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Background: Bacteria are becoming more and more resistant to antibiotics with very few new antibiotics being discovered and tested.  Essential oils derived from a variety of aromatic plants have and are known for their benefits in massage therapy, cleaning, personal hygiene and medicine for thousands of years.  We investigated its antimicrobial ability with MRSA and several other known human pathogens.

Methods: We began testing concentrations of a commercial essential oil blend containing Wild Orange, Clove, Cinnamon, Eucalyptus radiata, and Rosemary against the single essential oil Melaleuca, comparing their abilities to inhibit the growth of MRSA using varying concentrations of the two oils on separate paper disks placed on plates inoculated with 5 x 105 of 80 different MRSA isolates, then incubating the plates for 24 and 48 hours at 35°C. We measured the zone sizes and compared the results.  To further verify that the bacteria was being killed and not just inhibited, we then took 22 MRSA strains, 9 Pseudomonas aeruginosa strains, 2 mucoid colony strain types of Escherichia coli, 1 strain of Stenotrophomonas maltophilia and 2 strains of Burkholderia cepacia and using a method similar to the serum bactericidal titer method, tested each of these isolates individually against the blend in a Tryptic Soy Broth tube.  Added 1 milliliter of a 5×105 suspension of each organism and exposed it to 10 μl of the commercial blend in 990 μl  of Tryptic Soy Broth for 8, 12, 20, and 24 hours then inoculated on Mueller Hinton agar plates and incubated for 24 and 48 hours at 35°C. We checked for any colony growth for each organism.

 Results: In the 80 MRSA isolates tested, the commercial essential oil blend showed a greater than 26% increase in disk diffusion zone size over Melaleuca against MRSA.

In testing the additional isolates against the blend with 1 milliliter of 5×105 the 50 different isolates of pathogenic bacteria all exposed to 10 μl of the blend in 990 μl of Tryptic Soy Broth, after incubating 20μl of this combined solution onto Mueller Hinton agar, there was no colonies growing for any of the bacterial isolates tested.

Plates were held for an additional 24 hours (for a total of 48 hours) and of the 50 isolates tested there were 8 total colonies that grew after the 8 hour exposure to the blend and incubated at 48 hours on Mueller Hinton Agar. There were a total of 5 colonies after that grew from the organism broths that had been exposed to the blend for 12 hours and incubated at 48 hours on Mueller Hinton Agar. There was no colony growth for the 20 and 24 hour exposure broths and incubated at 48 hours on Mueller Hinton Agar.  

Conclusions:  The commercial essential oil blend in vitro effectively kills a wide variety of pathogens in less time than traditional antibiotics. Organisms exposed to a minute amount of the essential oil blend are unable to recover and attenuate after prolonged exposure of less than 24 hours.

Jennifer is certified as a Specialist in Medical Microbiology with over 21 years experience in the medical field, as well as 16 years experience with fungal air sampling. She graduated from Colorado State University with a bachelor degree in Microbiology. Jennifer is the lead microbiologist at a local hospital and actively participates in best practice methods for helping find the most effective ways to care for patients. She is currently researching the effects of essential oils on many different microbial strains and new research areas.