A novel colorimetric broth microdilution method to determine the minimum inhibitory concentration (MIC) of antibiotics and essential oils against Helicobacter pylori.

Helicobacter pylori infections have been associated with the pathogenesis of a number of stomach and gastroduodenal diseases. In order to find alternative drugs for their treatment the search is increasingly focused on new antimicrobial products. However, no standardized methods are available to test the anti-Helicobacter pylori activity in particular of natural substances. Therefore we developed a broth microdilution assay to investigate the susceptibility of this fastidious slow growing bacterium against 15 essential oils widely used to treat disorders of the gastrointestinal tract. The MIC values were determined colorimetrically using p-iodonitrophenyltetrazolium violet (INT) as an indicator for bacterial cell viability. The test sytem was evaluated with three common antibiotics: amoxicillin, ampicillin and levofloxacin. The antibiotic MICs were controlled by Etest. The Helicobacter reference strain was remarkably susceptible to both the antibiotics (amoxicillin MIC: 0.02 microg/ml, ampicillin MIC: 0.064 microg/ml, levofloxacin MIC: 0.39 microg/ml) and the essential oils. Most of their MICs ranged from 0.015 to 0.064% (v/v) and about 140.0 to 280.0 microg/ml, respectively. Interestingly, chamomile oil, orange flower oil and ginger oil inhibited the bacterial growth in extraordinarily low concentrations of 0.0075% (v/v) and about 65 microg/ml, respectively. The bactericidal concentrations were generally one to two dilution steps higher. In conclusion, we could develop an innovative assay for the MIC determination of essential oils and antibiotics against Helicobacter pylori, which is simple to handle, accurate, reproducible and not as time- and material-consuming as traditional agar dilution techniques.

Antifungal effect of Australian tea tree oil on Malassezia pachydermatis isolated from canines suffering from cutaneous skin disease.

The lipophilic yeast Malassezia pachydermatis is part of the normal skin flora of most warm-blooded organisms. In a number of surveys it could be demonstrated that this yeast species might be involved in different skin diseases like seborrhoeic dermatitis, especially in dogs and cats. In order to look for an alternative therapeutic agent to the commonly used antimycotic and antiseptic synthetic substances the in vitro activity of Australian tea tree oil, the essential oil of Melaleuca alternifolia, against several strains of Malassezia pachydermatis was examined. All tested strains showed remarkably high susceptibility to tea tree oil. With these results the excellent antibacterial activity of tea tree oil is extended to a new group of fungal pathogens colonizing mainly mammals' skin. During the last ten years there was an increasing popularity of tea tree oil containing human health care products. The presented data open up new horizons for this essential oil as a promising alternative agent for topical use in veterinary medicine as well.

Comparative investigation of the antimicrobial activity of PADMA 28 and selected European herbal drugs.

OBJECTIVE: PADMA 28 is a multicompound preparation of 20 herbs, calcium sulphate, and camphor, derived from Tibetan medicine. It is usually used in the treatment of peripheral circulatory disorders, accompanied by the symptoms tingling, formication, heaviness and tenseness in arms and legs, numbness in hands and feet, and cramps in the calf. Recently, the question of whether appropriate preparations of PADMA 28 also exhibit antibacterial and antimycotic activity has often been raised. As there are as yet no experimental findings that answer this question, an in vitro study was carried out. In a parallel survey we investigated the antimicrobial properties of 5 herbal drugs which are commonly used in the traditional European folk medicine for the topical treatment of mild skin infections, wounds and eczematous skin lesions. METHODS: The minimum inhibitory concentrations (MIC) and the minimum bactericidal concentrations (MBC) of alcohol-based (tinctures) and aqueous (teas) herbal drug preparations were determined in vitro by a broth microdilution method for 5 Gram-positive and 5 Gram-negative bacteria, as well as the yeast Candida albicans. RESULTS: The aqueous and alcohol-based PADMA 28 preparations as well as the corresponding preparations of the European herbal drugs showed an antibacterial effect against Gram-positive bacteria in vitro. These bacteria revealed a somewhat higher sensitivity to the teas prepared from the European herbal drugs (MIC: 1.3-20.0 mg/ml) than to the aqueous preparations of PADMA 28 (MIC: 5.0-40.0 mg/ml). The better antibacterial activity of the European herbal drugs is probably based on their relatively high amount of tanning agents. On the other hand, all tested plant preparations inhibited not at all or only insufficiently the growth of the Gram-negative bacteria tested and that of Candida albicans. The ethanolic PADMA 28 tinctures showed an improved inhibitory effect on the Gram-positive bacteria (MIC: 0.38-1.51% tincture or 0.38-1.51 mg PADMA 28/ml) compared with the aqueous preparations; this effect is comparable to the ethanolic tinctures of the tested European herbal drugs (MIC: 0.4-1.6/3.2% tincture or 0.4-1.6/3.2 mg herbal drug/ml). CONCLUSION: All tested tea preparations and alcoholic tinctures of PADMA 28 as well as those of the selected European herbal drugs exhibited evident antibacterial effects against Gram-positive bacteria in vitro. On the other hand, except for Klebsiella pneumoniae, all Gram-negative bacteria tested and the yeast Candida albicans were insensitive against the different aqueous and alcohol-based plant extracts.

A current review of the antimicrobial activity of Hypericum perforatum L.

A petrolether extract of the areal parts of Hypericum perforatum L. was reported to be active against gram-positive bacteria. Hyperforin, a phloroglucin derivative was shown to be the antimicrobial principle. Hyperforin exhibited an excellent effect against methicillin-resistant strains of Staphylococcus aureus with a MIC value of 1.0 microg/ml. A butanol fraction of St. John's Wort revealed anti-Helicobacter pylori activity with MIC values ranging between 15.6 and 31.2 microg/ml. Recently, hydrous solutions of Hypericum perforatum teas were found to be antimicrobially effective against gram-positive bacteria with special activity towards methicillin-restistant strains of Staphylococcus aureus (MIC values: 1.3 to 2.5 mg herb/ml).