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.