Mounting Evidence Supports Role of Bacterial Biofilms in Chronic Infections of Middle Ear and Sinuses

For Richard A. Chole, MD, PhD, Lindburg Professor and Chairman of the Department of Otolaryngology at Washington School of Medicine in St. Louis, this was a landmark study that builds on prior observations of the presence of live bacteria in chronic middle-ear effusions. However, he reiterated that causation between these bacterial biofilms and chronic middle-ear effusions and inflammation still remains unknown.

The most parsimonious explanation is that the biofilm forms on the epithelial surface and then produces inflammatory factors, endotoxins and exotoxins, that maintain an inflammatory state, he said. Nevertheless, critics will demand that the causation question be answered.

Although acknowledging that biofilms play an integral part in the pathogenesis of these chronic otolaryngological conditions, Hassan H. Ramadan, MD, MSc, Professor and Vice Chairman of the Department of Otolaryngology-Head and Neck Surgery at West Virginia University in Morgantown, W. Va., raised a question that speaks to the need to demonstrate causality. If biofilms are present in the middle-ear mucosa of the majority of kids in the study, why do some of these kids have episodes of no fluid in their middle ears and no symptoms?

J. Christopher Post, MD, PhD

This question and others remain to be answered, but the recognition that biofilms are present in these chronic conditions suggests to all these experts the need to rethink the way in which antibiotics are used to treat these conditions.

If biofilms are involved in these cases, then supposedly higher doses of antibiotics than we usually use are needed to treat these individuals, said Dr. Ramadan, and even so may not be successful.

Dr. Desrosiers agrees. Treating them [bacteria] with regular doses of antibiotics is not sufficient. Even when you can kill them with high doses of antibiotics, a certain number persist.

The lack of efficacy of antibiotics for these chronic conditions is one reason investigators have started looking at mechanisms of infection, such as biofilms, that may be targeted to prevent ongoing or recurrent infection.

According to Dr. Chole, antibiotics will be only partially effective to treat these chronic conditions if bacterial biofilms are involved because of the altered phenotype of these bacteria that are highly resistant to antibiotics. The bacteria in a biofilm are in equilibrium with planktonic, motile bacteria, he said. In their planktonic phenotype bacteria may be sensitive to the antibiotic so the antibiotic may ameliorate the disease without destroying the underlying biofilm.