Abstract:

Objective To observe the effect of 5-aminolevulinic acid-based photodynamic therapy （ALA-PDT） on S. epidermidis planktonic cells, and to determine the optimal concentration and incubation time of ALA. Methods Some S. epidermidis planktonic cells were divided into 3 groups to be incubated with ALA at 50 mmol/L for different durations （3, 5, 8, 12, 16, 18, 20 and 24 hours） at 37 ℃ in dark room （group 1）, with ALA at various concentrations （10, 20, 30, 40 and 50 mmol/L） for 16 hours at 37 ℃ in dark room （group 2）, and with fresh trypticase soya broth （TSB） solution for 24 hours at 37 ℃ in dark room （group 3） , respectively. Confocal laser scanning microscopy （CLSM） was used to measure the fluorescence intensity of protoporphyrin IX （PpIX） in bacterial suspensions at different time points. Additionally, some S. epidermidis planktonic cells in group 1 were irradiated with red light at 30, 50, 70, 90 and 100 J/cm2 after incubation with ALA at 50 mmol/L for 16 hours, some in group 2 were irradiated with red light at 100 J/cm2 after incubation with ALA for 16 hours, those cells in group 3 received no irradiation （blank control group）, and some S. epidermidis planktonic cells receiving only irradiation and no pretreatment with ALA served as the laser control group; subsequently, the bacterial suspension was inoculated onto trypticase soy agar （TSA） followed by the calculation of colony forming units （CFUs） of S. epidermidis. Results Brick red fluorescence was observed by CLSM in S. epidermidis planktonic cells in group 1 and 2, but not in those in group 3, and the fluorescence intensity was enhanced with the increase in incubation time and concentration of ALA. In detail, the fluorescence intensity was significantly higher in planktonic S. epidermidis cells after 16-, 18-, 20- and 24-hour incubation than in those after 3-, 5-, 8- and 12-hour incubation with ALA at 50 mmol/L （all P < 0.05）, and higher in those incubated with ALA at 50 mmol/L than in those with ALA lower than 50 mmol/L （all P < 0.05）. After irradiation, the number of surviving S. epidermidis planktonic cells declined with the increase in ALA concentration and red light doses, statistically lower in the group 1 and 2 than in the blank control group （both P < 0.05）, but similar between the blank control and laser control group （P > 0.05）. The growth of planktonic cells was inhibited after incubation with ALA at 50 mmol/L and irradiation with red light at 100 J/cm2. Conclusions ALA-PDT shows a marked inhibitive effect on S. epidermidis planktonic cells, with the optimal working concentration of ALA being 50 mmol/L, incubation time 16 hours, and dose of red light 100 J/cm2.

Key words: Planktonic cells