Assessment of Genetic Diversity, Micromorphology and Antimicrobial Activity in Nepeta cataria L.

The mosquito repellent Nepetalactone rich Nepeta cataria L. (catmint) plant has a variety of therapeutic and industrial potential. Reports on the genetic diversity of N. cataria germplasm are minimal globally and need attention for adding a new variety into commercial cultivation. The present study, therefore, assessed the genetic diversity among thirteen half-sib genotypes of N. cataria using agro economic and phytochemical traits. The experimental set has shown substantial variation for agro economic traits studied. Among all the studied populations, fresh herb-based essential oil content ranged from 0.1 % to 0.3 %, with a grand mean of 1.67 %. However, the estimated oil yield ranged from 44.4 kg/h to 120.73 kg/h with an average of 71.34 kg/h. Among the eleven phytochemical constituents detected in different concentrations in the essential oil of experimental sets, 4aα,7α,7aα-Nepetalactone (67.9-87.5 %) constituted the significant proportion of essential oil. Altogether, based on mean comparison, the population NC8 was found to be promising for estimated oil yield and 4aα,7α,7aα-Nepetalactone content. The greater heritability estimates (h2 bs) and genetic advance as percent of mean (GAM) were observed for important economic parameters, i. e., oil content, herb yield, and oil yield. The cluster analysis revealed the least interactions between various agro economic and phytochemical variables. The microscopic study of trichome showed a positive correlation of abaxial leaf surface with essential oil content. The promising antimicrobial potential of catmint oil was also observed against human health-related pathogens. The results infer from our study provide valuable insight for genetic improvement and product development in the catmint germplasm.

Citral, a monoterpenoid aldehyde interacts synergistically with norfloxacin against methicillin resistant Staphylococcus aureus.

BACKGROUND: Staphylococcus aureus (SA), is a major human pathogen causing wide range of clinical infections, which has been further complicated by drug resistance like methicillin resistant S. aureus (MRSA), vancomycin intermediate S. aureus (VISA)/vancomycin resistant S. aureus (VRSA), etc. The present study was aimed at determining anti-staphylococcal potential of citral against drug resistant clinical isolates alone and in combination with antibiotics. PURPOSE: To assess the potential of citral in combination with norfloxacin in treating drug resistant infections of SA. STUDY DESIGN: In the present study, synergistic interaction of citral and norfloxacin against drug resistant SA strains was evaluated. Further the efficacy and possible mechanism of action of the combination was also evaluated using in vitro and in vivo assays. METHOD: The anti-staphylococcal activity of each of the monoterpene and the antibiotic was determined in terms of MIC and the effective concentration of both compounds in combination was obtained by checkerboard assay. In vivo efficacy and oral acute toxicity was evaluated in Swiss albino mice model. To understand the mechanism of action, time-kill curve, bacteriolysis, leakage, membrane depolarization, salt tolerance and ethidium bromide efflux assays were performed. RESULTS: Citral was found effective against clinical isolates of SA with MIC values ranging from 75 to 150 µg ml-1 exhibiting bacteriostatic activity. Citral interacted synergistically, reducing MIC of norfloxacin up to 32-folds with FICI ≤ 0.50. Citral did not affect cell wall, but could damage cell membrane, inhibit efflux pump and affect the membrane potential. Citral could reduce the staphylococcal load of spleen and liver tissues in a dose-dependent manner which was further reduced when used in combination with norfloxacin. Citral did not exhibit any mortality or morbidity up to 500 mg kg-1 body weight and found to prolong the post-antibiotic effect of norfloxacin. CONCLUSION: Based on these observations, citral could be a lead candidate phytomolecule for further developing it into an anti-staphylococcal agent. The observations of combination study will help in reducing the burden of antibiotics leading to delayed resistance development.

Membrane-damaging potential of natural L-(-)-usnic acid in Staphylococcus aureus.

