Nasty bugs: ear infections may hold bugs in tough biofilms that are hard to treat.© Punchstock

Bacteria clumped into tough biofilms are behind the widespread and persistent ear infections that vex kids, researchers have confirmed, supporting the idea that deploying antibiotics against these conditions is futile.

The middle-ear inflammation called otitis media is the most common reason for children's doctor visits and antibiotic prescriptions in the United States alone. Some are acute infections that clear up rapidly with a dose of antibiotics. But others persist for weeks or months, and doctors have struggled to pin down their cause because it is hard to extract and culture microbes from the ear.

Now researchers have confirmed that bacteria are indeed to blame, but they are clustered into biofilms that are almost impossible to grow in the laboratory and are impervious to antibiotics.

"We need to start thinking about ear infection in a different way," says Joseph Kerschner, one of the lead researchers at the Medical College of Wisconsin, Milwaukee.

Listen up

Researchers began to suspect that biofilms were responsible for chronic middle-ear infections more than a decade ago, when they pulled out telltale traces of bacterial DNA from the ears of patients.

To prove it, Kerschner and his colleagues painstakingly collected minuscule tissue samples from the ears of 26 children with either a recurring or a chronic ear infection. They added stains that would highlight several species of bacteria and then pieced together three-dimensional images under the microscope.

The team found that 92% of infected ears harboured biofilms containing many different types of microbe. Samples taken from the ears of eight healthy children and adults showed no sign of biofilms. The researchers publish their results in the Journal of the American Medical Association¹.

The finding strengthens the argument that prescribing antibiotics in the face of chronic infection is pointless, as some doctors already know. Many long-term ear infections are treated instead by surgically inserting a small tube that, the authors of the study now suggest, may help to disrupt the biofilm.

It is even possible that treating acute infections with antibiotics could encourage the survival of hardy microbes. "It may push them to adopt a biofilm mode," says Garth Ehrlich, at the Allegheny-Singer Research Institute in Pittsburgh, Philadelphia, who co-authored the paper. The idea has not been extensively tested, however.

Targeted attack

Researchers would now like to probe these infectious biofilms to find more effective treatments.

One plan is to identify exactly which of their 40 or 50 species provoke the most inflammation, says biofilm expert Bill Costerton of the University of Southern California, Los Angeles. Drugs could then target specific microbes or block them from forming biofilms. Or probiotic therapy could inoculate the nose and ear with healthy bacteria to keep malicious ones from gaining a foothold.

The study adds to a list of chronic infections now attributed to bacterial biofilms, including inflammation of the prostate gland and the lung infections that plague sufferers of cystic fibrosis. "We're sure many other chronic conditions will turn out to be biofilms as well," says Ehrlich, such as those in sinus infections and burn wounds.

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• References

  1. Stoodley L.H., et al. J. Am. Med. Assoc., 296. 202 - 211 (2006).