Enterococcus faecium has appeared as an important opportunistic pathogen that can cause urinary tract infections, surgical site infections, bacteremia, and endocarditis. Therefore, it is imperative to develop alternative therapeutic methods to treat enterococcal infections. Sophoraflavanone G (5,7,2′,4′-tetrahydroxy-8-lavandulylflavanone, SPF-G) exhibited the strongest antibacterial activity based on the minimum inhibitory concentration values on two E. faecium strains (6.25 and 12.5 μg/ml at 24 and 48 hours of treatment, resp.) in the broth microdilution assay among the tested compounds and a remarkable bactericidal effect with a 12.5 μg/ml minimum bactericidal concentration value. Sophoraflavanone G (12.0 ± 2.3 mm inhibition zone for Korean Agricultural Culture Collection, Korea (KACC) 11954 and 11.0 ± 3.0mm for Culture Collection of Antimicrobial Resistant Microbes, Korea (CCARM) 5506) also exhibited the highest susceptibility based on the agar diffusion assay. Membrane-permeabilizing agents with a low dose of sophoraflavanone G synergistically activated anti-E. faecium activity through a 67% reduction of E. faecium growth, and E. faecium-derived peptidoglycans (PGN) blocked the antibacterial activity. These results indicate that sophoraflavanone G could bind to the bacterial cell wall and induce E. faecium cell wall damage. Transmission electron microscopy (TEM) images of E. faecium treated with sophoraflavanone G also exhibited cell lysis, followed by leakage of intracellular components, confirming that sophoraflavanone G has anti-E. faecium activity by binding to the PGN and disrupting the cell wall. This study showed the possible usage of sophoraflavanone G as an effective natural anti-E. faecium compound.
Key words: E. faecium, sophoraflavanone G, antibacterial activity, natural compound, bacteria
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