Abstract:

Objective To evaluate the effect of 5-aminolevulinic acid-based photodynamic therapy （ALA-PDT） on S. epidermidis biofilms. Methods S. epidermidis was cultured on cover glasses, with or without the presence of ALA at 50 mmol/L for 16 hours followed by the exposure to different doses （100, 200, 300 J/cm2） of red light. S. epidermidis receiving neither pretreatment nor irradiation served as the negative control. Subsequently, confocal laser scanning microscopy （CLSM） was used to observe the structure and evaluate the biological activity of S. epidermidis biofilms; colony forming units （CFUs） of S. epidermidis were counted for the evaluation of killing effect of ALA-PDT; scanning electron microscopy （SEM） was used to observe the morphological structure of the biofilms. Results The number of colony forming units per milliliter （CFU/ml） was （210 ± 7.55） × 105, （91 ± 1.53） × 105, （16 ± 1.52） × 105 for S. epidermidis pretreated with ALA followed by irradiation with red light at 100, 200 and 300 J/cm2 respectively, significantly different from untreated S. epidermidis （（388 ± 8.89） × 105, all P < 0.01） and S. epidermidis irradiated with red light only. Increased ratio of dead to live cells was observed in ALA-pretreated S. epidermidis irradiated with red light at 100, 200 and 300 J/cm2 compared with untreated S. epidermidis （1.254 ± 0.096, 1.301 ± 0.160 and 3.410 ± 1.140 vs. 0.358 ± 0.057, all P < 0.01） and S. epidermidis irradiated with red light only. SEM showed that the biofilm structure was loose and obscure in S. epidermidis treated with ALA-PDT, and even disappeared with S. epidermidis distributed in single colonies when the dose of red light was 300 mJ/cm2. Conclusion ALA-PDT shows a potential bactericidal activity against S. epidermidis in biofilms, which can not only reduce biofilm vitality, but also damage biofilm structure.

Key words: biofilm