RESUMEN
A comparative study on antimicrobial activity was carried out using ethanolic extracts from different parts of three Senecio [chachacoma] species collected in the province of San Juan [Argentina]. At 33 mg/ml, growth inhibition was detected against Micrococcus luteus ATCC 9341 in all extracts belonging to S. eriophyton J. Remy, S. nutans Sch. Bip. [chachacoma] [S. graveolens Weddell] and S. oreophyton J. Remy, with the exception of young and adult stems of S. nutans. The highest inhibitory activity was exhibited by leaves [equivalent to 3x10[-4] mg/ml amoxicillin] and capitula containing flower and fruit [equivalence: 4x10[-4] mg/ml amoxicillin] of S. nutans. These two last extracts were the only active on E. coli [equivalence: 2x10[-2] mg/ml cephazolin] and C. albicans [equivalence: 10[-2] and 10[-1] mg/ml miconazole, respectively]. They were inactive on Proteus mirabilis and Pseudomonas aeruginosa. Activity against Staphylococcus aureus oxacillin-sensitive was showed by extracts from S. nutans Sch. Bip. "chachacoma" [Senecio graveolens Weddell] corresponding to leaves and capitula containing flower and fruit [equivalence: 10[-2] mg/ml cephazolin] as well as by leaves, capitula containing flower and fruit and young stems from S. oreophyton [equivalence: 3xl0[-3], 3xl0[-3] and 1 x 10[-1] mg/ml cephazolin, respectively. Minimal inhibitory concentration [MIC] was evaluated in the most active extracts, corresponding to S. nutans. Values were 8 mg/ml for leaves and 8, 4 and 16 for capitula containing fruit and flower on S, aureus, E coli and C. albicans, respectively. Minimal bactericidal concentration [MBC] was also assayed. The MBC/ MIC ratio was clearly higher than 1, indicating a bacteriostatic effect of the extracts on the micro-organisms tested. The results herein reported would suggest the potential usefulness of the components of these extracts as antiseptic agents