The purpose of this investigation was to try to understand the antibacterial mechanism of L-(-)-usnic acid isolated for the first time from fruticose lichen Usnea subfloridana using clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). The minimum inhibitory concentration (MIC) of L-(-)-usnic acid against the clinical isolates of MRSA and reference strain S. aureus MTCC-96 (SA-96) was in the range 25-50 µg/ml. Treatment of both reference and clinical strains (MRSA-ST 2071) with four-fold MIC concentrations (100-200 µg/ml) of L-(-)-usnic acid reduced the viability of cells without damaging the cell wall. However, the loss of 260 nm absorbing material and increase in propidium iodide uptake was observed in both of the strains. Similarly, a combined effect of L-(-)-usnic acid (25-50 µg/ml) and 7.5 % NaCl resulted in a reduced number of viable cells within 24 h in comparison to the control. These observations clearly indicate that L-(-)-usnic acid exerts its action by disruption of the bacterial membrane. Further, in vivo efficacy showed that L-(-)-usnic acid significantly (p < 0.001) lowered the microbial load of spleen at doses ranging from 1 to 5 mg/kg. Further, toxicity studies in infected mice at doses 20 times higher than the efficacious dose indicated L-(-)usnic acid to be safe. Paradoxically, L-(-)usnic acid exhibited changes in serum triglycerides, alkaline phosphatase (ALKP) and liver organ weight in the healthy mice administered with only 25 mg/kg body weight. The results obtained in this study showed that natural L-(-)-usnic acid exerts its antibacterial activity against MRSA by disruption of the cell membrane. Further, the natural L-(-)-usnic acid was found to be safe up to 100 mg/kg body weight, thereby, making it a probable candidate for treating S. aureus infections.

Antifungal activity of Glycyrrhiza glabra extracts and its active constituent glabridin.

Glabridin, an active constituent of Glycyrrhiza glabra roots, was found to be active against both yeast and filamentous fungi. Glabridin also showed resistance modifying activity against drug resistant mutants of Candida albicans at a minimum inhibitory concentration of 31.25-250 microg/mL. Although the compound was reported earlier to be active against Candida albicans, but this is the first report of its activity against drug resistant mutants.

Antimicrobial potential of Glycyrrhiza glabra roots.

The present study was aimed to investigate antimicrobial potential of Glycyrrhiza glabra roots. Antimycobacterial activity of Glycyrrhiza glabra was found at 500 microg/mL concentration. Bioactivity guided phytochemical analysis identified glabridin as potentially active against both Mycobacterium tuberculosis H(37)Ra and H(37)Rv strains at 29.16 microg/mL concentration. It exhibited antimicrobial activity against both Gram-positive and Gram-negative bacteria. Our results indicate potential use of licorice as antitubercular agent through systemic experiments and sophisticated anti-TB assay.

Cytotoxic agents from Terminalia arjuna.

Although a number of chemicals have been isolated from Terminalia arjuna, only a few have been evaluated for their biological significance. As a part of our drug discovery programme for cytotoxic agents from Indian medicinal plants, four novel cytotoxic agents arjunic acid (1), arjungenin (2), arjunetin (3) and arjunoglucoside I (4) were isolated from the bark of T. ARJUNA. Out of the four compounds, arjunic acid (1) was significantly active against the human oral (KB), ovarian (PA 1) and liver (HepG-2 & WRL-68) cancer cell lines. Further, the most active compound arjunic acid was converted into seven semi-synthetic ester derivatives 5 - 11. 2-O-Palmitoyl arjunic acid (6) showed two times more activity, while 2, 3-di-O-acetyl-, 2-O-p-anisoyl-, 2, 3-di-O-benzoyl- and 2, 3-di-O-p-nitrobenzoyl arjunic acid (7 - 10) showed 1.7 - 2.3 times less activity than the cytotoxic drug vinblastine against the liver cancer cell lines HepG-2 and WRL-68 respectively.

Antibacterial activity of Ailanthus excelsa (Roxb).

The antibacterial activity of different fractions of a methanol extract obtained from the dried stem bark of Ailanthus excelsa (Roxb) was studied using different bacterial strains. The ethyl acetate fraction inhibited the growth of all test bacteria. The MIC of the EA fraction was found to be 6 mg/disc.