Antimicrobial activity of Portuguese Asphodelus root extracts against multidrug-resistant bacteria

Antimicrobial resistance (AMR) is a growing global health concern due to the loss of efficacy of first-line antibiotics and the development of multidrug-resistance in many pathogens. In this context, ethnomedical information plays an increasingly important role, since herbal medicines have shown high potential as anti- infective agents. Root tubers of the Portuguese endemism Asphodelus bento-rainhae and its coexisting species Asphodelus macrocarpus have been traditionally used to treat skin diseases and infections, therefore the present study aims to detect and identify the potential secondary metabolites of antimicrobial markers using an in vitro bioguided procedure. The hydroethanolic (70%) extracts of both medicinal plants were subjected to liquid-liquid separation with solvents of increasing polarity, generating the diethyl ether, ethyl acetate and aqueous fractions. Phytochemical screening of the potential extracts was performed using TLC and LC-UV/DAD-ESI/MS chromatography techniques and broth microdilution method was used for in vitro evaluations of antimicrobial activity. The diethyl ether L-L fractions of both species showed the highest activity against all tested Gram-positive microorganisms (MIC: 16 to 1000 μg/mL). Chrysophanol derivatives have been identified as major marker compounds and have shown high antimicrobial activity, particularly against Staphylococcus epidermidis (MIC: 3.2 to 100 μg/mL). The studied Asphodelus species found to be a potential source of antimicrobial agents against multidrug-resistant pathogens and the obtained results contribute to the concrete validation of the use of these medicinal plants as future herbal products.