Composição química e efeito antibiótico das frações diclorometânicas floral e foliar de Vernonia polyanthes Less. (Asteraceae Bercht. & J. Presl)

Abstract

Vernonia polyanthes Less. (Asteraceae Bercht & Presl.), is a native South American plant, popularly known in Brazil as "assa-peixe" and traditionally used in the treatment of flu, cold, bronchitis, intestinal and kidney disorders, uterine infection, ulcers and fever. Thus, the present study aimed to investigate the chemical compositions and antibiotic effects of floral (DF-Vp) and foliar (DL-Vp) dichloromethane fractions. Fresh leaves and flowers were extracted with hydroethanolic solutions 70% and subjected to liquid / liquid partition with hexane (HF-Vp / HL-Vp) and dichloromethane (DF-Vp / DL-Vp). Initially, an in vitro screening of the antibiotic effect of extracts and fractions from this plant species was established by determining the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC), followed by the classification of the antibiotic effect against Staphylococcus aureus (ATCC® 25923™, 29213™ and 6538™), Escherichia coli (ATCC® 10536™ and 25922™), Salmonella Choleraesuis (ATCC® 10708™), Salmonella Typhimurium (ATCC® 13311 ™) and Pseudomonas aeruginosa (ATCC® 9027 ™ and 27853 ™), revealing DF-Vp and DL-Vp as the most promising. DF-Vp and DL-Vp chemical profiles were analyzed by gas chromatography coupled to a mass spectrometry detector (GC-MS) that showed the presence of terpenoids and flavonoids, chemotaxonomic markers of V. polyanthes. The antibiotic effect of DL-Vp and DF- Vp was further investigated against Salmonella Choleraesuis (ATCC® 10708™), Salmonella Typhimurium (ATCC® 13311™) and Salmonella Enteritidis 1428260 and Salmonella spp. 1507708 clinical strains by the combinatorial effect, time kill, cellular viability and leakage of compounds absorbing at 280 nm assays. Additionally, we investigated if lupeol could be the main responsible for the antibiotic effect of this plant species. DL-Vp was active against S. Choleraesuis (ATCC® 10708 ™), S. Typhimurium (ATCC® 13311™), and Salmonella spp. 1502596 and 1266695, with MIC values of 625 μg/mL, and Salmonella spp. 1553217 and 1507708 and S. Enteritidis 1428260, with MIC of 1250 μg/mL. DF-Vp was active against Salmonella spp. 1502596 (MIC = 625 μg/mL) and also against S. Choleraesuis (ATCC® 10708™), S. Typhimurium (ATCC® 13311™) and S. Enteritidis 1428260 with MIC values of 1250 μg/mL, and Salmonella spp. 1507708 and 1266695 (MIC = 2500 μg/mL). With the exception of DL-Vp against S. Typhimurium (ATCC® 13311™) with MIC values of 5000 μg/mL and bactericidal effect, the other fractions were classified as bacteriostatic against the other strains. The synergism between DL-Vp and DF-Vp and the antibiotics was dependent strain. The time kill test showed that DL-Vp and DF-Vp decreased bacterial population density, and in most cases, treatments with these fractions were more efficient than the antibiotics. Finally, cytotoxicity was determined by Artemia salina bioassay and the dichloromethanic fractions were classified as nontoxic. The results revealed the promising antibiotic effect of V. polyanthes, mainly against Salmonella, including clinical strains that were resistant to levofloxacin and ampicillin. In addition, it was possible to affirm that it was observed that lupeol was not the main responsible for this effect in this plant species.