhibited a 32-fold increase in antibacterial activity and an enhanced bactericidal rate against E. coli. In addition, the conjugation enabled the parent peptides to exhibit antiproliferative activity against cancer cells. Interestingly, TAT-F9-kunitzin-OV2 (TAT-F9-KOV2) showed stronger antiproliferative activity against human breast cancer (MCF-7) and human glioblastoma (U251MG) cell lines, which TAT-KOV2 did not possess. Moreover, TAT-F9-KOV2 showed a 20–25-fold increase in antiproliferative capacity against human lung cancer (H157, H460) cell lines compared with TAT-KOV2. Therefore, the conjugation of CPPs effectively solves the problem of cell penetration that short KTIs lack and provides evidence for new potential applications for their subsequent development as new antibacterial and anticancer agents.

Prevention, inhibition, and degradation effects of melittin alone and in combination with vancomycin and rifampin against strong biofilm producer strains of methicillin-resistant Staphylococcus epidermidis

Methicillin-resistant Staphylococcus epidermidis (MRSE) bacteria are being recognized as true pathogens as they are able to resist methicillin and commonly form biofilms. Recent studies have shown that antimicrobial peptides (AMPs) are promising agents against biofilm-associated bacterial infections. In this study, we aimed to explore the antibiofilm activity of melittin, either alone or in combination with vancomycin and rifampin, against biofilm-producing MRSE strains. Minimum biofilm preventive concentration (MBPC), minimum biofilm inhibition concentration (MBIC), and minimum biofilm eradication concentration (MBEC), as well as fractional biofilm preventive-, inhibitory-, and eradication concentrations (FBPCi, FBICi, and FBECi), were determined for the antimicrobial agents tested. Cytotoxicity and hemolytic activity of melittin at its synergistic concentration were examined on human embryonic kidney cells (HEK-293) and Red Blood Cells (RBCs), respectively. The effect of melittin on the downregulation of biofilm-associated genes was explored using Real-Time PCR. MBPC, MBIC, and MBEC values for melittin were in the range of 0.625-20, 0.625-20, and 10-40 μg/μL, respectively. Melittin showed high synergy (FBPCi, FBICi and FBECi < 0.5). The synergism resulted in a 64-512-fold, 2-16 and 2-8-fold reduction in melittin, rifampicin and vancomycin concentrations, respectively. The synergistic melittin concentration found to be effective did not manifest either cytotoxicity on HEK-293 or hemolytic activity on RBCs. Results showed that melittin downregulated the expression of biofilm-associated icaA, aap, and psm genes in all isolates tested, ranging from 0.04-folds to 2.11-folds for icaA and from 0.05 to 3.76-folds for aap and psm. The preventive and therapeutic indexes of melittin were improved 8-fold when combined with vancomycin and rifampin. Based on these findings, the combination of melittin with conventional antibiotics could be proposed for treating or preventing biofilm-associated MRSE infections.

Synthesis and characterization of a collagen-based composite material containing selenium nanoparticles

Multidrug-resistant bacterial strains represent an emerging global health threat and a great obstacle for bone tissue engineering. One of the major components of the extracellular matrix of the bone is a collagen protein, while selenium is an element that has antimicrobial potential, and is also important for bone metabolism and bone health. Here we represent the incorporation of selenium nanoparticles (SeNPs) synthesized by the green chemical reduction method into collagen gels to produce a composite material, collagen/SeNPs, with antimicrobial properties. The samples were comprehensively characterized by zeta potential measurements, dynamic light scattering inductively coupled plasma-mass spectrometry (ICP-MS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), optical microscopy, field-emission scanning electron microscopy (FE-SEM), and differential scanning calorimetry The cytotoxicity of the SeNPS, as well as collagen/SeNPs, was tested on the MRC-5 cells. It was revealed that collagen/SeNPS expressed a lower cytotoxic effect. Collagen/SeNPs showed significant antibacterial activity against all tested Gram-positive strains, the major causative agents of orthopedic infections as well as Candida albicans. Furthermore, three-dimensional β-tricalcium phosphate (3D-TCP) scaffolds were fabricated by a well-established 3D printing (lithography) method, and afterward preliminary coated by newly-synthesized SeNPs or collagen/SeNPs. In addition, uncoated 3D-TCP scaffolds as well as coated by collagen/SeNPs were subjected to biofilm formation. The production of Staphylococcus aureus biofilm on coated scaffolds by collagen/SeNPs was significantly reduced compared to the uncoated ones.

