The study evaluated the bacteriostatic activity of 13 essential oils against 64 bacterial strains, including antibiotic-sensitive and resistant isolates, using an agar dilution technique. Cinnamon bark oil showed the strongest activity against all community and hospital strains, with an MIC90 below 1.5%. Oregano, ajowan, thyme, clove, cinnamon leaves, lemon grass and tea tree oils also exhibited good activity overall. Cinnamon bark oil was the most effective against Pseudomonas aeruginosa, with an MIC of 0.31%. The essential oils containing phenols and aldehydes generally demonstrated greater bacteriostatic effects.

1. Bacteriostatic activity of 13 essential oils on antibiotic-resistantBacteriostatic activity of 13 essential oils on antibiotic-resistant
clinical isolatesclinical isolates
L. MayaudL. Mayaud11
, A. Carricajo, A. Carricajo11
, A. Zhiri, A. Zhiri22
, D. Baudoux, D. Baudoux22
, G. Aubert, G. Aubert11
11
Bacteriology Laboratory, CHU Bellevue Hospital, 42055, Saint-Etienne, FranceBacteriology Laboratory, CHU Bellevue Hospital, 42055, Saint-Etienne, France
22
Pranarom International S.A., B-7822 Ghislenghien, BelgiumPranarom International S.A., B-7822 Ghislenghien, Belgium
The aim of the study was toThe aim of the study was to determine the bacteriostatic activity of 13 essential oils (EOs) against 64determine the bacteriostatic activity of 13 essential oils (EOs) against 64
bacterial strains,bacterial strains, eithereither sensitive or resistant to antibiotics, using the agar dilution techniquesensitive or resistant to antibiotics, using the agar dilution technique
(standardized and reproducible).(standardized and reproducible).
The Second International Symposium on Aromatic and Medicinal Plants
Marrakech – Morocco September 14-16 2006
Materials and methodsMaterials and methods
Materials: 13 chemotyped EOs analyzed by GC-MS (supplied by Pranarôm), 64 bacterial strains
ATCC and clinical: 38 strains sensitive to antibiotics (including E. coli 0157H7, Vibrio cholerae,
Pasteurella multocida, Salmonella sp, Streptococccus pyogenes, S. anginosus, S. sanguis,
S. intermedius, Enterococcus bovis, Staphylococcus aureus, S. hemolyticus, S. epidermidis, S. varneri, S. xylosus and Listeria
monocytogenes) and 26 strains resistant to antibiotics (including methicillin-resistant Staphylococcus aureus, GISA and heteroGISA,
Enterococcus van A, van B and van C, penicillin-resistant Streptococcus pneumoniae, enterobacteria with penicillinase or ESBL or
AmpC ß-lactamase, Acinetobacter baumanii with imipenemase or VEB1, Stenotrophomonas maltophilia, Aeromonas hydrophila and
Pseudomonas aeruginosa with and without ESBL).
Methods: agar dilution technique (1)
(CLSI recommendations) : two-fold serial dilutions of each EO ranging from 50% to 0.1% (v/v) were
prepared in agar solution 0.15% (v/v). Dilute and pure EOs (4 mL) were added to sterile molten MH with or without sheep blood (36 mL)
giving final concentrations in the range of 0.01-10%. The mixtures were all homogenized and poured into sterile Petri dishes.
Inoculation was performed by means of spots containing 105
CFU/spot using a “Steers” system. MH broth with agar solution (without
essential oils) was used as a positive growth control. The inoculated plates were incubated at 37°C for 48h. MICs were taken as the
lowest concentrations of oil inhibiting visible growth of each organism on the agar plate. The presence of one or two colonies was
disregarded. All tests were performed in duplicate.
ConclusionConclusion
The most effective EOThe most effective EO against all the bacterial strains of communityagainst all the bacterial strains of community
and hospitable origin was cinnamon bark oiland hospitable origin was cinnamon bark oil. Oregano, ajowan, thyme, clove, cinnamon. Oregano, ajowan, thyme, clove, cinnamon
leaves, lemon grass and tea tree oil exhibited excellent bacteriostatic activity exceptleaves, lemon grass and tea tree oil exhibited excellent bacteriostatic activity except
againstagainst Pseudomonas aeruginosaPseudomonas aeruginosa. The in vitro and in vivo bactericidal activity of these. The in vitro and in vivo bactericidal activity of these
EOs should beEOs should be investigatedinvestigated if they are to be used as antiseptics.if they are to be used as antiseptics.
