A team of researchers, led by a Case Western Reserve University microbiologist, has discovered that a bacterium found in oral periodontal disease enters the blood, targets placentas and amniotic fluid of pregnant mice and triggers preterm or term stillbirths and infant deaths.

Yiping Han from the Case School of Dentistry and other researchers injected mice with the bacterium, Fusobacterium nucleatum, which had been isolated from the placenta and amniotic fluids of women who had given birth to premature infants. Within 24 hours of injection, the bacteria had already affected the placentas of some mice, and within 48-72 hours, most mice gave birth to stillborn pups.

This animal model mimics the human situation in three ways, according to the team of researchers: The infection spread only to the uterus and did not affect other organs, live bacteria could be isolated from the placenta and the infection spread to the amniotic fluid and fetal membranes mimicking an infection in humans known as chorioamnionitis, which is associated with preterm birth.

Studies of the placentas and amniotic fluids of women who have undergone premature labor have indicated the presence of F. nucleatum in as many as 30 percent. Han said she wanted to find out how the bacteria reach the sterile environment of the womb because F. nucleatum's presence is uncommon in the vaginal tract but frequent in the mouth.

These new research results, which are similar in humans and mice, not only strengthen the link between the oral bacteria and preterm births but also suggest that transmission to the placenta occurs through the bloodstream, according to Han.

"The number of bacteria can increase 10,000-fold when periodontal disease is present," Han said. "This bacterium may take the opportunity to enter the blood stream when bleeding occurs with the gum disease."

According to Han, the immune system during pregnancy also may be "turned down" to protect the baby and, hence, may have a harder time warding off and keeping in check the numbers of the bacteria normally present in the mouth.

She advises women who are thinking about getting pregnant or are expecting a baby, to visit the dentist for a checkup and maintain healthy oral hygiene practices by brushing and flossing daily.

One of the reasons for pursuing these studies, according to Han, is because despite improvements in medicine, the number of premature births has remained constant over the past 40 years. Han wants to find the reason why women give birth early in order to help prevent it.

The poster, "Fusobacterium nucleatum induces premature and term stillbirth in pregnant mice: Implication of oral bacteria in preterm birth," which Han presented to the Infectious Disease Society of Obstetrics and Gynecology, won the best poster award during the group's 30th annual meeting in Cape Cod, Mass.

Other researchers on the project were Raymond Redline and Thomas McCormick from the Case School of Medicine, Mei Li and Lihong Yin from the Case School of Dentistry and Gale Hill from the Duke University Medical Center.

Return to the online edition of the 9-11-03 Campus News.