Mechanism of Honey Bacteriostatic Action Against MRSA and VRE Involves Hydroxyl Radicals Generated from Honey's Hydrogen Peroxide

Long-term stability and the physical and chemical factors predictive for antimicrobial activity in Australian honey

The growing burden of expired medicines contributes to environmental contamination and landfill waste accumulation. Medicinal honey, with its non-toxic nature and potentially long shelf-life, represents a promising and underutilised therapeutic that avoids some of these issues. However, limited knowledge on how its antimicrobial properties change over time combined with a lack of reliable processes in the honey industry for measuring antimicrobial potential, hinder its clinical adoption. Using a diverse selection of 30 Australian honey samples collected between 2005 and 2007, we comprehensively evaluated their antibacterial and antifungal activity and pertinent physical and chemical properties with the aims of assessing the effect of long-term storage on activity, pinpointing factors associated with antimicrobial efficacy, and establishing robust assessment methods. Minimum inhibitory concentration (MIC) assays proved superior to the standard phenol equivalence assay in capturing the full range of antimicrobial activity present in honey. Correlations between activity and a range of physical and chemical properties uncovered significant associations, with hydrogen peroxide, antioxidant content, and water activity emerging as key indicators in non-Leptospermum honey. However, the complex nature and the diverse composition of honey samples precludes the use of high-throughput chemical tests for accurately assessing this activity, and direct assessment using live microorganisms remains the most economical and reliable method. We provide recommendations for different methods of assaying various honey properties, taking into account their accuracy along with technical difficulty and safety considerations. All Leptospermum and fourteen of seventeen non-Leptospermum honey samples retained at least some antimicrobial properties after 15-17 years of storage, suggesting that honey can remain active for extended periods. Overall, the results of this study will help industry meet the growing demand for high-quality, medicinally active honey while ensuring accurate assessment of its antimicrobial potential.

Natural phenolic compounds: Antimicrobial properties, antimicrobial mechanisms, and potential utilization in the preservation of aquatic products

Natural antibacterials have stood out in the last decade due to the growing demand for reducing chemical preservatives in food. In particular, natural phenolic compounds are secondary metabolites produced by plants for numerous functions including antimicrobial defence. Polyphenol has significant antimicrobial activity, but its antimicrobial properties are affected by the cell structure difference of bacteria, the concentration, type, and extraction method of polyphenol, and the treatment time of bacteria exposed to polyphenol. Therefore, this paper analyzed the antibacterial activity and mechanism of polyphenol as an antimicrobial agent. However, there remained significant considerations, including the interaction of polyphenols and food matrix, environmental temperature, and the effect of color and odor of some polyphenols on sensory properties of aquatic products, and the additive amount of polyphenols. On this basis, the application strategies of polyphenols as the antimicrobial agent in aquatic products preservation were reviewed.

The Antibacterial Properties of Polish Honey against Streptococcus mutans-A Causative Agent of Dental Caries

Streptococcus mutans is considered the main pathogen responsible for dental caries, one of the major infectious diseases, affecting more than 4 billion people worldwide. Honey is a natural product with well-known antibacterial potential against several human pathogens. The aim of the study was to evaluate the antibacterial efficacy of Polish honey against S. mutans and analyze the role of some bioactive substances on its antibacterial action. The antibacterial potential of different honey varieties (goldenrod, buckwheat, honeydew, and lime) was analyzed using a microdilution assay. Manuka and artificial honey were used as controls. The content of GOX, hydrogen peroxide, total polyphenols, and antioxidant potential was assayed in honey. The influence of catalase and proteinase K on antibacterial activity as well as antibiofilm action was also determined. The strongest antibacterial activity was observed for buckwheat, honeydew, and manuka honey, which were also characterized by the highest antioxidant activity and polyphenols content. Catalase treatment decreases the antibacterial activity of honey, while proteinase K treatment influences the antibacterial potential of honey slightly less. Obtained results suggest that honey can be a good natural product against S. mutans, and hydrogen peroxide was identified as a crucial contributor to its antimicrobial action.

Evaluation of the generation of reactive oxygen species and antibacterial activity of honey as a function of its phenolic and mineral composition

The antibacterial activity (ABA) of honey is associated with the generation of reactive oxygen species (ROS), where polyphenols (PFs) play a key role due to their pro-oxidant action modulated by metallic cations. In this work, the contents of PFs, H₂O₂, OH radicals, Cu, Fe, Mn, Zn, and ABA against Staphylococcus epidermidis and Pseudomonas aeruginosa were determined in honeys from central Chile. Then, their relationships were evaluated through partial least squares regression. The average contents of phenolic acids, flavonoids and metals in honey ranged from 0.4 to 4 μg/g, 0.3-1.5 μg/g and 3-6 μg/g, respectively. All honeys showed accumulation of H₂O₂ (1-35 μg/g) and OH radicals. The PLS showed that gallic acid, p-coumaric acid, chrysin, kaempferol, Fe, and Mn stimulate the generation of ROS. Quercetin, Cu, and Zn showed marginal antioxidant effects. PFs favor the ABA of honey against both bacteria and H₂O₂ against S. epidermidis.

Flavonoids and Phenylethylamides Are Pivotal Factors Affecting the Antimicrobial Properties of Stingless Bee Honey

Despite the recent approval of stingless bee honey to the Argentine Food Code, there are still many gaps in information. Likely, the main reason for this is that multiple ecological and chemical factors influence their production and antimicrobial properties. This work combined metabolomic, microbiological, and physicochemical analyses to characterize the honey ofTetragonisca fiebrigifrom Northeastern Argentina. The antimicrobial activity tests showed that honey samples (n = 24) inhibited some Gram-positive and Gram-negative bacteria at different sensitivity levels. Furthermore, samples selected for their high bioactivity revealed crystallizations, a positive correlation with fungal growth, and the presence of flavonoids. The major polyphenols annotated by liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis and supported by metabolomic tools were quercetin 3,4'-dimethyl ether, pachypodol, jaceoside, irigenin trimethyl ether, corymboside, chrysoeriol 7-neohesperidoside, and corymboside. In contrast, samples missing antimicrobial activity did not crystallize, lacked flavonoids, and were enriched in phenylethylamides. Based on these findings, we discuss the significance of flavonoids and phenylethylamides on honey's antimicrobial activity and food quality and how they may indeed reflect essential parameters of the hive, such as microbial balance and eubiosis.

The in vitro and in vivo antibacterial activities of uniflorous honey from a medicinal plant, Scrophularia ningpoensis Hemsl., and characterization of its chemical profile with UPLC-MS/MS

ETHNOPHARMACOLOGICAL RELEVANCE

According to the Compendium of Materia Medica, honey has been used as a traditional medicine in treatment against mucositis, tinea, hemorrhoids and psoriasis. In complementary medicine, due to its significant antimicrobial activity, honey has been widely used as a remedy for skin wounds and gastrohelcosis for thousands of years.

AIM OF THE STUDY

This study is aimed at exploring the antimicrobial activity and mechanisms of honey sourced from medicinal plants, and revealing the composition-activity relationship, to facilitate their complementary and alternative application in the therapy of bacterial infectious diseases.

