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Insight into Ear Infections
Chronic infection or inflammation of the middle ear, the area just behind the
eardrum, is a common problem for children. Technically called otitis media, three
of every four children have at least one episode by their third birthday. Almost
half of those who get them will have three or more ear infections during their
first three years. A new study shows why this problem can be so persistent: bacteria
can form a "biofilm" on the middle ear that helps them resist both the body's defenses
and antibacterial treatments.
A biofilm is a rich community of bacteria attached to a surface by long-chained
sugars that the bacteria produce. The elaborate matrix created by the bacteria
protects them from the body's defense system. Bacteria deep within the biofilm
can also enter a metabolic state that renders antibiotics ineffective.
Previous studies showed that a biofilm grows on the middle-ear mucosa (MEM) — a
mucus-secreting membrane in the middle ear — in chinchillas with otitis media.
A team led by researchers at the Center for Genomic Sciences at the Allegheny-Singer
Research Institute in Pittsburgh, PA, wanted to see whether children with chronic
otitis media also have biofilms on their MEMs.
In a study largely funded by NIH's National Institute on Deafness and Other
Communication Disorders, the researchers took MEM biopsy specimens from 26 children,
from two and a half to 14 years old, who were undergoing tympanostomy and tube
placement, a surgical treatment for chronic otitis media. For comparison, they
took MEM specimens from three children and five adults undergoing another surgical
procedure for the ear unrelated to otitis media. They then looked at the samples
using confocal laser scanning microscopy, in which a laser light beam is used
to produce a three-dimensional image of a specimen.
The researchers report in the July 12, 2006 issue of the Journal of the American
Medical Association that they saw biofilms in 92% of the samples from children
with otitis media. Molecular biological techniques confirmed the presence of
specific pathogenic bacteria in the biofilms. The researchers didn't see biofilms
in any of the specimens from people without otitis media.
This study supports the idea that chronic cases of otitis media, so common in
children, are caused by the formation of biofilms. Recent research suggests that
microbial biofilms may also play a role in other types of chronic human infections.
In order to develop better treatments for such infections, researchers are now
investigating how bacteria form biofilms, and how these structures help them
resist both the body's immune response and antibiotic treatments.
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