'Friendly bacteria' found in yoghurt has been genetically modified by a team of US researchers headed by an Indian American to produce a drug that blocks HIV infection.

Although the bacteria has only been tested in a lab dish, scientists are optimistic the technique could provide a cheaper and more effective way of delivering drugs to fight the spread of AIDS, by getting the bugs to live right where the drugs are needed most, Nature magazine reported.

The bacterium (Lactococcus lactis) the researchers have modified naturally produces lactic acid, and so is used to produce cheese and yoghurt. It is also found in some parts of the human anatomy, including the gut and the vagina, where the acid it produces damps down the growth of other, harmful bacteria, Nature said.

Some 'probiotic' yoghurts are loaded with such beasties with the aim of keeping consumers' guts healthy. Bharat Ramratnam, an HIV specialist at Brown Medical School, Providence, Rhode Island, and his colleagues have now altered the genetic make-up of L.lactis so that it generates cyanovirin, a drug that has prevented HIV infection in monkeys and human cells, and is on track for human trials in 2007, the magazine reported.

ANI adds: Cyanovirin binds to sugar molecules attached to the HIV virus, blocking a receptor that  HIV uses to infect cells.

"It's basically passive immunization," says Sean Hanniffy, a molecular biologist  at  the Institute of Food Research, Norwich, UK, and part of the team.Gels containing cyanovirin could afford some protection for women  against  the transmission of HIV, but since the drug breaks down quickly these would have to be used just before sex. "In some countries there's a reluctance to use these gels frequently," explains Hanniffy.

Because lactic-acid bacteria live naturally in the vagina, one application of a bacterial goop should see the modified bugs thrive there for at least a week, says Hanniffy. "The next  step might be to use other bacteria that can survive for even longer," he adds.