Photodynamic therapy (PDT) for clinical treatment of cancer has been widely pursued. Research has shown that PDT can also kill bacteria, and such a procedure is called Photodynamic inactivation (PDI). PDI may be an effective approach to treating infection by antibiotic-resistant bacteria. Such infections have become a big challenge in the past 20 years.
This study investigated the stoichiometry of PDI using Methylene Blue (MB) as the photosensitizer (PS) to kill E. coli cells, in other words, how many photons must be absorbed by photosensitizer within each bacterium in order to achieve cell death. E. coli are a Gram (-) bacteria which are resistant to many PS, but MB has a positive charge and is expected to be taken up by E. coli.
The threshold radiant exposure for PDI to achieve bacterial cell death was measured by colony formation experiment. The MB concentration inside the E. coli cells was calculated using light transmission measurements. The PDI threshold dose (photons absorbed by PS per cm3 cells) that achieved inactivation was calculated.