The present study was on the analysis of phytochemical constituents of Coleus forskohlii rhizome collected from Thiruvannamalai of Tamil Nadu and testing for its antimicrobial potential against human bacterial pathogens. The dried tubers were extracted using different solvents such as ethanol, aqueous, acetone, chloroform and petroleum ether and screened. The total tannin and saponin content in the extract was estimated. The crude ethanolic solvent extract of C. forskohlii was tested for its antimicrobial activity using disc diffusion method. Phytochemical screening of the crude solvent extracts revealed the presence of tannins, phenols, saponins, quinone, flavonoids, cardiac glycoside, terpenoids, steroids, alkaloids, and coumarins. Tannic acid was found in the level of 53.47 ±0.37 mg TAE/g. Saponin content was 2.42±0.63 mg/g dry weight. The crude ethanolic rhizome extract was tested in three different concentrations (10, 20 and 30mg/ml). Maximum antibacterial activity was noted against Bacillus subtilis (15 mm), followed by Bacillus cereus (14 mm), P. aeruginosa (12 mm) and S. aureus (12mm). E. coli was not inhibited even at the highest concentration tested (i.e.) 30mg/ml. The minimum inhibitory concentration (MIC) values of the pathogens tested were 1.4±0.02, 1.590±0.02, 1.820±0.02 and 2.350±0.02 mg/ml respectively to B. subtilis, B. cereus, P. aeruginosa , and S. aureus. Similarly, the minimum bactericidal concentration (MBC) for B. subtilis, B. cereus, P. aeruginosa , and S. aureus were respectively of 2.89±0.02, 3.833±0.05, 3.842±0.01 and 4.856±0.05 mg/ml. In time-kill assay 3 Log reduction was found to be around 11 h for B. subtilis, around 12 h for B. cereus for P. aeruginosa around 13 h and above 14 and less than 15 h for S. aureus. The study showed the antimicrobial potential of ethanol extract of C. forskohlii tuber against human bacterial pathogens and hence it seems to be useful in the preparation of drug formulations.
Coleus forskohlii, phytochemical screening, tannin, saponin, antibacterial activity, MIC, MBC, Time-kill assay.
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