Comparative metabolite profiling of four polyphenol rich Morus leaves extracts in relation to their antibiofilm activity against Enterococcus faecalis

Enterococci are a common cause of urinary tract infections. The severity of enterococcal infections is associated with their ability to form biofilms. Morus leaves are known as a natural antibacterial, however, their antibiofilm activity against Enterococcus remains unveiled. This study aimed to evaluate the ability of four polyphenol-rich Morus leaves extracts (Morus nigra, M. rubra, M. macroura, and M. alba) to inhibit biofilm formed by enterococcal clinical isolates in relation to their metabolic profiling. Results revealed that 48% of the isolates formed strong biofilm, 28% formed moderate biofilm, 20% formed weak biofilm, and only 4% did not form a biofilm. The strong biofilm-forming isolates were E. faecalis, and hence were chosen for this study. The antibiofilm activity of the four polyphenol-rich Morus leaves extracts revealed that the M. nigra extract exhibited the highest percentage of biofilm inhibition followed by M. rubra then M. macroura and the least inhibition was detected in M. alba, and these results were in accordance with the phenolic and flavonoid contents of each extract. UPLC-ESI-MS/MS identified 61 polyphenolic compounds in the four extracts. Further, multivariate analysis confirmed clear segregation of M. nigra from the other species suggesting disparity in its metabolome, with accumulation of flavonoids, anthocyanidins, phenolic acids and coumarin derivatives. Quercetin and kaempferol glycosides were found to be positively and significantly correlated to the antibiofilm activity. In conclusion, M. nigra ethanolic extracts showed the highest phenolic content and antibiofilm activity and they could be developed as a complementary treatment for the development of antimicrobial agents.