Bacteria and corneal ulcers

The cornea is a key component of the eye that allows it to focus on light, enabling people and animals to see clearly. But what happens if a dog’s cornea is no longer clear and healthy?

Corneal health can be affected by diseases such as bacterial ulcerative keratitis, a common eye infection that causes inflammation and severe pain and can lead to blindness. 

“Ulcerative keratitis is one of the leading causes of vison and globe loss in dogs,” says Dr. Stephanie Osinchuk, a veterinary ophthalmologist and a former assistant professor at the Western College of Veterinary Medicine (WCVM). “We are treating corneal ulcers several times a week.”

When bacterial ulcerative keratitis occurs, the bacteria produce enzymes that cause corneal malacia — a melting of the cornea that can cause the ulcer to deepen and the eye to rupture. Bacterial keratitis can be managed medically or surgically. 

“When the ulcer on the surface of the eye exceeds 50 per cent of the depth, we recommend [conjunctival pedicle graft] surgery that can essentially patch the defect,” says Osinchuk.

However, the WCVM ophthalmology team has recently encountered problems with their surgical patients that may be associated with necrotizing bacteria. A number of ulcer cases at the WCVM Veterinary Medical Centre have developed postoperative complications that have caused the graft to become devascularized and necrotic. 

“When the failed cases were cultured for bacteria, a lot of them came back positive for Streptococcus canis, a bacterium that is a part of the normal skin microflora in dogs,” says Osinchuk.

Now, Osinchuk and veterinary ophthalmologist Dr. Lynne Sandmeyer are conducting research to determine if there is an association between the graft failures and the presence of S. canis bacteria. They are also investigating the most common bacterial pathogens associated with complex ulcers to determine their antimicrobial resistance profiles. 

“I think the bacteria that are present in the ulcer are a contributing factor to the outcome,” says Osinchuk. “Given the changing bacterial population that we see, it is critical that we monitor that over time as well as their response to antibiotic treatments, especially in an era of increased antimicrobial resistance.”

Although several other studies have identified the most common bacteria associated with corneal ulcers, this investigation will be the first one to describe the corneal bacteria found in Western Canada. 

The project will investigate potential predisposing factors that are associated with the development of complex corneal ulcers. Previous studies have found that brachycephalic breeds such as pugs and bulldogs may be more susceptible because their eyes are more prominent, and they have decreased corneal sensitivity and insufficient tears. 

With a better understanding of the bacterial populations and the predisposing factors, more targeted and more effective antibiotics and treatments can be used — and more eyes can be saved. 

Xiao Ma of Winnipeg, Man., is a third-year veterinary student at the Western College of Veterinary Medicine (WCVM).