Bacteria rarely live alone, but are most commonly organized into multicellular communities that form protective barriers against our body’s immune defenses. Like a coral reef, these single celled organisms attach to one another and secrete a matrix that connects and protects them from the outside, while at the same time providing channels for delivery of nutrients. It is believed that most chronic ear infections and chronic sinus infections contain biofilms, and that many are in part due to the presence of such biofilms.

Are biofilms common?

We all have them! Dental plaque, the thick white debris that accumulates between our teeth is a biofilm. The slime that accumulates on boat hulls is a biofilm, costing the US Navy over $100 million per year in fuel. The deposits inside your water and sewer pipes contain biofilms, as do infected medical devices, such as ear tubes, intravenous lines, urinary catheters, and heart valves. In the sinuses, biofilms contribute to the crusts we call boogers.  In the tonsils, small yellow stones accumulate in the pits and cause bad breath (halitosis). In the salivary glands, gallbladder and kidneys, biofilms are often found to be the source of painful, obstructing stones.

Why are biofilms so hard to treat?

Most antibiotics work by disrupting the production of key elements for cell growth, or by lysing (popping) the cell during multiplication and division. In a biofilm, the cell is rarely dividing, but is either resting, or is participating in the activity of the community, producing polysaccharides and glycoproteins to protect the community, transporting nutrients, or providing other functions.  These activities are not inhibited by common antibiotics. Moreover, the matrix itself protects the bacteria from antibiotics. In this protected micro-environment, the bacteria can reproduce and grow slowly, relatively resistant to most antibiotics.

What is the treatment for biofilms?

Mechanical cleaning is the most important method to treat biofilm growth.  We floss our teeth, scrub and paint boat hulls, and remove catheters that have become infected. When ear tubes drain persistently after a myringotomy, we remove or replace them.  When paranasal sinuses are chronically infected, we perform endoscopic sinus surgery and flush them clean with warm saline.   When the tonsils become persistently enlarged or painful, we perform a tonsillectomy.

Why are topical antibiotics better at treating biofilms?

Oral and intravenous (IV) antibiotics are distributed throughout the body by the blood stream, and distribute into the tissue, within or between the cells of the body.  Some antibiotics distribute evenly, while other are more concentrated in specific organs. These are generally effective for invasive bacteria that enter our body, and that are in a rapidly reproducing state. Biofilms, however, rest on the surface of devices, wounds and body cavities – they have no blood flow. Therefore, systemic antibiotics (oral or IV) do not effectively penetrate the biofilm. Topical antibiotics generally have a much higher concentration at the site of application than antibiotics administered by mouth, and therefore they have a better chance of diffusing into the biofilm.  Common examples of topical antibiotic use include bacitracin ointment on an open wound, ciprofloxacin ear drops after myringotomy with ear tubes, and antibiotic irrigations after sinus surgery.  Richmond ENT recently participated in a phase 3 clinical trial evaluating ciprofloxacin gel  for the prevention of ear drainage after myringotomy tubes.

Why have I never heard of biofilms?

Most of what we learned in high school about bacterial diseases was a description of planktonic bacteria – bacteria that are freely floating as individual cells that can be examined under a microscope and grown in petri dishes.  Until the 21st century, we really did not have the tools or understanding to fully describe the complex communities of biofilms, which are generally attached to a surface and too diverse to be considered a “pure” culture.  In the 19th century, Robert Koch postulated that a disease-causing organism should be present in disease states, but not in health, grow in a pure culture, and cause disease when introduced to a healthy individual. With these postulates in mind, culture techniques over the past 150 years have been designed to isolate and replicate single free floating bacteria, not to analyze a community. It is like trying to describe the ecology of the African Savannah by breeding a single captured wildebeest that has strayed from the herd.

What is on the horizon?

With 21st century molecular analysis of biofilms, we can now identify numerous bacteria in a single sample, and even calculate the relative contributions of each species, regardless of whether they can grow easily in a petri dish. Like a crime scene investigator, we now have the tools to extract and identify small particles of DNA and to know with certainty “who was at the scene.” Koch’s postulates have been revised and new questions are being asked in order to determine the causes of bacterial diseases: Is the bacterial DNA always present during the disease, and rarely in health? Does the bacterial DNA decrease when the disease is resolved, and increase if the disease returns? Can the bacterial DNA be found specifically on or within the diseased host cells?

Richmond ENT continues to participate in research projects contributing to our modern understanding and treatment of chronic sinus and ear infections.