Antibacterial effect of sophoraflavanone G by destroying the cell wall of Enterococcus faecium

ABSTRACT

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 therapeuticmethods 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. faeciumstrains (6.25 and 12.5 μg/ml at 24 and 48 hours of treatment, resp.) in the broth microdilution assay among thetested 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) alsoexhibited the highest susceptibility based on the agar diffusion assay. Membrane-permeabilizing agents with a lowdose of sophoraflavanone G synergistically activated anti-E. faecium activity through a 67% reduction of E. faeciumgrowth, and E. faecium-derived peptidoglycans (PGN) blocked the antibacterial activity. These results indicate thatsophoraflavanone G could bind to the bacterial cell wall and induce E. faecium cell wall damage. Transmissionelectron microscopy (TEM) images of E. faecium treated with sophoraflavanone G also exhibited cell lysis, followedby leakage of intracellular components, confirming that sophoraflavanone G has anti-E. faecium activity by bindingto the PGN and disrupting the cell wall. This study showed the possible usage of sophoraflavanone G as an effectivenatural anti-E. faecium compound