Horsin’ Around

Bacteriophage therapy has been under the radar of researches as the damning issue of antibiotic resistance begins to plaque the globe. As plan B antibiotics are being rendered useless, phage therapy has high hopes to save the crisis, but not only for humans. Phage research has been done on livestock in order to improve animal health and productivity. Of particular interest to me is the studies involving bacterial keratitis in horses, having owned a horse with keratitis I have first-hand experienced the difficult and expensive process of finding antibiotics that work.

Vet examining a horse with possible bacterial keratitis. Retrieved from https://equimanagement.com/articles/research-on-ulcerative-keratitis-in-horses

What is keratitis? Equine keratitis is an infection of the cornea often resulting in an ulcer which if left untreated can lead to blindness in the eye [1]. Racehorses are most prone to this disease due to their heads being in constant movement, increasing amount of eye surface area available. This creates a greater risk of the nasty bacteria creeping in [2]. It is also an issue in competition, such as in polo where horses who are blind, even if only one eye, are unable to compete. This disease can be identified by staining the cornea to see defects produced or production of an ulcer.

From L to R: Healthy horse eye without keratitis. Retrieved from https://www.horseandhound.co.uk/horse-care/5-incredible-facts-horses-eyes-636770 Horse eye with keratitis which has been stained. Retrieved from https://thehorse.com/130567/corneal-disease/ .

The biggest issue in treating keratitis is the emerging bacterial resistance. Getting the infection just once creates the horse to be more prone to contracting the bacteria again. This is often due to the environment the horse is in, being exposed to the same conditions increases the risk of it being in contact with the same bacteria [3]. As antibiotics are prescribed, they are becoming less and less effective, due to this overuse, leading to the question of what is next? Phage therapy was bought to the table and has produced promising results.

A study in Japan has shown this by the use of a model organism mouse [2]. They were able to incorporate the bacteria into the animal and successfully insert a bacteriophage to kill the strain before an ulcer could form. Their aim was to find an alternative to racehorse antibiotic washes which were used immediately after running to prevent infection to begin with. These washes were becoming ineffective and increasing bacterial resistance when applied so often. To begin with they followed a very similar protocol to find the bacteriophages we have done in Phage Hunt but instead of using Mycobacterium smegmatis [4] they used a Pseudomonas aeruginosa bacteria strain. Pseudomonas aeruginosa is a common rod-shaped bacterium found in both animals and humans [5]. They isolated [6] their samples from sewage material and were able to purify, amplify and view under an electron microscope just as I did with my phage Gavin.

Phage that were isolated from sewage material. Top phage are Podovirade and bottom phage are Myrovirdae. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4988198/#B26

The resulting phage were identified to be of Myrovirdae and Podovirdae families, since Podovirade phage are more broad specific they decided to experiment on this phage for a greater chance of infecting the bacteria [7]. The mice were infected with the disease and phage samples were added, ensuring they were absorbed and not spilled out as tears. Results showed that the phage sample was effective until 3 hours after infection, the bacteria was successfully attacked by the phage and no ulcers or cornea damage was seen.

Although 3 hours is a very short period of time, for the purpose of preventing the infection in this racehorse situation it could be ideal to replace the antibiotic wash with a phage wash. The antibiotic washes are possibly not as effective due to not being well absorbed or retained when applied and it also helps to decrease antibiotic resistance.

My horse Millie who recovered from Bacterial Keratitis without going blind. Photo credit: Carole Pinkney

A small step in the right direction may be all it is but with more research phage therapy could be adapted for long term treatment of equine keratitis and other bacterial infections. Phage therapy, once forgotten could now be the answer to all our questions, including our newly discovered phage from Phage Hunt. Who knows, maybe one day my phage Gavin will be saving an eye or a life.

Bibliography

1. Nasisse, M.P. and Nelms, S. (1992) Equine Ulcerative Keratitis. Veterinary Clinics of North America – Equine Practice 8 (3), 537-555.

2. Furusawa, T. et al., Phage Therapy Is Effective in a Mouse Model of Bacterial Equine Keratitis, 2016, pp. 5332-5339.

3. Keller, R.L. and Hendrix, D.V.H., Bacterial isolates and antimicrobial susceptibilities in equine bacterial ulcerative keratitis (1993-2004), 2005, pp. 207-211.

4. Hatfull. G., J.-S.D., Pope. W., Poxleitner. M., & Sivanathan. V, The Science Education Alliance-Phage Hunters Advancing Genomics and Evolutionary Science Discovery Guide, 2018.

5. Cohen-Cymberknoh, M. et al. (2017) Clinical impact of Pseudomonas aeruginosa colonization in patients with Primary Ciliary Dyskinesia. Respiratory Medicine 131, 241-246.

6. Tanji, Y. et al., Spontaneous deletion of a 209-kilobase-pair fragment from the Escherichia coli genome occurs with acquisition of resistance to an assortment of infectious phages, 2008, pp. 4256-4263.

7. Jonczyk, E. et al., The influence of external factors on bacteriophages-review, 2011, pp. 191-200.

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