- Caseous lymphadenitis (CL) is a highly contagious and chronic disease that effects sheep and goats and is caused by the bacteria Corynebacterium pseudotuberculosis. Due to the nature of this pathogen, CL is very difficult to treat with standard antibiotics. C. pseudotuberculosis is also highly resilient and able to survive in the environment for extended periods of time where it can be easily spread throughout a flock. This disease causes a decrease in production in these animals and therefore a loss of income for farmers. The purpose of this project is to find an alternative method of treatment and/or control of the disease by using essential oil components with known antimicrobial properties. If effective these essential oils could be used as an oral or topical antibiotic for effected small ruminants or as a disinfectant for contaminated farm surfaces.
- The efficacy of several essential oil components as antimicrobials against C. pseudotuberculosis will be tested using a standard disk diffusion assay. The most effective of these components will then be tested for cytotoxic effects against mammalian immune cells to determine the safety of using them on or around small ruminants.
- Conclusions have not yet been determined.
1. To determine which essential oil constituents are most effective as antimicrobials against C. pseudotuberculosis
2. To determine the cytotoxic effects of select essential oils on mammalian immune cells
3. To evaluate stimulatory effects of essential oil constituents on immune-related genes in macrophage and neutrophil cells
The purpose of this project is to find an alternative method of treatment and control of caseous lymphadenitis (CL) using constituents of essential oils with known antimicrobial properties. CL is an extremely prevalent disease that affects sheep and goats across the country and worldwide. A 2012 SARE-funded study of Maine sheep found that approximately 22% of Maine sheep tested positive for CL exposure using the Synergistic Hemolysin Inhibition assay. Additionally, 43% of the Maine sheep farms had at least one animal that tested positive for CL. Due to the highly contagious nature of the pathogen and the prevalence observed on Maine farms, it could be predicted that the total percentage of infected sheep has since increased, unless proper biosecurity methods were administered. External abscesses caused by CL infection can significantly decrease the value of the animal hide as well as the amount of wool production. The disease can even be fatal when internal abscesses, often occurring in the lungs and abdominal cavities, rupture and release bacterial toxins. There are currently no widely effective control and prevention measures for this disease making it an ongoing issue in the small ruminant industry. Recent research has shown that certain essential oil components have antimicrobial properties against even highly antibiotic resistant bacteria. If successful, the results of this project could give farmers the option for alternative CL treatment that may be easier and more cost-effective than using an antibiotic regimen.
The essential oil constituents that will be evaluated for their antimicrobial activity against Corynebacterium pseudotuberculosis will be drawn from a list including cinnamic acid, p-anisaldehyde, B-pinene, carvacrol, cinnamaldehyde, B-citronellol, cuminaldehyde, a-terpinene, terpinolene, and thymol. These compounds were chosen due to their growth inhibition abilities of Mycobacterium tuberculosis, a closely related bacterium to C. pseudotuberculosis. (Andrade-Ochoa et al., 2015) Antimicrobial activity will be evaluated by determining the minimum inhibitory concentration (MIC) values, or the lowest possible concentration of the chemical that prevents visible growth of the bacteria. The values will be determined using an agar disk diffusion test, a standard procedure in the microbiology field for testing antimicrobial efficacy in vitro. The ATCC strain of C. pseudotuberculosis is spread evenly on the surface of Brain Heart Infusion (BHI) agar plates. Different concentrations of essential oil components diluted in Tween and water are then added to sterile 6 mm paper disks in the center of each plate. The plates are incubated at ideal growth conditions for C. pseudotuberculosis (37° C, 5% CO2). The zones of inhibition around each disk (area where the bacteria is unable to grow) are measured after 24, 48, and 72 hours of incubation. This is repeated until the minimum concentration of each essential oil constituent that is able to inhibit C. pseudotuberculosis growth is determined. This is the stage of the project that is currently being worked on.
We are currently working on Phase 1 of the project which involves determining the minimum inhibitory concentrations of essential oil constituents against C. pseudotuberculosis. We have some preliminary results for the essential oil components and the final results should be determined by February.
Conclusions have not yet been determined.
Education & Outreach Activities and Participation Summary
A presentation was given at the 2018 Maine Sheep Conference and Annual Meeting in Bangor, Maine. The conference was attended by approximately 15 sheep producers of the Maine Sheep Breeders Association (MSBA) as well as members of the University of Maine Cooperative Extension. This presentation covered general information about caseous lymphadenitis (CL) such as disease prevalence, transmission, and prevention. We also discussed our current research using essential oil components as antimicrobials for Corynebacterium pseudotuberculosis, the causative agent of CL.
A journal article will be prepared and submitted once we have determined the minimum inhibitory concentrations of each of the essential oil components against C. pseudotuberculosis. An additional journal article may be submitted upon completion of the project.
The project results will also be presented at the University of Maine Student Symposium in Bangor, Maine on April 10, 2019. This symposium is attended by UMaine students, faculty, and the general public.
Conclusion have not yet been made for this study therefore the project outcomes cannot be determined.
Through this project I have gained a better understanding for the struggles that many small-scale farmers face in controlling diseases such as CL. I hope to continue to do research on the control and prevention of infectious diseases in livestock and other farm animals.