Identification and antimicrobial activity of most representative secondary metabolites from different plant species

Background: The plant kingdom constitutes an enormous reservoir of bioactive molecules, generally used by plants to prevent or to protect themselves from pathogens’ attacks. To date, several primary or secondary plant metabolites have been already proven to exert antibiotic activities; nonetheless, researchers are still continuing to lavish great eforts to identify and characterize new natural molecules one by one. Aiming at the replacement of synthetic chemical products, the bioactivity of plant extracts should be assessed case by case, and active substances should be tested as individuals to obtain accurate information on the real usefulness of plant metabolites. In this work major glycoalkaloids obtained from Solanum nigrum, glucosinolates from Armoracia rusticana, and cannabinoids from Cannabis sativa were identifed. The antimicrobial activity of crude extracts and pure components against Gram+ (Bacillus cereus (A1I), Bacillus thuringiensis (B7I2), and Bacillus amyloliquefaciens (A5TI)) and Gram− bacteria (Pseudomonas orientalis (A14-1II),and Stenotrophomonas maltophilia (B9TIII)), employed as model organisms, was tested. Result: Major glycoalkaloids, glucosinolates, and cannabinoids were identifed in crude plants’ extracts using highresolution LC–ESI-FTICR/MS. From antimicrobial assays useful information towards a few of biological activities of crude extracts and individual components were obtained. Solanum nigrum extracts revealed inhibition activity on all bacteria tested as well as the main active glycoalkaloids, solamargine and solasonine, which were found to be active even when tested individually. At assayed concentrations, A. rusticana extract was active towards a few of the microorganisms tested, confrming that the activity of glucosinolates can be referred only partially to the mother molecules, while biological efciency of such kind of compounds is mainly due to their enzymatic breaking of, where myrosinase converts them into isothiocyanates and/or thiocyanates. Hemp-type C. sativa extract showed antimicrobial activity only against Gram+ bacteria, but the main individual components tested showed always a limited bioactivity. Conclusion: Promising results were obtained, but tests performed in vitro are only the frst step of a wider investigation as required for an extensive application. Further research eforts are necessary to demonstrate the efciency of natural substances in diferent target environments.