ENVIRONMENTAL INTERFERENCE IN THE SYNTHESIS OF ANTIMICROBIAL SUBSTANCES FROM Sida rhombifolia L. (MALVACEAE) (Atena Editora)

Abstract

The same plant species may present variation in its chemical composition depending on the stage of its development, place of collection and time of year in which it is collected. The objective of this work was to compare the antimicrobial activity of two specimens of Sida rhombifolia, collected at the same stage of development, in the same period of the year, in different locations in the State of Acre. Crude extracts were obtained from leaves, stem-twigs, flowers and roots by cold exhaustion with hexane, acetone and ethanol. The antimicrobial activity was evaluated against Gram-positive, Gram-negative and acid-fast bacteria, in addition to the yeast Candida albicans. Paper disks were impregnated with 25µL of each extract, at a concentration of 4mg/mL, and deposited on the previously inoculated medium. The experiments were incubated at 36ºC and the results evaluated after 24h of microbial growth. The extracts were also submitted to thin layer chromatography, using the solvent system TOLUOL/ETHYL ACETATE (85:15v/v), in order to verify differences in the chemical composition between the specimens. The chromatoplates were visualized under ultraviolet light and developed with resublimated iodine vapors. It was found that extracts of Sida rhombifolia, obtained from specimen I, showed antimicrobial activity against all microorganisms tested, while those obtained from specimen II were inactive against the same microorganisms. The leaves showed a higher concentration of active principles, which were extracted mainly by ethanol, producing inhibition halos of up to 17mm in diameter. The chromatographic tests revealed differences in the chemical composition between the two specimens, both with regard to the content of substances, which were more concentrated in specimen I, and the presence of possible antagonistic substances in specimen II. It can be concluded that the specimens of Sida rhombifolia showed qualitative and quantitative variations in their chemical composition and that these variations interfered in the antimicrobial potential of the species.