Introduction Pathogenic gut microorganisms, and dysbiosis of the gastrointestinal microbiota are a significant cause of mortality and morbidity worldwide, for instance infection with Clostridium difficile or Salmonella species can prove fatal, whereas alteration of the gastrointestinal microbiota has been implicated in irritable bowel syndrome. Due to increasing resistance of gastrointestinal pathogens to conventional antibiotics, alternative antimicrobial agents are urgently needed. The aim of this study is to investigate whether essential oils (concentrated mixtures of aromatic compounds obtained by the distillation of plant tissues) have antimicrobial activity against selected gastrointestinal pathogens.

Methods We have investigated the antimicrobial activity of essential oils of a wide range of culinary and medicinal herbs against type strains of selected gastrointestinal pathogens, namely Salmonella enterica, Clostridium difficile, two strains of Escherichia coli, and Candida albicans by disc diffusion assays. Grapeseed oil was the negative control. If the essential oils inhibited the growth of the organisms, a clear halo was seen around the test discs. This was measured. The experiments were performed three times and results were analysed by two sample T Tests. Essential oils were analysed by thermal desorption gas chromatography with mass spectrometry to identify the compounds present.

Results Seven of the essential oils (aniseed, asafoetida, cinnamon, clove, oregano, thyme and winter savoury) produced a strong and statistically significant inhibition of the growth of all five of the organisms tested whereas a further seven essential oils (coriander, garlic, lemon balm, lemon grass, May Chang, peppermint and rosemary) markedly inhibited the growth of three or four of the organisms (and these results were also statistically significant). Batch to batch variation was evident in the antimicrobial activity of some of the essential oils. This might correlate with variations in the profile of compounds present in the essential oils.

Conclusion Some of the essential oils studied might be therapeutically useful against gastrointestinal pathogens. Quality control of the oils would be necessary and further work is needed to identify the active antimicrobial compounds in the oils.

Disclosure of Interest None Declared.