Outstanding Antibacterial Activity of -Comparison of the Antimicrobial Effects of Extracts and Fractions from Four Species Growing in Bulgaria with a Focus on Prenylated Phloroglucinols.

Microbial infections are by no means a health problem from a past era due to the increasing antimicrobial resistance of infectious strains. Medicine is in constant need of new drugs and, recently, plant products have had a deserved renaissance and garnered scientific recognition. The aim of this work was to assess the antimicrobial activity of ten active ingredients from four species growing in Bulgaria, as well as to obtain preliminary data on the phytochemical composition of the most promising samples. Extracts and fractions from Griseb. ex Schenk, L., Jacq. and Boiss. obtained with conventional or supercritical CO extraction were tested on a panel of pathogenic microorganisms using broth microdilution, agar plates, dehydrogenase activity and biofilm assays. The panel of samples showed from weak to extraordinary antibacterial effects. Three of them (from and ) had minimum inhibitory concentrations as low as 0.625-78 mg/L and minimum bactericidal concentrations of 19.5-625 mg/L against and other Gram-positive bacteria. These values placed these samples among the best antibacterial extracts from the genus. Some of the agents also demonstrated very high antibiofilm activity against methicillin-resistant . Ultra-high-performance liquid chromatography-high-resolution mass spectrometry revealed the three most potent samples as rich sources of biologically active phloroglucinols. They were shown to be good drug or nutraceutical candidates, presumably without some of the side effects of conventional antibiotics.