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The antimicrobial effects of the Mexican medicinal plants Guazuma ulmifolia, Justicia spicigera, Opuntia joconostle, O. leucotricha, Parkinsonia aculeata, Phoradendron longifolium, P. serotinum, Psittacanthus calyculatus, Tecoma stansand Teucrium cubensewere tested against several human multi-drug resistant pathogens, including three Gram (+) and five Gram (-) bacterial species and three fungal species using the disk-diffusion assay. The cytotoxicity of plant extracts on human cancer cell lines and human normal non-cancerous cells was also evaluated using the MTT assay. Phoradendron longifolium, Teucrium cubense, Opuntia joconostle, Tecoma stansand Guazuma ulmifoliashowed potent antimicrobial effects against at least one multidrug-resistant microorganism (inhibition zone > 15 mm). Only Justicia spicigeraand Phoradendron serotinumextracts exerted active cytotoxic effects on human breast cancer cells (IC50≤30 μg/mL). The results showed that Guazuma ulmifoliaproduced potent antimicrobial effects against Candida albicansand Acinetobacter lwoffii, whereas Justicia spicigeraand Phoradendron serotinumexerted the highest toxic effects on MCF-7 and HeLa, respectively, which are human cancer cell lines. These three plant species may be important sources of antimicrobial and cytotoxic agents.

Multi-drug resistance is of great concern for public health worldwide and necessitates the search for new antimicrobials from sources such as plants. Several Magnolia(Magnoliaceae) species have been reported to exert antimicrobial effects on sensitive and multidrug-resistant microorganisms. However, the antimicrobial properties of Magnolia dealbatahave not been experimentally evaluated. The antimicrobial effects of an ethanol extract of Magnolia dealbataseeds (MDE) and its active compounds honokiol (HK) and magnolol (MG) were tested against the phytopathogen Clavibacter michiganensis subsp. michiganensisand several human multi-drug resistant pathogens using the disk-diffusion assay. The effects of MDE and its active compounds on the viability of human peripheral blood mononuclear cells (PBMC) were evaluated using MTT assay. MDE and its active compounds had antimicrobial activity (inhibition zone > 10 mm) against C. michiganensis, Pseudomonas aeruginosa, Acinetobacter baumannii, Acinetobacter lwoffii, Candida albicans, Candida tropicalisand Trichosporon belgeii.The results suggest that M. dealbataand its active compounds have selective antimicrobial effects against drug-resistant fungal and Gram (-) bacteria and exert minimal toxic effects on human PMBC.

An efficient protocol for the in vitro propagation of Magnolia dealbata Zucc., an important medicinal plant that is the source of the anxiolytic and anticancer compounds honokiol and magnolol, was established. This plant is wild-crafted, and conservationists have expressed concerns with regard to the sustainability of production. In the present work, two factors were found to be of importance for the regeneration of M. dealbata and the production of honokiol and magnolol. These factors were the type of explants and the combination and concentration of plant-growth regulators. Green, compact, nodular organogenic callus was obtained from leaf explants in a medium fortified with Murashige and Skoog salts and supplemented with 1.5 mg/L 2,4-dicholorophenoxyacetic acid and 1.5 mg/L kinetin. Shoot multiplication from callus cultures was achieved in the Murashige and Skoog (MS) medium with 1.5 mg/L thidiazuron (TDZ). Phenol secretion was controlled by the addition of 250 mg/L of activated charcoal. For rooting, shoots were transferred to MS medium supplemented with several auxins. After root induction, the plants were hardened in earthen pots containing sand, soil, and vermiculite.The contents of honokiol (HK) and magnolol (MG) were determined in different plant materials by high-performance liquid chromatography-diode-array detection techniques. This analysis revealed that the honokiol and magnolol content in aerial and underground parts of micropropagated M. dealbata were higher than that observed in wild plants (both 6 months old). Our results suggest that conservation of M. dealbata is possible by means of in vitro multiplication of leaf-derived callus. The usefulness of M. dealbata regeneration and production of HK and MG may be attributed to the proper selection of explant sourcing and identification of the correct growth medium to support adequate growth. This careful selection of explants and growth medium leads to a very useful source of plant material for pharmacological and phytomedicinal screening applications and, above all, would safeguard this plant species from the threat of extinction.

Honokiol and magnolol, important anxiolytic and anti-cancer agents, have been produced in cell-suspension cultures of the endangered Mexican plant Magnolia dealbataZucc. In vitrocultures of the plant were established, and the accumulation of honokiol and magnolol in callus and cell-suspension cultures was measured. Leaf samples were the best explants for callus establishment and metabolite production, and Murashige and Skoog medium supplemented with 1 mg/L 2, 4-dichlorophenoxyacetic acid and 1 mg/L kinetin yielded 2.3 mg/g of honokiol and 5.9 mg/g of magnolol. Bacterial and fungal contamination was inhibited with a multiple-step tissue sterilization procedure. Oxidation was inhibited with 1 g/L activated charcoal. Cell-suspension batch cultures derived from friable callus obtained from leaves of this species were grown for 30 days in shaker flasks containing Murashige and Skoog medium. Throughout the growth cycle, honokiol and magnolol levels, fresh and dry weight, and sucrose uptake were determined. The effects of carbon source concentration on biomass accumulation and the synthesis of bioactive compounds were studied. By using 3 mL of inocula supplemented with 3% (w/v) sucrose, maximum yields of honokiol (8.1 mg/g) and magnolol (13.4 mg/g) were obtained after 25 days. These yields were 300% and 382%, respectively, of the yields of honokiol and magnolol obtained from field-grown plants.