Antibacterial, Antibiofilm, and Synergistic Effects of Eremanthus crotonoides Against Multidrug-Resistant Staphylococcus Strains

The ethanolic extract and five fractions from Eremanthus crotonoides (DC.) Sch. Bip., Asteraceae, leaves were tested by the agar dilution method against sixteen bacterial strains acquired from hospital infection sites and 12 strains from the American Type Culture Collection. A total of 26 human pathogenic strains were inhibited by the dichloromethane fraction at a minimum inhibitory concentration ≥ 128 µg/ml, and this fraction also showed inhibition zones between 9 and 21.7 mm diameter by the disc diffusion agar method. The dichloromethane fraction suggested bactericide mode of action and showed a synergistic effect with the standard oxacillin, but any antibiofilm activity was observed. A bioassay-guided fractionation of this active fraction was followed by column chromatography, and centratherin was identified as the most active compound. Centratherin minimum inhibitory concentration was 64 µg/ml against Staphylococcus aureus ATCC 33,591 and 32 µg/ml against a clinical isolate. It also showed antibiofilm activity at 128 µg/ml against the ATCC 33,591 stain. This compound showed more selectivity to S. aureus ATCC 33,591 and the clinical strain when tested with MA-104 (fibroblast). Graphical abstract