J Appl Microbiol. 2000 Feb;88(2):308-16. Antimicrobial agents from plants: antibacterial activity of plant volatile oils. Dorman HJ, Deans SG. Aromatic and Medicinal Plant Group, Scottish Agricultural College, Auchincruive, South Ayrshire, UK.

The volatile oils of black pepper [Piper nigrum L. (Piperaceae)], clove [Syzygium aromaticum (L.) Merr. & Perry (Myrtaceae)], geranium [Pelargonium graveolens L’Herit (Geraniaceae)], nutmeg [Myristica fragrans Houtt. (Myristicaceae), oregano [Origanum vulgare ssp. hirtum (Link) Letsw. (Lamiaceae)] and thyme [Thymus vulgaris L. (Lamiaceae)] were assessed for antibacterial activity against 25 different genera of bacteria. These included animal and plant pathogens, food poisoning and spoilage bacteria. The volatile oils exhibited considerable inhibitory effects against all the organisms under test while their major components demonstrated various degrees of growth inhibition. Publication Types: Research Support, Non-U.S. Gov’t PMID: 10736000 [PubMed - indexed for MEDLINE] Mem Inst Oswaldo Cruz. 2006 Jun;101(4):387-90. Synergism between plant extract and antimicrobial drugs used on Staphylococcus aureus diseases. Betoni JE, Mantovani RP, Barbosa LN, Di Stasi LC, Fernandes Junior A. Departamento de Farmacologia, Instituto de Biociencias, Universidade Estadual Paulista Julio de Mesquita Filho, Botucatu, SP, 18618-000, Brasil.

Searches for substances with antimicrobial activity are frequent, and medicinal plants have been considered interesting by some researchers since they are frequently used in popular medicine as remedies for many infectious diseases. The aim of this study was to verify the synergism between 13 antimicrobial drugs and 8 plant extracts—“guaco” (Mikania glomerata), guava (Psidium guajava), clove (Syzygium aromaticum), garlic (Allium sativum), lemongrass (Cymbopogon citratus), ginger (Zingiber officinale), “carqueja” (Baccharis trimera), and mint (Mentha piperita)--against Staphylococcus aureus strains, and for this purpose, the disk method was the antimicrobial susceptibility test performed. Petri dishes were prepared with or without dilution of plant extracts at sub-inhibitory concentrations in Mueller-Hinton Agar (MHA), and the inhibitory zones were recorded in millimeters. In vitro anti-Staphylococcus aureus activities of the extracts were confirmed, and synergism was verified for all the extracts; clove, guava, and lemongrass presented the highest synergism rate with antimicrobial drugs, while ginger and garlic showed limited synergistic capacity. Publication Types: Research Support, Non-U.S. Gov’t PMID: 16951808 [PubMed - indexed for MEDLINE] Lett Appl Microbiol. 2003;36(3):162-7. Antibacterial activity of selected plant essential oils against Escherichia coli O157:H7. Burt SA, Reinders RD.

Department of Public Health and Food Safety, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, The Netherlands.

AIMS: To quantify the antibacterial properties of five essential oils (EO) on a non-toxigenic strain of Escherichia coli O157:H7 in the presence and absence of a stabilizer and an emulsifier and at three different temperatures. METHODS AND RESULTS: Five EOs known to exhibit antibacterial properties were screened by disc diffusion assay and the most active were selected for further study in microdilution colorimetric assays. Oregano (Origanum vulgare) and thyme (Thymus vulgaris; light and red varieties) EO had the strongest bacteriostatic and bactericidal properties, followed by bay (Pimenta racemosa) and clove bud (Eugenia caryophyllata synonym: Syzygium aromaticum) EO. Oregano oil was colicidal at 625 microl l(-1) at 10, 20 and 37 degrees C. The addition of 0.05% (w/v) agar as stabilizer reinforced the antibacterial properties, particularly at 10 degrees C, whereas 0.25% (w/v) lecithin reduced antibacterial activity. Scanning electron micrographs showed extensive morphological changes to treated cells. CONCLUSIONS: Oregano and thyme EO possess significant in vitro colicidal and colistatic properties, which are exhibited in a broad temperature range and substantially improved by the addition of agar as stabilizer. Bay and clove bud EO are less active. Lecithin diminished antibacterial properties. The bactericidal concentration of oregano EO

irreversibly damaged E. coli O157:H7 cells within 1 min. SIGNIFICANCE AND IMPACT OF THE STUDY: Oregano and light thyme EO, particularly when enhanced by agar stabilizer, may be effective in reducing the number or preventing the growth of E. coli O157:H7 in foods. Publication Types: Comparative Study PMID: 12581376 [PubMed - indexed for MEDLINE] J Agric Food Chem. 2005 Aug 24;53(17):6939-46. Solid- and vapor-phase antimicrobial activities of six essential oils: susceptibility of selected foodborne bacterial and fungal strains. Lopez P, Sanchez C, Batlle R, Nerin C. Department of Analytical Chemistry, Aragon Institute of Engineering Research, CPS-University of Zaragoza, Maria de Luna st. 3, E-50018 Zaragoza, Spain.

