Essential Oils as a Disinfectant in Poultry

Escherichia coli and Aspergillus fumigatus are environmental pathogens that cause disease in domestic poultry flocks and economic losses for farmers. Antibiotic use, while effective against E coli, has disadvantages, including drug residues in meat and eggs and the selection of multidrug resistant pathogens. Antimycotics are expensive and cannot be used in animals intended for human consumption. Therefore, infection prevention is crucial in controlling these diseases.

Researchers in Italy recently performed an investigation looking at the in vitro antimicrobial effect of 16 essential oils against E coli and A fumigatus. The results of their work were published recently in Veterinary Sciences.

Study Design

The essential oils tested were lemon verbena, incense, cinnamon, bitter orange, bergamot, lemon, mandarin, lemon grass, eucalyptus, litsea, lavender, basil, tea tree, geranium, peppermint, and clove. Additionally, 5 essential oil mixtures were also tested: litsea and lemon grass (M1), litsea and lemon verbena (M2); lemon verbena and lemon grass (M3); litsea, lemon grass, and lemon verbena (M4); and cinnamon and clove (M5). The essential oils were incubated on inoculated blood agar plates and the minimum inhibitory concentration (MIC) and fractional inhibitory concentration index (FICI) were calculated. FICI is used to evaluate synergy or antagonism in the components of the mixtures.

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Results

Growth inhibition zones were seen on the E coli plates treated with cinnamon, lemon grass, litsea, peppermint, basil, geranium, and clove. No inhibition zones were seen with the remaining EOs. Cinnamon (MIC 2.52 mg/mL), clove (1.318 mg/mL), lemon grass (1.118 mg/mL), litsea (1.106 mg/mL) and peppermint (1.14 mg/mL) were the most effective, with considerably lower MIC values than basil (9.15 mg/mL) and geranium (17.8 mg/mL). All of the essential oil mixtures were effective to some extent against E coli, with M5 (cinnamon and clove) having the lowest MIC (2.578 mg/mL). The other mixtures were not considered to have good antibacterial action as their components were found to have an antagonistic effect on each other.

Of the A fumigatus plates lemon verbena (MIC 0.855 mg/mL), lemon grass (0.895 mg/mL), litsea (1.77 mg/mL), and tea tree (1.78 mg/mL) were found to have the best antifungal action. Cinnamon (5.05 mg/mL), bergamot (8.70 mg/mL), lemon (4.25 mg/mL), mandarin (4.25 mg/mL), eucalyptus (4.575 mg/mL), lavender (8.86 mg/mL), basil (9.15 mg/mL), peppermint (9.12 mg/mL), and clove (8.95 mg/mL) had some antifungal activity but relatively high MIC values. The remaining essential oils and all of the mixtures had no antifungal action—all the mixtures were found to have antagonistic components when looking at the FICI values.

Implications

The authors concluded that the findings from this study indicate that there may be practical uses for essential oils in the environmental disinfection of poultry farms and/or hatcheries. The mixture of cinnamon and clove could be an alternative treatment for E coli, while lemon verbena could be used against A fumigatus spores. Because litsea showed efficacy against both E coli and A fumigatus, it could be considered for use as a sole agent, potentially reducing the risk of infection for both animals and humans.

Dr. Sewell received her BVetMed MRCVS in 2008 from the Royal Veterinary College in London. She previously worked in mixed animal practice before settling in Essex, United Kingdom to focus on companion animals and exotics.