News and Research
Immune System
Case Researchers Substantiate Bacterial Link To Preterm
Birth Through Mice Studies
3-25-2004
CLEVELAND -- A team of researchers, led by microbiologist
Yiping Han from Case Western Reserve University School of
Dental Medicine, have discovered that a bacterium (Fusobacterium
nucleatum) found in periodontal disease enters the blood,
specifically targets placentas and amniotic fluid of pregnant
mice and triggers preterm or term stillbirths as well as
early death for live-born mice. The researchers reported
their findings in the March 25th issue of the Journal of
Infection and Immunity.
The
researchers also injected mice with the live bacteria, Fusobacterium
nucleatum, from the placenta and amniotic fluids of women
who had given birth to preemie babies. These bacteria also
provided the same results in mice to forge an even stronger
link between the oral bacteria and preterm births and its
transmission to the placenta through the blood.
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After
the bacteria were injected into pregnant mice, the bacteria did
not attack the liver or spleen. Within 24 hours of injection,
some mice already were affected by the bacteria and within 72
hours were giving birth to stillborn pups.
Follow-up
microbiology studies were done on the placentas and amniotic fluids
of women who have undergone premature labor. While the studies
were done years ago, Han said no one make the link until recently
to verify the presence of F. nucleatum in as many as 30 percent
of the women.
Han
said she wanted to find out how the bacteria reach the sterile
environment of the womb because F. nucleatum's presence is rarely
found in the vaginal tract.
"The number of bacteria can increase 10,000 fold
when periodontal disease is present. This bacterium takes the opportunity
to enter the blood stream when bleeding occurs with the gum disease,"
states Han.
She also adds that periodontal disease and pregnancy,
with its hormonal changes, both challenge the immune system, which
may have a harder time warding off and keeping the numbers of the
bacteria normally present in the mouth in check.
When the immune system is compromised in some way,
Han noted that F. nucleatum particularly targets the placenta and
eventually the amniotic fluid.
The researchers found that the animal model mimicked
the human situation in three ways:
- The
infection is localized to the uterus and is not a systemic infection.
- Live
bacteria were isolated from infected mice placenta.
- The
infection eventually spread to the amniotic fluid of the mouse uterus
and mimicked an infection in humans associated with preterm birth.
"Periodontal disease is treatable and preventable,"
Han states. She advises women, who are thinking about getting pregnant
or are expecting a baby, to visit the dentist for a check-up and maintain
healthy oral hygiene practices of brushing and flossing at least twice
daily.
Other researchers on the project were Raymond Redline
and Thomas McCormick from the Case School of Medicine and Gale B.
Hill from the Duke University Medical Center.
One of the reasons for studying this, according to
Han, is that the number of premature births has remained constant
over the past 20 years. Han wants to find the reason why women give
birth early and then prevent it.
This story has been adapted from a news release issued
by Case Western Reserve University, www.cwru.edu.
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