Time-kill Study of Ethyl Acetate Extract of Stinging Nettle on Bacillus subtilis subsp. spizizenii ATCC CRM-6633 Strain NRS 231

Abstract

Aims: This work investigated the antibacterial activity of selected ethyl acetate extract of Urtica dioica against Bacillus subtilis subsp. spizizenii ATCC® CRM-6633™ Strain NRS 231 (subtilin producer) based on the time-kill approach. Also for further study, the effects of the ethyl acetate extract on B. subtilis cells was studied by performing Scanning Electron Microscope (SEM). Study Design: Prospective Methodology: According to our previous result, ethyl acetate extract was selected to be more potent against Bacillus subtilis subsp. spizizenii ATCC® CRM-6633™ Strain NRS 231 based on its inhibition zone diameter. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of ethyl acetate extract against tested bacteria were performed and time-kill study as well as using SEM for further study on structural degeneration of the selected bacterial cells were performed. Results: The MIC and MBC of the ethyl acetate extract against tested bacteria were found at 8.33 and 16.67 mg/mL from broth micro-dilution assay, respectively. The SEM observations gave ideas on the effects of ethyl acetate extract of U. dioica on the growth of B. subtilis subsp. spizizenii ATCC® CRM-6633™ Strain NRS 231. However, the results from SEM suggested that the antibacterial action was due to the internal shrinkage of the cells which collapsed finally. The time-kill approach, determined the kill rate of ethyl acetate extract of U. dioica against B. subtilis subsp. spizizenii ATCC® CRM-6633™ Strain NRS 231 and significantly inhibited the cell growth and possessed bacteriostatic activity at lower concentration (8.33 mg/mL). Conclusion: This study showed the potential of U. dioica extract as alternative therapy against bacterial infection.