Creating Robust Antimicrobial Materials with Sticky Tyrocidines

Modified antimicrobial and antifouling materials and surfaces can be used to limit the propagation of microorganisms on various surfaces and minimise the occurrence of infection, transfer, and spoilage. Increased demand for ‘green’ solutions for material treatment has pushed the focus towards to naturally produced antimicrobials. Tyrocidines, cyclo-decapeptides naturally produced by a soil bacterium Brevibacillus parabrevis, have a broad spectrum of activity against Gram-positive and Gram-negative bacteria, filamentous fungi, and yeasts. Continual losses in tyrocidine production highlighted the possible association of peptides to surfaces. It was found in this study that tyrocidines readily associates with many materials, with a selectivity towards polysaccharide-type materials, such as cellulose. Peptide-treated cellulose was found to remain active after exposure to a broad pH range, various temperatures, salt solutions, water washes, and organic solvents, with the sterilising activity only affected by 1% SDS and 70% acetonitrile. Furthermore, a comparison to other antimicrobial peptides showed the association between tyrocidines and cellulose to be unique in terms of antimicrobial activity. The robust association between the tyrocidines and various materials holds great promise in applications focused on preventing surface contamination and creating self-sterilising materials.

Antibacterial, anti-biofilm, and anti-adhesive activities of melittin, a honeybee venom-derived peptide, against quinolone-resistant uropathogenic Escherichia coli (UPEC)

Here, we demonstrated the in vitro and in vivo antibacterial and anti-biofilm activities of melittin, a peptide derived from honeybee venom, against uropathogenic Escherichia coli (UPEC) resistant to quinolones. The minimum inhibitory concentration (MIC) of melittin varied from 0.5 to 8 μM. The bactericidal effect was considered rapid and potent (ranging from 3.0 to 6.0 h after incubation) against a quinolone-resistant and Extended Spectrum Beta-lactamase (ESBL)-producing UPEC strain. Prior exposure to melittin did not reduce the MIC of the quinolones tested, but it decreased the MIC of ceftizoxime by 8-fold due to its ability to form pores in the membrane. Furthermore, melittin disrupted mature biofilms (39.58% at 32 μM) and inhibited the adhesion of this uropathogen to the surfaces of urethral catheter. These results show that melittin is a promising molecule that can be incorporated into invasive urethral medical devices to prevent urinary infections caused by multidrug-resistant UPECs.

Melittin-Based Nano-Delivery Systems for Cancer Therapy

Melittin (MEL) is a 26-amino acid polypeptide with a variety of pharmacological and toxicological effects, which include strong surface activity on cell lipid membranes, hemolytic activity, and potential anti-tumor properties. However, the clinical application of melittin is restricted due to its severe hemolytic activity. Different nanocarrier systems have been developed to achieve stable loading, side effects shielding, and tumor-targeted delivery, such as liposomes, cationic polymers, lipodisks, etc. In addition, MEL can be modified on nano drugs as a non-selective cytolytic peptide to enhance cellular uptake and endosomal/lysosomal escape. In this review, we discuss recent advances in MEL’s nano-delivery systems and MEL-modified nano drug carriers for cancer therapy.

