Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Thu, 03 Jan 2019 11:35:28 Sensitivity of pathogenic and commensal bacteria from the human colon to essential oils Dinesh Thapa, 1 Riccardo Losa, 2 Be ´ atrice Zweifel 2 and R. John Wallace 1 Correspondence R. John Wallace john.wallace@abdn.ac.uk Received 4 June 2012 Revised 20 July 2012 Accepted 8 August 2012 1 Gut Health Theme, Rowett Institute of Nutrition and Health, University of Aberdeen, Bucksburn, Aberdeen AB21 9SB, UK 2 Agolin SA, 1145-Bie ` re, Switzerland The microbiota of the intestinal tract plays an important role in colonic health, mediating many effects of dietary components on colonic health and during enteric infections. In the context of the increasing incidence of antibiotic resistance in gut bacteria, complementary therapies are required for the prevention and treatment of enteric infections. Here we report the potential application of essential oils (EO) and pure EO compounds to improve human gut health. Nerolidol, thymol, eugenol and geraniol inhibited growth of the pathogens Escherichia coli O157 : H7(VT ” ), Clostridium difficile DSM1296, Clostridium perfringens DSM11780, Salmonella typhimurium 3530 and Salmonella enteritidis S1400 at a half-maximal inhibitory concentration (IC 50 ) varying from 50 to 500 p.p.m. Most EO showed greater toxicity to pathogens than to commensals. However, the beneficial commensal Faecalibacterium prausnitzii was sensitive to EO at similar or even lower concentrations than the pathogens. The EO showed dose-dependent effects on cell integrity, as measured using propidium iodide, of Gram-positive bacteria. These effects were not strongly correlated with growth inhibition, however, suggesting that cell membrane damage occurred but was not the primary cause of growth inhibition. Growth inhibition of Gram-negative bacteria, in contrast, occurred mostly without cell integrity loss. Principal component analysis showed clustering of responses according to bacterial species rather than to the identity of the EO, with the exception that responses to thymol and nerolidol clustered away from the other EO. In conclusion, the selective effects of some EO might have beneficial effects on gut health if chosen carefully for effectiveness against different species. INTRODUCTION Essential oils (EO) are steam-volatile or organic solvent extracts of plants, comprising mainly terpene, terpenoid and other aromatic and aliphatic constituents of fairly low molecular mass (Bakkali et al., 2008). Typically, EO contain a mixture of about 20–60 different compounds with two or three at high concentration (20–70 %). Throughout his- tory, herbs and spices and their constituent EO have been used as antiseptics, to preserve food and to enhance flavour (Shelef, 1984). More recently, EO have been used in ani- mal feeds to combat infection and improve productivity (Wallace et al., 2002, 2010; Newbold et al., 2004; Wallace, 2004; Franz et al., 2010). For example, EO and EO com- pounds, including thymol, carvacrol and eugenol, reduced the bacterial load in different parts of the gut and lowered the shedding of Clostridium perfringens in broiler chickens (Mitsch et al., 2004). EO also improved productivity in ruminants by altering the community of commensal bac- teria in the rumen, altering protein degradation and reducing ammonia losses (Wallace et al., 2002; McIntosh et al., 2003; Wallace, 2004). In man, however, the roles of EO in microbial manipulation and gut fermentation have not been evaluated. The main targets relating to gut health in man are enteric infection, inflammation and carcinogenesis. Enteric infec- tions by gut pathogens, such as Escherichia coli, Salmonella spp., Campylobacter spp. and Clostridium spp., occur when host defences fail to prevent colonization and prolifera- tion (Sekirov & Finlay, 2009). The complex community of commensal bacteria has a role to play in protecting against this type of infection. They also have a role in gastro- intestinal homeostasis. Dysbiosis of intestinal microbiota occurs in ulcerative colitis, irritable bowel syndrome and colon cancer (Moore & Moore, 1995; Flint et al., 2007; Flint & Wallace, 2010; Noor et al., 2010; Sekirov et al., 2010). In a recent cohort study, the microbial community of patients with Crohn’s disease was found to be markedly different from healthy controls and their unaffected relatives (Joossens et al., 2011). Density gradient gel electrophoresis (DGGE) of ribosomal PCR amplicons indicated that num- bers of Faecalibacterium prausnitzii and Bifidobacterium Abbreviations: EO, essential oils; PCA, principal component analysis; PI, propidium iodide; RFU, relative fluorescence units. Microbiology (2012), 158, 2870–2877 DOI 10.1099/mic.0.061127-0 2870 061127 G 2012 SGM Printed in Great Britain