Reference : (1) Remmal A, Bouchikhi T, Rhayour K, Ettayebi M. Improved Method for
the Determination of Antimicrobial Activity of Essential Oils in Agar Medium.
J Essent Oil Res 1993; 5: 179-184
Results and discussionResults and discussion:: Table of MICs of EOs (% v/v) against 64 strainsTable of MICs of EOs (% v/v) against 64 strains
EOs containing phenol (carvacrol, thymol, eugenol) and aldehyde (cinnamaldehyde, geranial) exhibited marked activity with MIC90
< 1.5%. Alcohol-based EOs exhibited varying degrees of activity depending on alcohol content (terpinen-1-ol-4, linalol, geraniol) and
whether the strains were Gram- or Gram+. Against P. aeruginosa, only cinnamon bark oil presented a low MIC of 0.31%, with the MIC of the
other EOs ranging from 2 to > 10%. Levels of sensitivity of clinical bacterial strains to EOs were independent of respective levels of
resistance to antibiotics.
Streptococcus pyogenes before and after cinnamon bark
treatment (0.6 % v/v, 15 min) - I. Anselme – Bertrand - CMES -
Faculty of Medicine – University of Saint-Etienne
Cinnamon
bark
Cinnamomum
verum
Oregano
Origanum
compactum
Ajowan
Trachyspermum
ammi
Thyme
Thymus
satureioïdes
Clove
Eugenia
caryophyllus
Cinnamon
leaves
Cinnamomum
verum
Lemon
grass
Cymbopogon
citratus
Tea tree
Melaleuca
alternifolia
Palmarosa
Cymbopogon
martinii
Eucalyptus
Eucalyptus
globulus
Cajuput
Melaleuca
cajuputii
Lavender
Lavandula
angustifolia
Orange
Citrus
sinensis
n (Gram+ and Gram-) 62 62 62 61 62 62 57 62 62 60 59 62 59
range 0.02-0.16 0.12-0.46 0.12-0.62 0.12-1.25 0.16-0.62 0.23-1.25 0.12-1.25 0.16-1.88 0.12-10 0.94-10 1.25-10 0.16->10 0.62->10
MIC 50 % 0.08 0.23 0.23 0.31 0.46 0.46 0.46 0.46 0.31 5 5 1.88 10
MIC 90 % 0.16 0.31 0.46 0.62 0.62 1.25 1.25 1.88 10 7.5 10 >10 >10
n (Gram+) 35 35 35 34 35 35 30 35 35 33 32 35 32
Range 0.02-0.16 0.12-0.46 0.23-0.46 0.16-1.25 0.16-0.62 0.31-1.25 0.12-0.62 0.16-1.88 0.12-0.46 0.94-10 1.25-10 0.16-20 1.25->10
MIC 50 % 0.08 0.23 0.23 0.31 0.46 0.62 0.31 0.94 0.31 5 5 1.88 10
MIC 90 % 0.16 0.31 0.46 0.94 0.62 1.25 0.62 1.88 0.31 7.5 7.5 5 >10
n (Gram-) 27 27 27 27 27 27 27 27 27 27 27 27 27
Range 0.03-0.12 0.12-0.31 0.12-0.62 0.12-0.62 0.23-0.62 0.23-0.62 0.12-1.25 0.31-0.94 0.12-10 1.25-10 1.25-10 0.23->10 0.62->10
MIC 50 % 0.08 0.23 0.23 0.31 0.46 0.46 0.62 0.62 0.46 5 5 5 10
MIC 90 % 0.12 0.23 0.31 0.46 0.62 0.62 1.25 0.94 10 10 7.5 >10 >10
n (Pseudomonas
aeruginosa) 2 2 2 2 2 2 2 2 2 2 2 2 2
range 0.16-0.31 1.88-2.5 7.5-10 >10 10->10 10->10 10->10 10->10 >10 >10 10->10 >10 >10