Applications and evolution of melittin, the quintessential membrane active peptide

Melittin, the main venom component of the European Honeybee, is a cationic linear peptide-amide of 26 amino acid residues with the sequence: GIGAVLKVLTTGLPALISWIKRKRQQ-NH₂. Melittin binds to lipid bilayer membranes, folds into amphipathic α-helical secondary structure and disrupts the permeability barrier. Since melittin was first described, a remarkable array of activities and potential applications in biology and medicine have been described. Melittin is also a favorite model system for biophysicists to study the structure, folding and function of peptides and proteins in membranes. Melittin has also been used as a template for the evolution of new activities in membranes. Here we overview the rich history of scientific research into the many activities of melittin and outline exciting future applications.

Evaluation of a strawberry fermented beverage with potential health benefits

Background

Functional fermented beverages are popular worldwide due to their potential to promote health. Starter culture is the main determinant of the final quality and flavor of fermented beverages. The co-cultivation of lactic acid bacteria (LAB) and yeast makes a significant contribution to the safe flavor of fermented beverages. However, the research on the potential of antioxidant, antimicrobial, and anti-biofilm formation of strawberry fermented beverage obtained by combining the LAB and yeast as starter cultures has not been well explored.

Methods

In this study, LAB and yeast were combined as starter culture to obtain strawberry fermented beverage. Fourier transform infrared (FTIR ) spectroscopy was used for the qualitative analysis of the fresh strawberry juice and fermented beverage. From the changes in antioxidant content, free radical scavenging ability, total superoxide dismutase (T-SOD) activity and total antioxidant capacity (T-AOC) to evaluate the antioxidant capacity of fermented beverage in vitro. The antibacterial ability was tested by the Oxford cup method. The biofilms of Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 under fermented beverages treatment was observed by Fluorescence microscope. In addition, sensory analysis was conducted in this study.

Results

In this study, the absorption peaks of Fourier transform infrared between 1,542 cm^-1 and 976 cm^-1, suggest the existence of organic acids, sugars and ethanol. The total phenols and total flavonoids content decreased by 91.1% and 97.5%, respectively. T-SOD activity increased by 33.33%.The scavenging ability of fermented beverage on superoxide anion free radicals was enhanced, and the scavenging ability on DPPH free radicals, hydroxyl free radicals, and ABTS free radicals was weakened. However, the T-AOC increased from 4.15 ± 0.81 to 8.43 ± 0.27 U/mL. Fermented beverage shows antibacterial activity against four pathogens. The minimum inhibitory concentration (MIC) values of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 6538 were 0.05 mL/mL and 0.025 mL/mL, respectively, and the minimum bactericidal concentration (MBC) were both 0.2 mL/mL. It was observed by fluorescence microscope that the green fluorescence area of the two biofilms is greatly reduced after being treated with fermented beverage. Sensory analysis results show that the average scores of fermented beverage in color, appearance and taste were increased. The overall impression and flavor were decreased.

Conclusion

These results demonstrated that strawberry fermented beverage has potential benefits such as an antioxidant, antibacterial, and anti-biofilm formation, providing the potential for the fermented beverage to become promising candidates for natural antioxidants, antibacterial agents and anti-biofilm agents.

Promising Antimicrobial Properties of Bioactive Compounds from Different Honeybee Products

Bee products have been known for centuries for their versatile healing properties. In recent decades they have become the subject of documented scientific research. This review aims to present and compare the impact of bee products and their components as antimicrobial agents. Honey, propolis, royal jelly and bee venom are bee products that have antibacterial properties. Sensitivity of bacteria to these products varies considerably between products and varieties of the same product depending on their origin. According to the type of bee product, different degrees of activity were observed against Gram-positive and Gram-negative bacteria, yeasts, molds and dermatophytes, as well as biofilm-forming microorganisms. Pseudomonas aeruginosa turned out to be the most resistant to bee products. An analysis of average minimum inhibitory concentration values for bee products showed that bee venom has the strongest bacterial effectiveness, while royal jelly showed the weakest antibacterial activity. The most challenging problems associated with using bee products for medical purposes are dosage and safety. The complexity and variability in composition of these products raise the need for their standardization before safe and predictable clinical uses can be achieved.

