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

Abstract

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 Hypericum species growing in Bulgaria, as well as to obtain preliminary data on the phytochemical composition of the most promising samples. Extracts and fractions from H. rochelii Griseb. ex Schenk, H. hirsutum L., H. barbatum Jacq. and H. rumeliacum Boiss. obtained with conventional or supercritical CO2 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 H. rochelii and H. hirsutum) had minimum inhibitory concentrations as low as 0.625–78 mg/L and minimum bactericidal concentrations of 19.5–625 mg/L against Staphylococcus aureus and other Gram-positive bacteria. These values placed these samples among the best antibacterial extracts from the Hypericum genus. Some of the agents also demonstrated very high antibiofilm activity against methicillin-resistant S. aureus. 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.

Cytotoxic and Antibacterial Prenylated Acylphloroglucinols from Hypericum olympicum L.

“…The best activity was observed against Staphylococcus aureus , where the lowest MIC observed was 0.78 mg/L or 1.57 μM for 4 and a range of MIC values of 0.78–2 mg/L (1.57–4.14 μM). S aureus once again turned out to be the most susceptible strain as in our previous research [ 56 ].…”

Chitosan Membranes Containing Plant Extracts: Preparation, Characterization and Antimicrobial Properties

“…It is known that the antimicrobial activity of plant extracts is the cumulative effect of polyphenols (flavonoids or hydrolysable tannins) containing one or more phenolic groups [70]. The most known active compounds of H. perforatum that exhibit antimicrobial activity include hypericin, pseudohypericin, naphthodianthrones, flavonoids, phloroglucinols, hyperforin and adhiperforin [66,71]. The main compounds identified in the extract from our study were isoquercitin, epicatechin, rutin and ellagic acid.…”

“…H. perforatum, the best-known species of the genus Hypericum, is widely used in traditional medicine for its sedative, analgesic, anthelmintic, anti-inflammatory, and antimicrobial properties [65,66]. The literature data frequently refer to the bactericidal potential of both extracts and essential oils of T. perforatum, which are mainly effective against Grampositive bacteria [65,67,68], but not exclusively [69].…”

Liposomal Rifabutin—A Promising Antibiotic Repurposing Strategy against Methicillin-Resistant Staphylococcus aureus Infections

“…It is well documented that established biofilm infections are, in general, more resistant to antimicrobial agents than free-living bacteria [ 20 , 43 , 44 ]. Nevertheless, several reports on the antibacterial effect of distinct compounds against MRSA have found MBIC 50 values similar [ 45 ] or even inferior to MIC [ 46 , 47 , 48 , 49 ].…”