This study was undertaken to evaluate the effect of Alternathera brasiliana (Amaranthaceae) extracts as
photosensitizing agents in photodynamic antimicrobial
therapies (PACT) against Staphylococcus aureus, Staphylococcus epidermidis and Candida dubliniensis. The crude
hexane and
ethanol extracts were obtained from A. brasiliana whole plant and showed absortion from 650 to 700 nm. Also, singlet molecular
oxygen (1O2) production (type II
photosensitization reaction) was examined, and the results show that
1,3-diphenylisobenzofuran photodegradation was greatly enhanced in the presence of the A. brasiliana extracts. One plate in each assay was irradiated while the other was not irradiated, the number of colony-forming units per milliliter (CFU/mL) was obtained, and data analyzed by the Tukey test. The chemical composition of the extracts was determined by chromatographic and spectrometric techniques;
steroids,
triterpenes, and
flavonoids were identified.
Laser irradiation alone at 685 nm using
diode laser, output power of 35 mW, and energy of 28 J/cm2, or non-irradiated
crude extracts in sub-inhibitory concentration did not reduce the number of CFU/mL significantly, whereas irradiated
hexane and
ethanol extracts, in sub-inhibitory concentrations, inhibited the growth of these microorganisms. The photoactivation of
hexane and
ethanol extracts of A. brasiliana, in sub-inhibitory concentrations, using red
laser radiation at 685 nm had an antimicrobial effect.