Artichoke and milk thistle pills and syrups as sources of phenolic compounds with antimicrobial activity

Dietary supplements based on hepatoprotective plants have been increasingly used in the prevention of liver injuries. In the present work, the aim was to study the phenolic profile and possibly relate it to the in vitro antimicrobial activity of two different formulations (pills and syrups) of artichoke and milk thistle, the antioxidant and anti-hepatocellular carcinoma activities of which were previously reported by our research group. The phenolic profiles were obtained by HPLC-DAD-ESI/MS, and the antimicrobial activity evaluation was performed with the clinical isolates of multiresistant bacteria (Escherichia coli, extended spectrum β-lactamases (ESBL) producing Escherichia coli, Proteus mirabilis, methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa). Artichoke syrup revealed the presence of vanillic acid and luteolin-7-O-glucoside while the pills possessed higher concentrations of 4-O-caffeoylquinic, 5-O-caffeoylquinic and 1,3-O-dicaffeoylquinic acids, this latest being able to inhibit the growth of MRSA. Regarding milk thistle formulations, the syrup presented isorhamnetin-O-deoxyhexoside-O-dihexoside, isorhamnetin-O-deoxyhexoside-O-hexoside and isorhamnetin-3-O-rutinoside as the major phenolic constituents whereas the pills were richer in taxifolin, silymarin derivatives and hydroxylated silibinin; the syrup revealed antimicrobial activity against all the studied bacteria with the exception of Proteus mirabilis whereas the pills revealed activity against ESBL producing Escherichia coli. Overall, all of the studied formulations revealed to be a good source of phenolic compounds, among which milk thistle syrup presented the highest variety and concentration of flavonoids, which is possibly related to its strongest antimicrobial activity.