Two common antibiotics taken in combination may help delay symptoms of Alzheimer's disease, according to the surprising results of a new Canadian study.

The study, to be presented at the annual meeting of the Infectious Diseases Society of America, was conducted by a research team led by Dr. William Molloy at the St. Peter's Centre for Studies in Aging, in Hamilton, Ontario.

Armed with the knowledge that plaques formed in the brain have been associated with jumbled memories, and the fact that researchers have also found the chlamydia pneumoniae bacterium in the brains of people with Alzheimer's disease, Molloy came up with a novel hypothesis.

He theorized an infection might trigger the disease and if that was the case, then an antibiotic might help.

Dr. Molloy told CTV's Canada AM he decided to assemble a research team and take a chance.

"We literally took a shot in the dark ... (We) picked some antibiotics, picked the doses, picked the duration and said let's go for it. We did the study and you could have knocked us over with a feather when we got the results," he said.

Using a test group of 101 Canadian patients with mild to moderate Alzheimer's, Molloy's team gave half the participants a combination of two 100 mg tablets of doxycycline and one 300 mg tablet rifampin every day for three months. The other half received a placebo.

The researchers chose the two common, generic antibiotics when drug companies with newer antibiotics refused to fund the research. Doxycycline is used to treat various bacterial infections, and rifampin is commonly used to treat tuberculosis.

According to McMaster University associate professor Dr. Mark Loeb, when the trial was over, the placebo group's health had deteriorated as expected.

"Most people in our study had been on other medications, and were not doing very well. Patients who took antibiotics had significantly less of a mental decline than those who were given the placebo," Loeb said in a statement.

Buoyed by the results, Molloy said the study shows the treatment is doing more than alleviating symptoms -- it has a disease-modifying effect.

"You treat them for three months and at the end of the year they're better than the placebo group, so the effect lasts for a year," he said, adding it appears to be more effective than the existing array of Alzheimer's medications.

But, Molloy said he could not be certain what his team witnessed was an anti-bacterial effect or something else.

"It could be an independent effect. It may not actually be an anti-bacterial effect. We have no clue," he told Canada AM.

While Dr. Sandra Black is encouraged by the "pioneering" spirit of the research team, the Sunnybrook & Women's Health Sciences neurologist warns it's too soon to start recommending the treatment.

"The potential is very promising, but I'm not sure we're at the point we should be recommending this to families.

"I would advise some caution. These medications do have side effects. They can cause damage to the liver, they can interact with other medications... so they are not innocent. But they are available, and in wide use for other conditions," Black told CTV News.

Now, the Hamilton research team is hoping scientists worldwide will try to replicate their success with further testing of the combination of common, inexpensive antibiotics.

Molloy said he next hopes to see if he can use the results to prevent Alzheimer's.

"We'd like to get people ... before they get Alzheimer's and give them these antibiotics in different doses for different durations and see if we can prevent people from getting it," he said.

With files from CTV's Avis Favaro