Vaccine and Infectious Disease Division

Bacterial effects on pregnancy and HIV shedding

The vagina is normally colonized by lactobacilli, which produce lactic acid and maintain the normal low pH of the vaginal ecosystem.  Bacterial vaginosis is an infection that occurs when these protective bacteria are overrun by other bacterial species.  Normally a minor infection, BV can cause greater problems in some individuals, such as pregnant women, where it is associated with a higher chance of preterm labor, or HIV positive women, where it is associated with increased HIV viral shedding from the genital tract.

In two recent studies, VIDI affiliate investigator Dr. Caroline Mitchell and colleagues explored the effects of BV on these two populations.  To identify whether specific bacterial types in BV cause increased HIV shedding or changes in vaginal pH, Mitchell and other researchers, including VIDI associate member Dr. David Fredricks, classified bacteria from 51 HIV positive women with and without BV using a sensitive molecular technique.  They found a trend toward increased HIV shedding with certain BV-associated bacteria, called BVAB1, 2 and 3 and a significant association between those species and increased vaginal pH.  The vagina is normally an acidic environment, and low pH is known to inactivate HIV, so the boost these bacteria give to vaginal pH may explain the link between BV and increased HIV shedding.

Mitchell and her colleagues also looked at how traditional treatments for BV affected the vaginal ecosystem in pregnant women.  Their study evaluated 108 pregnant women with BV, who were treated with either oral or vaginal metronidazole.  The researchers looked at which vaginal bacteria were present in these women before and after treatment, how treatment affected symptoms and changes in pro-inflammatory molecules (the cytokines IL-1b, IL-6 and IL-8) after treatment.  They found that most of the women being treated had reductions in BV-associated bacteria, but only one third achieved the strict FDA definition of cure of BV, and most did not regain the protective lactobacilli bacteria.  Their findings suggest that metronidazole may not alleviate BV’s negative effects for pregnant women.

Detection of fastidious vaginal bacteria in women with HIV infection and bacterial vaginosis.  Mitchell C, Moreira C, Fredricks D, Paul K, Caliendo AM, Kurpewski J, Ingersoll J, Cu-Uvin S.  Infect Dis Obstet Gynecol. 2009;2009:236919.

Changes in the vaginal microenvironment with metronidazole treatment for bacterial vaginosis in early pregnancy.  Mitchell C, Balkus J, Agnew K, Lawler R, Hitti J.  J Womens Health (Larchmt). 2009 Nov;18(11):1817-24.

Fred Hutchinson Cancer Research Center is a world leader in research to prevent, detect and treat cancer and other life-threatening diseases.