Papers by Katherine Hammer
The American journal of tropical medicine and hygiene, Jan 19, 2016
Globally, scabies affects more than 130 million people at any time. In the developed world, outbr... more 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 available scabicides in reducing the inflammatory skin reactions and pyodermal progression that occurs in predisposed patient cohorts. Tea tree oil (TTO) has demonstrated promising acaricidal effects against scabies mites in vitro and has also been successfully used as an adjuvant topical medication for the treatment of crusted scabies, including cases that did not respond to standard treatments. Emerging acaricide resistance threatens the future usefulness of currently used gold standard treatments (oral ivermectin and topical permethrin) for scabies. The imminent development of new chemical entities is doubtful. The cumulative acaricidal, antib...
The Australasian journal of dermatology, Jan 21, 2016
The efficacy, tolerability and acceptability of a tea tree oil gel (200 mg/g) and face wash (7 mg... more 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. 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 4, 8 and 12 weeks. Efficacy was determined from total numbers of facial acne lesions and the investigator global assessment (IGA) score. Tolerability was evaluated by the frequency of adverse events and the mean tolerability score determined at each visit. Product acceptability was assessed via a questionnaire at the end of the study period. Altogether 18 participants were enrolled, of whom 14 completed the study. Mean total lesion counts were 23.7 at baseline, 17.2 at 4, 15.1 at 8 and 10.7 at 12 weeks. Total lesion counts differed significantly over time by repeated measures anova (P < 0.0001). The mean IGA score was 2.4 at baseline, 2.2 at 4, 2.0 at 8 and 1....
Organic & biomolecular chemistry, Jan 9, 2015
Thirty two new binaphthyl-based, functionalized oxazole and thiazole peptidomimetics and over thi... more 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 observed for all new compounds across Gram positive isolates with MICs ranging from 1-16 μg mL(-1). Results for Gram negative E. coli and A. baumannii were more variable, but MICs as low as 4 μg mL(-1) were returned for two examples. Significantly, the in vitro results with a fluoromethyl-oxazole derivative collectively represent the best obtained to date for a member of our binaphthyl peptide antimicrobials.
Org. Biomol. Chem., 2015
Clostridium difficile (C. difficile) is a problematic Gram positive bacterial pathogen causing mo... more 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-configured cationic amino acid residues, with a common 1,2,3-triazole ester isostere at the C-terminus. Copper- and ruthenium-click chemistry facilitated the generation of a 46 compound library for in vitro bioactivity assays, with structure-activity trends over the largest compound subset revealing a clear advantage to triazole-substitution with a linear or branched hydrophobic group. The most active compounds were dicationic-dipeptides where the triazole was substituted with a 4- or 5-cyclohexylmethyl or 4,5-diphenyl moiety, providing MICs of 4 μg mL(-1) against three human isolates of C. difficile. Further biological screening revealed significant antimicrobial activity for several compounds against other common bacterial pathogens, both Gram positive and negative, including S. aureus (MICs ≥2 μg mL(-1)), S. pneumoniae (MICs ≥1 μg mL(-1)), E. coli (MICs ≥4 μg mL(-1)), A. baumannii (MICs ≥4 μg mL(-1)) and vancomycin-resistant E. faecalis (MICs ≥4 μg mL(-1)).
International journal of antimicrobial agents, 2015
Over-the-counter acne treatments containing tea tree oil from the plant Melaleuca alternifolia ar... more 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 safety and tolerability and to discuss the underlying modes of therapeutic action.
Thormar/Lipids and Essential Oils as Antimicrobial Agents, 2010
Page 1. 9 Chemistry and Bioactivity of Essential Oils Christine F. Carson and Katherine A. Hammer... more Page 1. 9 Chemistry and Bioactivity of Essential Oils Christine F. Carson and Katherine A. Hammer Discipline of Microbiology and Immunology, School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, WA, Australia ...
