Image copyright Getty Images Image caption BV bacteria covering cells

US doctors are hoping to start offering women vaginal fluid transplants and have set up a programme to screen potential donors.

They believe some women could benefit from a dose of healthy vaginal microbes to protect against an infection called bacterial vaginosis (BV).

The Johns Hopkins University team say they were inspired by the success of faecal or poo transplants.

Although antibiotics can treat BV, it often comes back.

What is BV?

BV is not a sexually transmitted disease, despite being an infection.

It's quite common and women who have it may notice that they have an unusual discharge that has a strong fishy smell.

The condition is not usually serious, but should be treated because having BV makes women more vulnerable to catching sexually transmitted infections and getting urinary infections.

If the woman is pregnant, it increases the risk of her having the baby early.

Why might donor vaginal fluid help?

BV can happen when there is a change in the natural balance of bacteria in the vagina.

The vagina, like the gut, is home to lots of different microorganisms.

Our diets, lifestyles and some types of medication that we may take can upset this finely balanced ecosystem.

While there has been a large amount of work into the gut microbiome, less is known about the vagina.

Experts know healthy microorganisms in the vagina prefer an acidic environment, and when the pH becomes too alkaline other bacteria - including those that cause BV - can thrive.

A number of factors can raise vaginal pH and make BV more likely, including having sex (semen and saliva are slightly alkaline) and using douches or vaginal washes, as well as hormonal changes at particular times of the month during a woman's menstrual cycle.

What would the transplant involve?

The researchers have been looking at what makes a fit, safe donation in preparation for starting to offer women with BV the transplants - which they hope to do soon now that they have regulatory approval from the Food and Drugs Administration.

They screened a small number of volunteers and have reported their findings in the journal Frontiers in Cellular and Infection Microbiology.

Based on the 20 women they have tested, the researchers say they have gained some insights into what might make an "ideal" donor.

Vaginal fluid samples dominated by a bacterium called Lactobacillus crispatus tended to have higher protective lactic acid content and a lower pH which might be beneficial, they say.

As a precaution, donors would be asked to abstain from sex for at least 30 days before giving a sample and would be screened for any infections, including HIV, to prevent them being passed on to any recipient, they add.

One of the researchers, Dr Laura Ensign, said: "The donation is a self collection, which we know people tend to prefer."

The woman inserts and then removes a flexible plastic disc - similar to a menstrual cup or a contraceptive diaphragm - to collect the sample.

"It's quick and easy and one sample collected like that would be enough material to make one dose for transfer," she said.

It would be drawn up into an applicator for the recipient to insert in a similar way to a tampon.

Dr Ensign said: "If we can get funding, we could start right away. Some of the donors that we studied said they would want to take part.

"We'd plan to give transplants to 40 recipients to begin with. Some would receive the real thing and others a placebo. All of them would get antibiotics for their BV too though."