Biofilms in chronic diabetic foot ulcers—a study of 2 cases

Abstract

Among the 55 million people in Europe diagnosed as having diabetes mellitus (www.diabetesatlas.org), the lifetime risk of developing a foot complication—often infected wounds—could be as high as 25% (Boulton et al. 2005). Many of the patients with severe infections will require amputation within the foot or above the ankle. Approximately 85% of lower-limb amputations in patients with diabetes are preceded by infected foot ulceration (Adler et al. 1999). Polymicrobial infections predominate in severe diabetic foot infections (Dowd et al. 2008a) and the medical community is now beginning to realize that the diversity of bacterial populations in chronic wounds (Dowd et al. 2008b, James et al. 2008) may be an important contributor to the chronicity of wounds, such as diabetic foot ulcers. In addition, another obstacle to the healing of chronic wounds is the biofilm mode of growth of the infecting organisms (Wolcott and Rhoads 2008). By definition, biofilms are microbial populations that are attached to a surface, or to the surfaces of other organisms, and encase themselves in hydrated extracellular polymeric substance (EPS), which is also referred to as “slime”. The chemical and physical properties of EPS can vary, but it is mainly composed of polysaccharides. EPS is also associated with other macromolecules such as proteins, DNA, lipids, and even humic substances (Nielsen et al. 1996, Tsuneda et al. 2003). Biofilm-related diseases are usually persistent infections that develop slowly. They appear to be rarely cleared by the host immune system and are highly resistant to antimicrobial therapy (Stewart and Costerton 2001). For example, antibiotic resistance in biofilm bacteria of up to 1,000 times that of planktonic bacteria has been extensively documented in experiments in vitro (Stewart and Costerton 2001). Infected diabetic foot ulcers share these characteristics, and it has been hypothesized that biofilms may play a role in these infections (Davis et al. 2006, Dowd et al. 2008a). We evaluated debrided soft tissue from infected diabetic foot ulcers by confocal laser scanning microscopy (CLSM). Part of the debrided tissue was also analyzed using culture methods to evaluate bacterial diversity of the biofilms.