# Development and Control of Biofilms in Diabetic Foot Infections: A Narrative Review
## 2 Biofilms in Diabetic Foot Infections  
Patients with diabetes are often in a chronic hyperglycemic state, which creates an ideal environment for the growth of microbes, specifically _Pseudomonas aeruginosa_ and _Staphylococcus aureus_. These microbes thrive and produce toxins that form biofilms [1; 2]. Biofilms are complex structures formed by a variety of pathogens, notably _S. aureus_, _P. aeruginosa_, and _Escherichia coli_. The biofilms formed by _S. aureus_ and _P. aeruginosa_ are particularly problematic due to their thicker and more resilient nature compared to those formed by other organisms [8]. Biofilms generally consist of extracellular polymeric substances (EPS), including DNA, glycoproteins, proteins, and polysaccharides, produced by sessile microorganisms [3]. Elevated glucose levels stimulate EPS production, causing microorganisms to become sessile and embed into the biofilm matrix [4; 5]. This matrix hinders antibiotic penetration and reduces treatment effectiveness due to both the thickness of the biofilm and the presence of efflux pumps. Additionally, EPS reduces the phagocytic activity of leukocytes [6], impeding their ability to penetrate the biofilm [7]. The detailed mechanism of biofilm formation and methods to study biofilms have been reviewed elsewhere and are not the focus of this review. _P. aeruginosa_ produces alginate, which not only protects its own biofilm but also enhances the protection of _S. aureus_ biofilms, creating a synergistic and heterogeneous biofilm environment [8; 9; 10]. Moreover, this biofilm environment favors horizontal gene transfer [10], a key mechanism for the spread of antibiotic resistance among microorganisms. The mutation rate of sessile organisms within biofilms is higher compared to planktonic cells, leading to the acquisition of resistance genes by microbes that were initially non-resistant to antibiotics [11]. Since the most common pathogens are _S. aureus_, _P. aeruginosa_, _E. coli_ which are potent biofilm formers [12], the consequent increase in the ability of the horizontal gene transfer among the biofilm forming organisms leads to initially susceptible microbes becoming resistant to antimicrobial compounds. This complicates treatment and accelerates foot deformity and ulceration, potentially progressing to gangrene if not effectively managed. DFUs typically begin with callus formation, which progresses into a subcutaneous hemorrhage as the skin becomes dry, followed by erosion of the callus, finally becoming an ulcer, often leading to foot deformities and sensory neuropathy [13]. Ulcers have about a 50-60% chance of developing into an infection which could be polymicrobial, and form biofilms consisting of _S. aureus_ and _P. aeruginosa_, which play a critical role in the pathogenesis of DFUs. Gangrene can also be caused by Panton-Valentine leukocidin produced by _S. aureus_, as well as hydrogen cyanide (HCN), pyocyanin, and pyoverdin produced by _P. aeruginosa_. These toxins induce cell death, leading to tissue necrosis and ultimately gangrene formation [14]. In addition, biofilms accelerate the progression of foot deformities, causing lower-grade ulcers to intensify into more severe ulcers, potentially reaching grade 4 or 5 and leading to gangrene [15]. Gangrenous tissue is severe and often necessitates amputation to prevent its spread to the rest of the body [16]. Current treatment for DFUs involves addressing both the infection and the underlying biofilm-related resistance issues. Conservative treatments may fail, requiring amputation for advanced ulcers (grades 4 and 5) to prevent the spread of gangrene throughout the body [16]. Recalcitrant wounds that become gangrenous are often difficult to treat due to factors such as increased biofilm formation and simultaneous antimicrobial resistance [17]. The need for amputation depends on the condition of the foot and the extent of gangrene, with amputation being necessary for grade 5 ulcers and potentially for grades 4 and 3 depending on the situation [18].