Attenuation of Quorum Sensing in the Pathogen <i>Acinetobacter baumannii</i> Using Non-native <i>N</i>‑Acyl Homoserine Lactones

Many bacterial pathogens use quorum sensing (QS) to control virulence. As a result, the development of methods to intercept QS has attracted significant interest as a potential anti-infective therapy. <i>Acinetobacter baumannii</i> has emerged as a pan-drug-resistant pathogen and displays a remarkable ability to persist in hospital settings despite desiccation and antimicrobial treatment. Recent studies have shown that <i>A. baumannii</i> QS mutants have limited motility and fail to form mature biofilms; these phenotypes are linked to its ability to persist on biotic and abiotic surfaces and increase its pathogenicity. <i>A. baumannii</i> uses <i>N-</i>(3-hydroxydodecanoyl)-l-homoserine lactone (OH-dDHL) and its putative cognate receptor, AbaR, for QS. We sought to identify non-native ligands capable of blocking or promoting AbaR activity in <i>A. baumannii</i> for use as chemical probes to modulate QS phenotypes in this pathogen. We screened a focused library of synthetic, non-native <i>N</i>-acyl homoserine lactones (AHLs) to identify such compounds, and several highly potent antagonists and agonists were uncovered, with IC₅₀ and EC₅₀ values in the low micromolar range, respectively. The strongest AbaR antagonists largely contained aromatic acyl groups, whereas the AbaR agonists closely resembled OH-dDHL. Notably, the 10 most potent AbaR antagonists also strongly inhibited <i>A. baumannii</i> motility, and five antagonists reduced biofilm formation in <i>A. baumannii</i> by up to 40%. The discovery of these compounds is significant, as they represent, to our knowledge, the first non-native modulators of QS in <i>A. baumannii</i> to be reported and could find utility as new tools to study the role and timing of QS phenotypes in <i>A. baumannii</i> infections

Predominant PCR/ESI-MS sequence types and rep-PCR types analyzed by Kullback-Leibler (KL) and Pearson correlation (PC) methods.

*<p>rep-PCR did not differentiate among ST 10, ST 12, ST 1 and ST 86.</p

Simpson's Diversity index (<i>DI</i>) of PCR/ESI-MS, rep-PCR and the combination of PCR/ESI-MS and rep-PCR.

<p>Simpson's Diversity index (<i>DI</i>) of PCR/ESI-MS, rep-PCR and the combination of PCR/ESI-MS and rep-PCR.</p

Origin, sequence type and antibiotic susceptibility of <i>Acinetobacter baumannii</i> from Ohio.

<p>Distribution of 122 <i>A. baumannii</i> isolates by hospital of origin (hospitals A, B, C and D), year, sequence type (ST) determined by PCR/ESI-MS, worldwide clone type (WW) and susceptibility to carbapenems and ampicillin/sulbactam.</p

Genetic similarity among <i>A. baumannii</i> isolates.

<p>Representative <i>A. baumannii</i> isolates typed by rep-PCR, analyzed with the Kullback-Leibler method. Five strain types with >95% similarity are illustrated, and further discriminated by year, hospital of origin, PCR-ESI/MS sequence type (ST), and worldwide (WW) clone types.</p

Strategic Approaches to Overcome Resistance against Gram-Negative Pathogens Using β‑Lactamase Inhibitors and β‑Lactam Enhancers: Activity of Three Novel Diazabicyclooctanes WCK 5153, Zidebactam (WCK 5107), and WCK 4234

Limited treatment options exist to combat infections caused by multidrug-resistant (MDR) Gram-negative bacteria possessing broad-spectrum β-lactamases. The design of novel β-lactamase inhibitors is of paramount importance. Here, three novel diazabicyclooctanes (DBOs), WCK 5153, zidebactam (WCK 5107), and WCK 4234 (compounds <b>1</b>–<b>3</b>, respectively), were synthesized and biochemically characterized against clinically important bacteria. Compound <b>3</b> inhibited class A, C, and D β-lactamases with unprecedented <i>k</i>₂/<i>K</i> values against OXA carbapenemases. Compounds <b>1</b> and <b>2</b> acylated class A and C β-lactamses rapidly but not the tested OXAs. Compounds <b>1</b>–<b>3</b> formed highly stable acyl-complexes as demonstrated by mass spectrometry. Crystallography revealed that <b>1</b>–<b>3</b> complexed with KPC-2 adopted a “chair conformation” with the sulfate occupying the carboxylate binding region. The cefepime-<b>2</b> and meropenem-<b>3</b> combinations were effective in murine peritonitis and neutropenic lung infection models caused by MDR <i>Acinetobacter baumannii</i>. Compounds <b>1</b>–<b>3</b> are novel β-lactamase inhibitors that demonstate potent cross-class inhibition, and clinical studies targeting MDR infections are warranted