Role of ethylene diamine tetra-acetic acid (EDTA) in catheter lock solutions: EDTA enhances the antifungal activity of amphotericin B lipid complex against Candida embedded in biofilm

Ethylene diamine tetra-acetic acid (EDTA) is an anticoagulant with antibiofilm-enhancing activity. We therefore used an in vitro biofilm model to determine the activity of amphotericin B lipid complex (ABLC) with or without EDTA against Candida embedded in biofilm on silicone disk surfaces. Clinical blood isolates from cancer patients infected with Candida albicans or Candida parapsilosis were used. Silicone disks were colonised with C. albicans or C. parapsilosis and were sequentially incubated in plasma and then in Mueller-Hinton broth containing 10⁵ colony-forming units of each organism. All tests were performed in triplicate. The disks were subsequently placed and incubated for 6 h and 8 h in solutions containing ABLC alone, EDTA alone, ABLC + EDTA or broth (control). Disks were then removed, sonicated and colony counts were determined. ABLC + EDTA (30 mg/mL) was significantly more effective than ABLC, EDTA and control against C. parapsilosis at 6 h (P ≤ 0.01) and against C. albicans at 8 h (P ≤ 0.04). In patients with catheter-related candidaemia when catheter removal is not feasible, the combination of ABLC + EDTA may be considered for antifungal catheter lock solution as part of a catheter salvage therapy.