Book Description

Many bacteria use small molecule or peptidic signals to assess their local population densities in a process called quorum sensing (QS). The concentration of QS signals in a given environment can be correlated with cell density. Once bacteria reach a sufficiently large population, they can use QS to shift from a unicellular to more of a multicellular existence and modify gene expression levels to initiate a broad range of group behaviors that benefit the growing community. These QS phenotypes include biofilm formation, virulence factor production, swarming, sporulation, conjugation, and bioluminescence, and often play a critical role in mediating pathogenic or symbiotic relationships with a eukaryotic host. For instance, several of the most deadly human pathogens use QS to initiate infections and become virulent only after perceiving that a "quorum" of cells has been reached, thus increasing the probability that the bacterial population can survive the host immune response. Copious questions remain about QS signaling mechanisms and their roles in host-bacteria interactions, specifically in infections. Therefore, methods to block bacterial QS would be valuable to study this signaling process at a fundamental level and could provide a route to the development of novel anti-infective strategies. The goal of this dissertation was to develop non-native molecules capable of intercepting QS signaling in human pathogens, with a primary focus on italicStaphylococcus aureusitalic, italicAcinetobacter baumanniiitalic, italicPseudomonas aeruginosaitalic, italicBurkholderia malleiitalic and italicB. thailandensisitalic. The Gram-positive bacterium italicS. aureusitalic uses QS to regulate an arsenal of virulence factors and phenotypes, and its primary QS signals are cyclic autoinducing peptides (AIPs). I designed and synthesized three collections of AIP analogs using solid-phase synthetic techniques, and evaluated their ability to attenuate QS in italicS. aureusitalic. A set of AIP analogs strongly reduced two virulence traits--hemolysis and the production of toxic shock syndrome toxin-1 (TSST-1). These analogs were then incorporated in polymeric coatings and were found to be active when released from materials of biomedical and consumer relevance. I applied a similar strategy to develop the first reported non-native QS modulators in the Gram-negative bacterium italicA. baumanniiitalic. Gram-negative bacteria commonly use italicNitalic-acyl homoserine lactones (AHLs) for QS. I determined the stereochemistry of the native 3-OH AHL signal used by italicA. baumanniiitalic, and then screened a library of non-native AHLs for QS agonists and antagonists in this human pathogen. Several potent AHL antagonists were uncovered in reporter gene assays, and the most potent were capable of limiting bacterial motility and biofilm production in italicA. baumanniiitalic. Building on this work, I designed and synthesized a set of second-generation AHLs to uncover additional QS modulators in italicA. baumanniiitalic and clarify SARs for non-native AHL activity in italicA. baumanniiitalic and italicP. aeruginosaitalic. A number of 3-OH AHL and triazole-HL analogs were revealed capable of modulating QS in both italicA. baumanniiitalic and italicP. aeruginosaitalic. Lastly, I identified the first non-native AHLs capable of blocking QS in the pathogens italicB. malleiitalic (now classified as a biological warfare agent) and italicB. thailandensisitalic. These compounds are anticipated to similarly modulate QS in italicB. pseudomalleiitalic, which utilizes LuxR-type QS receptors largely identical to those initalic B. malleiitalic anditalic B. thailandensisitalic to regulate virulence.