Norman Swan: The microbiome is on everyone's lips at the moment, so to speak. That's the huge largely bacterial population that lives on our skin, in our noses and gut. But one place which isn't often discussed when it comes to the microbiome is the vagina. The vaginal microbiome is important for women's well-being. Ask any woman who has had candidiasis. It can even make them more resistant or vulnerable to specific diseases such as chlamydia.

Jacques Ravel is an authority on this. He is a Professor of Microbiology and Immunology at the University of Maryland in Baltimore, second one of the day, and is in Australia for a conference on chlamydia. Welcome, Jacques, to the Health Report.

Jacques Ravel: A pleasure to be here.

Norman Swan: You talk about the mycobiome. What is the mycobiome in the vagina?

Jacques Ravel: So there are two types, if you want, of microbes that can live in the vagina. There's bacteria, and that would be the microbiome, and there is fungi and that would be the mycobiome.

Norman Swan: And candida is one of those fungi.

Jacques Ravel: Candida is one of the fungi that can live in the vagina.

Norman Swan: So what do we know about the vaginal microbiome? Because women have known about this forever really, without calling it the microbiome.

Jacques Ravel: So what we know is that it is often dominated by one species of bacteria, and that species name is lactobacillus.

Norman Swan: So unlike the bowel where there is millions of things which we don't fully understand, it's kind of a mono-bacterial population.

Jacques Ravel: So in a context of health, a healthy state, it would be basically almost like a monoculture of lactobacillus. And we know lactobacillus because it's a species that is very well-known in the food industry, we use it to make yoghurt. It's a lactic acid bacteria, and it ferments sugar to make a very acidic environment, and we use it basically in the dairy industry.

Norman Swan: So what affects the lactobacilli, what changes the microbiome in the vagina and what are the consequences?

Jacques Ravel: So lactobacillus is there in a healthy state, and you can have disruption of that dominance by lactobacillus, and those disruptions can come in from diet, obesity for example is associated, we just talked about it, is associated with a loss of lactobacillus.

Norman Swan: Why?

Jacques Ravel: It's something that we are still investigating, we don't fully understand the link that exists between the gut microbiota, so the bacteria that lives in our gut and those that live in a vagina, but there is certainly a link between the two that we still don't understand how they can communicate between one another. Sexual intercourse also can affect the composition of the microbiota.

Norman Swan: Because you inherit your partner's microbiome.

Jacques Ravel: Absolutely. So the male partner can actually be, if you want, a vector of transmission for bacteria. That can go from…

Norman Swan: These bastard men, you can't trust them for a minute. So presumably antibiotics?

Jacques Ravel: Antibiotics, just like in gut bacteria, antibiotics can basically eliminate lactobacillus and give the opportunity to other bacteria that are not very welcome there to grow and thrive in that environment.

Norman Swan: And menstruation as well, the periods can…?

Jacques Ravel: Absolutely, so physical changes to the environment, so for example a certain woman will use a vaginal douche and that will change the physical environment and the biochemical environment, and menses is just the same way. Oxygen is different during menses, you have a lot more oxygen because of blood, and that can actually also affect the composition of the microbiota.

Norman Swan: So you've got some evidence to suggest that if the microbiome in the vagina changes you can become more susceptible to an STD like chlamydia.

Jacques Ravel: Absolutely. So those facts have been established for quite some time, that the lack of lactobacillus in the vagina increases the susceptibility to sexually transmitted infection, including HIV, chlamydia, gonorrhoea and so on.

Norman Swan: So you want a healthy population of lactobacilli in your vagina. How do you induce that? Do probiotics work?

Jacques Ravel: My laboratory actually is involved in the development of a new solution that is based on probiotics that are coming directly from the bacteria, from lactobacillus that we isolated from women. So we developed this concoction, if you like, of microbes that we hope to deliver to women to maintain this very healthy state.

Norman Swan: In a pessary or orally?

Jacques Ravel: So those would be delivered vaginally, not orally.

Norman Swan: And the interruptions in diet, do we know the diet that is good for lactobacillus? Is it lots of yoghurts and fermented food or what?

Jacques Ravel: We don't know if fermented food or eating yoghurt actually increases the abundance of lactobacillus in the vagina. This is one of the…like I mentioned earlier, one of the secrets that we still haven't broken.

Norman Swan: Candida is a huge problem for women, very uncomfortable and the cause of a lot of morbidity. Do we know why Candida occurs apart from, say, antibiotics which clear out the lactobacilli? Do we know how Candida gets in?

Jacques Ravel: So Candida can be transferred from a partner, but basically at any given time about 20% of all women carry Candida. Not all 20% have candidiasis but they do carry Candida.

Norman Swan: In their mycobiome.

Jacques Ravel: In their mycobiome. And then a disruption of the microbiome, whether it's through antibiotic or other things like sexual intercourse can actually trigger the growth of Candida by often lowering the microbiota. So if you lower the amount of bacteria, you open the ecological space for Candida to grow and thrive, and that's when disease develops.

Norman Swan: So no clear answers yet but we are on the way.

Jacques Ravel: We're on the way.

Norman Swan: Jacques, thank you very much for joining us.

Jacques Ravel: Thank you very much.

Norman Swan: Jacques Ravel is a Professor of Microbiology and Immunology at the University of Maryland in Boston and a University of Technology Sydney distinguished scholar.