DPPH-scavenging and antimicrobial activities of Asteraceae medicinal plants on uropathogenic bacteria

Asteraceae species were widely applied in traditional medicines in Asia countries as sources of natural antioxidants and antimicrobial agents. This study aimed to evaluate DPPH-scavenging capacities and antimicrobial activities of nine Asteraceae species collected from Southern Vietnam. Antioxidant and antimicrobial activities were determined by standard protocols. Essential oils from Ageratum conyzoides, Helianthus annuus, Artemisia vulgaris indicated significant inhibitory effects on Staphyloccocus aureus and Candida spp.. Crude extracts and fractions from Taraxacum officinale, Chrysanthemum morifolium, Ageratum conyzoides, Tagetes erecta showed inhibitory ability on at least one testing bacterial strains including S. aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa. Study on clinical isolates, ethyl acetate fraction from A. conyzoides displayed the most potent effect on uropathogenic E. coli and K. pneumoniae with MIC at 1.25-10 mg/ml and 5-12.5 mg/ml, respectively. DPPH scavenging assay indicated that Tagetes erecta extract had the lowest IC50 (17.280 g/ml) and 2.5 times higher than vitamin C (7.321 g/ml). This study revealed that A. conyzoides has good potential against uropathogenic E. coli and K. pneumoniae, and could, therefore, apply to prophylactic urinary tract infection.