A common ingredient found in toothpastes and handwashes could make antibiotics less effective in treating conditions like urinary tract infections (UTIs), which, if left untreated, can become life-threatening, say researchers.

Triclosan is the active ingredient responsible for the "antibacterial" property which is added to toothpaste, mouthwash, cosmetics. It is even added to clothing, baby toys and credit cards with the intention of reducing or preventing bacterial growth.

According to the study, led by researchers at the Washington University in St. Louis, triclosan exposure may inadvertently drive bacteria into a state in which they are able to tolerate normally lethal concentrations of antibiotics, including those that are commonly used to treat UTIs.

UTIs occur when bacteria, primarily Escherichia coli (E. coli), enter and infect the urinary tract. Antibiotics such as Cipro are commonly used to kill the bacteria and treat the infection. UTIs are common, so is exposure to triclosan. About 10 per cent of adults have levels high enough to prevent E. coli from growing.

In the study, published in the journal Antimicrobial Agents and Chemotherapy, the team examined whether triclosan's presence in the body interferes with treating UTIs. They found that mice which drink triclosan-spiked water have urine triclosan levels similar to those reported in humans.

"This result meant we could actually test the impact that human urine levels of triclosan have during antibiotic treatment of UTIs in mice," said Petra Levin, Professor at the varsity.

After antibiotic treatment, mice with triclosan exposure had a large number of bacteria in their urine and stuck to the bladder, but mice without exposure had significantly lower bacterial counts. They found 100 times more bacteria in the urine of triclosan-treated mice, suggesting that antibiotics are less effective at treating UTIs when triclosan is around.