Antimicrobial sesquiterpenes from the cultured mycobiont against methicillin-resistant isolated from Vietnamese street foods.

Traditionally, lichen has been used for many purposes, but there remains a lack of understanding regarding the chemical composition and antimicrobial characteristics of , a lichen native to Vietnam. In this study, four sesquiterpenes, diorygmones B-E (1-4), one phenolic compound, 3,5-dihydroxy-4-methoxybenzoic acid (5), and one sterol, β-sitosterol (6), were isolated and structurally elucidated from the cultured mycobiont of the lichen . Additionally, two compounds, stictic acid (7) and norstictic acid (8), were also isolated from the lichen Compounds 2-4 were new compounds. Their chemical structures were established using comprehensive spectroscopic data, and the absolute configurations were confirmed through the analysis of NOESY and electronic circular dichroism (ECD). Moreover, , a Gram-positive bacterium, has been responsible for various infections, including food poisoning. Herein, we identified and isolated 13 strains of from street food sources. Among these strains, one was identified as a multidrug-resistant variant, designated as SAX15, and was subsequently used for further antimicrobial testing. Compounds 1-3 produced zones of inhibition against SAX15 (each 5 mm) in comparison to commercial drugs such as penicillin, ciprofloxacin, gentamicin, cefoxitin, and clarithromycin, which displayed inhibitory zones of 7, 5, 10, 9.7, and 7 mm, respectively.