Achillea millefolium (Yarrow)has been used as a medicinal herb for thousands of years. There is historical evidence that many cultures including the Greeks, Native Americans, and Dutch have used yarrow medicinally. In the United States, there has been a recent resurgence in the use of essential oils and other homeopathic treatments. Many companies claim that some essential oils, including yarrow, have antimicrobial properties. Our study tested the antimicrobial capabilities of four commercially produced yarrow extracts against four bacterial strains. We used the Kirby Bauer Disk Susceptibility Test on two Gram negative bacteria species, Pseudomonas aeruginosa and Escherichia coli, and two Gram positive species, Bacillus cereus and Staphylococcus aureus. Distilled water was used as a control. Each species was treated with all four oils and the control with three replicates of each treatment. After 24 hour incubation, we measured the zones of inhibition and used paired t-tests to determine if the effects differed significantly among the treatments and the species. All four purchased oils showed significant growth inhibition on B. cereus. Two of the oils showed significant zones of inhibition on S. aureus and E. coli when compared with controls. P. aeruginosa, which is known for having very high antibiotic resistance,showed no measurable zones of inhibition for any of the four oils. In the future, we plan to use steam distillation to prepare yarrow extracts from local plant material and test this known oil in the manner described above.

1. Antimicrobial Effects of Yarrow
(Achillea millefolium) Essential Oil
Victoria A. Roy
Kimberly A. Hays, Ph.D.
Department of Natural Science
Dalton State College

2. Achillea millefolium
• Herbaceous, perennial, flowering plant
•Native to Asia, Europe and North America
•Strong, sweet scent
•Flowers May – June
•Three color morphs

3. Yarrow History
• Achilles
– Soldiers wounds
– Scientific name origin
• Native Americans
– 46 tribes
• Algonquin
• Lenape
– 28 ailments
• Kidney disorders
• Stomach disorders
• Open wounds
• Greece
– Military herb

4. Essential Oils: Growing Popularity

5. Objective
The objective of our study was to determine
the antimicrobial effects of four commercially
purchased yarrow extracts against four
common strains of bacteria.

6. Bacillus cereus
• Gram-positive
• Rod shaped
• Endospore forming
• Pathology
– Two types of food poisoning
• Enteric and emetic

7. Escherichia coli
• Gram-negative
• Rod-shaped
• Found in lower intestine
of homoeothermic organisms
• Opportunistic pathogen
• Pathology
– Food poisoning, urinary tract infections, neonatal
meningitis, Gram-negative pneumonia

8. Staphylococcus aureus
• Gram-positive
• Coccal
• Opportunistic pathogen
• Found in normal skin flora
• Pathology
– MRSA
– Staphylococcal scalded skin syndrome
• Produces toxins that cause blisters
• Ritter’s disease

9. Pseudomonas aeruginosa
• Gram-negative
• Rod-shaped
• Opportunistic pathogen
– Burn victims
– Cystic fibrosis
• Adheres to tissue surfaces
• Replicates to infectious critical mass
• Damage with virulence factors

10. Materials and Methods
• Kirby Bauer Disk Diffusion Susceptibility Test
– 4 bacteria species
• Confluent growth
– TSA agar
– Impregnate paper disks with 15 μL of oil/water
• DI Water control
• Eden’s Garden (EOE)
• Artisan Aromatics (EOA)
• Nature’s Kiss (EOK)
• Nature’s Oil (EON)

11. Photo: Misty Wheeler

12. Materials and Methods
• Kirby Bauer Disk Diffusion Susceptibility Test
– Three replicates
– 24 hour incubation at 37o C
– Measure zones of inhibition if present

14. 1
2
3
4

15. 0
2
4
6
8
10
12
EON EOE EOA EOK Water
AverageZoneofInhibition(mm)
Treatment
B. cereus
E. coli
S. aureus
P. aeruginosa
Average Zone of Inhibition Per Treatment

16. Statistical Analyses
• Two-tailed T-tests (α < 0.05) were used to
compare the average zones of inhibition
between:
– Oils vs. DI water control
– Oils vs. oils

17. Results: B. cereus
EON – Natures’ Oil
EOE – Eden’s Garden
EOA – Artisans Aromatics
EOK – Nature’s Kiss
P values C EON EOE EOA EOK
C
EON 0.000043
EOE 0.00041 0.75
EOA 0.00019 0.00071 0.0049
EOK 0.00291 0.0202 0.011 0.14

18. 0
2
4
6
8
10
12
EON EOE EOA EOK Water
AverageZoneofInhibition(mm)
Treatment
B. cereus
E. coli
S. aureus
P. aeruginosa
Average Zone of Inhibition Per Treatment

19. Results: E. coli
EON – Natures’ Oil
EOE – Eden’s Garden
EOA – Artisans Aromatics
EOK – Nature’s Kiss
P values C EON EOE EOA EOK
C
EON 0.000152
EOE 0.00026 0.81
EOA n/a 0.00015 0.00026
EOK n/a 0.00015 0.00026 n/a

20. 0
2
4
6
8
10
12
EON EOE EOA EOK Water
AverageZoneofInhibition(mm)
Treatment
B. cereus
E. coli
S. aureus
P. aeruginosa
Average Zone of Inhibition Per Treatment

21. Results: S. aureus
EON – Natures’ Oil
EOE – Eden’s Garden
EOA – Artisans Aromatics
EOK – Nature’s Kiss
P value C EON EOE EOA EOK
C
EON 0.00024
EOE 0.00088 0.101
EOA n/a 0.00024 0.00088
EOK n/a 0.00024 0.00088 n/a

22. 0
2
4
6
8
10
12
EON EOE EOA EOK Water
AverageZoneofInhibition(mm)
Treatment
B. cereus
E. coli
S. aureus
P. aeruginosa
Average Zone of Inhibition Per Treatment

23. Results: P. aeruginosa
EON – Natures’ Oil
EOE – Eden’s Garden
EOA – Artisans Aromatics
EOK – Nature’s Kiss
P value C EON EOE EOA EOK
C
EON n/a
EOE n/a n/a
EOA n/a n/a n/a
EOK n/a n/a n/a n/a

24. Summary of Results
• All essential oils showed significant zones of
inhibition on:
– B. cereus
• Two essential oils (EOE and EON) had
significant zones on inhibition on:
– S. aureus (Mean = 10.21mm)
– E. coli (Mean = 7.77mm)
• No measurable zones on inhibition on
– P. aeruginosa

25. Discussion
• Potential cause for differences:
– Gram interactions
• B. cereus and S. aureus = Gram positive
– No outer membrane
– More susceptible to antibiotics
• E. coli and P. aeruginosa = Gram negative
– Purity of oils
• Incorrect labeling and advertising
– Problems culturing P. aeruginosa
• Passed plates did not grow

26. Future Directions
• Steam distillation
– Requires large amounts of plant material
– Small product of essential oil
– Analysis of commercial and our oils

29. Future Directions
• Test more bacteria
– Because B. cereus had the largest zones of
inhibition, move on to Bacillus anthracis
(common in livestock and occasionally in
humans)

30. Acknowledgements
• Dr. April Kay
• Dr. Richard Collison
• Dr. Dean Turner
• MaryAnn McBrayer
• Misty Wheeler
• Josh Peppers
• Amanda Smith
• Dr. Jonathan Fisher
• DSC Foundation
• DSC Vice President of Academic Affairs Office

31. Questions?
Photo: Misty Wheeler