Chronic infection or inflammation of the middle ear, the area just behind the eardrum, is a common problem for children.  Technically called otitis media, this problem affects 3 of every 4 children at least once by their third birthday.  Almost half of those who get them will have 3 or more ear infections during their first 3 years.  A new study shows why the 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 sugars that the bacteria produce.  The structure created by the bacteria protects them from the body’s defense system.  Bacteria deep within the biofilm can also enter a metabolic state that makes 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.  Researchers funded by NIH wanted to see whether children with chronic otitis media also have biofilms on their MEMs.

The researchers took MEM biopsy specimens from 26 children, from 2½ to 14 years old, who were undergoing 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 a high-tech microscope that uses laser light to produce a three-dimensional image of a specimen.

The researchers saw biofilms in 92% of the samples from children with otitis media.  They confirmed the presence of disease-causing bacteria in the biofilms.  In contrast, they didn’t see biofilms in specimens from the 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 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 to resist both the body’s defenses and antibiotic treatments.