Optimization of ambuic acid as an anti-virulence agent against methicillin-resistant Staphylococcus aureus

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Isaiah O. Odoyo (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site: http://library.uncg.edu/
Nadja Cech

Abstract: Drug resistant bacterial infections are an increasing threat to human health across the globe. Current treatment options for combating these infections primarily rely on antibiotics. Overreliance on the antibiotic therapy continues to accelerate the increase in multi-drug resistant infections. Methicillin-Resistant Staphylococcus aureus (MRSA) is amongst the most notorious antibiotic resistant bacterial pathogens. Besides MRSA infections being difficult to treat, they also lead to complications in patient care resulting in extended hospital stays and recurrent visit to the doctors. This imposes a hefty burden on the economy. To address this public health challenge, alternative therapeutic strategies that mitigate proliferation of antibiotic resistance are crucial. A promising approach that is currently pursued as an alternative strategy against bacterial infections is to target bacterial pathogenesis. Pathogenesis in Staphylococcus aureus is controlled by a cell density-dependent regulatory (quorum sensing) system also known as the accessory gene regulator (agr) system. The agr system activates the upregulation of virulence factors that allows the bacteria to thrive in a host. Virulence factors refer to the sum of all the adaptations and compounds produced by an organism that contributes to how well it thrives in a host. Targeting the highly conserved binding sites of the agr system is a promising target for broad-spectrum anti-bacterial drugs. One of the compounds that has been reported to inhibit the agr system is ambuic acid, a secondary metabolite produced by the fungus Pestalotiopsis microspora. Extracts from this fungus exhibit quorum-quenching activity, but the relationship between compound structure and inhibitory activity of the agr system has not been established. To further the goal of developing an innovative countermeasure for MRSA infections that does not drive resistance and can be translated into approved therapeutics, the study seeks to identify additional analogs of ambuic acid that will provide insight into the relationship between chemical structure and quorum sensing inhibitory activity. To accomplish this goal, growth and extraction of Pestalotiopsis microspora fungal cultures were optimized in this study. To facilitate expeditious identification of known compounds in the extract and prioritize isolation of new novel analogs, hyphenated methods combining advanced chromatographic separation techniques, such as ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry, have been used. The mass spectrometry data set was subjected to mass defect filtering for identification of putative analogs. Nuclear magnetic resonance spectroscopy has been used to profile and characterize the structures of ambuic acid, and its related analogs isolated from the complex extracts. For evaluation of the inhibitory effect of the extracts on the agr system, production of the signaling molecule was investigated in a clinically relevant isolate of MRSA (LAC USA 300) cultured with the fungal extracts at two concentrations. The outcome of this study has been the identification of putative ambuic acid analogs that will provide a starting point for semi-synthetic studies to generate more analogs for further studies on the relationship between chemical structures and quorum sensing inhibitory activity. These studies will provide the much-needed insight to inform the developments of countermeasure for MRSA infections to augment the use of antibiotics.

Additional Information

Language: English
Date: 2020
Ambuic acid, Analogs, Fungal, Mass defect filtering, Staphylococcus aureus, Virulence
Staphylococcus aureus
Methicillin resistance
Virulence (Microbiology)

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