title: Comparison of the antibacterial activity of essential oils and extracts of medicinal and culinary herbs to investigate potential new treatments for irritable bowel syndrome.
abstract: BACKGROUND
  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. 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.
  
  
  METHODS
  Essential 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.
  
  
  RESULTS
  Most 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.
  
  
  CONCLUSIONS
  Many 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.
authors.affiliation: Biochemistry Group, College of Medicine, Care of Grove Reception, Swansea University, Singleton Park, Swansea SA2 8PP, UK. paula.row@cantab.net.
authors.forename: Aiysha
authors.initials: A
authors.lastname: Thompson
authors.forename: Dilruba
authors.initials: D
authors.lastname: Meah
authors.forename: Nadia
authors.initials: N
authors.lastname: Ahmed
authors.forename: Rebecca
authors.initials: R
authors.lastname: Conniff-Jenkins
authors.forename: Emma
authors.initials: E
authors.lastname: Chileshe
authors.forename: Chris O
authors.initials: CO
authors.lastname: Phillips
authors.forename: Tim C
authors.initials: TC
authors.lastname: Claypole
authors.forename: Dan W
authors.initials: DW
authors.lastname: Forman
authors.forename: Paula E
authors.initials: PE
authors.lastname: Row
mesh_terms: D000704:Analysis of Variance; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002957:Citrus / Q000737:chemistry; D028526:Coriandrum / Q000737:chemistry; D004926:Escherichia coli / Q000187:drug effects; D027541:Mentha / Q000737:chemistry; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects*; D009391:Nephelometry and Turbidimetry; D009822:Oils, Volatile / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry; D010938:Plant Oils / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D009822:Oils, Volatile; D010936:Plant Extracts; D010938:Plant Oils