Morus alba leaf extract: Metabolite profiling and interactions with antibiotics against Staphylococcus spp. including MRSA

Abstract

HPLC-DAD-ESI-Q-TOF-MS/MS metabolite profiling of Morus alba leaf extract led to the annotation of 25 constituents (two stilbene derivatives, 11 prenylflavonoids, five 2-arylbenzofurans, seven Diels–Alder type adducts). The extract was found to contain 57.83 mg/g flavonoids, 15.42 mg/g kuwanon G and 10.47 mg/g morusin. Despite its moderate antibacterial activity with minimum inhibitory concentration (MIC) values of 250 μg/mL against methicillin-resistant Staphylococcus aureus (MRSA) ATCC 33591 and ATCC 43300, methicillin-susceptible S. aureus (MSSA) ATCC 6538 and S. epidermidis ATCC 12228, Morus alba leaf extract reversed oxacillin-resistance of MRSA ATCC 43300. In addition, the extract showed synergy with gentamicin against MRSA ATCC 33591 and ATCC 43300 and S. epidermidis ATCC 12228, oxacillin against MRSA ATCC 33591 and tetracycline against S. epidermidis ATCC 12228. In these synergistic combinations, MIC values of antibiotics were significantly decreased (4–32-fold). These findings might be valuable for the development of novel treatment strategies in infections caused by MRSA and S. epidermidis.