Beehive Products as Antibacterial Agents: A Review

Honeybees are one of the most marvelous and economically beneficial insects. As pollinators, they play a vital role in every aspect of the ecosystem. Beehive products have been used for thousands of years in many cultures for the treatment of various diseases. Their healing properties have been documented in many religious texts like the Noble Quran and the Holy Bible. Honey, bee venom, propolis, pollen and royal jelly all demonstrated a richness in their bioactive compounds which make them effective against a variety of bacterial strains. Furthermore, many studies showed that honey and bee venom work as powerful antibacterial agents against a wide range of bacteria including life-threatening bacteria. Several reports documented the biological activities of honeybee products but none of them emphasized on the antibacterial activity of all beehive products. Therefore, this review aims to highlight the antibacterial activity of honey, bee venom, propolis, pollen and royal jelly, that are produced by honeybees.

Chemical Profiling and Antimicrobial Properties of Honey Bee (Apis mellifera L.) Venom

The incidence of antibiotic resistance in pathogenic bacteria has become an alarming clinical and social problem. Therefore, the demand for alternative antimicrobial compounds has increased. In this study, a chemical profile of honey bee (Apis mellifera L.) venom (HBV) has been determined by HPLC and FTIR-ATR spectroscopy, and tested for antibacterial activity, as well as efficiency with regard to conventional antibiotics. The investigated HBV was of high quality with melittin and total protein contents of 70.10 ± 7.01%, and 84.44 ± 3.12 g/100 g, respectively. The purity of HBV was confirmed by FTIR-ATR spectral profiling, which revealed a unique pattern of absorption bands that are characteristic of its major fractions. In addition, HBV showed a broad spectrum of activity against all three tested biomasses of potentially pathogenic Gram-positive and Gram-negative bacteria with MIC values ranging between 12.5 and 200 µg/mL, and MBC between 12.5 and 400 µg/mL. When compared to conventional antibiotics, HBV (400 µg) showed up to 27.8% efficiency of tetracycline (30 µg), 52.2% erythromycin (15 µg), 21.2% ciprofloxacin (5 µg), and 34.6% of ampicillin-sulbactam (20 µg). The overall results demonstrate the therapeutic potential of the analyzed HBV.

The antimicrobial peptide TAT-RasGAP317-326 inhibits the formation and expansion of bacterial biofilms in vitro

OBJECTIVES

Biofilms are structured aggregates of bacteria embedded in a self-produced matrix that develop in diverse ecological niches. Pathogenic bacteria can form biofilms on surfaces and in tissues, causing nosocomial and chronic infections that are difficult to treat. While antibiotics are largely inefficient in limiting biofilm formation and expansion, antimicrobial peptides (AMPs) are emerging as alternative antibiofilm treatments. In this study, we explore the effect of the newly described AMP TAT-RasGAP_317-326 on Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus biofilms.

METHODS

Efficiency of TAT-RasGAP_317-326 on biofilms was tested in vitro. Both viability of bacteria contained in the biofilm as well as biomass of the biofilm were quantified using resazurin and crystal violet staining, respectively. The antibiofilm effect of TAT-RasGAP_317-326 was compared with a selection of classical antibiotics and AMPs.

RESULTS

We observe that TAT-RasGAP_317-326 inhibits biofilm formation at concentrations equivalent or two times greater than the minimum inhibitory concentration (MIC) of planktonic bacteria. Moreover, TAT-RasGAP_317-326 limits the expansion of A. baumannii and P. aeruginosa established biofilms at twice the concentration inhibiting biofilm formation.

CONCLUSION

These results underscore the potential use of TAT-RasGAP_317-326 against biofilms and encourage further studies in the development of AMPs to treat biofilm-related infections.

