Katherine A. Hammer

University of Western Australia | UWA · School of Biomedical Sciences

With the steady rise in antifungal resistance amongst clinically important yeasts, antifungal drug discovery remains of the utmost importance. To determine the potential of some honeys as alternative antifungal agents, we quantified the antifungal activity of 12 Western Australian honey samples, two Manuka honey samples and an artificial honey agai...

This study is the first to report on the presence of oestrogenic compounds in different clover flower nectar samples, in bee-deposited nectars collected from hive combs (unripe honey) and in mature honeys harvested from the same hives. The clover species investigated were two red clover (Trifolium pratense) cultivars, bred specifically for high iso...

This paper reports on some physicochemical and phytochemical characteristics (i. e. pH, electrical conductivity, colour, moisture content, total phenolic content, sugar profile) and in vitro antioxidant activity of honeys harvested from five legume species, red clover ( Trifolium pratense ), balansa clover ( T. michelianum ), Persian clover ( T. re...

The aim of this study was to assess the release profile of components in five different honeys (a New Zealand Manuka and two Western Australian honeys, a Jarrah honey and a Coastal Peppermint honey) and their corresponding honey-loaded gel formulations using a custom-designed Franz-type diffusion cell in combination with High-Performance Thin-Layer...

Aims: This study aimed to evaluate the effects of storage and different temperatures on the antibacterial activity and physicochemical characteristics of several types of honey. Methods and results: Honeys stored for 16 weeks at 37°C and 45°C showed significant declines in antibacterial activity determined by minimum inhibitory concentrations, t...

This study presents data on the antioxidant and antibacterial activities of honey-based topical formulations incorporating four Western Australian (WA) honeys along with New Zealand Manuka honey as a comparator honey. The antioxidant activity of the pure honeys and the various honey-loaded topical formulations were assessed by the ferric reducing a...

Honey has widespread use as a nutritional supplement and flavouring agent. Its diverse bioactivities, including antioxidant, antimicrobial, antidiabetic, anti-inflammatory, and anticancer properties, have also made it an aspirant natural product for therapeutic applications. Honey is highly viscous and very sticky, and its acceptance as a medicinal...

Methylglyoxal (MGO) is considered to be one of the vital components responsible for the anti-bacterial activity of Leptospermum spp. (Manuka) honey. While many studies have demonstrated a dose-dependent antibacterial activity for MGO in vitro, from a therapeutic viewpoint, it is also important to confirm its release from Manuka honey and also from...

This study reports on the total phenolic content and antioxidant activity as well as the phenolic compounds that are present in Calothamnus spp. (Red Bell), Agonis flexuosa (Coastal Peppermint), Corymbia calophylla (Marri) and Eucalyptus marginata (Jarrah) honeys from Western Aus-tralia. The honey's total phenolic content (TPC) was determined using...

Honeys are commonly subjected to a series of post-harvest processing steps, such as filtration and/or radiation treatment and heating to various temperatures, which might affect their physicochemical properties and bioactivity levels. Therefore, there is a need for robust quality control assessments after honey processing and storage to ensure that...

Impetigo is a contagious skin disease caused by Staphylococcus aureus and Streptococcus pyogenes. Without treatment, impetigo may be recurrent, develop into severe disease, or have serious, life-threatening sequelae. Standard treatment consists of topical or systemic antibiotic therapy (depending on severity), however, due to antibiotic resistance...

Multidrug resistant (MDR) P. aeruginosa accounts for 35% of all P. aeruginosa isolated from respiratory samples of patients with cystic fibrosis (CF). The usefulness of β-lactam antibiotics for treating CF, such as carbapenems and later generation cephalosporins, is limited by the development of antibacterial resistance. A proven treatment approach...

This study reports on the development and validation of a HPTLC-derived database to identify phenolic compounds in honey. Two database sets are developed to contain the profiles of 107 standard compounds. Rich data in the form of Rf values, colour hues (H°) at 254 nm and 366 nm, at 366 nm after derivatising with natural product PEG reagent, and at...

The aim of this study was to optimise the so-called agar overlay assay to investigate the antimicrobial activity of some currently available topical antimicrobial products against a range of Gram positive and Gram negative bacteria. During the optimisation process, various assay parameters including base agar volume, overlay agar volume, overlay ag...

Background Honey has broad spectrum antibacterial activity against clinically important organisms and may be suitable for treating superficial bacterial infections. However, very little data are available describing potential interactions between honey and other topically applied agents such as antiseptics or essential oils. Methods Interactions b...

Variation in the antibacterial potency of manuka honey has been reported in several published studies. However, many of these studies examine only a few honey samples, or test activity against only a few bacterial isolates. To address this deficit, a collection of 29 manuka/Leptospermum honeys was obtained, comprising commercial manuka honeys from...

