Melanie Hesketh, who works at the Lifetime Wellness Center in Windsor, Ontario, told the Windsor Star she bought the cheeseburger without ketchup or mustard Dec. 29, 2010, as an experiment.
She left the unwrapped burger unrefrigerated on her counter for the past year and said not much has changed, apart from the bun turning stale. She said it "still smells slightly like a burger," although there has been no sign of mold, maggots or bacteria.
"Obviously it makes me wonder why we choose to eat food like this when even bacteria won't eat it," she told the Star.
McDonald's officials didn't respond to calls from the newspaper, but the company Web site says its "regular bun" contains at least 32 ingredients and the processed cheese slice has 15 ingredients.
Hesketh said she expects the cheeseburger will remain with her for a long time.
"I'm going to keep it forever -- it's a good conversation piece," she said.