EVALUATION OF ANTIOXIDANT, ANTIBACTERIAL ACTIVITY OF ETHANOLIC EXTRACT IN THE LEAVES OF COMBRETUM ALBIDUM AND GAS CHROMATOGRAPHY-MASS SEPTROMETRY ANALYSIS

ABSTRACTObjective: This study evaluates chemical composition, antioxidant, and antibacterial activity of ethanol extract from leaves of Combretum albidum.Methods: An evaluation of antibacterial activity was carried out by the disc-diffusion method and resazurin microplate assay to determine minimuminhibitory concentration (MIC). The anti-oxidant activity was done using 1,1-diphenyl-2-picrylhydrazyl (DPPH) method and superoxide assay. Thegas chromatography-mass septrometry evaluation of C. albidum was done to analyze the phytochemical constituents that are responsible for theantimicrobial and antioxidant property. The results were compared with NIST library.Results: The disc-diffusion method showed zone of inhibition that ranged from 19.8±0.57 (Bacillus subtilis) to 9.3±0.57 (metallo-beta-lactamaseproducing Escherichia coli [MBLe]), and the MIC was least for B. subtilis at 0.08 mg/ml. It was found that C. albidum exhibited antibacterial activityagainst all the 8 Gram-negative and Gram-positive bacteria including multidrug-resistant bacteria, MBL producing bacteria, and methicilin-resistantStaphylococcus aureus. The ICvalue for the antioxidant activity was 156.26 µg/ml and 69.03 µg/ml for DPPH and superoxide assay, respectively. Thisstudy yielded a total of 23 bioactive compounds with potent biological activity.50 Conclusion: The study proves the potential ability of C. albidum, suggesting its exploitation in bioactive compounds for the antimicrobial andantioxidant property.Keywords: Combretum albidum, Antioxidant activity, Antibacterial activity, Bioactive compounds

Use of succinic & oxalic acid in reducing the dosage of colistin against New Delhi metallo-β-lactamase-1 bacteria

Background & objectives: New Delhi metallo-β-lactamase 1 (NDM-1) cleaves the beta-lactam ring, and confers bacterial resistance against most of the beta-lactam antibiotics, except tigecycline and colistin. Among these two antibiotics, colistin is considered toxic, and therefore, its clinical use and dosage need cautious approach. In the present study, six organic acids were screened individually and in combination of two acids for their effectiveness against NDM-1 Escherichia coli and a combination of colistin and oxalic or succinic acid was tested to find out the potential of combination therapy for reducing the dose of toxic colistin. Methods: Antibacterial activity of the organic acid and their combinations was tested by disc diffusion method against NDM-1 E. coli, and minimum inhibitory concentration (MIC) was determined by broth dilution method. Synergistic effect between organic acids and colistin was tested by checkerboard method. Results: Oxalic acid showed the highest zone of inhibition (15±1 mm) followed by succinic acid, tartaric acid, fumaric acid, citric acid and malic acid. The combination of two acids did not increase the zone of inhibition significantly. MIC was found to be the lowest with oxalic acid and succinic acid (320 μg/ml). In the presence of 160 μg/ml oxalic acid or succinic acid, MIC of colistin was reduced from 8 to 4 μg/ml, indicating synergistic effect. Interpretation & conclusions: Our findings showed that combination therapy using colistin and oxalic acid or succinic acid might find safe clinical application of this antibiotic in controlling infections due to NDM-1 bacteria

Inhibition of New Delhi Metallo-β-Lactamase 1 (NDM-1) Producing Escherichia coli IR-6 by Selected Plant Extracts and Their Synergistic Actions with Antibiotics

Improper use of antibiotics has led to a great concern in the development of pathogenic microbial resistance. New Delhi metallo-β-lactamase 1 (NDM-1) producing bacteria are resistant to most of the β-lactam antibiotics, and so far, no new compounds have been clinically tested against these bacteria. In this study, ethanol extracts from the leaves of 240 medicinal plant species were screened for antibacterial activity against an NDM-1 Escherichia coli strain. The extracts that showed antibacterial activity were then tested for minimum inhibitory concentrations (MICs) and zones of inhibition. The extract from Combretum albidum G. Don, Hibiscus acetosella Welw. ex Hiern, Hibiscus cannabinus L., Hibiscus furcatus Willd., Punica granatum L., and Tamarindus indica L. showed bactericidal activity between 5 and 15 mg/ml and the MIC was between 2.56 and 5.12 mg/ml. All six plant extracts inhibited activity of the NDM-1 enzyme in vitro, and the IC50 value ranged between 0.50 and 1.2 ng/μl. Disruption of bacterial cell wall integrity by the plant extracts was clearly visible with scanning electron microscopy. Increases in membrane permeability caused 79.4–89.7% bacterial cell deaths as investigated by fluorescence-activated cell sorting. All the plant extracts showed synergistic effects when combined with colistin [fractional inhibitory concentration (ΣFIC) = 0.125–0.375], meropenem (ΣFIC = 0.09–0.313), and tetracycline (ΣFIC = 0.125–0.313). Thus, the plant extracts can be fractionated for the identification of active compounds, which could be used as new antibacterial compounds for the development of drugs against NDM-1 E. coli in addition to their use in combination therapy

Bacterial efflux transporters’ polyspecificity – a gift and a curse?

All mechanisms of clinical antibiotic resistance benefit from activities of polyspecific efflux pumps acting to reduce intracellular accumulation of toxins and antibiotics. In Gram-negative bacteria, the major polyspecific efflux transporters belong to the Resistance-Nodulation-cell Division (RND) superfamily of proteins, which are capable of expelling thousands of structurally diverse compounds. Recent structural and functional advances generated novel insights into mechanisms underlying the biochemical versatility of RND transporters. This opinion article reviews these mechanisms and discusses implications of the polyspecificity of RND transporters for bacterial survival and for the development of efflux pump inhibitors effective in clinic