Purified Quercetin From in vitro Cell Suspension Cultures of <em>Caesalpinia pulcherrima</em> Sw. and Its Antimicrobial Potentials

Tribal people use the flower extract of <em>Caesalpinia pulcherrima<strong> </strong></em>to cure liver, stomach and skin disorders in Indian traditional medicine. This study aimed to evaluate the protective roles of purified quercetin extracted from suspension culture of <em>C. pulcherrima</em> against selected bacterial and fungal pathogens. A simple protocol was developed for callus production using leaf explants<em>.</em> 2, 4-D (2.5 mg/l), BAP (2.5 mg/l) + kin (1 mg/ml) was effective for optimal callus induction. Subsequently, cell suspension culture was established.  Role of effect of elicitors in cell suspension culture was carried. Sucrose, ABA and salicylic acid (SA) at different concentrations influenced cell biomass and quercetin accumulation. Cells cultured in the medium fortified with 45 g/L sucrose without ABA/SA showed the highest quercetin content (16.5 mg/g). Flavonoids was purified, fractionated by HPLC-DAD followed by NMR revealed the presence of quercetin, isoquercetin, quercetrin, rutin, quercetin 3-O-β-D-xyloside, quercetin 3-Oarabinopyranoside, quercetin 3-O- α-arabinopyranosyl (1→2) β-galactopyranoside,  isorhamnetin 3-O-rutinoside and an unknown compound. Subsequently, anthocyanin was evaluated for antimicrobial activity against selected Gram-positive bacteria (<em>S. aureus, Bacillus subtilis</em>, and <em>Enterococcus faecalis</em><em>)</em>, Gram-negative bacteria (<em>E. coli, </em>and <em>Pseudomonas aeruginosa</em>) and fungi such as <em>Aspergillus flavus, Candida albicans </em>and <em>Trichophyton rubrum</em>. Quercetin was found to be active against four bacteria and the fungi- <em>Candida albicans</em>. The highest inhibitory effects were found on <em>S. aureus</em> and <em>Enterococcus faecalis</em>. Gram negative bacteria showed more resistance i.e., with insignificant MIC and MBC values. Among the fungi, <em>Aspergillus flavus</em> and <em>Trichophyton rubrum</em> displayed remarkable MIC and MKC values. These results suggest that quercetin may be used as a natural antimicrobial agent. Future works are designed to trace the molecular mechanism of antimicrobial potentiality of quercetin against these tested pathogens