Abstract
Quercus cortex (Oak bark) has been used in European folk medicine since medieval times for treatment of diarrhea, stomatitis, pharyngitis and skin inflammations. Its antimicrobial activity is a well-known therapeutic property of oak bark, and its novel anti-quorum sensing (QS) ability has also been described recently. In this study, we examined the bioactive compounds of Quercus cortex extract and compared their direct antibacterial and regulatory anti-QS effects against Chromobacterium violaceum CV026 in a biotest. Evaluation of the original Quercus cortex extract showed weak antibacterial and prominent anti-QS activities that were retained and completely restored when the samples were dried and re-hydrated. The one-step liquid chromatography result indicated that the anti-QS activity might be determined by hydrophobic compounds; however, the subsequent reverse phase high performance liquid chromatography led to dissipation and loss of the activity. The gas chromatography–mass spectrometry gave excellent resolution between a majority of the compounds. Based on this result, 10 of the 35 identified small molecules were selected for further screening. The subsequent investigation indicated several compounds determined both the antibacterial and anti-QS activities of the Quercus cortex extract. Direct antibacterial activity was shown for 1,2,3-benzenetriol and 4-propyl-1,3-benzenediol, while sub-inhibitory concentrations of these compounds led to anti-QS effects. Five compounds: 4-(3-hydroxy-1-propenyl)-2-methoxy-phenol; 3,4,5-trimethoxyphenol; 4-hydroxy-3-methoxybenzaldehyde; 7-hydroxy-6-methoxy-2H-1-benzopyran-2-one and 2H-1-benzopyran-2-one were characterized as QS inhibitors independent of any effect on bacterial growth. Biologically relevant concentrations of each single component showed weak activity only while reconstruction of the small molecule composition derived from the Quercus cortex extract provided comparable complementary activity against C. violaceum CV026 in the biotest as the crude extract.
Highlights
IntroductionThe Quercus genus belongs to the family Fagacae, subfamily Quercoideae, and contains about
The Quercus genus belongs to the family Fagacae, subfamily Quercoideae, and contains about400 species widespread in Europe, Asia and America
We examined the bioactive molecules of Quercus cortex (Oak bark) extract and compared their direct antibacterial and regulatory anti-quorum sensing (QS) effects against Chromobacterium violaceum (C. violaceum) CV026 in a biotest
Summary
The Quercus genus belongs to the family Fagacae, subfamily Quercoideae, and contains about. Typical QS involves the generation and release of small diffusible signal molecules—autoinducers; they accumulate in the environment to a certain threshold concentration, followed by recognition by receptor proteins that regulate the expression of a particular set of genes and control manifold activities [8] Since this mechanism is responsible for bacterial virulence induction, QS targeting could be a promising strategy to control pathogenic bacteria [9], and some medicinal plants are capable of inhibiting QS-related processes [10]. The tannins’ major mechanism of action is considered their ability to hydrogen bond their available polyhydroxyphenolic groups with proteins (especially proline-rich proteins) so the multivalent cross-linking leads to precipitation and aggregation effects [17,18] In this context, it is very interesting that certain hydrolysable tannins (ellagitannins), namely vescalagin and castalagin, first isolated from a medicinal plant of Southern Florida, Conocarpus erectus, exhibited anti-QS properties [19]. We examined the bioactive molecules of Quercus cortex (Oak bark) extract and compared their direct antibacterial and regulatory anti-QS effects against Chromobacterium violaceum (C. violaceum) CV026 in a biotest
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