Efficacy of different solvent extracts from the aerial parts of Costus speciosus (Koen.) for the potential antibacterial activity against selected human pathogenic bacteria

Abstract

Costus speciosus (Koen ex.Retz.) is an ornamental plant and has also been used in traditional medicinal systems, mainly in India and Sri Lanka. This research article reveals the antibacterial activity of the leaves of Costus speciosus (Koen.) and its efficacy in different solvents, acetone, ethanol and sterilized distilled water (aqueous), against selected human pathogenic bacteria, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The leaves were tested for antibacterial activity, using agar well diffusion method at the test concentrations of 25, 50 and 75mg/100µl of these solvents, separately. The maximum inhibitory action was observed in ethanol extracts against both bacterial strains at 75mg/100µl concentration. The Minimum Inhibitory Concentration (MIC) for Acetone and ethanol extracts of Costus speciosus were 12.5mg/100µl and 6.25mg/100µl respectively against E. coli whereas it was 12.5mg/100µl against S. aureus for both extracts. The aqueous, ethanol and acetone extracts showed concentration-dependent antibacterial activity against the tested bacteria with the zone of inhibition. Among the solvents used, the acetone showed higher inhibitory activity yet clear and significant inhibition zones were also observed from the aqueous and ethanol leaf extracts. Thereby, the results revealed the medicinal potential of the leaf extracts of Costus speciosus (Koen.) against various infectious diseases to develop a drug with appropriate solvents.

Phytochemical Analysis and In Vitro Antimicrobial Activity of Costus speciosus Extracts

“…GC-MS phytochemical analysis of these extracts confirmed that most of the active compounds were lipophilic fatty acids 37 . However, another study reported that C. speciosus leaf hexane, methanol and aqueous extracts showed no activity against B. subtilis, E. coli, K. pneumoniae, and S. aureus 17 .…”

“…Most of the previous studies on the antibacterial activity of C. speciosus focused on rhizome extracts. One such study found that the aqueous extract of the plant rhizome was effective against S. aureus, Staphylococcus epidermis, E. coli, P. aeruginosa, and S. typhimurium 38 17 . However, the aqueous extract of plant rhizome showed no such activity.…”

“…Several studies have shown that the phytochemical composition and ultimately the bioactivities of the plant extracts depend on the plant part used (e.g. rhizome, roots, seeds, leaves, flowers) 14 , extract preparation method 15,16 , solvents used in extraction [17][18][19] , soil nutrients 20 , harvesting season 21 , chemotypes 22 , and genetic variations (cytotypes) 23 .…”