MATERIALS AND METHODS

Eight kinds of medicinal plant-derived uniflorous honey, native to China, were gathered. Their antimicrobial activities were evaluated in vitro, and then in vivo with the systemically infected mouse model and the acute skin infection model. SYTOX uptake assay, scanning electron microscopy, DNA binding assay, and quantitative real-time PCR, were carried out to elucidate the antibacterial mechanisms. This was followed by an investigation of the componential profile with the UPLC-MS/MS technique.

RESULTS

It was found that Scrophularia ningpoensis Hemsl. (figwort) honey (S. ningpoensis honey) exhibited broad-spectrum and the strongest antibacterial potency (MICs of 7.81-125.00%, w/v), comparable to manuka honey. In the in vivo assays, S. ningpoensis honey significantly decreased the bacterial load of the muscles under the acute MRSA-infected skin wounds; the sera level of TNF-α in the S. aureus and P. aeruginosa-infected mice decreased by 45.38% and 51.75%, respectively, after the treatment of S. ningpoensis honey (125 mg/10 g). It was capable of killing bacteria through disrupting the cell membranes and the genomic DNA, as well as down-regulating the expression of genes associated with virulence, biofilm formation and invasion, including icaA, icaD, eno, sarA, agrA, sigB, fib and ebps in S. aureus, and lasI, lasR, rhlI, rhlR and algC in P. aeruginosa. Apart from H₂O₂, some other nonperoxide compounds such as adenosine, chavicol, 4-methylcatechol, trehalose, palmitoleic acid and salidroside, might play a vital role in the antibacterial properties of S. ningpoensis honey.

CONCLUSIONS

This is the first study to thoroughly investigate the antibacterial activity, mode of action, and componential profile of S. ningpoensis honey. It suggested that S. ningpoensis honey might be a potential supplement or substitute for manuka honey, for the prevention or treatment of bacterial infections. It will facilitate the precise application of medicinal plant-sourced honey, provide a new thread for the development of antibacterial drugs, and assist in the distinction of different kinds of honey.

Biological Efficacy of Compounds from Stingless Honey and Sting Honey against Two Pathogenic Bacteria: An In Vitro and In Silico Study

Honey inhibits bacterial growth due to the high sugar concentration, hydrogen peroxide generation, and proteinaceous compounds present in it. In this study, the antibacterial activity of stingless and sting honey against foodborne pathogenic bacteria isolated from spoiled milk samples was examined. The isolated bacterial strains were confirmed as Bacillus cereus and Listeriamonocytogenes through morphological, biochemical, and 16 s RNA analysis. Physiochemical characterizations of the honey samples revealed that both of the honey samples had an acidic pH, low water content, moderate reducing sugar content, and higher proline content. Through the disc diffusion method, the antibacterial activities of the samples were assayed and better results were observed for the 50 mg/disc honey. Both stingless and sting honey showed the most positive efficacy against Bacillus cereus. Therefore, an in silico study was conducted against this bacterium with some common compounds of honey. From several retrieved constituents of stingless and sting honey, 2,4-dihydroxy-2,5-dimethyl 3(2H)-furan-3-one (furan) and 4H-pyran-4-one,2,3-dihydro of both samples and beta.-D-glucopyranose from the stingless revealed high ligand-protein binding efficiencies for the target protein (6d5z, hemolysin II). The root-mean-square deviation, solvent-accessible surface area, the radius of gyration, root-mean-square fluctuations, and hydrogen bonds were used to ensure the binding stability of the docked complexes in the atomistic simulation and confirmed their stability. The combined effort of wet and dry lab-based work support, to some extent, that the antimicrobial properties of honey have great potential for application in medicine as well as in the food industries.

Hemithioindigo-Based Visible Light-Activated Molecular Machines Kill Bacteria by Oxidative Damage

Antibiotic resistance is a growing health threat. There is an urgent and critical need to develop new antimicrobial modalities and therapies. Here, a set of hemithioindigo (HTI)-based molecular machines capable of specifically killing Gram-positive bacteria within minutes of activation with visible light (455 nm at 65 mW cm-2 ) that are safe for mammalian cells is described. Importantly, repeated exposure of bacteria to HTI does not result in detectable development of resistance. Visible light-activated HTI kill both exponentially growing bacterial cells and antibiotic-tolerant persister cells of various Gram-positive strains, including methicillin-resistant S. aureus (MRSA). Visible light-activated HTI also eliminate biofilms of S. aureus and B. subtilis in as little as 1 h after light activation. Quantification of reactive oxygen species (ROS) formation and protein carbonyls, as well as assays with various ROS scavengers, identifies oxidative damage as the underlying mechanism for the antibacterial activity of HTI. In addition to their direct antibacterial properties, HTI synergize with conventional antibiotics in vitro and in vivo, reducing the bacterial load and mortality associated with MRSA infection in an invertebrate burn wound model. To the best of the authors' knowledge, this is the first report on the antimicrobial activity of HTI-based molecular machines.

Both Manuka and Non-Manuka Honey Types Inhibit Antibiotic Resistant Wound-Infecting Bacteria

Postoperative infections are a major concern in United States hospitals, accounting for roughly 20% of all hospital-acquired infections yearly. Wound-infecting bacteria, in particular, have a high rate of drug resistance (up to 65%), creating life-threatening complications. Manuka honey, native to New Zealand, has been FDA-approved for wound treatment in the United States after studies demonstrated its ability to inhibit a variety of bacterial species and facilitate wound healing. The aim of this study was to identify alternative (non-manuka) honey types that can be specifically used against antibiotic resistance bacteria in wound infections. We utilized a honey-plate method to measure the minimum inhibitory concentration (MIC) of honey to avoid the limitations of agar diffusion, where large, nonpolar polyphenols (which will not diffuse efficiently) play an important role in bioactivity. This study demonstrated that there are several alternative (non-manuka) honey types, particularly fresh raw Arkansas wildflower honeys, that comparably inhibit the growth of the antibiotic-resistant bacterial species specifically implicated in wound infections. Concentrations of 10-30% honey inhibited the growth of the highly antibiotic-resistant organisms colloquially referred to as "superbugs", which the WHO declared in 2017 to be in critical need of new antibiotics. There was no statistical difference between manuka honey and fresh summer Arkansas wildflower honey in overall bacterial inhibition. These results could transform wound care in the United States, where manuka honey can be expensive and difficult to obtain and where antibiotic resistance remains a troubling concern for wound treatment.

The role of honey in the ecology of the hive: Nutrition, detoxification, longevity, and protection against hive pathogens

Honey is the source of energy for the European honey bee, Apis mellifera. Beyond simple nutrition and a hedge against the seasonal, geographic, and chemical unpredictability of nectar, honey has properties that protect the hive against various stresses. Enzyme-mediated detoxification during honey ripening neutralizes potentially toxic phytochemicals, and bees that consume honey have enhanced tolerance to other ingested toxins. Catalase and antioxidant phenolics protect honey bees from oxidative damage caused by reactive oxygen species, promoting their longevity. Phytochemical components of honey and microRNAs have the potential to influence developmental pathways, with diet playing a large role in honey bee caste determination. Components of honey mediate stress response and promote cold tolerance during overwintering. Honey has a suite of antimicrobial mechanisms including osmotic pressure, low water activity, low pH, hydrogen peroxide, and plant-, honey bee-, and microbiota-derived compounds such as phytochemicals and antimicrobial peptides. Certain types of honey, particularly polyfloral honeys, have been shown to inhibit important honey bee pathogens including the bacteria responsible for American and European Foulbrood, the microsporidian Nosema ceranae, and the fungi responsible for Stonebrood. Understanding the diverse functional properties of honey has far-ranging implications for honey bee and hive health and management by beekeepers.

