Before the study, about 20 percent to 40 percent of E. coli in samples from all the women’s bodies were resistant to co-trimoxazole.

At the 12-month mark, between 80 percent and 95 percent of the bacteria were resistant in the women taking the antibiotic.

Rates of resistant E. coli were slightly lower at 12 months in women taking the probiotics than when the study began.

Similar changes in antibiotic resistance were seen for a range of other antibiotics, including ciprofloxacin and gentamicin, among both groups of women - which the researchers speculate might be because the same mechanism in certain bacteria allows them to resist several different drugs.

The absence of increased resistance among women taking the probiotics means that “lactobacilli may be an acceptable alternative for prevention of UTIs, especially in women who dislike taking antibiotics,” the researchers wrote in the Archives of Internal Medicine.

The study, however, had several limitations.

More than 80 women dropped out of the study by the end of the year because of side effects and other reasons. A greater number of those taking the probiotics had diarrhea compared to those taking the antibiotics, for instance. Other reasons for dropping out included the participant not thinking the treatment was working, or she couldn’t adhere to study’s directions.

As a result, the researchers did not have the number of participants in each group they would have liked to give the findings statistical weight.

Despite the study’s weaknesses, a commentary published in the same journal called the findings “exciting and compelling.”

“I think we need to appreciate that the normal flora in our body is another system we need for good health and antibiotics disrupt it and leave lasting effects… We need to think of antibiotics as a situation that has some risk,” Dr. Barbara Trautner, one of the commentary’s authors, told Reuters Health.

Trautner, of the Michael E. DeBakey Veterans Affairs Medical Center and Baylor College of Medicine in Houston, said that probiotics may be an acceptable alternative but they need further exploration.

Topical estrogen creams are sometimes used to prevent UTIs in menopausal women, but many women prefer to avoid using hormones.

In her commentary, Trautner wrote that 60 percent of women in the United States experience UTIs or bladder infections during their lifetimes, and they recur in about a third of those women.

“We don’t have terrific preventive strategies so a probiotic approach would be beneficial and promising,” Trautner said.

For right now, she said most women with recurring UTIs have exhausted any type of behavioral changes that might help prevent the infections, and are left with low-dose antibiotics as their only recourse.

SOURCE: Archives of Internal Medicine, May 2012.