In vitro effect of 5-aminolaevulinic acid plus visible light on Candida albicans

Abstract

Photodynamic therapy, currently used as an alternative technique for the treatment of superficial non-melanoma skin cancers, has been employed in vitro to kill different species of microorganisms. Here the development of Candida albicans colonies has been measured after application of 5-aminolaevulinic acid (ALA) plus visible light (VIS) irradiation. C. albicans suspensions (10 colony forming units µl⁻¹) have been prepared. For the experiment 30 µl of suspension have been incubated in the dark for 3 h, with increasing concentrations of ALA (125, 250, 300, 350, 400, 450, 500, 550, 600, 750, 1000 mg ml⁻¹) and then irradiated with a fixed dose (40 J cm⁻²) of VIS. Immediately after the irradiative session, the C. albicans suspensions were disseminated on dishes containing a Sabouraud agar + CAF medium and cultured in the dark at 27 °C; after 48 h colony development has been measured. In the same way four controls have been prepared: (i) C. albicans suspensions not treated with ALA-PDT; (ii) C. albicans suspensions incubated with increasing ALA concentrations without VIS; (iii) C. albicans suspensions irradiated with 40 J cm⁻² of VIS without ALA; (iv) C. albicans suspensions irradiated immediately after the addition of increasing concentrations of ALA without the 3 h incubation. Colonies treated with ALA-PDT have been studied with electron microscopy (E.M.). It was found that: (i) none of the controls prepared modified the development of C. albicans colonies; (ii) ALA plus VIS inhibited C. albicans growth in a concentration-dependent way: up to 250 mg ml of ALA concentrations did not affect C. albicans cells, 300 mg ml⁻¹ induced a 50% reduction in the number of colonies, a complete inhibition started from concentrations of 600 mg ml⁻¹; (iii) after ALA-PDT E.M. showed modifications of the cell membranes. From the results it is concluded ALA plus VIS light is able to kill C. albicans colonies, at least in vitro. Although other pharmacological approaches are available, further studies could show that PDT is a potential treatment for candidosis.