Biochemical Reactions and Their Biological Contributions in Honey

Honey is known for its content of biomolecules, such as enzymes. The enzymes of honey originate from bees, plant nectars, secretions or excretions of plant-sucking insects, or from microorganisms such as yeasts. Honey can be characterized by enzyme-catalyzed and non-enzymatic reactions. Notable examples of enzyme-catalyzed reactions are the production of hydrogen peroxide through glucose oxidase activity and the conversion of hydrogen peroxide to water and oxygen by catalase enzymes. Production of hydroxymethylfurfural (HMF) from glucose or fructose is an example of non-enzymatic reactions in honey.

A Review of Commonly Used Methodologies for Assessing the Antibacterial Activity of Honey and Honey Products

Honey, a naturally sweet and viscous substance is mainly produced by honeybees (Apis mellifera) from flower nectar. Honey exerts a plethora of biological and pharmacological activities, namely, antioxidant, antimicrobial and anti-inflammatory activity, because of the presence of an extensive variety of bioactive compounds. The antibacterial activity is one of the most reported biological properties, with many studies demonstrating that honey is active against clinically important pathogens. As a result, beside honey’s widespread utilization as a common food and flavouring agent, honey is an attractive natural antimicrobial agent. However, the use of neat honey for therapeutic purposes poses some problems, for instance, its stickiness may hamper its appeal to consumers and health care professionals, and the maintenance of an adequate therapeutic concentration over a sufficient timeframe may be challenging due to honey liquidity and leakage. It has motivated researchers to integrate honey into diverse formulations, for example, hydrogels, dressings, ointments, pastes and lozenges. The antibacterial activity of these formulations should be scientifically determined to underscore claims of effectiveness. Some researchers have made efforts to adapt the disc carrier and suspension test to assess the antimicrobial activity of topical products (e.g., silver-based wound dressings). However, there is currently no established and validated method for determining the in vitro antimicrobial potential of natural product-based formulations, including those containing honey as the active principle. Against the backdrop of a brief discussion of the parameters that contribute to its antibacterial activity, this review provides an outline of the methods currently used for investigating the antibacterial activity of neat honey and discusses their limitations for application to honey-based formulations.

Light-activated molecular machines are fast-acting broad-spectrum antibacterials that target the membrane

The increasing occurrence of antibiotic-resistant bacteria and the dwindling antibiotic research and development pipeline have created a pressing global health crisis. Here, we report the discovery of a distinctive antibacterial therapy that uses visible (405 nanometers) light-activated synthetic molecular machines (MMs) to kill Gram-negative and Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus, in minutes, vastly outpacing conventional antibiotics. MMs also rapidly eliminate persister cells and established bacterial biofilms. The antibacterial mode of action of MMs involves physical disruption of the membrane. In addition, by permeabilizing the membrane, MMs at sublethal doses potentiate the action of conventional antibiotics. Repeated exposure to antibacterial MMs is not accompanied by resistance development. Finally, therapeutic doses of MMs mitigate mortality associated with bacterial infection in an in vivo model of burn wound infection. Visible light-activated MMs represent an unconventional antibacterial mode of action by mechanical disruption at the molecular scale, not existent in nature and to which resistance development is unlikely.

Epidemiology, Pathophysiology, and Management Strategies of Neonatal Wound Care

Guidelines for neonatal skin care are scarce, and there is no consensus on the best management practices for neonatal skin breakdown. This review presents the pathology and phases of wound healing, reasons for neonatal skin fragility, and approaches to recognition of commonly encountered neonatal wounds. This review also provides general strategies for neonatal wound prevention, care, dressing, and management to avoid further damage to the fragile neonatal skin. The importance and role of retaining moisture in expediting wound healing is discussed, as well as updated classifications on how to grade and assess pressure ulcers and the role of negative pressure wound therapy and silver dressings. Lastly, this review discusses prevention and treatment options for surgical wounds, intravenous extravasation wounds, congenital wounds, and thermal injuries, in addition to how to differentiate these wounds from the common diaper dermatitis and contact dermatitis.

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.

Fighting against the second wave of COVID-19: Can honeybee products help protect against the pandemic?

Coronavirus Disease (COVID-19) has infected people in 210 nations and has been declared a pandemic on March 12, 2020 by the World Health Organization (WHO). In the absence of effective treatment and/or vaccines for COVID-19, natural products of known therapeutic and antiviral activity could offer an inexpensive, effective option for managing the disease. Benefits of products of honey bees such as honey, propolis, and bee venom, against various types of diseases have been observed. Honey bees products are well known for their nutritional and medicinal values, they have been employed for ages for various therapeutic purposes. In this review, promising effects of various bee products against the emerging pandemic COVID-19 are discussed. Products of honey bees that contain mixtures of potentially active chemicals, possess unique properties that might help to protect, fight, and alleviate symptoms of COVID-19 infection.

Development and validation of a new microplate assay that utilises optical density to quantify the antibacterial activity of honeys including Jarrah, Marri and Manuka

The phenol equivalence assay is the current industry-adopted test used to quantify the antibacterial activity of honeys in Australia and New Zealand. Activity is measured based on the diffusion of honey through agar and resulting zone of growth inhibition. Due to differences in the aqueous solubilities of antibacterial compounds found in honeys, this method may not be optimal for quantifying activity. Therefore, a new method was developed based on the existing broth microdilution assay that is widely used for determining minimum inhibitory concentrations (MICs). It utilises the four organisms Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853, and an optical density endpoint to quantify bacterial growth. Decreases in bacterial growth in the presence of honey, relative to the positive growth control, are then used to derive a single value to represent the overall antibacterial activity of each honey. Antibacterial activity was quantified for a total of 77 honeys using the new method, the phenol equivalence assay and the standard broth microdilution assay. This included 69 honeys with undisclosed floral sources and the comparators Manuka, Jarrah (Eucalyptus marginata), Marri (Corymbia calophylla), artificial and multifloral honey. For the 69 honey samples, phenol equivalence values ranged from 0-48.5 with a mean of 34 (% w/v phenol). Mean MICs, determined as the average of the MICs obtained for each of the four organisms for each honey ranged from 7-24% (w/v honey). Using the new assay, values for the 69 honeys ranged from 368 to 669 activity units, with a mean of 596. These new antibacterial activity values correlated closely with mean MICs (R2 = 0.949) whereas the relationship with phenol equivalence values was weaker (R2 = 0.649). Limit of detection, limit of quantitation, measuring interval, limit of reporting, sensitivity, selectivity, repeatability, reproducibility, and ruggedness were also investigated and showed that the new assay was both robust and reproducible.

Honey: Another Alternative in the Fight against Antibiotic-Resistant Bacteria?