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 activit...

This review covers a comprehensive overview of the phytoconstituents and bioactivities reported to date for clover honeys produced from various Trifolium spp. against the backdrop of a more general discussion of the chemistry and bioactivity of these important agricultural species. While research into the phytochemical composition of various honeys...

Honeys produced by Apis mellifera from different flowering plants can vary widely in their characteristics. Some floral sources yield honeys with especially high antibacterial and/or antioxidant activity, which may be candidates for further evaluation as therapeutic agents. This study investigated 115 honeys harvested from three Western Australian...

The aim of this review is to provide a comprehensive overview of the large variety of phenolic compounds that have to date been identified in a wide range of monofloral honeys found globally. The collated information is structured along several themes, including the botanical family and genus of the monofloral honeys for which phenolic constituents...

This study reports on the analysis of eleven Jarrah (Eucalyptus marginata) honeys, of which nearly half (n = 5) were re-classified as Blackbutt (E. patens) honey on the grounds of the predominant flower pollen identified by melissopalynology. Based on a comprehensive analysis of the honeys’ physico- and phytochemical characteristics and antioxidant...

Background Honey is considered as a functional food with health-promoting properties. Its potent antibacterial and antibiofilm effects are the major attributes of so called ‘medical-grade honey’ which is topically used for the treatment of burns, wounds and skin disorders. Nevertheless, the current set of honey quality parameters adopted in the Eur...

Broth microdilution assays were used to determine minimum inhibitory concentrations (MICs) and fractional inhibitory concentration indices (FICIs) of tea tree oil (TTO), tobramycin, colistin, and aztreonam against clinical cystic fibrosis-associated P. aeruginosa (CFPA) isolates (n=20). The minimum biofilm eradication concentration (MBEC) and fract...

Clostridioides (also known as Clostridium) difficile is a Gram-positive anaerobic, spore producing bacterial pathogen that causes severe gastrointestinal infection in humans. The current chemotherapeutic options are inadequate, expensive, and limited, and thus inexpensive drug treatments for C. difficile infection (CDI) with improved efficacy and s...

In this paper, we describe a novel approach to the development of a reference standard for the quality control of complex natural products, which will assist in the assessment of their authenticity and purity. The proposed method provides a template for the selection of samples, which can be pooled to obtain a reference standard. A shortfall of suc...

This paper presents the findings of a comprehensive review on common bee pollen processing methods which can impact extraction efficiency and lead to differences in measured total phenolic content (TPC) and radical scavenging activity based on 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) data. This hampers the c...

Honey, a concentrated natural product, is produced by honeybees (Apis mellifera) from the nectar of flowers. It contains over 200 compounds that exert various biological or pharmacological activities, ranging from antioxidant, anti-inflammatory, antimicrobial, and antihypertensive to hypoglycemic effects. Due to the presence of a plethora of bioact...

The use of High-Performance Thin-Layer Chromatography (HPTLC) coupled with the use of DPPH* (2,2-diphenyl-1-picrylhydrazyl) as a derivatisation reagent is a novel approach to the analysis of antioxidant activity of honeys. The method facilitates the visualisation of individual constituents that contribute to the overall antioxidant activity of the...

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, th...

Honey adulteration, where a range of sugar syrups is used to increase bulk volume, is a common problem that has significant negative impacts on the honey industry, both economically and from a consumer confidence perspective. This paper investigates High-Performance Thin Layer Chromatography (HPTLC) for the authentication and detection of sugar adu...

Sugars, in particular glucose and fructose, are the main constituents of honey, comprising up to 85% of its total weight. A high-performance thin-layer chromatography (HPTLC) method to identify and quantify common sugars (glucose, fructose and sucrose) in honey has been developed and fully validated according to the International Conference on Harm...

Using honey as a model sample, the aim of this study is to develop and validate a simple, rapid screening tool that allows for the visualization of constituents that contribute to the antioxidant activity of a complex natural product and to quantify their individual antioxidant effects even if their chemical identity is unknown. The method employs...

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 ne...

Clostridioides (formerly Clostridium) difficile is a Gram-positive anaerobic bacterial pathogen that causes severe gastrointestinal infection in humans. The current chemotherapeutic options are vastly inadequate, expensive and limited; this results in an exorbitant medical and financial burden. New, inexpensive chemotherapeutic treatments for C. di...

Synthetic small molecular antimicrobial peptidomimetics represent a promising new class of potential antibiotics due to their membrane-disrupting ability and their decreased propensity for bacterial resistance. A library of 43 mono- and di-cationic biaryl 1,2,3-triazolyl peptidomimetics was designed and synthesized based upon previously established...

