Antibacterial Potential of Rhinacanthus nasutus against Clinically Isolated Bacteria from Thai Cancer PatientsP. Siripong,* V. Wongseri, S. Piyaviriyakul, J. Yahaufai, R. Chanpai and K. Kanokmedakul
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The antibacterial potential of fifteen extracts from roots, leaves and stems of Rhinacanthus nasutus (family Acanthaceae) was evaluated by the agar dilution method. Four quality control isolates of bacteria; Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 together with 68 clinically isolated bacteria from Thai cancer patients; coagulase positive staphylococci (12), coagulase negative staphylococci (10), ƒÒ-hemolytic streptococci (16), enterococci (10), Escherichia coli (5), Klebsiella spp. (5), Enterobacter spp. (5) and Pseudomonas aeruginosa (5) were used as tested bacteria. The results demonstrated that n-hexane and chloroform extracts of roots and n-hexane extract of leaves showed potent antibacterial activity against Gram-positive bacteria, whereas the aqueous extracts of all parts, methanolic extracts of stems and leaves as well as 85% ethanolic extract of stems were inactive. None of the extracts showed activity against Gram-negative bacteria. Bioassay-directed fractionations of the active extracts led to the isolation of 3 main naphthoquinone esters which were classified by spectroscopic data as rhinacanthins-C, -N and -Q, respectively. Their antibacterial potential against the clinical and standard bacteria was then analyzed. Rhinacanthins-N, -Q and -C exhibited potent antibacterial activity against ƒÒ-hemolytic streptococci, enterococci and staphylococci, with potencies comparable to those of gentamicin, an antibiotic drug. Among them, rhinacanthin-N was the most active compound with the MIC50 and MIC90 values of 4.9 and 9.76 ƒÝg/ml, respectively. Our findings suggest that it is of interest to further study the activity and usage of the Rhinacanthus plant as an antimicrobial drug for the treatment of infectious diseases in patients.
Keyword:
Acanthaceae, antibacterial potential, cancer patients, clinically isolated bacteria, naphthoquinone esters, Rhinacanthus nasutus
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