Unveiling the functional components and antivirulence activity of mustard leaves using an LC-MS/MS, molecular networking, and multivariate data analysis integrated approach

Plant extracts have recently received increased attention as alternative sources of antimicrobial agents in the fight against multidrug-resistant bacteria. Non-targeted metabolomics liquid chromatography-quadrupole time-of-flight tandem mass spectrometry, molecular networking, and chemometrics were used to evaluate the metabolic profiles of red and green leaves of two Brassica juncea (L.) varieties, var. integrifolia (IR and IG) and var. rugosa (RR and RG), as well as to establish a relationship between the elucidated chemical profiles and antivirulence activity. In total, 171 metabolites from different classes were annotated and principal component analysis revealed higher levels of phenolics and glucosinolates in var. integrifolia leaves and color discrimination, whereas fatty acids were enriched in var. rugosa, particularly trihydroxy octadecadienoic acid. All extracts demonstrated significant antibacterial activity against Staphylococcus aureus and Enterococcus faecalis, presenting the IR leaves the highest antihemolytic activity against S. aureus (99 % inhibition), followed by RR (84 %), IG (82 %), and RG (37 %) leaves. Antivirulence of IR leaves was further validated by reduction in alpha-hemolysin gene transcription (∼4-fold). Using various multivariate data analyses, compounds positively correlated to bioactivity, primarily phenolic compounds, glucosinolates, and isothiocyanates, were also identified.