, 1995). Psuedomonas aeruginosa is an opportunistic pathogen that accounts for a considerable portion of hospital-acquired infections and is also a common source of infection for sufferers of cystic fibrosis (CF). Psuedomonas aeruginosa uses two HL signaling systems, which combined regulate over 300 genes (Schuster & Peter Greenberg, 2006), many of which are implicated in virulence factor production. HL signaling results in extensive changes in gene expression affecting secondary metabolism,

sporulation, the elaboration of virulence factors and the formation of biofilms (Schuster & Peter Greenberg, 2006). Because HL concentration in the extracellular medium increases with population density, the system allows bacteria to coordinate population-wide gene expression simultaneously. Studies have find more shown that another related HL produced by P. aeruginosa was able to abrogate Candida albicans filamentation (Hogan & Kolter, 2002; Hogan et al., 2004), a virulence trait. This study provides a striking example of competitive exclusion because restricting the ability of C. albicans to transition between morphotypes

(an important virulence trait) presumably gives P. aeruginosa a competitive advantage. HLs play a central role in regulating and coordinating infection. As a result, considerable research has been directed at identifying inhibitor HL systems. For example, a tetrazole with a 12C alkyl tail (Muh et al., 2006) was recently identified as an effective inhibitor (IC50=30 nM) of P. aeruginosa. Importantly, this molecule may not interfere with the growth of P. check details aeruginosa. This means that while highly effective

at disrupting the machinery used to coordinate infection, the compound does not create a strong selective pressure to develop resistance unlike current therapeutics. This is another emerging common theme among chemical inhibitors of small-molecule signals. Vibrio cholerae is the etiological agent of the debilitating human disease cholera. While V. cholerae uses the autoinducer-2 (AI-2, described in Etomidate more detail later in the review) like many other bacterial species, in addition, it also uses a unique autoinducer, cholerae autoinducer 1 (CAI-1), an α-hydroxyketone. CAI-1 serves to terminate host colonization, halting biofilm formation and virulence factor expression (Higgins et al., 2007). This observation is consistent with V. cholerae’s transmission route, where bacteria leave the host simultaneously during the onset of the diarrhea that characterizes the illness. Thus, host colonization and biofilm formation continue until the population reaches a sufficient density, at which point the bacteria reverse the colonization process to spread to other hosts. Exploiting the small-molecule signaling involved in V. cholerae infection is quite simple, as introducing high concentrations of the HL autoinducer will terminate host colonization, thus ending the infection.