Multifunctional application of seagrass-derived rosmarinic acid in mitigating biofilm and quorum-sensing virulence transcripts of methicillin-resistant Staphylococcus aureus

Anti-microbial drug resistance is a primary public health concern, andthe occurrence of methicillin-resistant Staphylococcus aureus (MRSA) infections is gradually increasing. Considering the folk medicinal value of the seagrass Cymodocea rotundata and its antioxidant potential, the aim of this study was to assess C. rotundata for bioactive constituents that mitigate biofilm formation and quorum-sensing (QS) mechanism of MRSA. Different solvent extracts (chloroform, ethyl acetate, methanol, and distilled water) of C. rotundata were used, of which the methanolic extract exhibited maximum biofilm inhibition with complete cell lysis in 2h. Column fractionation of the methanolic extract was performed, and 22 fractions were obtained. Fraction 7 exhibited maximum anti-biofilm potential, and the lead molecule was separated using thin-layer chromatography and characterized with high-performance liquid chromatography and nuclear magnetic resonance spectroscopy. The active constituent was identified as rosmarinic acid (RA), and the minimum inhibitory concentration was found to be 61.5µg/mL; RA inhibited MRSA virulence factors such as protease by 89.37%, lipase by 87.69%, α-hemolysin by 91.52%, and exopolysaccharides by 81.79%, with an effective anti-adherence potential. Moreover, the lead molecule RA exhibited significant downregulation of QS-mediated virulence genes such as agrA, sarA, RNAIII, fnbA, fnbB, icaA, and icaD. Thus, seagrass C. rotundata has bioactive compounds with anti-microbial potential, and RA was found to control MRSA infection.