Abstract
BackgroundIrritable bowel syndrome (IBS) is a common functional gastrointestinal disorder, which may result from alteration of the gastrointestinal microbiota following gastrointestinal infection, or with intestinal dysbiosis or small intestinal bacterial overgrowth. This may be treated with antibiotics, but there is concern that widespread antibiotic use might lead to antibiotic resistance. Some herbal medicines have been shown to be beneficial, but their mechanism(s) of action remain incompletely understood. To try to understand whether antibacterial properties might be involved in the efficacy of these herbal medicines, and to investigate potential new treatments for IBS, we have conducted a preliminary study in vitro to compare the antibacterial activity of the essential oils of culinary and medicinal herbs against the bacterium, Esherichia coli.MethodsEssential oils were tested for their ability to inhibit E. coli growth in disc diffusion assays and in liquid culture, and to kill E. coli in a zone of clearance assay. Extracts of coriander, lemon balm and spearmint leaves were tested for their antibacterial activity in the disc diffusion assay. Disc diffusion and zone of clearance assays were analysed by two-tailed t tests whereas ANOVA was performed for the turbidometric assays.ResultsMost of the oils exhibited antibacterial activity in all three assays, however peppermint, lemon balm and coriander seed oils were most potent, with peppermint and coriander seed oils being more potent than the antibiotic rifaximin in the disc diffusion assay. The compounds present in these oils were identified by gas chromatography mass spectrometry. Finally, extracts were made of spearmint, lemon balm and coriander leaves with various solvents and these were tested for their antibacterial activity against E. coli in the disc diffusion assay. In each case, extracts made with ethanol and methanol exhibited potent antibacterial activity.ConclusionsMany of the essential oils had antibacterial activity in the three assays, suggesting that they would be good candidates for testing in clinical trials. The observed antibacterial activity of ethanolic extracts of coriander, lemon balm and spearmint leaves suggests a mechanistic explanation for the efficacy of a mixture of coriander, lemon balm and mint extracts against IBS in a published clinical trial.
Highlights
Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder, which may result from alteration of the gastrointestinal microbiota following gastrointestinal infection, or with intestinal dysbiosis or small intestinal bacterial overgrowth
Disc diffusion assays to examine the antibacterial activity of essential oils against E. coli Plant essential oils were tested for their antibacterial activity against E. coli DH5α by disc diffusion assays
Since IBS has been linked to intestinal dysbiosis or small intestinal bacterial overgrowth, we have investigated the antibacterial activity of the essential oils of a range of culinary and medicinal herbs, many of which have traditionally been used as digestives or are present in herbal medicines that have been shown to be effective in treating IBS in clinical trials, in three assays: the disc diffusion assay, the turbidometric assay and the zone of clearance assay
Summary
Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder, which may result from alteration of the gastrointestinal microbiota following gastrointestinal infection, or with intestinal dysbiosis or small intestinal bacterial overgrowth. This may be treated with antibiotics, but there is concern that widespread antibiotic use might lead to antibiotic resistance. Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder, which affects 10 – 22% of the UK population and is responsible for 20 – 50% of the workload of gastroenterology departments [1]. More recently the gastrointestinal microbiota of IBS patients have been compared with those from healthy subjects by bacterial culture or molecular approaches [reviewed in 7,8]. The findings vary, but a common feature seems to be a reduction in the number of Bifidobacteria and increased numbers of Firmicutes and Enterobacteriaceae in samples from IBS patients compared to control samples
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