RAPID AND SIMPLE DETERMINATION OF MINIMUM BIOFILM ERADICATION CONCENTRATION BY A COLORIMETRIC MICROBIAL VIABILITY ASSAY BASED ON REDUCTION OF A WATER-TETRAZOLIUM SALT AND COMBINATED EFFECT OF ANTIBIOTICS AGAINST MICROBIAL BIOFILM

Rapid and simple method for the determination of minimum biofilm eradication concentration (MBEC) using a colorimetric microbial viability assay based on reduction of a tetrazolium salt WST-8 and the biofilm formation method on 96-pegs on the lid of a microtiter plate was developed. The biofilms formed on the 96 pegs were challenged by antibiotics, and the MBEC was then determined from the microbial viability of the biofilms formed on the 96 pegs, assessed by the WST-8 colorimetric assay. The MBECs obtained by the proposed and conventional methods favorably agreed. The most effective inhibitors of S. aureus and P. aeruginosa biofilms were vancomycin and ciprofloxacin, respectively. In addition, we clarified that Staphylococcus aureus biofilm was maximally suppressed by a combination of vancomycin, daptomycin, and teicoplanin. The proposed method yields similar performance to conventional methods, but is faster and more easily implemented. Therefore, the proposed method alleviates the tediousness and time-consuming nature of conventional biofilm susceptibility assay.