The role of biofilms in chronic infections

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Bacteria in contact with living tissues form layers that resist penetration by the immune system or antibiotics, but promising treatments abound.
Bacteria in contact with living tissues form layers that resist penetration by the immune system or antibiotics, but promising treatments abound.

What are some of the most challenging clinical problems you see in everyday practice? Do they include chronic sinusitis refractory to multiple antibiotics? Recurrent, difficult-to-treat urinary tract infections? Poorly healing ulcers resistant to topical antibiotics and successive debridement? Seemingly ineradicable bacterial vaginosis and Candida vaginitis? Or, alternatively, chronic progressive periodontal disease with not just local dental but also systemic manifestations, such as heightened risk for cardiovascular disease?

When antibiotics fail, we put the blame on bacterial resistance. There is much substantiation for the idea that selective pressure on microbes pushes their adaptive mechanisms forward, resulting in the development of "superbugs." Drug development efforts continually seek to expand our arsenal of new, ever more powerful antibiotics. The traditional approach to infections involves the "culture and sensitivity." But a marked disconnect has arisen between in vitro results and clinical responses. Why?

A new understanding has emerged of how pathogens persist and thrive within human hosts. In contrast to what we are used to seeing with traditional microscopes, bacteria and fungi in contact with living tissues or inert surfaces form complex communities: biofilms. Multiple species comprising thousands or millions of organisms may coexist in polysaccharide matrices elaborated by the microorganisms themselves; these form nearly impregnable slime layers that resist penetration by antibiotics or humoral defenses elaborated by immune system cells. The result may be infections that are difficult to eradicate.

Examples of biofilm

A common example of a biofilm is the "scum" that accumulates on our tooth surfaces between brushings. Run your fingernail over a front incisor, and you will harvest a slimy, whitish accretion that constitutes an oral biofilm. If left to accumulate, the biofilm will produce dental plaque and tartar, resulting in tooth decay and periodontal disease.

Tenacious biofilms can contaminate household appliances like coffee makers, ice makers, and humidifiers if these items are not frequently cleaned.

Even disinfectants do not seem to daunt biofilms, as evinced by the slime that accumulates on swimming pool walls despite aggressive chlorination and the use of chemical retardants.

In medicine, biofilms often clog catheters and foul medical devices, where they form dense layers that cling to artificial surfaces. It has been reported that most if not all implant infections can be attributed to biofilms, including infections in vascular stents, artificial heart valves, dental prostheses, joint replacements, breast implants, cardiac pacemakers, cerebrospinal shunts, urinary catheters, biliary stents, intrauterine devices, peritoneal dialysis catheters, and contact lenses.

Biofilms and infections

Biofilms have been demonstrated to be implicated in a wide array of chronic infections, including sinusitis, otitis media, chronic obstructive pulmonary disease (COPD), endocarditis, decubitus and diabetic ulcers, prostatitis, conjunctivitis, superficial skin infections, airway infections in cystic fibrosis, vulvovaginitis, urinary tract infections, and periodontitis. It has been estimated that biofilms complicate the majority of bacterial infections in humans.1

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