Antibacterial resistance has become a challenging situation worldwide. The increasing emergence of multidrug-resistant pathogens stresses the need for developing alternative or complementary antimicrobial strategies, which has led the scientific community to study substances, formulas or active ingredients used before the antibiotic era. Honey has been traditionally used not only as a food, but also with therapeutic purposes, especially for the topical treatment of chronic-infected wounds. The intrinsic characteristics and the complex composition of honey, in which different substances with antimicrobial properties are included, make it an antimicrobial agent with multiple and different target sites in the fight against bacteria. This, together with the difficulty to develop honey-resistance, indicates that it could become an effective alternative in the treatment of antibiotic-resistant bacteria, against which honey has already shown to be effective. Despite all of these assets, honey possesses some limitations, and has to fulfill a number of requirements in order to be used for medical purposes.

In vitro antibacterial activity of honey against multidrug-resistant Shigella sonnei

BACKGROUND AND PURPOSE

The health benefits of honey as an oral therapeutic agent for the treatment of diarrhoea caused by Shigella sonnei depend on the ability of honey to withstand human gastrointestinal conditions. This study aimed to investigate whether honey could withstand and inhibit the growth of Shigella sonnei under such conditions.

MATERIALS AND METHODS

We initially evaluated the survival of Shigella sonnei in human simulated gastric conditions (SGC) and simulated intestinal conditions (SIC). This was followed by determination of the susceptibility of Shigella sonnei to Manuka and Talah honey under gastrointestinal conditions. The colony forming units (CFU) of Shigella sonnei and minimum inhibitory concentrations (MICs) of honey were calculated.

RESULTS

Shigella sonnei was unable to survive in the acidic environment of the stomach without food matrix and survived only when inoculated with a food source, resulting in 1.5 × 10⁵ ± 0.2 CFU at 60 min and 1.7 × 10⁵ ± 0.3 CFU after 120 min of incubation. In SIC, it survived both with and without food matrix at the same CFU (1.2 × 10⁷ ±0.4) at 60 min and 1.7 × 10⁷ ±0.2 CFU after 120 min of incubation. Growth of Shigella sonnei was not observed in SGC in the presence of either honey at different concentrations without a food source. In the presence of a food source, Manuka honey inhibited the growth of Shigella sonnei at 10% v/v and Talah honey at 20% v/v dilutions in SGC. In SIC, Manuka honey inhibited the growth of Shigella sonnei at 15% and 20% v/v dilutions, whereas Talah honey inhibited Shigella sonnei at 20% and 25% v/v dilutions without and with food sources, respectively.

CONCLUSION

Shigella sonnei can survive in the acidic environment of the stomach if inoculated with a food source. Acidic pH and pepsin had no deleterious effects on the antibacterial capability of honey. However, bile reduced the antibacterial activity of honey in the intestinal environment.

Use of a model to understand the synergies underlying the antibacterial mechanism of H2O2-producing honeys

Honey has been valued as a powerful antimicrobial since ancient times. However, the understanding of the underlying antibacterial mechanism is incomplete. The complexity and variability of honey composition represent a challenge to this scope. In this study, a simple model system was used to investigate the antibacterial effect of, and possible synergies between, the three main stressors present in honey: sugars, gluconic acid, and hydrogen peroxide (H₂O₂), which result from the enzymatic conversion of glucose on honey dilution. Our results demonstrated that the synergy of H₂O₂ and gluconic acid is essential for the antibacterial activity of honey. This synergy caused membrane depolarization, destruction of the cell wall, and eventually growth inhibition of E. coli K-12. The presence of H₂O₂ stimulated the generation of other long-lived ROS in a dose-dependent manner. Sugars caused osmosis-related morphological changes, however, decreased the toxicity of the H₂O₂/gluconic acid. The susceptibility of catalase and general stress response sigma factor mutants confirmed the synergy of the three stressors, which is enhanced at higher H₂O₂ concentrations. By monitoring cellular phenotypic changes caused by model honey, we explained how this can be bactericidal even though the antimicrobial compounds which it contains are at non-inhibitory concentrations.

A current perspective on hydrogen peroxide production in honey. A review

Hydrogen peroxide plays a key role in honey antibacterial activity. The production of H₂O₂ in honey requires glucose oxidase (GOx) that oxidizes glucose to gluconolactone and reduces molecular oxygen to hydrogen peroxide. The content of GOx of honeybee origin was believed to be the main predictor of H₂O₂ concentration in honey. The observed variations in H₂O₂ levels among honeys questioned however the direct GOx-H₂O₂ relationship and left its absence opened for exploration. Here, we evaluated principal causes underlying the imbalance in the quantitative enzyme-product relationship with respect to: (a) enzyme and the product inactivation or destruction by honey compounds; (b) non-enzymatic pathway of H₂O₂ formation, and (c) a potential contribution of enzymes with GOx activity originating from nectars and microorganisms inhabiting honey. We also bring new facts on the relationship between honey colloidal structure and H₂O₂ production that change our traditional understanding of honey function as antimicrobial agent.

Plant extracts rich in polyphenols: antibacterial agents and natural preservatives for meat and meat products

Plant extracts contain large amounts of bioactive compounds, mainly polyphenols. Polyphenols inhibit the growth of microorganisms, especially bacteria. Their mechanism of action is still not fully understood but may be related to their chemical structure. They can cause morphological changes in microorganisms, damage bacterial cell walls and influence biofilm formation. Polyphenols also influence protein biosynthesis, change metabolic processes in bacteria cells and inhibit ATP and DNA synthesis (suppressing DNA gyrase). Due to the antioxidant and antibacterial activity of phenolic compounds, plant extracts offer an alternative to chemical preservatives used in the meat industry, especially nitrates (III). They can inhibit the growth of spoilage and pathogenic microflora, suppress oxidation of meat ingredients (lipids and proteins) and prevent discoloration. In this paper, we describe the factors that influence the content of polyphenols in plants and plant extracts. We present the antimicrobial activities of plant extracts and their mechanisms of action, and discuss the effects of plant extracts on the shelf-life of meat and meat products.

Relationship among the minor constituents, antibacterial activity and geographical origin of honey: A multifactor perspective

Some minor constituents of honey samples were determined through a fluorometric-chemical characterization method and related multifactorially with their antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa and with their geographical origin. Rotated principal component analysis identified five significant components in honey: three related to antibacterial activity and linked to phenolic compounds; Maillard products; proteins; the concentration of H₂O₂ at 3 and 24 h of incubation; and a tyrosine-containing entity. On the other hand, five constituents (phenolic compounds were the most relevant) allowed the classification of honey samples by geographical origin with 87% certainty. The results showed that phenolic compounds and Maillard products are related to the sustained production of H₂O₂ over time, which in turn boosts the antibacterial activity of honey. Native flora could promote this capability. The results showed the effect of geographic origin on the content of the analyzed minor constituents of honey, particularly phenolic compounds.

Dissecting the Antimicrobial Composition of Honey

Honey is a complex sweet food stuff with well-established antimicrobial and antioxidant properties. It has been used for millennia in a variety of applications, but the most noteworthy include the treatment of surface wounds, burns and inflammation. A variety of substances in honey have been suggested as the key component to its antimicrobial potential; polyphenolic compounds, hydrogen peroxide, methylglyoxal and bee-defensin 1. These components vary greatly across honey samples due to botanical origin, geographical location and secretions from the bee. The use of medical grade honey in the treatment of surface wounds and burns has been seen to improve the healing process, reduce healing time, reduce scarring and prevent microbial contamination. Therefore, if medical grade honeys were to be included in clinical treatment, it would reduce the demand for antibiotic usage. In this review, we outline the constituents of honey and how they affect antibiotic potential in a clinical setting. By identifying the key components, we facilitate the development of an optimally antimicrobial honey by either synthetic or semisynthetic production methods.