Biofilms as Promoters of Bacterial Antibiotic Resistance and Tolerance

Multidrug resistant bacteria are a global threat for human and animal health. However, they are only part of the problem of antibiotic failure. Another bacterial strategy that contributes to their capacity to withstand antimicrobials is the formation of biofilms. Biofilms are associations of microorganisms embedded a self-produced extracellular matrix. They create particular environments that confer bacterial tolerance and resistance to antibiotics by different mechanisms that depend upon factors such as biofilm composition, architecture, the stage of biofilm development, and growth conditions. The biofilm structure hinders the penetration of antibiotics and may prevent the accumulation of bactericidal concentrations throughout the entire biofilm. In addition, gradients of dispersion of nutrients and oxygen within the biofilm generate different metabolic states of individual cells and favor the development of antibiotic tolerance and bacterial persistence. Furthermore, antimicrobial resistance may develop within biofilms through a variety of mechanisms. The expression of efflux pumps may be induced in various parts of the biofilm and the mutation frequency is induced, while the presence of extracellular DNA and the close contact between cells favor horizontal gene transfer. A deep understanding of the mechanisms by which biofilms cause tolerance/resistance to antibiotics helps to develop novel strategies to fight these infections.

Venom peptides in cancer therapy: An updated review on cellular and molecular aspects

Based on the high incidence and mortality rates of cancer, its therapy remains one of the most vital challenges in the field of medicine. Consequently, enhancing the efficacy of currently applied treatments and finding novel strategies are of great importance for cancer treatment. Venoms are important sources of a variety of bioactive compounds including salts, small molecules, macromolecules, proteins, and peptides that are defined as toxins. They can exhibit different pharmacological effects, and in recent years, their anti-tumor activities have gained significant attention. Several different compounds are responsible for the anti-tumor activity of venoms, and peptides are one of them. In the present review, we discuss the possible anti-tumor activities of venom peptides by highlighting molecular pathways and mechanisms through which these molecules can act effectively. Venom peptides can induce cell death in cancer cells and can substantially enhance the efficacy of chemotherapy and radiotherapy. Also, the venom peptides can mitigate the migration of cancer cells via suppression of angiogenesis and epithelial-to-mesenchymal transition. Notably, nanoparticles have been applied in enhancing the bioavailability of venom peptides and providing targeted delivery, thereby leading to their elevated anti-tumor activity and potential application for cancer therapy.

Scorpion-Venom-Derived Antimicrobial Peptide Css54 Exerts Potent Antimicrobial Activity by Disrupting Bacterial Membrane of Zoonotic Bacteria

Antibiotic resistance is an important issue affecting humans and livestock. Antimicrobial peptides are promising alternatives to antibiotics. In this study, the antimicrobial peptide Css54, isolated from the venom of C. suffuses, was found to exhibit antimicrobial activity against bacteria such as Listeria monocytogenes, Streptococcus suis, Campylobacter jejuni, and Salmonella typhimurium that cause zoonotic diseases. Moreover, the cytotoxicity and hemolytic activity of Css54 was lower than that of melittin isolated from bee venom. Circular dichroism assays showed that Css54 has an α-helix structure in an environment mimicking that of bacterial cell membranes. We examined the effect of Css54 on bacterial membranes using N-phenyl-1-naphthylamine, 3,3'-dipropylthiadicarbbocyanine iodides, SYTOX green, and propidium iodide. Our findings suggest that the Css54 peptide kills bacteria by disrupting the bacterial membrane. Moreover, Css54 exhibited antibiofilm activity against L. monocytogenes. Thus, Css54 may be useful as an alternative to antibiotics in humans and animal husbandry.

An updated review on bacterial community composition of traditional fermented milk products: what next-generation sequencing has revealed so far?