Essential oils from the Western Australian (WA) Eucalyptus mallee species Eucalyptus loxophleba, Eucalyptus polybractea, and Eucalyptus kochii subsp. plenissima and subsp. borealis were hydrodistilled from the leaves and then analysed by gas chromatography–mass spectrometry in addition to a commercial Eucalyptus globulus oil and 1,8-cineole. The ma...

Aims To investigate the mechanisms of action of natural products with bactericidal (cinnamon root powder, peppermint oil, trans‐cinnamaldehyde, menthol and zingerone) or bacteriostatic (fresh garlic bulb extract, garlic clove powder, Leptospermum honey and allicin) activity against two C. difficile strains. Methods and results Bactericidal product...

Abstract Clostridium difficile infection is a toxin-mediated disease of the colon. C. difficile virulence is primarily attributed to the production of toxin A and toxin B; thus this study was aimed to investigate the effect of a range of natural products on the production and activity of C. difficile toxins in vitro. Twenty-two natural products wer...

The spectrum of activity and mode of action of a novel antibacterial agent, 135C, was investigated using a range of microbiological and genomic approaches. Compound 135C was active against Gram-positive bacteria with MICs for Staphylococcus aureus ranging from 0.12–0.5 μg/ml. It was largely inactive against Gram-negative bacteria. The compound show...

Aims To investigate the effect of natural products on the spore cycle of C. difficile in vitro. Methods and results Twenty‐two natural products were investigated using four C. difficile strains. Effects on sporulation, determined using microscopy and a conventional spore recovery assay, showed that fresh onion bulb extract (6.3% v v⁻¹) and coconut...

Recent reports of Eremophila glabra (R.Br.) Ostenf. (Scrophulariaceae) displaying antibacterial activity has led us to investigate the bioactive secondary metabolites responsible for this activity. Bioassay-directed fractionation of solvent extracts prepared from the leaves of E. glabra led to the isolation of seven serrulatane diterpenes, three fl...

Aims: To investigate the antimicrobial activity of various natural products against C. difficile in vitro. Methods and results: The antibacterial activity of 20 natural products was determined by the agar well diffusion and broth microdilution assays against four C. difficile strains, three comparator organisms and four gastrointestinal commensa...

The physicochemical parameters and antibacterial activity of 10 Western Australian (WA) and two comparator honeys were determined. Honeys showed a pH range of 4.0-4.7, colour range of 41.3-470.7 mAU, methylglyoxal levels ranging from 82.2 to 325.9 mg kg(-1) and hydrogen peroxide levels after 2 h of 22.7-295.5 µM. Antibacterial activity was assessed...

Background: The efficacy, tolerability and acceptability of a tea tree oil gel (200 mg/g) and face wash (7 mg/g) were evaluated for the treatment of mild to moderate facial acne. Methods: In this open-label, uncontrolled phase II pilot study, participants applied tea tree oil products to the face twice daily for 12 weeks and were assessed after...

Globally, scabies affects more than 130 million people at any time. In the developed world, outbreaks in health institutions and vulnerable communities result in a significant economic burden. A review of the literature demonstrates the emergence of resistance toward classical scabicidal treatments and the lack of effectiveness of currently availab...

Thirty two new binaphthyl-based, functionalized oxazole and thiazole peptidomimetics and over thirty five novel leucine-containing intermediate oxazoles and thiazoles were prepared in this study. This includes the first examples of the direct C-5 arylation of an amino acid dipeptide-derived oxazole. Moderate to excellent antibacterial activity was...

This study investigated the hypothesis that the salt adaptation response of Enterococcus faecalis alters susceptibility to tea tree oil (TTO). Six E. faecalis isolates were adapted to 6.5 % NaCl, and then exposed to TTO in phosphate-buffered saline (PBS). One isolate was also exposed to TTO in Brain Heart Infusion Broth (BHIB). The viability of sal...

Clostridium difficile (C. difficile) is a problematic Gram positive bacterial pathogen causing moderate to severe gastrointestinal infections. Based on a lead binaphthyl-tripeptide dicationic antimicrobial, novel mono-, di-and tri-peptidomimetic analogues targeting C. difficile were designed and synthesized incorporating one, two or three D-configu...

Increasing numbers of biological applications of fullerenyl amino acids and their derivatives encouraged us to synthesise [60]fullerenyldihydropyrrole peptides, prepared from the coupling of mono- and bis[60]fullerenyldihydropyrrolecarboxylic acids 4, 5 and 41 with presynthesised peptides 13, 16, 24, 28, 29 and 46. The resulting hydrophobic scaffol...

Over-the-counter acne treatments containing tea tree oil from the plant Melaleuca alternifolia are widely available, and evidence indicates that they are a common choice amongst those self-treating their acne. The aims of this review were to collate and evaluate the clinical evidence on the use of tea tree oil products for treating acne, to review...

