AI-2 quorum-sensing inhibitors affect the starvation response and reduce virulence in several Vibrio species, most likely by interfering with LuxPQ

Abstract

The increase of disease outbreaks caused by Vibrio species in aquatic organisms as well as in humans, together with the emergence of antibiotic resistance in Vibrio species, has led to a growing interest in alternative disease control measures. Quorum sensing (QS) is a mechanism for regulating microbial gene expression in a cell density-dependent way. While there is good evidence for the involvement of auto-inducer 2 (AI-2)-based interspecies QS in the control of virulence in multiple Vibrio species, only few inhibitors of this system are known. From the screening of a small panel of nucleoside analogues for their ability to disturb AI-2-based QS, an adenosine derivative with a p-methoxyphenylpropionamide moiety at C-39 emerged as a promising hit. Its mechanism of inhibition was elucidated by measuring the effect on bioluminescence in a series of Vibrio harveyi AI-2 QS mutants. Our results indicate that this compound, as well as a truncated analogue lacking the adenine base, block AI-2-based QS without interfering with bacterial growth. The active compounds affected neither the bioluminescence system as such nor the production of AI-2, but most likely interfered with the signal transduction pathway at the level of LuxPQ in V. harveyi. The most active nucleoside analogue (designated LMC-21) was found to reduce the Vibrio species starvation response, to affect biofilm formation in Vibrio anguillarum, Vibrio vulnificus and Vibrio cholerae, to reduce pigment and protease production in V. anguillarum, and to protect gnotobiotic Artemia from V. harveyi-induced mortality. INTRODUCTIONVibrio species are ubiquitous in marine environments worldwide (Igbinosa & Okoh, 2008). As opportunistic pathogens they can cause mild to severe infections in humans and marine animals. Vibriosis is one of the most prevalent fish diseases, mainly caused by Vibrio anguillarum, Vibrio alginolyticus, Vibrio parahaemolyticus, Vibrio harveyi and Vibrio campbellii (Garcia et al., 1997;Austin & Zhang, 2006). Other Vibrio species are pathogenic for humans. Vibrio vulnificus is associated with gastrointestinal infections primarily following the consumption of raw and undercooked seafood, but it can also cause wound or soft-tissue infections (Bross et al., 2007). In addition, systemic V. vulnificus infections are notorious for their high mortality rate (Chiang & Chuang, 2003). Vibrio cholerae is responsible for pandemic and epidemic outbreaks of cholera (Griffith et al., 2006). V. cholerae serotype O1 causes the majority of the outbreaks worldwide, while the O139 serotype has only been detected in South-East and East Asia (Sack et al., 2004;Griffith et al., 2006). Cellcell communication (quorum sensing; QS) in Vibrio species plays an important role in virulence. QS in Vibrio species involves three types of signal molecules. NAcylhomoserine lactones (AHLs) are used in the LuxM/N QS system, cholera auto-inducer 1 (CAI-1) in the CqsA/S system and auto-inducer 2 (AI-2) in the LuxS/PQ QS system (Bassler et al., 1993(Bassler et al., , 1997Higgins et al., ...

Structure-Activity Relationship of Cinnamaldehyde Analogs as Inhibitors of AI-2 Based Quorum Sensing and Their Effect on Virulence of Vibrio spp

“…The assay for the effect on constitutively expressed bioluminescence (using E. coli DH5α pBlueLux containing the luxCDABE genes) and the bioassay to determine the molecular target of the compounds tested (using V. harveyi BB120, BB152, BB170, BB886, BNL258, JAF375, JAF553, JAF483, JMH597 and MM30) were conducted as described previously [27]. Each compound was tested at least six times in triplicate (n≥18).…”

Innovative Strategies for Combating Biofilm-Based Infections

“…6.3 ) blocks AI-2-based QS without affecting bacterial growth. This compound was subsequently shown to affect biofi lm formation in several Vibrio species (Brackman et al 2009 ). Another enzyme involved in the biosynthesis of both AI-2 and AHLs is 5′-methylthioadenosine nucleosidase (MTAN), which catalyzes the N -glycosyl hydrolysis of SAM and other adenosyl derivatives (Ronning et al 2010 ;Gutierrez et al 2009 ).…”

Species-specific patterns in the vulnerability of ­carbon-starved bacteria to protist grazing

“…As a possible alternative, it remains to be examined whether high concentrations of this bacterial strain trigger regulatory shifts, e.g. by components involved in quorum sensing, known to affect both virulence and the starvation survival response in Vibrio strains (McDougald et al 2000, Brackman et al 2009). Nevertheless, this is, to our knowledge, the first documented case of a bacterial strain which can change from a highly edible to an unpalatable food when entering the starvation state.…”