Anti-Infective Metabolites of a Newly Isolated Bacillus thuringiensis KL1 Associated with Kalmegh (Andrographis paniculata Nees.), a Traditional Medicinal Herb

This study was conducted to isolate endophytic bacteria possessing anti-infective property from Kalmegh (Andrographis paniculata Nees.), a well-known medicinal plant. A total of 23 strains were isolated from this plant among which the strain KL1, isolated from surface-sterilized leaf of this medicinal herb, showed broad-spectrum antagonism against an array of Gram-positive and -negative bacterial pathogens. Ethyl acetate extract of KL1-fermented media yielded a greenish amorphous substance retaining anti-infective property. Solvent-extracted crude material was separated by thin-layer chromatography, and the active ingredient was located by autobiogram analysis. The purified anti-infective compound was found as anthracene derivative as analyzed by ultraviolet and Fourier transform infrared spectroscopy. The strain was identified as Bacillus thuringiensis KL1 from cultural, physiochemical, and molecular aspects. The above results indicate the pharmaceutical potential of the candidate isolate.