| Kha-ling (Alpinia conchigera) is plant commonly used as food and medicine, especially in infectious treatment. This study was aimed to preliminary study antimicrobial activity of Kha-ling extract in hexane, ethyl acetate, and methanol against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Enterococcus faecalis as well as evaluate activity on E. faecalis growing in a form of either planktonic or biofilm. The optimal time for its antimicrobial activity was also investigated. The rhizomes of Kha-ling were extracted by percolation with hexane, ethyl acetate, and methanol, respectively. The antimicrobial effect of various extracts was first investigated using agar disc diffusion assay. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by agar dilution method. The MBC and contact time of various extracts on E. faecalis biofilm were also investigated. The results showed that all three extracts of Kha-ling inhibited S. aureus which hexane extract has higher activity than ethyl acetate and methanol. They had weakly effects on E. coli, Ps. aeruginosa, but had no activity on C. albicans. All hexane, ethyl acetate, and methanol extracts inhibited E. faecalis that grew in a planktonic form with an inhibition zone of 11.52±0.07, 9.87±1.04 และ 7.27±2.57 mm, respectively. MIC were 25.0, 12.5 และ 50.0 mg/mL for hexane, ethyl acetate, and methanol extracts, respectively. MBC of hexane, ethyl acetate, and methanol extracts were 50.0, 50.0, and 100.0 mg/mL, which were increased to >125.0, 125.0, and 250 mg/mL, respectively in E. faecalis biofilms. In addition, ethyl acetate (125 mg/mL) and ethanol (250 mg/mL) extracts showed bactericidal effects when incubated with E. faecalis biofilms for 4 and 6 hours, respectively.
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