Open Access

Fatma Aly

• In this study we investigated the synergistic antimicrobial effect of a dual protocol combining cold atmospheric pressure plasma (CAP) and antimicrobial photodynamic therapy (aPDT) against different planktonic bacterial and yeast species including methicillin-sensitive and methicillin-resistant Staphylococcus aureus, Escherichia coli, extended-spectrum β-lactamase-positive Escherichia coli and Candida albicans. A DBD plasma device was used for CAP treatment while for aPDT, toluidine blue O (TBO) was the photosensitizer (PS) of choice and a radiator emitting visible and water-filtered-Infrared A light (VIS-wIRA) was used as irradiation source. Microbial suspensions were either exposed to CAP treatment alone, aPDT treatment alone or aPDT followed by CAP exposure in a dual treatment protocol. Aliquots from each suspension were plated on agar plates and the number of colonies surviving after each treatment was counted. Under the experimental conditions conducted in this study, combining sub-lethal exposure doses of CAP and aPDT treatment showed significantly higher antimicrobial efficacy (P<0.0001) compared to single treatments against all tested microorganisms suggesting a synergistic effect which yielded at least 3.3 log microbial reduction corresponding to 99.6 % microbial death. In the dual CAP-aPDT approach, aPDT did not interfere with CAP-induced acidification of solution, a crucial feature for CAP antimicrobial efficiency, which further confirms the promising clinical potential of this combination regime. We believe that the CAP-aPDT dual approach described in this study holds great potential as a successful novel antimicrobial and healing-supporting strategy especially when directed for the management of acute and chronic wounds and possibly other skin and soft tissue infections. The use of a VIS-wIRA light source in treating skin infections is preferential, due to the additional therapeutic effects of wIRA in wound healing. Furthermore, the enhanced antimicrobial effects of aPDT when combined with CAP as shown in this study may grant for a reduction in treatment times and costs as well as improving patient compliance.