The engineered bacteria showed promise in laboratory testing, and researchers now plan to try them out in animals, said John A. Lewicki of Osel Inc., in Santa Clara, Calif.
The most common way AIDS is transmitted is through heterosexual intercourse, with women particularly vulnerable in countries where condoms and other protective measures are less available.
Researchers used a strain of Lactobacillus jensenii, generally abundant in mucus secreted by the mucous membrane lining a healthy vagina. The bacteria were modified to produce a protein called CD4, which binds to the HIV virus that causes AIDS.
In laboratory tests, the enhanced bacteria reduced the rate of HIV infection in susceptible cells by at least half, the researchers said. Their findings are reported in this week's online issue of Proceedings of the National Academy of Science.
"The paper presents our first prototype for a product that will come to use," Lewicki said in a telephone interview. His company develops therapeutic products from common bacteria.
"This is something we believe is moving toward a clinical reality," he said. But, he said, animal testing is needed and the developers will work closely with the Food and Drug Administration before human testing can be done.
Roberta Black, the topical microbicide team leader at the National Institute of Allergy and Infectious Disease, said the researchers "have shown proof of concept in the laboratory, and that's certainly where everything starts, ... but it's a big jump to people."
Nonetheless, she said, this is a "highly innovative approach that exploits a naturally occurring defense mechanism."
The researchers need to avoid problems like that with nonoxynol-9, a microbicide that was promoted for similar use, but it irritated vaginal tissue and increased the chance of HIV infection.
Lactobacillus works differently from nonoxynol-9, Lewicki stressed, by enhancing the protective bacteria rather than damaging them.
The research was led by Peter P. Lee of Stanford University, who said in a statement that he envisions the research eventually leading to creation of a small vaginal suppository that a woman could use on a regular basis.
"It would be as discreet as can be," said Lee, adding that each dose could last a week or longer and could be inserted at any time. He said he hopes to translate the technology to other viruses, such as the human papilloma virus, the herpes virus, even the common cold or flu.
By Randolph E. Schmid