The antimicrobial activity of essential oils (EOs) of cinnamon (Cinnamon zeylanicum), clove (Syzygium aromaticum), basil (Ocimum basillicum), rosemary (Rosmarinus officinalis), dill (Anethum graveolens), and ginger (Zingiber officinalis) was evaluated over a range of concentrations in two types of contact tests (solid and vapor diffusion). The EOs were tested against an array of four Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, and Listeria monocytogenes), four Gram-negative bacteria (Escherichia coli, Yersinia enterocolitica, Salmonella choleraesuis, and Pseudomonas aeruginosa), and three fungi (a yeast, Candida albicans, and two molds, Penicillium islandicum and Aspergillus flavus). The rationale for this work was to test the possibility of creating a protective atmosphere by using natural compounds that could extend the shelf life of packaged foodstuffs while minimizing organoleptic alterations. In the solid diffusion tests, cinnamon and clove gave the strongest (and very similar) inhibition, followed by basil and rosemary, with dill and ginger giving the weakest inhibition. The fungi were the most sensitive microorganisms, followed by the Gram-positive bacterial strains. The Gram-negative strain P. aeruginosa was the least inhibited. The composition of the atmosphere generated by the EOs, and their minimum inhibitory concentrations (MICs), were determined using a disk volatilization method, in which no inhibition from rosemary or basil was observed. Cinnamon and clove, once again, gave similar results for every microorganism. As a general rule, MIC (fungi) << MIC (bacteria) with no clear differences between Gram-positive or negative strains except for P. aeruginosa, which was not inhibited by any of the EOs in the vapor phase. The atmosphere generated from the EOs was analyzed by means of solidphase microextraction combined with gas chromatography-ion trap mass spectrometry. Differences among the volatiles in the EOs, which may be responsible for the differences in their antimicrobial performances, were found. Publication Types: Research Support, Non-U.S. Gov’t PMID: 16104824 [PubMed - indexed for MEDLINE] Mycoses. 2006 Jul;49(4):316-23. In vitro efficacy of 75 essential oils against Aspergillus niger. Pawar VC, Thaker VS. Department of Biosciences, Saurashtra University, Rajkot, Gujarat, India.

Aspergillus niger is an opportunistic human pathogen and a strong air pollutant. A study was conducted with 75 different essential oils for the inhibition of hyphal growth and spore formation in Aspergillus niger. Cinnamomum zeylanicum (bark), Cinnamomum zeylanicum (leaf), Cinnamomum cassia, Syzygium aromaticum and Cymbopogon citratus were the top five essential oils which demonstrated marked inhibitory effect against hyphal growth and spore formation of A. niger. The chemical composition of these five most active essential oils was investigated by gas chromatography-mass spectra (GC-MS). Most of the other essential oils were found challenging to combat A. niger, suggesting their use as strong aroma therapeutic agents. Publication Types: Research Support, Non-U.S. Gov’t

PMID: 16784447 [PubMed - indexed for MEDLINE] Nippon Ishinkin Gakkai Zasshi. 2005;46(1):27-33. Protection of oral or intestinal candidiasis in mice by oral or intragastric administration of herbal food, clove (Syzygium aromaticum). Taguchi Y, Ishibashi H, Takizawa T, Inoue S, Yamaguchi H, Abe S. Research and Development Division, S & B Foods Inc., 38-8 Miyamoto-cho, Itabashiku, Tokyo 174-8651, Japan.

We examined the effect of a clove (Syzygium aromaticum) administered by two different routes on Candida albicans growth, using a murine oral candidiasis model. When the clove preparation was administered into the oral cavity of Candida-infected mice, their oral symptoms were improved and the number of viable Candida cells in the cavity was reduced. In contrast, when the clove preparation was administered intragastrically, oral symptoms were not improved, but viable cell numbers of Candida in the stomach and feces were decreased. These findings demonstrate that oral intake of an herbal food, clove, may suppress the overgrowth of C. albicans in the alimentary tract including the oral cavity. PMID: 15711533 [PubMed - indexed for MEDLINE]