Quantitative evaluation of growth rate and survival of planktonic yeast under dual-parameter photodynamic treatment

Abstract

Photodynamic Antimicrobial Chemotherapy (PACT) relies on the concomitant use of light and a photosensitizer molecule for microbial disinfection. Adding the dimension of light to the system increases the difficulty and variables to consider, yielding time and material-consuming experiments, with their reproducibility depending greatly on the disclosure of the light irradiation conditions. In the present work we analyse the effect of increasing irradiant exposures and rose bengal (RB) concentrations against Candida albicans ATCC 10231, in a checkerboard fashion. For this, we propose the use of the exponential phase coefficients, growth rate and initial number of cells, to assess the efficiency of the treatment. The coefficients are able to accurately describe the decrease of starting number of cells as consequence of the PACT effect, while also showing the metabolic burden of the presence of RB at high concentrations, with further hints that the incorrect combination of RB and radiant exposure decreases the growth rate without affecting the survivability. Our proposed methodology can then be used as a high-throughput screening method for new photosensitizers and new formulations, exploring their needs of radiant exposure for an efficient microbial disinfection.