First it was the gut. Then came the vagina. Now it seems microorganisms in the female bladder could play an important role in health too.

For the first time, Australian researchers have identified a collection of bacteria living in the female bladder that exists even in the absence of infection.

They've dubbed it the "bladder microbiome".

The findings paint the most comprehensive picture of the bladder ecosystem to date, and may provide new insights into the prevention and treatment of urinary tract infections, said Samuel Forster, lead author of the study published in Nature.

The idea that the human bladder (and therefore urine) is sterile is a pervasive medical myth.

Scientists have known for a long time that the bladder can harbour bacteria, but it is usually in the case of infection.

"Now, the research is showing bacteria associated with health in the female reproductive tract are also able to colonise the bladder without causing infection," said Dr Forster, of the Hudson Institute of Medical Research.

Dr Forster said the discovery of the "mini microbiome" will help scientists better understand why some people are more susceptible to UTIs (especially recurring infections), and may provide new approaches to effective treatment.

Bladder and vagina microbiome interconnected

Dr Forster and his colleagues, using genome-sequencing technology, isolated 149 strains of bacteria from the bladders of 77 women.

They found both healthy and disease-causing bacteria moved freely between the bladder and the female reproductive tract, even in healthy women.

"This suggests the female bladder is part of an interconnected bacterial community with the female reproductive tract," Dr Forster said.

Dr Forster said the discovery of the microbiome suggests UTIs, which are caused by bacteria entering the urethra, may be affected by the existing balance of "good" and "bad" bacteria in the bladder.

Currently, it is standard practice to treat UTIs with a course of antibiotics, which essentially wipes out all bacteria in the area.

"It raises the question: if antibiotics are used to kill the 'bad' bacteria in patients with UTIs, could this also upset the balance of healthy bacteria that have a protective effect, much like in the gut?" Dr Forster said.

In Australia, more than 70,000 people are hospitalised with kidney or urinary tract infections each year, and one in two women will suffer a UTI in their lifetime.

In some cases, UTIs don't respond to normal treatment, leaving some women with painful, recurring infections.

Dr Forster said the research could help to unearth new treatments that harness the protective effects of the "good" bacteria, rather than wiping out the bacterial community altogether.

"We can also start to do experiments that enable us to say: this bacteria is causing a particular condition, and therefore it's a worthwhile target from a therapeutic perspective."

Helping fight antibiotic resistance

Iain Duggin, a microbiologist from the University of Technology Sydney who was not involved in the research, said the "landmark study" could help in the quest to find treatments for UTIs that are otherwise untreatable because of antibiotic resistance.

"Antibiotic resistance is drastically on the rise globally, and UTIs are one of the most common infections in the world," Associate Profession Duggin said.

"There's real need for research into new treatment options in cases of UTIs and any other infection caused by bacteria."

The next stage of the research, according to Dr Forster, is to look more closely at the different types of bacteria in the bladder, and how they might work to help or hinder our immune defences.

Samuel Forster's team found about two-thirds of all bacterial species in the bladder are also found in the female reproductive tract. ( Supplied: Hudson Institute of Medical Research )

"The species we're looking at, at least in the female reproductive tract, are fundamentally associated with health," he said.

"It suggests that they're probably acting in a way that's promoting health, but we don't actually know that yet.

"More research is needed to examine whether bacteria associated with health or disease in the female reproductive tract have the same positive or negative effect in the bladder, and vice versa."

In the meantime, Dr Forster said antibiotics remain the best course of treatment for UTIs.

"It's not that we shouldn't be using antibiotics, it's just that we should be considering our use of them, and seeing if we can come up with better alternatives that would be preferable in some circumstances," he said.