Crude extract and 9-methoxyisomoschatoline from Guatteria hispida as photosensitizers in antimicrobial photodynamic inactivation (PDI)

Abstract

Guatteria hispida (R. E. Fr.) Erkens & Maas (Annonaceae) is a small tree that occurs in the Brazilian Amazon forest. This study was undertaken to evaluate the effect of methanol crude extract and alkaloid 9-methoxyisomoschatoline isolated from the bark of G. hispida as photosensitizers in antimicrobial photodynamic inactivation (PDI) of bacteria and yeast. Methanol extract and isolated alkaloid (9-methoxyisomoschatoline) were tested, in sub-inhibitory concentration, against Staphylococcus aureus ATCC14458, Escherichia coli ATCC10799, Proteus vulgaris, Candida albicans ATCC1023, C. albicans ATCC10231, Candida dubliniensis ATCC778157 and C. dubliniensis ATCC777. One plate (n=6) was subjected to irradiation with a 660nm diode laser with an output power of 35 mW distributed through the well cross section yielding an energy dosage of 28J/cm2, and one was not irradiated. The absorption spectrum of the samples presented maximum bands at 330 and 620nm, and when irradiated with these wavelengths showed high fluorescence intensity. At photochemical assay, the 1.3DPBF photodegradation was significantly enhanced in the presence of crude extract and isolated alkaloid indicating the production of singlet oxygen. The biological assays suggest inhibition of the growth of microorganisms tested in the presence of methanol extract and isolated alkaloid as photosensitizers in PDI. Laser irradiation alone or crude extracts or alkaloid at sub-inhibitory concentration are not bioactive. Further investigations are necessary to confirm the potential of these natural products as photosensitizers in PDI.