A grant proposal entitled “Mechanistic Studies on Staphylococcal Quorum Quenching Natural Products” has been selected for funding under the R01 mechanism from the National Center for Complementary and Alternative Medicine at the US National Institutes of Health. The five year research project, totaling $1.829 million dollars, will be led by Dr. Cassandra Quave (PI) at Emory University and conducted in partnership with Dr. Alex Horswill (Co-I) at the University of Iowa and with collaborators at the Emory Institute for Drug Discovery (Dr. Dennis Liotta, Dr. Richard Arrendale, Dr. Michael Natchus, and Dr. Randy Howard) and Dr. Jovanka Voyich at Montana State University. The purpose of this project is to further investigate novel natural product inhibitors of Staphylococcus aureus virulence, with the long-term goal of discovering/developing new classes of antibiotics from medicinal plants to use in the war against deadly, drug resistant Staph infections.
PUBLIC HEALTH RELEVANCE: Staphylococcus aureus causes devastating infections, and the current repertoire of anti-staphylococcal drugs is insufficient. The proposed work is aimed at developing a popular plant-based complementary and alternative medical therapy for applications in the treatment of S. aureus infection.
PROJECT DESCRIPTION: Staphylococcus aureus is a highly problematic pathogen. Rates of infection in both the community and healthcare setting are on the rise, and coupled with its highly antibiotic-resistant nature, this makes S. aureus a top public health concern. In fact, invasive methicillin-resistant S. aureus (MRSA) is responsible for more deaths in the USA than AIDS. Nevertheless, the number of new antibiotic leads in the pipeline is diminishing, and many scientists have put out a call for the discovery and development of a new class of drugs which could mediate microbial pathogenicity rather than growth and survival. The staphylococcal quorum-sensing pathway, controlled by the accessory gene regulator (agr) system, is a potential target for such anti-pathogenic drug discovery efforts, as it serves as a global regulator of staphylococcal virulence. Following extensive studies on the complementary and alternative medical (CAM) practices of southern Italians in the treatment of skin and soft tissue infection, over 100 plant samples were identified, collected, extracted, and examined for their anti-staphylococcal potential. Among the tests included was a screen for the inhibition of delta-hemolysin, a translational protein product of RNAIII, whose production is regulated through the agr quorum-sensing pathway. Extract 134, which is derived from a popular tree with edible fruits and medicinal leaves and bark, was found to exhibit a strong dose-dependent inhibition of delta-hemolysin at sub-inhibitory concentrations for growth. The dose-dependent quorum-quenching effects of Extract 134 were confirmed through the use of fluorescent genetic reporters for agr (types I-IV). This activity is important based upon previous animal studies with agr knockout mutants that show a diminished capacity to initiate and persist in a skin infection model. In the proposed study, we seek to improve our understanding of the mechanistic basis for Extract 134’s quorum-quenching effects and evaluate the therapeutic relevance of such an anti-virulence therapy using in vivo models. The study will address four specific aims: 1) identification and structural elucidation of the active constituent(s) (or marker compounds for standardization) in Extract 134; 2) elucidation of the mechanism of action for the quorum-quenching effects observed; 3) determination of drug metabolism and pharmacokinetic parameters (DM/PK) of the bioactive constituent(s); and 4) evaluation of efficacy in treating S. aureus skin infection in a murine model.
