Presence of Lactobacillus May Reduce HIV Concentration in Vaginal Fluid

A Study Summary by Jane Hitti, M.D., M.P.H.

In this summary of her study, Jane Hitti, M.D., M.P.H., of the University of Washington at Seattle, examines study findings suggesting that a bacteria known as lactobacillus, which occurs naturally in the vaginal flora of many women (and is similar to a bacteria found in yogurt), appears to reduce vaginal HIV viral load.

Jane Hitti: We were interested to see how healthy vaginal bacteria, as well as abnormal vaginal bacteria, might influence the amount of HIV found in the vagina, for women who are HIV positive. And so we followed a group of 57 women from Seattle, Washington, and from Rochester, New York, for up to five years, and followed them sequentially, and looked at changes in their vaginal bacteria, as well as changes in the vaginal viral load, and the plasma viral load.1 And what we found, just to summarize in a nutshell, first of all, is that only about half of the women at any given time were carrying the good bacteria called lactobacillus, and that some women switched back and forth between carrying the good bacteria and not having it. When these women had the healthy lactobacillus in the vagina they tended to have a lower viral load in the vagina. And this was statistically significant, even when you corrected for other factors like how much HIV was in their plasma, and whether or not they were on antiretroviral therapy.

Jane Hitti, M.D., M.P.H.
Jane Hitti, M.D., M.P.H.

So we took it one step further and looked at two visits for the same woman over time, which we call the visit pair, and looked at changes in the vaginal viral load if the women went from not having the healthy lactobacillus to actually carrying it, or the reverse, and compared that to women who always had the healthy bacteria. And what we found was that women who acquired the healthy bacteria, the lactobacillus, had a .7 log decrease in their vaginal viral load, compared to women who were stable the whole time. And conversely, women who lost the healthy bacteria, the lactobacillus, had a .5 log decrease in their viral load. And this remained statistically significant.

So, what I think is important about these findings is that it stresses the importance of maintaining a healthy lactobacillus vaginal flora for HIV-infected women. One of the logical next steps here might be to think about -- since not all of these women had the good bacteria all of the time -- whether or not it might be possible to develop some strategies to promote vaginal health by increasing the likelihood that women would carry these healthy vaginal bacteria as possibly a way to decrease the amount of HIV in the vagina, which could be helpful in terms of preventing spread of HIV in the future.

Reporter #1: Dr. Hitti, did you say that when women lost lactobacillus, they had a 5% decrease in the vaginal viral load?

Jane Hitti: No. They had a .5 log increase in vaginal viral load when they lost. That means that their viral load went up in the vagina. The amount of HIV in their vagina went up when they lost the lactobacillus.

Reporter #2: I asked you this question at the presentation, as well. How might one supplement lactobacillus? This is also, it occurs to me, something that has been done with over-the-counter preparations, as well. So if this sort of news gets out, women might be wanting to deal with this themselves.

Jane Hitti: Yes. I appreciated your question at the presentation. As Dr. Hillier was saying, lactobacillus is a kind of bacteria that's commonly found in a lot of different settings, including in yogurt. And way back in the 1970s there was interest in douching with yogurt to try to cure yeast infections, and that kind of thing. I think the ideal approach here is to use the lactobacillus that specifically likes to live in the vagina. So the lactobacillus in yogurt is kind of a cousin, but it doesn't really feel at home in the vagina. So the optimal approach, from my perspective, would be to take a well-characterized preparation of lactobacillus, so that you know exactly what's in that capsule. And that means probably F.D.A. approved and regulated, as opposed to less stringently prepared preparation. And do trials to look at whether or not it's possible to achieve colonization with that type of lactobacillus in the vagina. Now, these studies have been done, to some degree, among HIV-negative women, to look at colonization, and also to look at short-term treatment for conditions like bacterial vaginosis and urinary tract infections. But to my knowledge I don't think any similar trials have as yet been done in HIV-positive women. And that's a direction that I hope that we can go in.

Reporter #3: I was wondering if you could explain: Why is it that the colonization with lactobacillus seems to have some affect on the HIV? And also, I was wondering: Why is it that the women seem to vary? What are the factors that might cause variance?

Jane Hitti: Variability in that? Those are two really good questions. In terms of why lactobacillus might affect HIV and be protective: Some kinds of lactobacillus can make factures, like hydrogen peroxide, but other antibacterial and antiviral factures, that help to control and minimize other kinds of bacterial and viral infections. And there have been some studies in a laboratory setting, suggesting that, at least in the laboratory, lactobacillus can inhibit HIV. This is taking those kinds of studies one step further.

In terms of why some women are colonized, and some are not: that's a great question, and I think it's a really important thing to understand. And I don't have a full answer to that question. There are some studies that suggest that HIV-positive women may be less likely to be able to maintain colonization of lactobacillus, but that's not really consistent across studies.

Reporter #4: I've heard HIV-positive women get upset about controlling HIV for the purposes of transmission to other people and it's offensive to them, to some degree. That's what I've heard. And so I was wondering: the lowering of HIV in the vagina is a good thing, isn't it?

Jane Hitti: Yes. Absolutely, it's a good thing.

Reporter #5: Yes. To follow up on that question: Although it would make HIV less transmissible for the individual, is there any clinical benefit for a person who maintains a normal vaginal flora, for example? And one other thing is: In clinical medicine, we often associate the perturbance of normal flora with treatment of infections, rather than the infections themselves. And I'm just wondering: Did you see this decrease in lactobacillus in people associated with the disease, or with the disease while being treated, or after treatment?

Jane Hitti: That's a complicated question, with several parts in it. To take the first part, in terms of: Is there a direct treatment benefit to the woman, too? I think that since lactobacillus have been shown to be such key regulators of vaginal health, in terms of suppressing other infections, I think that if it were possible to successfully replace lactobacillus in women who are deficient, I think that it's quite plausible that there would be a direct benefit to that woman, beyond the potential benefit of decreasing viral load and decreasing transmissibility.

The second part of your question, in terms of disruptions in the vaginal flora associated with antibiotic treatment: that's not something that we directly looked at in the study. We did, when we found bacterial vaginosis, provide antibiotic treatment and track what happened to the vaginal flora after that. And we found that treatment for bacterial vaginosis, which is very targeted to the anaerobic bacteria, the bad bacteria, in the vagina, can be successful in reducing the bad bacteria, but it doesn't automatically replace the good bacteria. And that's the challenge.

This transcript has been lightly edited for clarity.


  1. Hitti J, Paul K, Agnew K, et al. Protective effect of vaginal lactobacillus on genital HIV-1 RNA concentrations: Longitudinal data from a United States cohort study. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston, Mass Abstract 27LB.

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