The emergence of next-generation sequencing (NGS) technologies has revolutionized the way to investigate the microbial diversity in traditional fermentations. In the field of food microbial ecology, different NGS platforms have been used for community analysis, including 454 pyrosequencing from Roche, Illumina's instruments and Thermo Fisher's SOLiD/Ion Torrent sequencers. These recent platforms generate information about millions of rDNA amplicons in a single running, enabling accurate phylogenetic resolution of microbial taxa. This review provides a comprehensive overview of the application of NGS for microbiome analysis of traditional fermented milk products worldwide. Fermented milk products covered in this review include kefir, buttermilk, koumiss, dahi, kurut, airag, tarag, khoormog, lait caillé, and suero costeño. Lactobacillus-mainly represented by Lb. helveticus, Lb. kefiranofaciens, and Lb. delbrueckii-is the most important and frequent genus with 51 reported species. In general, dominant species detected by culturing were also identified by NGS. However, NGS studies have revealed a more complex bacterial diversity, with estimated 400-600 operational taxonomic units, comprising uncultivable microorganisms, sub-dominant populations, and late-growing species. This review explores the importance of these discoveries and address related topics on workflow, NGS platforms, and knowledge bioinformatics devoted to fermented milk products. The knowledge that has been gained is vital in improving the monitoring, manipulation, and safety of these traditional fermented foods.

In-depth characterization of antibacterial activity of melittin against Staphylococcus aureus and use in a model of non-surgical MRSA-infected skin wounds

Skin infections caused by methicillin-resistant Staphylococcus aureus (MRSA) require the development of new and effective topical antibiotics. In this context, melittin, the main component of apitoxin, has a potent antibacterial effect. However, little is known regarding the anti-inflammatory potential this peptide in infection models, or its ability to induce clinically important resistance. Here, we aimed to conduct an in-depth characterization of the antibacterial potential of melittin in vitro and evaluate the pharmaceutical potential of an ointment containing melittin for the treatment of non-surgical infections induced by MRSA. The minimum inhibitory concentration of melittin varied from 0.12 to 4 μM. The antibacterial effect was mainly bactericidal and fast (approximately 0.5 h after incubation) and was maintained even in stationary cells and mature MRSA biofilms. Melittin interacts synergistically with beta-lactams and aminoglycosides, and its ability to form pores in the membrane reverses the resistance of vancomycin-intermediate Staphylococcus aureus (VISA) to amoxicillin, and vancomycin. Its ability to induce resistance in vitro was absent, and melittin was stable in several conditions often associated with infected wounds. In vivo, aointment containing melittin reduced bacterial load and the content of pro-inflammatory cytokines, such as tumor necrosis factor-α, interleukin-6 (IL-6), and IL-1 beta. Collectively, these data point to melittin as a potential candidate for topical formulations aimed at the treatment of non-surgical infections caused by MRSA.

Inhibition of quorum sensing-controlled virulence factors with natural substances and novel protease, obtained from Halobacillus karajensis

INTRODUCTION

In recent years, a challenge in clinical treatment has developed due to bacterial resistance to antibiotics. One of the new mechanisms against infections is virulence factor inhibition. Many virulence factors are controlled by quorum sensing pathways such as biofilm formation and pyocyanin production. The goal of the present study was to investigate the effect of an obligate halophilic bacterial strain on Pseudomonas aeruginosa and Staphylococcus aureus, due to its halo-tolerant substances and enzymes.

METHODS

The effect of Halobacillus karajensis on bacterial growth and production of virulence factors was studied in this work. The obligate halophile cells and supernatant fractions were extracted by the methanol/chloroform method and characterized by Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Gas Chromatography-Mass Spectrometry (GC-MS), and zymography. The effects of these fractions were studied on biofilm formation in P. aeruginosa and S. aureus as well as on pyocyanin production in P. aeruginosa. The effective protein in the fraction was analyzed by the SDS-PAGE method, and all protein fragments were studied for pyocyanin inhibition.

RESULTS

The crude supernatant extract, MMS fraction, from H. karajensis was effective for the biofilm reduction in S. aureus (74%) and P. aeruginosa (27%). Two proteases in this fraction, which were recognized by zymography on skim milk, were the probable causes for extracellular polymeric substances (EPS) hydrolysis in the biofilm matrix. Also, halide crystals and branched fatty acids, 12methyl-tetradecanoic acid, in the other fractions decreased the biofilm by 18% in S. aureus. The results showed that a new 25 kD protein, which was obtained from MMS fraction, inhibited pyocyanin production by 60% in P. aeruginosa. The zymogram and bioinformatics studies showed that this protein was a serine alkaline metalloprotease and had an interaction with AHL molecules.

