Antibacterial effect of ethylacetate fraction of Orostachys japonicus on Enterococcus faecalis causing Endophthalmitis

Endophthalmitis is a disease that causes ocular inflammation and has a catastrophic effect on eyesight. Recent studies show that Enterococcus faecalis is rapidly increasing causative bacterium of endophthalmitis. It is predicted that the increased endophthalmitis by E. faecalis is presumable due to the high resistance of E. faecalis to moxifloxacin (MFX), which is a common antibiotic used for eye drop. Because of the need for therapeutic agents to overcome this problem, this study sought to explore the feasibility of developing a combination therapy using Orostachys japonicus. The ethylacetate fraction of O. japonicus (OJA) used in this study. Antimicrobial activity was tested 13 E. faecalis strains including one E. faecalis standard strain, eight clinically isolated E. faecalis strains and four quinolone resistant E. faecalis strains using CLSI antibiotic susceptibility test method. Minimal Inhibitory Concentration (MIC) of OJA was confirmed to be $500{\mu}g/ml$ for all 13 strains. Then we tested for the synergistic effect of OJA to MFX using checkboard test method. The MIC of MFX was $0.25{\mu}g/ml$ for the standard strain and 8 for the clinical isolates, and $16{\sim}64{\mu}g/ml$ for the quinolone - resistant strains. When OJA was mixed with MFX, no synergistic effect was observed in all strains, but the antibacterial activity of OJA remained unchanged. Most ocular other strains can be removed by MFX except the MFX resistant E. faecalis, which can be removed by OJA in combination therapy. Therefore, OJA can be a potential candidate for the combined treatment endophthalmitis.