Photodynamic therapy based on 5-aminolevulinic acid and its use as an antimicrobial Agent

Abstract

Exogenous 5-aminolevulinic acid (ALA) is taken up directly by bacteria, yeasts, fungi, and
some parasites, which then induces the accumulation of protoporphyrin IX (PPIX). Subsequent light
irradiation of PPIX leads to the inactivation of these organisms via photodamage to their cellular
structures. ALA uptake and light irradiation of PPIX produced by host cells leads to the inactivation of
other parasites, along with some viruses, via the induction of an immune response. ALA-mediated
PPIX production by host cells and light irradiation result in the inactivation of other viruses via either
the induction of a host cell response or direct photodynamic attack on viral particles. This ALAmediated
production of light-activated PPIX has been extensively used as a form of photodynamic
therapy (PDT) and has shown varying levels of efficacy in treating conditions that are associated with
microbial infection, ranging from acne and verrucae to leishmaniasis and onychomycosis. However, for
the treatment of some of these conditions by ALA-based PDT, the role of an antimicrobial effect has
been disputed and in general, the mechanisms by which the technique inactivates microbes are not well
understood. In this study, we review current understanding of the antimicrobial mechanisms used by
ALA-based PDT and its role in the treatment of microbial infections along with its potential medical
and nonmedical applications.