CONCLUSION

The inhibitory effects of the non-toxic natural substances and proteases on biofilm formation and pyocyanin production, specifically the 25 kD protease, are novel in this study and make them a good candidate for infected wound healing and inhibiting the virulence factors.

Combined Effect of Melittin and DNase on Enterococcus faecalis Biofilms and Its Susceptibility to Sodium Hypochlorite

Biofilm communities are tolerant to antimicrobials and difficult to eradicate. This study aimed to investigate the effect of melittin, an antimicrobial peptide, either alone or in combination with deoxyribonuclease (DNase), an inhibitor of extracellular deoxyribonucleic acid (eDNA), against Enterococcus faecalis (E. faecalis) biofilms, and biofilm susceptibility to sodium hypochlorite (NaOCl). Biofilms of E. faecalis were developed in root canals of bovine teeth. The biofilms were treated with distilled water (control), melittin, DNase, or DNase+melittin. The antibiofilm effects of the treatments were analyzed using colony forming unit (CFU) assay, crystal violet staining, confocal laser scanning microscopy (CLSM), and field emission scanning electron microscope (FE-SEM). The susceptibility of DNase+melittin-treated biofilms to NaOCl (0%, 2.5% and 5%) was investigated by the CFU assay. The data were statistically analyzed using one-way analysis of variance, followed by Tukey's test. A p-value of <0.05 was considered significant. Specimens treated with DNase+melittin showed a more significant decrease in the CFUs, eDNA level, and biofilm formation rate than those treated only with melittin or DNase (p < 0.05). CLSM analysis showed DNase+melittin treatment significantly reduced the volume of biofilms and extracellular polymeric substance compared to either treatment alone (p < 0.05). FE-SEM images showed a high degree of biofilm disruption in specimens that received DNase+melittin. 2.5% NaOCl in specimens pretreated with DNase+melittin showed higher antibacterial activity than those treated only with 5% NaOCl (p < 0.05). This study highlighted that DNase improved the antibiofilm effects of melittin. Moreover, DNase+melittin treatment increased the susceptibility of biofilms to NaOCl. Thus, the complex could be a clinical strategy for safer use of NaOCl by reducing the concentration.

Antimicrobial Properties of Apis mellifera's Bee Venom

Bee venom (BV) is a rich source of secondary metabolites from honeybees (Apis mellifera L.). It contains a variety of bioactive ingredients including peptides, proteins, enzymes, and volatile metabolites. The compounds contribute to the venom’s observed biological functions as per its anti-inflammatory and anticancer effects. The antimicrobial action of BV has been shown in vitro and in vivo experiments against bacteria, viruses, and fungi. The synergistic therapeutic interactions of BV with antibiotics has been reported. The synergistic effect contributes to a decrease in the loading and maintenance dosage, a decrease in the side effects of chemotherapy, and a decrease in drug resistance. To our knowledge, there have been no reviews on the impact of BV and its antimicrobial constituents thus far. The purpose of this review is to address the antimicrobial properties of BV and its compounds.

Quantitative Measurement of Melittin in Asian Honeybee Venom Using a New Method Including UPLC-QqTOF-MS

Asian honeybee venom is widely used in traditional oriental medicine. Melittin is the main component of Asian honeybee venom. In the present study, an ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QqTOF-MS) method was used for accurate qualitative and quantitative analyses of melittin in Asian honeybee venom. The results showed that the dynamic linear range of melittin was from 0.094 to 20 μg/mL, and the limit of quantification was 0.3125 μg/mL. The spiking recovery of melittin in honeybee venom ranged from 84.88% to 93.05%. Eighteen Asian honeybee venom samples in eighteen batches were collected from two different zones of China, and their melittin contents were measured. The contents of melittin in Asian honeybee venom samples was 33.9–46.23% of dry weight. This method proved a useful tool for the rapid evaluation of the authenticity and quality of Asian honeybee venom in terms of the melittin contents, and will contribute to a broader understanding of Asian honeybee venom.