International Journal of Antimicrobial Agents, 2012
Monoterpenoids and phenylpropanoids are major components of many plant essential oils and are rel... more 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 faecalis following exposure to the monoterpenoids carvacrol, 1,8-cineole and terpinen-4-ol and the phenylpropanoids eugenol and cinnamaldehyde. Melaleuca alternifolia (tea tree) essential oil was also investigated. The fluorescent dyes DiOC 2 (3) (3,3 -diethyloxacarbocyanine oxide) and TO-PRO ® -3 were used to assess membrane potential and permeability, respectively, following treatment with the minimum inhibitory concentration (MIC) of each test compound for 5 min and 30 min. Four subpopulations of cells were identified based on polarity and permeability. Eugenol treatment resulted in the greatest depolarisation and permeabilisation at 5 min, followed by carvacrol. Cinnamaldehyde, whilst having the lowest MICs (0.006-0.1%, v/v), did not induce changes in polarity or permeability at the MIC, and substantially higher concentrations were required to induce significant effects. At 30 min, treatment with all six compounds resulted in significant depolarisation (60.9-99.3% of cells), whereas fewer compounds (ranging from two to five per organism) resulted in significant permeabilisation. The extent of permeabilisation was always less than depolarisation, with overall means for all treatments of 46.1% and 89.4% of cells permeabilised and depolarised, respectively, at 30 min. These data demonstrate that several monoterpenoids and phenylpropanoids as well as tea tree oil alter membrane properties by decreasing polarity and increasing permeability in a time-and concentration-dependent manner.
Healthcare Infection, 2005
Antimicrobial Agents and Chemotherapy, Feb 1, 2000
The in vitro activities of ketoconazole, econazole, miconazole, and tea tree oil against 54 Malas... more The in vitro activities of ketoconazole, econazole, miconazole, and tea tree oil against 54 Malassezia isolates were determined by agar and broth dilution methods. Ketoconazole was more active than both econazole and miconazole, which showed very similar activities. M. furfur was the least susceptible species. M. sympodialis, M. slooffiae, M. globosa, and M. obtusa showed similar susceptibilities to the four agents.
Microbios
A broth micro-dilution method was used to examine the susceptibility of Escherichia coli (n = 110... more A broth micro-dilution method was used to examine the susceptibility of Escherichia coli (n = 110) and Staphylococcus aureus (n = 105) to the essential oil of Melaleuca alternifolia (tea tree oil). The detergent Tween 80 was used successfully to enhance the solubility of tea tree oil in the test medium. The MIC90 of tea tree oil for E. coli was 0.25% while for S. aureus it was 0.50%.
Antimicrobial Agents and Chemotherapy
Tea tree oil, an essential oil from the Australian plant Mela- leuca alternifolia, has broad anti... more 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 pessaries. After treatment, the pa- tient was symptom free and the vaginal flora comprised predom- inantly gram-positive bacilli. It was suggested that the use of tea tree oil for the treatment of BV be further assessed. Therefore, the aim of this study was to evaluate the activities of tea tree oil against lactobacilli and a range of organisms associated with BV. Reference (n 5 9) and stored clinical (n 5 24) isolates were obtained from the culture collections of the Western Austra- lian Centre for Pathology and Medical Research (PathCentre) and the Department of Microbiology at The University of West- ern Australia. Recent clinical isolat...
Lakartidningen
Jävsdeklaration: Alla författare har tidigare erhållit forskningsstöd eller konsultarvode från Au... more Jävsdeklaration: Alla författare har tidigare erhållit forskningsstöd eller konsultarvode från Australiensiska staten och/eller från industrin för forskning angående essentiella oljor eller naturläkemedel.
Revue du Rhumatisme, 2006
en 2001 par Riente et al. [8] avec un typage HLA ne montrant pas les antigènes habituellement ass... more en 2001 par Riente et al. [8] avec un typage HLA ne montrant pas les antigènes habituellement associés avec la PR.
The aim of this research was to investigate the activity of a commercial extract derived from the... more 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 aureus [including meticillin-resistant S. aureus (MRSA)], with minimum inhibitory concentrations (MICs) as low as 0.31-0.78% (v/v). In contrast, the extract showed little activity against all other test organisms (n=79), with MICs for most ranging from 6.25% to 50% (v/v). In conclusion, olive leaf extract was not broad-spectrum in action, showing appreciable activity only against H. pylori, C. jejuni, S. aureus and MRSA. Given this specific activity, olive leaf extract may have a role in regulating the composition of the gastric flora by selectively reducing levels of H. pylori and C. jejuni.
European Journal of Organic Chemistry, 2014
2015). Synthesis of mono and bis[60]fullerene-based dicationic peptoids.
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Papers by Katherine Hammer