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Biofilms To Blame for Chronic Ear Infections

Drug-resistant communities of bacteria pose a challenge for treatment.

Middle-ear infections, the most common reason that children visit doctors, are usually cleared up with antibiotics. But occasionally they persist and become a chronic illness that only a surgical procedure can fix. A recent study published in the Journal of the American Medical Association shows that tight-knit communities of bacteria called biofilms are the culprit of this chronic form of ear infections.

Dense bacterial communities, called biofilms, may cause chronic middle-ear infections. The biofilm shown here was isolated from the ear of an infected child. Streptococcus pneumoniae, one of several infectious bacteria found in this biofilm, is stained in red. (Courtesy of L. Hall-Stoodley and L. Nistico.)

In fact, biofilms, which are resistant to many conventional antibiotics, are being implicated in several chronic infections. And while some researchers have been skeptical that biofilms cause chronic ear infections, researchers at the Allegheny-Singer Research Institute in Pittsburgh, led by Garth Ehrlich and Christopher Post, have been building evidence in animals over the past few years that biofilms are behind these intractable infections. Their new study provides direct evidence in children that biofilms are present.

Ehrlich says that both the temporary and chronic ear infections are caused by the same bacteria – yet only in some cases do the bacteria form a biofilm. “They build a little house for themselves,” Ehrlich explains.

Biofilms are made of a sticky, nonliving matrix that surrounds the bacteria. Sequestered inside these structures, the bacteria settle into a largely inactive state. Penicillin and other antibiotics are ineffective against these dormant bacteria because the drugs work by interfering with activities like reproduction. “If the process isn’t going on, you can’t disturb the process,” Ehrlich says.

Joseph Kerschner, an otolaryngologist at the Medical College of Wisconsin and co-author of the study, says that the findings are particularly relevant for children who get recurrent middle-ear infections that seem to go away with treatment and then return. “These kids that are chronically getting infected – maybe it isn’t new infections every time,” he says. Instead, a persistent biofilm may be to blame.

Biofilms have already been linked to chronic inflammation and infections in the prostate, teeth and gums, tonsils, bladder, bone, and lungs, as well as the middle ear. And several companies are working on developing new materials and surface coatings that disrupt the ability of bacteria to attach to implantable medical devices or drugs that interfere with biofilms in chronic infections.

Australia’s Biosignal has been developing anti-biofilm compounds based on chemicals excreted by a type of seaweed. Sequoia Sciences in San Diego, CA, is also focusing on identifying compounds in plants that keep biofilms from forming. And NovaCal Pharmaceuticals in Emeryville, CA, is using bleach-like chemicals, naturally produced by white blood cells of the immune system, to disrupt biofilms.

Despite this intense work into finding ways to break up biofilms, it’s not clear that scientists will easily find a way to thwart these tenacious structures. “I’m not aware of anything that looks to me like a home run,” Ehrlich says. “Biofilms are the preferred mode of growth for most bacteria – they’ve been doing it for literally billions of years.”

He and colleagues are looking toward prevention rather than treatment. In the case of middle-ear infections, for instance, they believe that giving children specially engineered probiotics, or “good” bacteria, early in life may help prevent infectious bacteria from settling down in the ears in the first place.

Whatever the best cure turns out to be, though, this finding – that biofilms may underlie ear and other chronic infections – suggests that trying to treat them with rounds of conventional antibiotics is futile, and only promotes drug resistance. Bill Costerton, director of the University of Southern California’s Center for Biofilms, calls this study a “pivotal paper” that will change the way these infections are treated and persuade doctors, particularly those in the United States, to “stop throwing antibiotics at biofilm infections that are basically resistant.”

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