Anti-biofilm effects and characterisation of the hydrogen peroxide activity of a range of Western Australian honeys compared to Manuka and multifloral honeys

The antibacterial activity of honeys derived from the endemic flora of the southwest corner of Western Australia, including the trees Jarrah (Eucalyptus marginata) and Marri (Corymbia calophylla), remains largely unexplored. Investigation of these honeys showed minimum inhibitory concentrations (MICs) of 6.7-28.0% (w/v) against Gram positive and negative bacteria. Honey solutions showed enhanced antibacterial activity after hydrogen peroxide was allowed to accumulate prior to testing, with a mean MIC after accumulation of 14.3% compared to 17.4% before accumulation. Antibacterial activity was reduced after treatment with catalase enzyme, with a mean MIC of 29.4% with catalase compared to 15.2% without catalase. Tests investigating the role of the Gram negative outer membrane in honey susceptibility revealed increases in activity after destabilisation of the outer membrane. Honeys reduced both the formation of biofilm and the production of bacterial pigments, which are both regulated by quorum sensing. However, these reductions were closely correlated with global growth inhibition. Honey applied to existing biofilms resulted in decreased metabolic activity and minor decreases in viability. These results enhance our understanding of the mechanisms of antibacterial action of Jarrah and Marri honeys, and provide further support for the use of honey in the treatment of infected wounds.

Advanced strategies for combating bacterial biofilms

Biofilms are communities of microorganisms that are formed on and attached to living or nonliving surfaces and are surrounded by an extracellular polymeric material. Biofilm formation enjoys several advantages over the pathogens in the colonization process of medical devices and patients' organs. Unlike planktonic cells, biofilms have high intrinsic resistance to antibiotics and sanitizers, and overcoming them is a significant problematic challenge in the medical and food industries. There are no approved treatments to specifically target biofilms. Thus, it is required to study and present innovative and effective methods to combat a bacterial biofilm. In this review, several strategies have been discussed for combating bacterial biofilms to improve healthcare, food safety, and industrial process.

In vitro evaluation of methicillin-resistant and methicillin-sensitive Staphylococcus aureus susceptibility to Saudi honeys

Background

Honey has been increasingly recognized as a potential therapeutic agent for treatment of wound infections. There is an urgent need for assessment and evaluation of the antibacterial properties against wound pathogens of honeys that have not yet been tested.

Methods

Ten Saudi honeys collected from different geographical locations were screened initially for their antibacterial potential against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA) by the agar well diffusion method. Manuka honey (UMF-12) was used for comparison. Of the tested honeys, the honey that exhibited the greatest antibacterial activity in the agar well diffusion assay was further evaluated for its minimum inhibitory concentration (MIC) against ten MRSA clinical isolates and three American Type Culture Collection (ATCC) reference strains by the microbroth dilution method.

Results

Locally produced honeys exhibited variable antibacterial activity against the tested isolates in the agar well diffusion assay. They were unable to exhibit antibacterial activity against MSSA and MRSA at 25% dilutions (w/v) in catalase solution. However, Sumra and Talha honeys showed a zone of inhibition at 50% dilutions (w/v) in catalase solution. This finding means that both honeys possess weak non-peroxide-based antibacterial activity. Moreover, Sumra honey showed a larger inhibition zone at 50 and 25% dilutions (w/v) in distilled water than Manuka honey against both MSSA and MRSA. This result demonstrates that Sumra honey has more hydrogen peroxide-related antibacterial activity or total antibacterial activity than Manuka honey. In addition, MIC results obtained through a microbroth dilution assay showed that Sumra honey inhibited the growth of all MRSA clinical isolates (n = 10) and reference strains [MRSA (ATCC 43300) and MSSA (ATCC 29213)] at lower concentrations (12.0% v/v) than those required for Manuka honey-mediated inhibition (14.0% v/v). This result means that Sumra honey has more peroxide or synergistic antibacterial activity than Manuka honey. An equivalent MIC (15.0% v/v) was observed for E. coli (ATCC 25922) between Manuka honey and Sumra honey.

Conclusions

Sumra honey may be used as an alternative therapeutic agent for infected wounds and burns, where additional hydrogen peroxide-related antibacterial activity is needed. In the future, the physiochemical characteristics of Sumra honey may be evaluated and standardized.

Use of an engineered honey to eradicate preformed biofilms of important wound pathogens: an in vitro study

OBJECTIVE

We previously reported on the ability of SurgihoneyRO (SHRO), an engineered honey, to prevent biofilm formation in vitro, but data were lacking regarding the activity against preformed biofilms. This study aims to assess whether SHRO has any antibacterial activity against mature, preformed biofilms and whether there is any evidence to support the observed clinical effectiveness when SHRO has been used anecdotally on acute and chronic wounds where biofilm is most likely present.

METHOD

We tested the in vitro antibacterial activity of SHRO against the mature biofilms of 16 clinically relevant wound pathogens, in terms of impacts on biofilm seeding and biofilm biomass. The honey was serially double diluted from 1:3 down to 1:6144, and the lowest dilution achieving a statistically significant reduction in biomass of ≥50%, compared with untreated controls, was recorded.

RESULTS

All 16 bacterial isolates were susceptible to SHRO, with reduced biofilm seeding observed for all, and percentage reductions ranging from 58% (ACI_C59) to 94.3% (MDR_B) for the strongest concentration of honey (1:3). Furthermore at this concentration, biofilm seeding of the test biofilm was reduced by 80-94.3% (when compared with the positive control) for 12/16 isolates. We additionally demonstrated that SHRO has antibiofilm impacts, with the 24 hour exposure resulting in disruption of the biofilm, reduced seeding and reduced biomass.

CONCLUSION

SHRO is effective at reducing seeding of preformed biofilms of clinically important wound pathogens in vitro, and also has antibiofilm activity. This supports the anecdotal clinical data for antibiofilm efficacy, and supports the use of SHRO as a promising topical wound care agent.

Antibacterial Potency of Honey

Despite the developments in controlling infectious disease around the world, they are still the second biggest cause of morbidity and mortality due in part to the increase in drug resistance among large numbers of the bacterial strains. This means that new strategies are needed to prevent and treat infectious disease. As a result, several ancient methods have been re-evaluated and the substances/procedures employed historically to cure diseases are now attracting renewed scientific attention. Honey is one such product that used to be widely used to combat bacteria. This review covers the antibacterial activity of honey, its use in the treatment of infection and diseases, and the features that are relevant to its activity.

Antibacterial Activity of Different Blossom Honeys: New Findings

Antibacterial activity is the most investigated biological property of honey. The goal of this study was to evaluate the antibacterial activity of 57 Slovak blossom honeys against Staphylococcus aureus and Pseudomonas aeruginosa and investigate the role of several bioactive substances in antibacterial action of honeys. Inhibitory and bactericidal activities of honeys were studied to determine the minimum inhibitory and bactericidal concentrations. The contents of glucose oxidase (GOX) enzyme, hydrogen peroxide (H2O2), and total polyphenols (TP) were determined in honeys. We found that honey samples showed different antibacterial efficacy against the tested bacteria as follows: wildflower honeys > acacia honeys > rapeseed honeys. Overall antibacterial activity of the honeys was statistically-significantly correlated with the contents of H2O2 and TP in honeys. A strong correlation was found between the H2O2 and TP content. On the other hand, no correlation was found between the content of GOX and level of H2O2. Antibacterial activity of 12 selected honeys was markedly reduced by treatment with catalase, but it remained relatively stable after inactivation of GOX with proteinase-K digestion. Obtained results suggest that the antibacterial activity of blossom honeys is mainly mediated by H2O2 levels present in honeys which are affected mainly by polyphenolic substances and not directly by GOX content.

