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Bacteria-rich 'Biofilm' May Give Rise to Chronic Otitis Media
An intricate layer of bacteria and its end products growing on a membrane in the middle ear could be the source of the chronic form of otitis media, says an article in the April 3, 2002, issue of the Journal of the American Medical Association. The finding could help reverse a longstanding belief among researchers that chronic otitis media is a bacteria-free inflammation caused by the body's immune system. In addition, certain physical and environmental features of the layer--or biofilm--enable bacteria that reside there to be more robust than free-living bacteria of the same species.
"An important outcome of these findings may be the development of novel approaches for the treatment of chronic otitis media," said Dr. Thomas M. Johnson, program director for otitis media in the Scientific Programs Branch of the National Institute on Deafness and Other Communication Disorders. "Such approaches could focus on the destruction or circumvention of the biofilm’s protective effect on the embedded bacteria."
Otitis media, an inflammation of the middle ear that commonly affects children and costs the country billions of dollars each year in medical costs and lost wages, is characterized by the accumulation of fluid in the middle ear, called an effusion. The fluid build-up can be painful and can adversely affect an individual's hearing and language development. Although effusions in the acute form of otitis media have been found to contain free-living bacteria that can be treated with antibiotics, effusions in the chronic form have tested negative for free-living bacteria and are resistant to antibiotics.
In a study supported by the National Institute on Deafness and Other Communication Disorders, the National Science Foundation, and the Center for Genomic Sciences at the Allegheny Singer Research Institute, researchers have identified the presence of a biofilm on the middle-ear mucosa--a mucus-secreting membrane in the middle ear--in otitis media-infected chinchillas through two imaging techniques: scanning-electron microscopy and confocal laser scanning microscopy. Scanning-electron microscopy uses electrons to produce a highly magnified, high-resolution, three-dimensional image, while confocal laser scanning microscopy uses a laser light beam to do so. The biofilm began to form within 24 hours after the chinchillas were infected. It increased in thickness five days following the infection, stabilized after 10 days, and began to dissipate after 21 days.
A biofilm is a topographically and ecologically rich community composed of bacteria affixed to a surface by means of long-chained sugars that the bacteria produce. Bacteria adhering to the elaborate sugar matrix form towers that create a wall of protection against bacteria-devouring phagocytes of the body's immune system. In addition, although bacteria living on the periphery of a biofilm may be susceptible to antibiotics, those living near the center are resistant to their killing effects. And because one biofilm can contain many ecological niches, bacteria vary widely in their metabolic and reproductive rates, increasing the community's tolerance to environmental stresses.
The researchers recommend that imaging studies be conducted endoscopically on people with otitis media to determine if a relationship between biofilm formation and chronic otitis media exists in humans. Biofilms or biofilm-like structures have been found to play a role in prosthetic infections, periodontal disease, and cystic fibrosis.
The study was a collaborative effort of researchers from the Allegheny Singer Research Institute, Pittsburgh; the MCP Hahnemann School of Medicine, Philadelphia; and Montana State University, Bozeman. As the nation’s focal point for research in human communication, the National Institute on Deafness and Other Communication Disorders supports and conducts research and research training on normal mechanisms as well as diseases and disorders of hearing, balance, smell, taste, voice, speech, and language that affect millions of Americans.