Multidrug-resistant (MDR) bacteria are increasing due to the abuse and misuse of antibiotics, and nosocomial infections by MDR bacteria are also increasing. The aim of this study was to
identify new substances that can target MDR bacteria among 12 plant extracts that are known to have
antibacterial effects. The experiments were performed by the disk diffusion test and microdilution
minimum inhibitory concentration (MIC) test, as described by the Clinical and Laboratory Standards
Institute (CLSI). By screening against methicillin-sensitive Staphylococcus aureus (MSSA), grapefruit
seed extract (GSE) was selected from 12 plant extracts for subsequent experiments. GSE showed
antibacterial effects against methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus
(VRSA) in the disk diffusion test. Even at the lowest concentration, GSE showed antibacterial activity
in the microdilution MIC test. As a result, we can conclude that GSE is a naturally derived antibacterial substance that exhibits a favorable antibacterial effect even at a very low concentration, so it is a
good candidate for a natural substance that can be used to prevent or reduce nosocomial infections
as coating for materials used in medical contexts or by mixing a small amount with other material