Study of the Anti-Staphylococcal Potential of Honeys Produced in Northern Poland

The antimicrobial activity of 144 samples of honeys including 95 products from apiaries located in Northern Poland was evaluated. The antibacterial activity of those natural products, their thermal stability, and activity in the presence of catalase was investigated by microdilution assays in titration plates. The MTT assay was performed for the determination of anti-biofilm activity. Spectrophotometric assays were used for the determination of antioxidant potential, total phenolic content, and ability to generate hydrogen peroxide. Some of the investigated honeys exhibited surprisingly high antimicrobial, especially anti-staphylococcal, potential, with Minimal Inhibitory Concentration (MIC) values of only 1.56% (v/v). Much higher resistance was observed in the case of staphylococci growing as biofilms. Lower concentrations of the product, up to 12.5% (v/v) stimulated its growth and effective eradication of biofilm required concentration of at least 25% (v/v). Hydrogen peroxide has been identified as a crucial contributor to the antimicrobial activity of honeys supplied by Polish beekeepers. However, some of the results suggest that phytochemicals, especially polyphenols, play an important role depending on botanical source (both positive, e.g., in the case of buckwheat honeys as well as negative, e.g., in the case of some rapeseed honeys) in their antimicrobial potential.

Role of Honey in Topical and Systemic Bacterial Infections

BACKGROUND

The development of bacterial resistance to antibiotics has made it more difficult and expensive to treat infections. Honey is getting worldwide attention as a topical therapeutic agent for wound infections and potential future candidate for systemic infections.

OBJECTIVES

The purpose of this review was to summarise different antibacterial bio-active compounds in honey, their synergistic interaction and their clinical implications in topical and systemic infections. In addition, contemporary testing methods for evaluating peroxide and non-peroxide antibacterial activity of honey were also critically appraised.

DESIGN

MEDLINE, EMBASE, Cochrane Library, Pub Med, reference lists and databases were used to review the literature.

RESULTS

Honey contains several unique antibacterial components. These components are believed to act on diverse bacterial targets, are broad spectrum, operate synergistically, prevent biofilm formation, and decrease production of virulence factors. Moreover, honey has the ability to block bacterial communication (quorum sensing), and therefore, it is unlikely that bacteria develop resistance against honey. Bacterial resistance against honey has not been documented so far. Unlike conventional antibiotics, honey only targets pathogenic bacteria without disturbing the growth of normal gastrointestinal flora when taken orally. It also contains prebiotics, probiotics, and zinc and enhances the growth of beneficial gut flora. The presence of such plethora of antibacterial properties in one product makes it a promising candidate not only in wound infections but also in systemic and particularly for gastrointestinal infections. Agar diffusion assay, being used for evaluating antibacterial activity of honey, is not the most appropriate and sensitive assay as it only detects non-peroxide activity when present at a higher level. Therefore, there is a need to develop more sensitive techniques that may be capable of detecting and evaluating different important components in honey as well as their synergistic interaction.

CONCLUSIONS

Keeping in view the current guidelines for treatment of diarrhea, honey is considered one of the potential candidates for treatment of diarrhea because it contains a natural combination of probiotics, prebiotics, and zinc. Therefore, it would be worthwhile if such a combination is tested in RCTs for treatment of diarrhea.

Pt-Decorated MWCNTs-Ionic Liquid Composite-Based Hydrogen Peroxide Sensor To Study Microbial Metabolism Using Scanning Electrochemical Microscopy

Hydrogen peroxide (H2O2) is a highly relevant metabolite in many biological processes, including the oral microbiome. To study this metabolite, we developed a 25 μm diameter, highly sensitive, nonenzymatic H2O2 sensor with a detection limit of 250 nM and a broad linear range of 250 nM to 7 mM. The sensor used the synergistic activity of the catalytically active Pt nanoparticles on a high surface area multiwalled carbon nanotube and conducting ionic liquid matrix to achieve high sensitivity (2.4 ± 0.24 mA cm-2 mM-1) for H2O2 oxidation. The unique composite allowed us to miniaturize the sensor and couple it with a Pt electrode (25 μm diameter each) for use as a dual scanning electrochemical microscopy probe. We could detect 65 ± 10 μM H2O2 produced by Streptococcus gordonii (Sg) in a simulated biofilm at 50 μm above its surface in the presence of 1 mM glucose and artificial saliva solution (pH 7.2 at 37 °C). Because of its high stability and low detection limit, the sensor showed a promising chemical image of H2O2 produced by Sg biofilms. We were also able to detect 30 μM H2O2 at 50 μm above the biofilm in the presence of the H2O2-decomposing salivary lactoperoxidase and thiocyanate, which would not otherwise be possible using an existing H2O2 assay. Thus, this sensor can potentially find applications in the study of other important biological processes in a complex matrix where circumstances demand a low detection limit in a compact space.

MIC and MBC of Honey and Gold Nanoparticles against methicillin-resistant (MRSA) and vancomycin-resistant (VRSA) coagulase-positive S. aureus isolated from contagious bovine clinical mastitis

Staphylococcus aureus is one of the major causative agents of the bovine clinical mastitis. This study aimed to isolate and identify S. aureus from cases of bovine clinical mastitis followed by phenotypic detection of MRSA and VRSA. The genotypic detection of MRSA was done through PCR detection of the resistance mecA gene. Furthermore, this study aimed to investigate the in vitro MIC and MBC of the Dodonaea angustifolia plant extract, Honey, and AuNPs against the clinically isolated MRSA and VRSA. Of 93 mastitis milk samples examined, 54 (58.1%) S. aureus were isolated and identified {CP S. aureus = 46 (85.2%) and CN S. aureus = 8 (14.8%)}. The whole MRSA, VRSA, MSSA, and VSSA detected were 19 (35.2%), 7 (13%), 35 (65%), and 47 (87%) respectively. The mean counts of S. aureus were between 8.6 × 104 ± 3.5 × 105 CFU/ml. The oxacillin and vancomycin MICs against MRSA and VRSA respectively, were >256 µg/ml. AuNPs sized 30 nm produce observable in vitro anti-MRSA and anti-VRSA activities. Imtenan® citrus blossom honey has also antibacterial activities against MRSA and VRSA with general MBC and MIC range values were observed at a concentration of 0.625, 1.25, 2.5, and 5 (%v/v). In the present study, the most significant result obtained when AuNPs was mixed with Imtenan® citrus blossom honey (1:1 = v:v) with the best MBC was observed at the concentration of 0.56 × 109:0.3 (NP/ml: honey %v/v).

