Castanea sativa (European Chestnut) Leaf Extracts Rich in Ursene and Oleanene Derivatives Block Staphylococcus aureus Virulence and Pathogenesis without Detectable Resistance

Abstract

The Mediterranean is home to a rich history of medical traditions that have developed under the influence of diverse cultures over millennia. Today, many such traditions are still alive in the folk medical practices of local people. Investigation of botanical folk medicines used in the treatment of skin and soft tissue infections led us to study Castanea sativa (European Chestnut) for its potential antibacterial activity. Here, we report the quorum sensing inhibitory activity of refined and chemically characterized European Chestnut leaf extracts, rich in oleanene and ursene derivatives (pentacyclic triterpenes), against all Staphylococcus aureus accessory gene regulator (agr) alleles. We present layers of evidence of agr blocking activity (IC50 1.56–25 μg mL-1), as measured in toxin outputs, reporter assays hemolytic activity, cytotoxicity studies, and an in vivo abscess model. We demonstrate the extract’s lack of cytotoxicity to human keratinocytes and murine skin, as well as lack of growth inhibitory activity against S. aureus and a panel of skin commensals. Lastly, we demonstrate that serial passaging of the extract does not result in acquisition of resistance to the quorum quenching composition. In conclusion, through disruption of quorum sensing in the absence of growth inhibition, this study provides insight into the role that non-biocide inhibitors of virulence may play in future antibiotic therapies.

Coagulase-Negative Staphylococcal Strain Prevents Staphylococcus aureus Colonization and Skin Infection by Blocking Quorum Sensing

“…Staphylococcus epidermidis has already been tested in depth (Otto et al, 2001; Otto et al, 1999), and thus we focused on other staphylococcal species. For reporters, we used S. aureus strains representing all four agr types containing P3 promoter YFP-fusions that have been previously used to assess quorum-sensing activity (Kirchdoerfer et al, 2011; Quave et al, 2015). In our assays, Staphylococcus capitis and multiple clinical isolates of Staphylococcus lugdunensis did not affect S. aureus agr activation, while agr P3 inhibition was observed in spent media from Staphylococcus intermedius and Staphylococcus caprae (Fig.…”

“…To investigate the potential of the S. caprae AIP as an anti-MRSA intervention, we evaluated its capacity to influence the infectious outcome of cutaneous challenge with the USA300 CA-MRSA strain LAC ( agr type I, hereafter called MRSA) (Muhs et al, 2017; Quave et al, 2015; Todd et al, 2017). The USA300 MRSA strains are the dominant cause of skin infection and thus serve as an appropriate output for testing (King et al, 2006; Moran et al, 2006).…”

“…AH2759, a USA300 MRSA (LAC) strain containing the agr P3:: lux reporter plasmid was tested in a manner that was similar to previously described (Muhs et al, 2017; Quave et al, 2015). The strain was grown overnight in TSB with 10 μg/mL chloramphenicol.…”

Signal Biosynthesis Inhibition with Ambuic Acid as a Strategy To Target Antibiotic-Resistant Infections

“…Western blots for alpha-toxin were performed as previously described (38). To purify RNA, overnight cultures were diluted 1:100 in triplicate in TSB supplemented with either 100 M ambuic acid or 0.35% dimethyl sulfoxide (DMSO) as a vehicle control and grown for 6 h in a 48-well plate at 37°C with shaking at 750 rpm in a Stuart incubator.…”

Anti-Acne Activity of Italian Medicinal Plants Used for Skin Infection

“…Our research group has already demonstrated interesting anti-staphylococcal activity (in terms of growth, biofilm, and quorum sensing inhibitory action) in the Quave Natural Products Library (QNPL), which includes a collection of plant and fungal extracts derived from natural ingredients used specifically in the treatment of SSTIs—caused by a number of skin pathogenic bacteria, including Propionibacterium acnes —and other health concerns in the Mediterranean and other parts of the world (Quave et al, 2012, 2015). Extracts from Italian species in the QNPL are uniquely tied to ethnopharmacological data documented in field studies conducted by Quave and colleagues, and the detailed reports of ethnopharmacological uses of these species have been previously published (Pieroni et al, 2002, 2004a,b; Pieroni and Quave, 2005; Quave et al, 2008b).…”