Antimicrobial activity of Gentiana lutea L. extracts and isolated compounds mangiferin, isogentisin and gentiopicrin

Plant material of Gentiana lutea L. was collected on the mountain Suvobor. Air-dried leaves and flowers were extracted with methanol in a Soxhlet apparatus for 24h. Evaporated dry extracts were used for experiments. Mangiferin (MG), isogentisin (IG) and gentiopicrin (GP) have been isolated according to previously published procedures [1] and their structures were confirmed using UV-VIS, IR and NMR techniques. A variety of microorganisms Escherichia coli (ATCC 25922), Salmonella typhimurium (ATCC 14028), Enterobacter cloacae (ATCC 13883), Pseudomonas aeruginosa (ATCC 27853), P. tolaasii (NCTC 387), Proteus mirabilis (ATCC 14273), Staphylococcus aureus (ATCC 25923), S. epidermidis (ATCC 12228), Streptococcus faecalis (ATCC 12952), Bacillus subtilis (ATCC 6051), Micrococcus luteus (ATCC 10240), M. flavus (ATCC 14452), Sarcina lutea (ATCC 10054), Listeria monocytogenes (ATCC 15313) as well as human pathogen fungi Candida albicans were used in the antimicrobial assay. The MIC values have been determined using the broth microdilution method in 96-hole plates according to NCCLS [2]. Serial dilutions of the stock solutions of tested extracts in broth medium (Muller-Hinton broth or Sabouraud broth) were prepared in a microtiter plate. The microbial suspensions were added in the microwells at the concentration of 5×105 organisms/mL. MICs were determined as the lowest concentrations preventing visible growth. The standard antibiotic streptomycin was used to control the sensitivity of tested bacteria, whereas nystatin was used as a control against the fungi. Each assay was repeated two times. Leaves contained 9.57±0.4mg/g dw of MG, 12.86±0.7mg/g dw of IG and 38.85±0.7mg/g dw of GP while flowers contained 8.98±0.4mg/g dw of MG, 123.23±3.1mg/g dw of IG and 48.38±1.4mg/g dw of GP. Mangiferin, isogentisin and gentiopicrin as well as extracts of leaves and flowers showed antimicrobial activity with MIC values ranging from 117–310µg/ml. References: [1] Menković, N (1997) Ph D. Thesis, Faculty of Pharmacy, Belgrade. [2] NCCLS (2000) Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard – Fifth Edition. NCCLSocument M7-A5. NCCLS: Wayne, PA, USA.