Antioxidative and immunity-enhancing effects of heat-killed probiotic Enterococcus faecium KU22001 without toxin or antibiotic resistance.

This study evaluated the probiotic properties, safety profile, and antioxidative and immune system-enhancing effects of Enterococcus faecium strains isolated from human infant feces. E. faecium KU22001, E. faecium KU22002, and E. faecium KU22005 exhibited potential probiotic properties; however, to eliminate concerns about toxin production and antibiotic resistance, the E. faecium strains were heat-treated prior to experimental usage. E. faecium KU22001 showed the highest antioxidant activity and lowest reactive oxygen species production among the three strains. The immune system-enhancing effects of heat-killed E. faecium strains were evaluated using a nitric oxide assay. E. faecium KU22001 induced an increase in the mRNA expression of inducible nitric oxide synthase, cyclooxygenase-2, and proinflammatory cytokines, including tumor necrosis factor-α, interleukin-1β, and interleukin-6 in RAW 264.7 cells. Furthermore, E. faecium KU22001 activated the mitogen-activated protein kinase pathway, which was a key regulator of the immune system. These results demonstrate the potential use of E. faecium KU22001 as a multifunctional food material.