본 연구에서는 은행잎 추출물의 Staphylococcus aureus에 대한 항균효과를 검증하기 위해 먼저 에탄올 농도별로 bilobalide와 ginkgolide A, B의 성분을 분석한 결과 40% 에탄올 용매를 최적 활성농도로 결정하였다. Disc diffusion test, Optical density test을 통한 S. aureus 항균실험 결과 에탄올 추출농도가 증가할수록 항균효과가 증가하나 40% 에탄올 이상에서는 항균활성에 큰 차이가 없었다. 주사전자현미경을 통하여 은행잎 에탄올 40% 추출물 16배 농축액을 처리한 균의 세포표면을 확인한 결과 심하게 손상되었음을 확인할 수 있었다. 투과전자현미경을 이용하여 관찰한 결과 은행잎 추출물로 처리한 균주에서는 세포벽이 관찰되지 않았으며, 이는 은행잎 추출물의 주성분인 bilobalide와 ginkgolide A, B가 세포벽 합성을 저해하는 것으로 보여진다.
A optimal condition for the Ginkgo biloba extraction in ethanol and water binary solvent system has been proposed based on concentration of bilobalide and ginkgolide known as having a antimicrobial components in the range 5% to 70% ethanol in water at $80^{circ}C$. Concentration of bilobalide as a single component of Ginkgo biloba leaves extract is the highest at the 60% ethanol and ginkgolide A and B is highest at 50% ethanol. Antimicrobial effect of Ginkgo biloba leaves extracts on the S. aureus was also examined by disc diffusion test and optical density test. In case of the disc diffusion test, the clean zone diameter was increased from 0.95 cm to 1.70 cm as ethanol concentration increased from 5 to 70%. However, over the 40% of ethanol concentration the antimicrobial effect was almost flat. Based on these results, we propose that the 40% of ethanol and 60% water solvent is most desirable for Ginkgo biloba extract considering vapor pressure problem in concentrating process after extraction. We introduced SEM and TEM to figure out the morphological change on the surface and inside body of S. aureus when Ginkgo biloba leaves extract was treated. After mixed with Ginkgo biloba leaves extract blast like blebs appeared on the surface of S. aureus cells and cell wall was not observed. From the these results, it seems that the Ginkgo biloba leaves extract including bilobalide and ginkgolide A, B prevent cell wall synthesis.
