Evaluation of the Effect of Methanol Extract from the Leaves of Annona cacans and Their Fractions in Antimicrobial Photodynamic Inactivation (PDI)
The Annonaceae is a tropical and subtropical family that comprising more than 2500 species. Annona cacans, popularly known as “coração de boi”, occurs in the southeast and south of Brazil and have nutritional and medicinal uses. This study was undertaken to evaluate the potential effect of methanol crude extract (EBAC), the neutral (FCAAC) and alkaloidal (FNAC) fractions of A. cacans as photosensitizers in antimicrobial photodynamic inactivation (PDI) of bacteria. Methanol extract and its fractions were tested, in sub-inhibitory concentration (0.5 mg/mL), against Enterococcus faecalis, Staphylococcus aureus ATCC 6538, Escherichia coli ATCC10799, Staphylococcus epidermidis ATCC 12228 (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. In each assay one plate was subjected to irradiation and another was not, the number of colony-forming units per milliliter (CFU/mL) was obtained, and data analyzed by the Tukey test. The absorption spectrum of the samples presented maximum bands at 340 and 660nm, and when irradiated with 405nm the FCNAC showed high fluorescence intensity. 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. cacans extract and fractions. Laser irradiation alone, or non-irradiated crude extract and fractions in sub-inhibitory concentration did not significantly reduce the number of CFU/mL, whereas irradiated methanol extract of A. cacans and their alkaloidal and neutral fractions, in sub-inhibitory concentrations, inhibited the growth of these microorganisms and promoted an antimicrobial effect. Further investigations are necessary to confirm the potential of these natural products as photosensitizers in PDI.