In vitro antibacterial, phototoxic, and synergistic activity of ethanol extracts from Costus cf. arabicus L.

In this study, ethanol extracts of stems and leaves of Costus cf. arabicus L. were evaluated for antibacterial activity against multidrug-resistant strains of Escherichia coli and Staphylococcus aureus. The antibacterial and modulatory activities of the extracts were assayed by microdilution. The light-enhanced antibacterial activity was assayed by a light regimen. The growth of the bacteria tested was not inhibited by the extracts. The minimum inhibitory concentration values were ≥1,024 μg/mL. However, the antibiotic activity of aminoglycosides was synergistically enhanced when these extracts at subinhibitory concentrations were combined with the antibiotics. Also, both extracts showed activity against the wild-type bacterial strains, but the leaf extract was the more active extract, being active against both S. aureus and E. coli. Therefore, we conclude that the ethanol extracts of stems and leaves of C. cf. arabicus L. have potential light-induced antibacterial activity and synergistic antibiotic activity. This study showed that these extracts may be a promising source of antibacterial and modulatory agents.