Honey-sensitive Pseudomonas aeruginosa mutants are impaired in catalase A

The antimicrobial power of honey seems to be ascribable to several factors, including oxidative and osmotic stress. The aim of this study was to find genetic determinants involved in the response to honey stress in the opportunistic pathogen Pseudomonas aeruginosa, chosen as model micro-organism. A library of transposon mutants of P. aeruginosa PAO1 was constructed and only four mutants unable to grow in presence of fir honeydew honey were selected. All four mutants were impaired in the major H2O2-scavenging enzyme catalase A (KatA). The knockout of katA gene caused sensitivity, as expected, not only to hydrogen peroxide but also to different types of honey including Manuka GMO 220 honey. Genetic complementation, as well as the addition of PAO1 supernatant containing extracellular catalase, restored tolerance to honey stress in all the mutants. As P. aeruginosa PAO1 catalase KatA copes with H2O2 stress, it is conceivable that the antimicrobial activity of honey is, at least partially, due to the presence of hydrogen peroxide in honey or the ability of honey to induce production of hydrogen peroxide. The katA-deficient mutants could be used as tester micro-organisms to compare the power of different types of natural and curative honeys in eliciting oxidative stress mediated by hydrogen peroxide.

Honey glycoproteins containing antimicrobial peptides, Jelleins of the Major Royal Jelly Protein 1, are responsible for the cell wall lytic and bactericidal activities of honey

We have recently identified the bacterial cell wall as the cellular target for honey antibacterial compounds; however, the chemical nature of these compounds remained to be elucidated. Using Concavalin A-affinity chromatography, we found that isolated glycoprotein fractions (glps), but not flow-through fractions, exhibited strong growth inhibitory and bactericidal properties. The glps possessed two distinct functionalities: (a) specific binding and agglutination of bacterial cells, but not rat erythrocytes and (b) non-specific membrane permeabilization of both bacterial cells and erythrocytes. The isolated glps induced concentration- and time-dependent changes in the cell shape of both E. coli and B. subtilis as visualized by light and SEM microscopy. The appearance of filaments and spheroplasts correlated with growth inhibition and bactericidal effects, respectively. The time-kill kinetics showed a rapid, >5-log10 reduction of viable cells within 15 min incubation at 1xMBC, indicating that the glps-induced damage of the cell wall was lethal. Unexpectedly, MALDI-TOF and electrospray quadrupole time of flight mass spectrometry, (ESI-Q-TOF-MS/MS) analysis of glps showed sequence identity with the Major Royal Jelly Protein 1 (MRJP1) precursor that harbors three antimicrobial peptides: Jelleins 1, 2, and 4. The presence of high-mannose structures explained the lectin-like activity of MRJP1, while the presence of Jelleins in MRJP1 may explain cell wall disruptions. Thus, the observed damages induced by the MRJP1 to the bacterial cell wall constitute the mechanism by which the antibacterial effects were produced. Antibacterial activity of MRJP1 glps directly correlated with the overall antibacterial activity of honey, suggesting that it is honey's active principle responsible for this activity.

Evaluation of the antibacterial activity of selected Pakistani honeys against multi-drug resistant Salmonella typhi

Background

The development of resistance to conventional anti-typhoid drugs and the recent emergence of fluoroquinolone resistance have made it very difficult and expensive to treat typhoid fever. As the therapeutic strategies become even more limited, it is imperative to investigate non-conventional modalities. In this context, honey is a potential candidate for combating antimicrobial resistance because it contains a broad repertoire of antibacterial compounds which act synergistically at multiple sites, thus making it less likely that the bacteria will become resistant. The in vitro antibacterial activity of 100 unifloral honey samples against a blood culture isolate of multi-drug resistant (MDR) Salmonella typhi were investigated.

Methods

All honey samples were evaluated for both total (acidity, osmolarity, hydrogen peroxide and non-peroxide activity) and plant derived non-peroxide antibacterial activity by agar well diffusion assay at 50% and 25% dilution in sterile distilled water and 25% in catalase solution. Manuka (Unique Manuka Factor-21) honey was used for comparison. The phenol equivalence of each honey sample from 2% to 7% (w/v) phenol was obtained from regression analysis. The antibacterial potential of each honey sample was expressed as its equivalent phenol concentration. The honey samples which showed antibacterial activity equivalent to or greater than manuka honey were considered therapeutically active honeys.

Results

Nineteen honey samples (19%) displayed higher hydrogen peroxide related antibacterial activity (16–20% phenol), which is more than that of manuka honey (21-UMF). A total of 30% of the honey samples demonstrated antibacterial activity between 11 and 15% phenol similar to that of manuka honey while 51% of the honey samples did not exhibit any zone of inhibition against MDR-S. typhi at 50% (w/v) dilution. None of the indigenous honey samples displayed non-peroxide antibacterial activity. Only manuka honey showed non-peroxide antibacterial activity at 25% dilution (w/v) in catalase solution.

Conclusions

The honey samples which displayed antibacterial activity equal to or greater than manuka honey may be useful in the clinical conditions where higher hydrogen peroxide related antibacterial activity is required. Manuka honey, which is known to possess non-peroxide antibacterial activity, warrants further evaluation in a suitable typhoid animal model.

Antibiotic-specific differences in the response of Staphylococcus aureus to treatment with antimicrobials combined with manuka honey

Skin infections caused by antibiotic resistant Staphylococcus aureus are a significant health problem worldwide; often associated with high treatment cost and mortality rate. Complex natural products like New Zealand (NZ) manuka honey have been revisited and studied extensively as an alternative to antibiotics due to their potent broad-spectrum antimicrobial activity, and the inability to isolate honey-resistant S. aureus. Previous studies showing synergistic effects between manuka-type honeys and antibiotics have been demonstrated against the growth of one methicillin-resistant S. aureus (MRSA) strain. We have previously demonstrated strong synergistic activity between NZ manuka-type honey and rifampicin against growth and biofilm formation of multiple S. arueus strains. Here, we have expanded our investigation using multiple S. aureus strains and four different antibiotics commonly used to treat S. aureus-related skin infections: rifampicin, oxacillin, gentamicin, and clindamycin. Using checkerboard microdilution and agar diffusion assays with S. aureus strains including clinical isolates and MRSA we demonstrate that manuka-type honey combined with these four antibiotics frequently produces a synergistic effect. In some cases when synergism was not observed, there was a significant enhancement in antibiotic susceptibility. Some strains that were highly resistant to an antibiotic when present alone become sensitive to clinically achievable concentrations when combined with honey. However, not all of the S. aureus strains tested responded in the same way to these combinational treatments. Our findings support the use of NZ manuka-type honeys in clinical treatment against S. aureus-related infections and extend their potential use as an antibiotic adjuvant in combinational therapy. Our data also suggest that manuka-type honeys may not work as antibiotic adjuvants for all strains of S. aureus, and this may help determine the mechanistic processes behind honey synergy.

A pilot study investigating lactic acid bacterial symbionts from the honeybee in inhibiting human chronic wound pathogens

Treatment and management of chronic wounds is a large burden on the health sector and causes substantial suffering for the patients. We believe that 13 lactic acid bacteria (LAB) symbionts isolated from the honey crop of the honeybee are important players in the antimicrobial action of honey, by producing antimicrobial substances and can be used in combination with heather honey as an effective treatment in wound management. A total of 22 patients with chronic ulcers were included; culture-dependent and molecular-based (MALDI-MS and 16S rRNA gene sequencing) techniques were used to identify bacteria from chronic wounds. These clinical isolates were used for in vitro antimicrobial testing with standardised viable LAB and sterilised heather honey mixture. Twenty of the patients' wounds were polymicrobial and 42 different species were isolated. Patient isolates that were tested in vitro were inhibited by the LAB and honey combination with inhibitory zones comparable with different antibiotics. LAB and heather honey in combination presents a new topical option in chronic wound management because of the healing properties of honey, antimicrobial metabolite production from the LAB and their bactericidal effect on common chronic wound pathogens. This new treatment may be a stepping stone towards an alternative solution to antibiotics.

