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

Abstract

There has been major interest by the scientific community in antivirulence approaches against bacterial infections. However, partly due to a lack of viable lead compounds, antivirulence therapeutics have yet to reach the clinic. Here we investigate the development of an antivirulence lead targeting quorum sensing signal biosynthesis, a process that is conserved in Gram-positive bacterial pathogens. Some preliminary studies suggest that the small molecule ambuic acid is a signal biosynthesis inhibitor. To confirm this, we constructed a methicillin-resistant Staphylococcus aureus (MRSA) strain that decouples autoinducing peptide (AIP) production from regulation and demonstrate that AIP production is inhibited in this mutant. Quantitative mass spectrometric measurements show that ambuic acid inhibits signal biosynthesis (50% inhibitory concentration [IC 50 ] of 2.5 Ϯ 0.1 M) against a clinically relevant USA300 MRSA strain. Quantitative real-time PCR confirms that this compound selectively targets the quorum sensing regulon. We show that a 5-g dose of ambuic acid reduces MRSA-induced abscess formation in a mouse model and verify its quorum sensing inhibitory activity in vivo. Finally, we employed mass spectrometry to identify or confirm the structure of quorum sensing signaling peptides in three strains each of S. aureus and Staphylococcus epidermidis and single strains of Enterococcus faecalis, Listeria monocytogenes, Staphylococcus saprophyticus, and Staphylococcus lugdunensis. By measuring AIP production by these strains, we show that ambuic acid possesses broad-spectrum efficacy against multiple Gram-positive bacterial pathogens but does not inhibit quorum sensing in some commensal bacteria. Collectively, these findings demonstrate the promise of ambuic acid as a lead for the development of antivirulence therapeutics.

Small-molecule AgrA inhibitors F12 and F19 act as antivirulence agents against Gram-positive pathogens

“…Other reported small-molecule inhibitors of AgrA include savirin 19 , hydroxyemodin 20 and phloretin 21 . Additionally, several natural products have been reported to inhibit the agr system, although it is not clear which component of agr is inhibited in these studies 22 – 24 . Agr -targeting quorum quenchers with demonstrated in-vivo activity have recently been reviewed by Salam and Quave 25 .…”

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

“…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).…”

Interference in Bacterial Quorum Sensing: A Biopharmaceutical Perspective

“…In lung infection models, P. aeruginosa colonization or related mortality was reduced by furanones (Hentzer et al, 2003 ; Wu, 2004 ), sub-minimal inhibitory concentrations of azithromycin (Hoffmann et al, 2007 ), garlic extract (Bjarnsholt, 2005a ), and also by the inhalation of the lactonase Sso Pox (Hraiech et al, 2014 ). In skin wound models, a wide range of QSIs reduced S. aureus pathogenicity (Cirioni et al, 2013 ; Simonetti et al, 2016 ; Muhs et al, 2017 ; Todd et al, 2017 ). Similar inhibition of pathogenicity was observed with an AIP-targeting antibody (Park et al, 2007 ).…”