Screening and evaluating honokiol from Magnolia officinalis against Nocardia seriolae infection in largemouth bass (Micropterus Salmoides).

Nocardiosis caused by Nocardia seriolae is a major threat to the aquaculture industry. Given that prolonged therapy administration can lead to a growth of antibiotic resistant strains, new antibacterial agents and alternative strategies are urgently needed. In this study, 80 medicinal plants were selected for antibacterial screening to obtain potent bioactive compounds against N. seriolae infection. The methanolic extracts of Magnolia officinalis exhibited the strongest antibacterial activity against N. seriolae with the minimal inhibitory concentration (MIC) of 12.5 µg/ml. Honokiol and magnolol as the main bioactive components of M. officinalis showed higher activity with the MIC value of 3.12 and 6.25 µg/ml, respectively. Sequentially, the evaluation of antibacterial activity of honokiol in vivo showed that honokiol had good biosafety, and could significantly reduce the bacterial load of nocardia-infected largemouth bass (p < .001). Furthermore, the survival rate of nocardia-infected fish fed with 100 mg/kg honokiol was obviously improved (p < .05). Collectively, these results suggest that medicinal plants represent a promising reservoir for discovering active components against Nocardia, and honokiol has great potential to be developed as therapeutic agents to control nocardiosis in aquaculture.

Antimycobacterial screening of selected medicinal plants against Mycobacterium tuberculosis H37Rv using agar dilution method and the microplate resazurin assay.

Background: Tuberculosis (TB), has been serious disease to the global human population causing millions of deaths worldwide. The recent increase in the number of multi-drug resistant clinical isolates of Mycobacterium tuberculosis has created an urgent need for the discovery and development of new anti-TB drugs. Medicinal plants have had a great influence on the daily lives of people living in developing countries, particularly in India. Medicinal plants were selected, and they were evaluated for its anti-TB activity against the pathogenic strain of M. tuberculosis H37Rv. Methods: Eleven medicinal plants were selected on the basis of its literature survey, and three different extracts were prepared. Antimycobacterial activities were screened using two in vitro assays, namely agar dilution assay and microplate resazurin assay against M. tuberculosis H37Rv at different concentrations of prepared extracts. We analyzed minimal inhibition concentrations and percentage of inhibition of the used strain of Mycobacteria. Isoniazid was used as a standard anti-TB drug. Results: The results of this study showed that aqueous extracts four selected medicinal plants Ocimum sanctum, Adhatoda vasica, Leptadenia reticulata, and Cocculus hirsutus having minimum inhibitory concentration at 500 µg/ml, 500 µg/ml, 250 µg/ml, and 250 µg/ml, respectively, and O. sanctum (60.24%), A. vasica (62.89%), L. reticulata (74.26%), and C. hirsutus (81.67%) showed significant anti-TB activity against M. tuberculosis. Conclusion: This study helps society to found new anti-TB agents having better anti-TB activity with lesser or no side effects.

Screening antimycobacterial activity of Baccharis dracunculifolia, Centella asiatica, Lantana camara and Pterodon emarginatus / Atividade anti-micobacteriana de Baccharis dracunculifolia, Centella asiatica, Lantana camara e Pterodon emarginatus

ABSTRACT The permanent investigation of new antimycobacterial drugs is necessary for the eradication programs of tuberculosis and other mycobacterium-related diseases. The aim of the present study is to search for new sources of antimycobacterial drugs using plant materials. In this study, 11 plant materials (extracts, essential oils and some fractions) obtained from 4 species of medicinal plants traditionally used as general therapeutics for different illnesses and specifically as treatment of tuberculosis, were evaluated using the microplate resazurin assay against 2 species of the Mycobacterium tuberculosis Complex and 3 nontuberculous mycobacteria. The results showed the hexane extract and the essential oil from fruits of Pterodonemarginatus (Vogel) as potential sources of antimycobacterial drugs against 4 species of tested mycobacteria. The hexane fraction of methanol extract from leaves of Centella asiatica also presented significant mycobacterial growth inhibition, but against M. chelonae only. In conclusion, it was possible to contribute to the antimycobacterial investigations by presenting three new samples of plants with significant antimicrobial activity against four Mycobacteriumspp and suggest future studies about the antimycobacterial properties of fruits from P. emarginatus.

RESUMO A investigação permanente de novas drogas antimicobacterianas é necessária no programa de erradicação da tuberculose e de outras doenças relacionadas com micobactérias. O objetivo deste estudo foi buscar novas fontes de drogas antimicobacterianas usando material vegetal. Neste estudo, 11 materiais de base vegetal (extratos, óleos essenciais e algumas frações) foram avaliados contra 5 espécies de micobactérias. Estes materiais foram obtidos a partir de 4 espécies de plantas medicinais tradicionalmente utilizadas como terapêutica geral para diferentes doenças e, especificamente, no tratamento de tuberculose (Baccharis dracunculifolia, Centella asiatica, Lantana camara, Pterodon emarginatus). Os ensaios foram realizados em microplacas com resazurina contra duas espécies do Complexo Mycobacteriumtuberculosis e 3 espécies de micobactérias não tuberculosas. Os resultados mostraram o extrato hexânico e o óleo essencial de frutos de P.emarginatus como potenciais fontes para drogas antimicobacterianas contra quatro espécies de micobactérias testadas. A fração hexânica do extrato metanólico das folhas de C. asiatica também apresentou significativa inibição do crescimento de micobactérias apenas contra M.chelonae. Em conclusão, foi possível contribuir para as investigações de antimicobacterianos por apresentar três novas amostras de plantas com atividade antimicrobiana significativa contra quatro Mycobacterium spp e sugerir a realização de estudos futuros sobre as propriedades antimicobacterianas de frutos de P. emarginatus.

Optimisation of the microplate resazurin assay for screening and bioassay-guided fractionation of phytochemical extracts against Mycobacterium tuberculosis.

INTRODUCTION: Because of increased resistance to current drugs, there is an urgent need to discover new anti-mycobacterial compounds for the development of novel anti-tuberculosis drugs. The microplate resazurin assay (MRA) is commonly used to evaluate natural products and synthetic compounds for anti-mycobacterial activity. However, the assay can be problematic and unreliable when screening methanolic phytochemical extracts. OBJECTIVE: To optimise the MRA for the screening and bioassay-guided fractionation of phytochemical extracts using Mycobacterium tuberculosis H37Ra. METHODS: The effects of varying assay duration, resazurin solution composition, solvent (dimethyl sulphoxide - DMSO) concentration and type of microtitre plate used on the results and reliability of the MRA were investigated. The optimal bioassay protocol was applied to methanolic extracts of medicinal plants that have been reported to possess anti-mycobacterial activity. RESULTS: The variables investigated were found to have significant effects on the results obtained with the MRA. A standardised procedure that can reliably quantify anti-mycobacterial activity of phytochemical extracts in as little as 48 h was identified. The optimised MRA uses 2% aqueous DMSO, with an indicator solution of 62.5 µg/mL resazurin in 5% aqueous Tween 80 over 96 h incubation. CONCLUSION: The study has identified an optimal procedure for the MRA when used with M. tuberculosis H37Ra that gives rapid, reliable and consistent results. The assay procedure has been used successfully for the screening and bioassay-guided fractionation of anti-mycobacterial compounds from methanol extracts of Canadian medicinal plants.