Investigação da atividade antibacteriana do extrato de lavagem foliar e do glaucolídeo A de Vernonia polyanthes Less. (Asteraceae)

Abstract

Vernonia polyanthes Less. (Asteraceae), popularly known as "assa-peixe", is a native species of South America, especially in Brazil. This medicinal plant is traditionally used in cases of cold, flu, cough, fever, bronchitis, bruise, hemorrhoid, uterus infection and malaria's treatment. Pharmacologically, V. polyanthes has been reported as anti-hypertensive, antinociceptive, anti-ulcerogenic, anti-inflammatory, leishmanicidal and antimicrobial. Phytochemical studies focusing this plant, available in the literature, report the presence of secondary metabolites mainly belonging to the flavonoids and terpene classes, especially sesquiterpene lactones. The present study investigated the antibacterial activity of the leaf rinse extract (VP extract) and the sesquiterpene lactone glaucolide A isolated from V. polyanthes in order to scientifically corroborate with the traditional use of this plant species and to verify the potential of VP extract and this molecule as probable herbal and an antibacterial agent prototype, respectively. VP extract was obtained by washing the dried intact leaves of V. polyanthes with dichloromethane and the glaucolide A, isolated from the VP extract fractionation by column chromatography methods. Antibacterial activity was established by the determination of the Minimal Inhibitory Concentration (MIC) using the microdilution method according to the Clinical Laboratory Standards Institute (CLSI) guidelines followed by the Minimal Bactericidal Concentration (MBC), classifying the pharmacological effect as bacteriostatic or bactericidal. Staphylococcus aureus ATCC® 6538™/ATCC® 29213™, Escherichia coli ATCC® 10536™/ATCC® 25922™, Salmonella enterica subsp. enterica serovar Choleraesuis ATCC® 10708™, Salmonella enterica subsp. enterica serovar Thyphimurium ATCC® 13311™ and Pseudomonas aeruginosa ATCC® 9027™/ATCC® 27853™ were used as reference bacterial strains. The VP extract revealed antibacterial activity against 5 of 8 tested strains, being more active against S. aureus ATCC® 6538™ and ATCC® 29213™ with MIC values of 0.625 mg/mL, demonstrating bacteriostatic effect and MBC of 2.5 mg/mL and 1.25 mg/mL, respectively. Glaucolide A showed antibacterial activity against S. aureus with MIC values of 250 µg/mL and 500 µg/mL and, revealing bacteriostatic effect and CBM of 500 µg/mL and > 500 µg/mL, in this order, being inactive against the other strains at the concentrations tested. Our results suggest the antimicrobial potential of V. polyanthes and glaucolide A, notably against S. aureus, and the VP extract activity is probably due to the synergism between this sesquiterpene lactone and other secondary metabolites of this medicinal plant.