Antimicrobial Activity of Five Apitoxins from Apis mellifera on Two Common Foodborne Pathogens

Antimicrobial resistance is one of today's major public health challenges. Infections caused by multidrug-resistant bacteria have been responsible for an increasing number of deaths in recent decades. These resistant bacteria are also a concern in the food chain, as bacteria can resist common biocides used in the food industry and reach consumers. As a consequence, the search for alternatives to common antimicrobials by the scientific community has intensified. Substances obtained from nature have shown great potential as new sources of antimicrobial activity. The aim of this study was to evaluate the antimicrobial activity of five bee venoms, also called apitoxins, against two common foodborne pathogens. A total of 50 strains of the Gram-negative pathogen Salmonella enterica and 8 strains of the Gram-positive pathogen Listeria monocytogenes were tested. The results show that the minimum inhibitory concentration (MIC) values were highly influenced by the bacterial genus. The MIC values ranged from 256 to 1024 µg/mL in S. enterica and from 16 to 32 µg/mL in L. monocytogenes. The results of this study demonstrate that apitoxin is a potential alternative agent against common foodborne pathogens, and it can be included in the development of new models to inhibit the growth of pathogenic bacteria in the food chain.

Pan-Drug Resistant Acinetobacter baumannii, but Not Other Strains, Are Resistant to the Bee Venom Peptide Mellitin

Acinetobacter baumannii is a prevalent pathogen in hospital settings with increasing importance in infections associated with biofilm production. Due to a rapid increase in its drug resistance and the failure of commonly available antibiotics to treat A. baumannii infections, this bacterium has become a critical public health issue. For these multi-drug resistant A. baumannii, polymyxin antibiotics are considered the only option for the treatment of severe infections. Concerning, several polymyxin-resistant A. baumannii strains have been isolated over the last few years. This study utilized pan drug-resistant (PDR) strains of A. baumannii isolated in Brazil, along with susceptible (S) and extreme drug-resistant (XDR) strains in order to evaluate the in vitro activity of melittin, an antimicrobial peptide, in comparison to polymyxin and another antibiotic, imipenem. From a broth microdilution method, the determined minimum inhibitory concentration showed that S and XDR strains were susceptible to melittin. In contrast, PDR A. baumannii was resistant to all treatments. Treatment with the peptide was also observed to inhibit biofilm formation of a susceptible strain and appeared to cause permanent membrane damage. A subpopulation of PDR showed membrane damage, however, it was not sufficient to stop bacterial growth, suggesting that alterations involved with antibiotic resistance could also influence melittin resistance. Presumably, mutations in the PDR that have arisen to confer resistance to widely used therapeutics also confer resistance to melittin. Our results demonstrate the potential of melittin to be used in the control of bacterial infections and suggest that antimicrobial peptides can serve as the basis for the development of new treatments.

Rational Substitution of ε-Lysine for α-Lysine Enhances the Cell and Membrane Selectivity of Pore-Forming Melittin

Here, we present a rational approach that enhances the membrane selectivity of a prolific pore-forming peptide, melittin, based on experimental observations that the cationic polymer, ε-polylysine, disrupts bacterial membranes with greater affinity over mammalian cells when compared to poly-l-lysine and poly-d-lysine. We systematically replaced three α-lysine residues in melittin with ε-lysine residues and identified key residues that are important for cytotoxicity. We then assessed the antimicrobial properties of the modified peptides which carry two or three ε-lysyl residues. Two modified melittin peptides displayed rapid bactericidal properties against antibiotic-resistant strains, low innate resistance development by pathogenic bacteria, remained nonimmunogenic for T lymphocytes, and increased bioavailability in tear fluids. In proof-of-concept in vivo experiments, one of the peptides was noncytotoxic for ocular surfaces and had comparable antimicrobial efficacy to that of fluoroquinolone antibiotics. The results uncover a simple and potential strategy that can enhance the membrane selectivity of cytolytic peptides by ε-lysylation.