Herein we describe the preparation and structure-activity relationship studies on range of stilbene based compounds and their antibacterial activity. Two related compounds, each bearing carboxylic acid moieties, exhibit good activity against several bacterial strains, including methicillin-resistant Staphylococcus aureus MRSA (ATCC 33592 and NCTC 1...

Tea tree oil, an essential oil from the Australian plant Mela- leuca alternifolia, has broad antimicrobial activity and is incor- porated into a diverse range of pharmaceutical and cosmetic products (2, 3). Blackwell (1) described a patient with typical signs and symptoms of bacterial vaginosis (BV) who treated her- self with tea tree oil vaginal p...

The aim of this study was to seek additional data on the antimicrobial susceptibility of Staphylococcus spp. after habituation to low levels of the topical antimicrobial agent tea tree (Melaleuca alternifolia) oil. Meticillin-susceptible Staphylococcus aureus (MSSA), meticillin-resistant S. aureus (MRSA) and coagulase-negative staphylococci (CoNS)...

Ethnopharmacological relevance: Eucalyptus kinos are tannin-rich, mostly red-coloured wood exudates. They have played an important role in the traditional medicines of Australian Aboriginal people and were also a valued source of antibacterial and astringent agents for early European settlers. Materials and methods: Nineteen different Eucalyptus...

The full text (in Swedish) available from Lakartidningen website http://www.lakartidningen.se/07engine.php?articleId=18503 Full text (in English) available from ResearchGate This publication is a Letter to the Editor written in response to: http://ltarkiv.lakartidningen.se/2011/temp/pda39894.pdf

Monoterpenoids and phenylpropanoids are major components of many plant essential oils and are relatively simple, low-molecular-weight compounds with antimicrobial activity. This study used multiparameter flow cytometry to examine changes in membrane polarity and permeability in Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faec...

This study investigated the effects of the volatile terpene-rich oil from Melaleuca alternifolia (tea tree oil) on the formation of biofilms and the adhesion of C. albicans cells to both biotic and abiotic surfaces. Biofilm formation on polystyrene was significantly inhibited for 70% of the isolates at the lowest test concentration of 0.016% of tea...

FULL TEXT available free from http://aac.asm.org/content/56/2/909.full.pdf+html?sid=0ae9b35e-045e-4400-bab9-1143f24802a5 This study examined the effect of subinhibitory Melaleuca alternifolia (tea tree) essential oil on the development of antibiotic resistance in Staphylococcus aureus and Escherichia coli. Frequencies of single-step antibiotic-res...

The aim of this study was to investigate the antimicrobial activity of a range of commercially available tea tree oil (TTO) products and to evaluate whether formulation plays a significant part in their antiseptic activity. The antimicrobial activity of the purchased products and control TTO solutions was assessed against Escherichia coli, Staphylo...

Secondary plant metabolites, and in particular monoterpenes, have been recognised as potential medicinal agents for centuries. As such, terpenes have been the focus of a plethora of scientific studies examining various aspects of their bioactivity. In particular, antimicrobial activity and anticancer potential have been studied extensively. Whilst...

Essential oils are bactericidal and fungicidal agents that are typically active at concentrations of 5% or less. Oils rich in aldehydes, phenols or alcohols generally show the greatest antimicrobial activity, since these component groups tend to be the most antimicrobially active. Lethal action is directly related to the solubility of oil component...

Essential oils are composed largely of monoterpenes, sesquiterpenes and their related alcohols. The number of components varies from approximately 10-100, although frequently the major portion of the oil is composed of only a few components. The composition and physico-chemical properties of oils are greatly influenced by extraction, packaging and...

Tea-tree oil (TTO) is the essential oil derived from an Australian native plant that has been used for hundreds of years, mainly for its antimicrobial and anti-inflammatory properties. With the advent of ever-increasing resistance to antibiotics and biocides amongst organisms, TTO may play an important role in the health industry in the fight again...

The aim of this study was to determine the spectrum of antimicrobial activity of 11 samples of stingless bee honey compared to medicinal, table and artificial honeys. Activity was assessed by agar diffusion, agar dilution, broth microdilution and time-kill viability assays. By agar dilution, minimum inhibitory concentration (MIC) ranges were 4% to...

The aim of this research was to investigate the activity of a commercial extract derived from the leaves of Olea europaea (olive) against a wide range of microorganisms (n=122). Using agar dilution and broth microdilution techniques, olive leaf extract was found to be most active against Campylobacter jejuni, Helicobacter pylori and Staphylococcus...

The antimicrobial activity of five samples of Taxandria fragrans essential oil was evaluated against a range of Gram-positive (n= 26) and Gram-negative bacteria (n= 39) and yeasts (n= 10). The majority of organisms were inhibited and/or killed at concentrations ranging from 0.06-4.0% v/v. Geometric means of MIC were lowest for oil Z (0.77% v/v), fo...