Antibacterial compounds of Canadian honeys target bacterial cell wall inducing phenotype changes, growth inhibition and cell lysis that resemble action of β-lactam antibiotics

Honeys show a desirable broad spectrum activity against Gram-positive and negative bacteria making antibacterial activity an intrinsic property of honey and a desirable source for new drug development. The cellular targets and underlying mechanism of action of honey antibacterial compounds remain largely unknown. To facilitate the target discovery, we employed a method of phenotypic profiling by directly comparing morphological changes in Escherichia coli induced by honeys to that of ampicillin, the cell wall-active β-lactam of known mechanism of action. Firstly, we demonstrated the purity of tested honeys from potential β-lactam contaminations using quantitative LC-ESI-MS. Exposure of log-phase E. coli to honey or ampicillin resulted in time- and concentration-dependent changes in bacterial cell shape with the appearance of filamentous phenotypes at sub-inhibitory concentrations and spheroplasts at the MBC. Cell wall destruction by both agents, clearly visible on microscopic micrographs, was accompanied by increased permeability of the lipopolysaccharide outer membrane as indicated by fluorescence-activated cell sorting (FACS). More than 90% E. coli exposed to honey or ampicillin became permeable to propidium iodide. Consistently with the FACS results, both honey-treated and ampicillin-treated E. coli cells released lipopolysaccharide endotoxins at comparable levels, which were significantly higher than controls (p<0.0001). E. coli cells transformed with the ampicillin-resistance gene (β-lactamase) remained sensitive to honey, displayed the same level of cytotoxicity, cell shape changes and endotoxin release as ampicillin-sensitive cells. As expected, β-lactamase protected the host cell from antibacterial action of ampicillin. Thus, both honey and ampicillin induced similar structural changes to the cell wall and LPS and that this ability underlies antibacterial activities of both agents. Since the cell wall is critical for cell growth and survival, honey active compounds would be highly applicable for therapeutic purposes while differences in the mode of action between honey and ampicillin may provide clinical advantage in eradicating β-lactam-resistant pathogens.

Methylglyoxal may affect hydrogen peroxide accumulation in manuka honey through the inhibition of glucose oxidase

Although hydrogen peroxide (H₂O₂) is one of the major antibacterial factors in most honeys, it does not accumulate in medical-grade manuka honey. The goal of this study was to investigate the effect of artificially added methylglyoxal (MGO) on H₂O₂ accumulation in natural non-manuka honeys. H₂O₂ concentrations in the honey solutions were determined using a fluorimetric assay. Two, the most potent H₂O₂ producers honeydew honeys were mixed with MGO at final concentrations of 250, 500, and 1000 mg/kg, and incubated for 4 days at 37°C. Subsequently, H₂O₂ concentrations were determined in 50% (wt/vol) MGO supplemented honey solutions. In vitro crosslinking of the enzyme glucose oxidase (GOX) after incubation with MGO was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tested honeys at a concentration of 50% (wt/vol) accumulated up to 495.8±9.1 μM H₂O₂ in 24 h. The most potent producers were the two honeydew honeys, whose 50% solutions accumulated 306.9±6.8 and 495.8±9.1 μM H₂O₂, respectively. Levels of H₂O₂ increased significantly over time in both honey solutions. Contrary to this, the MGO-treated honeys generated significantly lower amounts of H₂O₂ (P<.001), and this reduction was dose dependent. In addition, MGO-treated GOX formed high molecular weight adducts with increasing time of incubation accompanied by loss of its enzymatic activity. High levels of MGO in manuka honey, by modifying the enzyme GOX, might be responsible for suppressing H₂O₂ generation. These data highlight the detrimental effect of MGO on significant proteinaceous components of manuka honey.

A new look on protein-polyphenol complexation during honey storage: is this a random or organized event with the help of dirigent-like proteins?

Honey storage initiates melanoidin formation that involves a cascade of seemingly unguided redox reactions between amino acids/proteins, reducing sugars and polyphenols. In the process, high molecular weight protein-polyphenol complexes are formed, but the mechanism involved remains unknown. The objective of this study was twofold: to determine quantitative and qualitative changes in proteins in honeys stored for prolonged times and in different temperatures and to relate these changes to the formation of protein-polyphenol complexes. Six -month storage decreased the protein content by 46.7% in all tested honeys (t-test, p<0.002) with the rapid reduction occurring during the first three month. The changes in protein levels coincided with alterations in molecular size and net charge of proteins on SDS -PAGE. Electro-blotted proteins reacted with a quinone-specific nitro blue tetrazolium (NBT) on nitrocellulose membranes indicating that quinones derived from oxidized polyphenols formed covalent bonds with proteins. Protein-polyphenol complexes isolated by size-exclusion chromatography differed in size and stoichiometry and fall into two categories: (a) high molecular weight complexes (230-180 kDa) enriched in proteins but possessing a limited reducing activity toward the NBT and (b) lower molecular size complexes (110-85 kDa) enriched in polyphenols but strongly reducing the dye. The variable stoichiometry suggest that the large, "protein-type" complexes were formed by protein cross-linking, while in the smaller, "polyphenol-type" complexes polyphenols were first polymerized prior to protein binding. Quinones preferentially bound a 31 kDa protein which, by the electrospray quadrupole time of flight mass spectrometry (ESI-Qtof-MS) analysis, showed homology to dirigent-like proteins known for assisting in radical coupling and polymerization of phenolic compounds. These findings provide a new look on protein-polyphenol interaction in honey where the reaction of quinones with proteins and polyphenols could possibly be under assumed guidance of dirigent proteins.

Antimicrobial strategies centered around reactive oxygen species--bactericidal antibiotics, photodynamic therapy, and beyond

Reactive oxygen species (ROS) can attack a diverse range of targets to exert antimicrobial activity, which accounts for their versatility in mediating host defense against a broad range of pathogens. Most ROS are formed by the partial reduction in molecular oxygen. Four major ROS are recognized comprising superoxide (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), and singlet oxygen ((1)O2), but they display very different kinetics and levels of activity. The effects of O2•- and H2O2 are less acute than those of •OH and (1)O2, because the former are much less reactive and can be detoxified by endogenous antioxidants (both enzymatic and nonenzymatic) that are induced by oxidative stress. In contrast, no enzyme can detoxify •OH or (1)O2, making them extremely toxic and acutely lethal. The present review will highlight the various methods of ROS formation and their mechanism of action. Antioxidant defenses against ROS in microbial cells and the use of ROS by antimicrobial host defense systems are covered. Antimicrobial approaches primarily utilizing ROS comprise both bactericidal antibiotics and nonpharmacological methods such as photodynamic therapy, titanium dioxide photocatalysis, cold plasma, and medicinal honey. A brief final section covers reactive nitrogen species and related therapeutics, such as acidified nitrite and nitric oxide-releasing nanoparticles.