Biofilms and Their Potential Role in Wound Healing

Steven L. Percival, PhD; Philip G. Bowler, MPhil

Disclosures

Wounds. 2004;16(7) 

In This Article

Why Can Biofilms Be a Problem?

It has been estimated that biofilms are associated with 65 percent of nosocomial infections[12] and that treatment of these biofilm-associated infections costs greater than $1 billion annually in the United States.[1,13] The estimated cost of a hip replacement in the UK is A33,500, but the hospital costs associated with a subsequent infection can be as high as A330,000.[5] So why are biofilm-related infections such a problem to treat? The challenge arises as a consequence of the following several factors:

  1. Biofilm bacteria are less susceptible to our immune defense system, and consequently, a biofilm-associated infection can persist for a long period of time (i.e., progress from an acute to a chronic infection). Phagocytic cells have difficulty ingesting bacteria within a biofilm due to antiphagocytic properties of the biofilm matrix.[14,15] In the absence of specific antibodies, the polysaccharide component of the biofilm matrix also blocks complement activation. If antibodies are present, the polymeric matrix generally renders them ineffective. It has been shown that the biofilm matrix is also able to inhibit chemotaxis and degranulation by polymorphonucleocytes (PMNs) and macrophages and also depress the lymphoproliferative response of monocytes to polyclonal activators.[15,16] Not only are host defenses unable to deal effectively with biofilms, but their persistence can cause tissue damage (e.g., lung tissue in cystic fibrosis). Contact with a surface triggers the expression of a panel of bacterial enzymes that catalyze the formation of sticky polymers that promote colonization and protection. The structure of biofilms is such that immune responses may be directed only at those antigens found on the outer surface of the biofilm, and antibodies and other serum proteins often fail to penetrate into the biofilm. In addition, PMNs are unable to effectively engulf bacteria growing within a complex polymer matrix attached to a solid surface. This causes the PMNs to release large amounts of pro-inflammatory enzymes and cytokines, leading to chronic inflammation and destruction of nearby tissues (i.e., chronic inflammation). Bacteria that may be embedded within the wound biofilm matrix are likely to be resistant to both immunological and non-specific defense mechanisms of the body.

  2. Biofilms display innate resistance to antimicrobial agents, thus protecting associated bacteria. The reasons for this are not clear, but it is likely that antimicrobial agents are readily inactivated or fail to penetrate into the biofilm. Bacteria within biofilms may be up to 1,000 times more resistant to antimicrobial agents than those in a planktonic state.[17]

  3. Biofilms increase the opportunity for gene transfer between and among bacteria. This is important, since bacteria resistant to antibiotics may transfer the genes for resistance to neighboring susceptible bacteria. Also, gene transfer could convert a previous avirulent commensal organism into a highly virulent pathogen.[18]

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