Quorum sensing signals are produced by Aeromonas salmonicida and quorum sensing inhibitors can reduce production of a potential virulence factor

Abstract

Many pathogens control production of virulence factors by self-produced signals in a process called quorum sensing (QS). We demonstrate that acyl homoserine lactone (AHL) signals, which enable bacteria to express certain phenotypes in relation to cell density, are produced by a wide spectrum of Aeromonas salmonicida strains. All 31 typical strains were AHL producers as were 21 of 26 atypical strains, but on a strain population basis, production of virulence factors such as protease, lipase, A-layer or pigment did not correlate with the production and accumulation of AHLs in the growth medium. Pigment production was only observed in broth under highly aerated conditions. Quorum sensing inhibitors (QSIs) are compounds that specifically block QS systems without affecting bacterial growth and 2 such compounds, sulphur-containing AHL-analogues, reduced production of protease in a typical strain of Aeromonas salmonicida. The most efficient compound N-(heptylsulfanylacetyl)-L-homoserine lactone (HepS-AHL), reduced protease production by a factor of 10. Five extracellular proteases were detected on gelatin-containing sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) gels and 3 of these were completely down regulated by HepS-AHL. Hence, QSIs can curb virulence in some strains and could potentially be pursued as bacterial disease control measures in aquaculture.KEY WORDS: Acylated homoserine lactones · Aeromonas salmonicida · Pigment · Protease · Quorum sensing inhibitors Resale or republication not permitted without written consent of the publisherDis Aquat Org 78: [105][106][107][108][109][110][111][112][113] 2007 2005). QS controls several of the putative virulence factors in aquatic bacteria, such as protease in V. anguillarum (Croxatto et al. 2002) and A. hydrophila (Swift et al. 1999), siderophores in V. harveyi (Lilley & Bassler 2000), and haemolysin in V. vulnificus (Kim et al. 2003). However, the role of the QS systems in expression of virulence in fish pathogenic bacteria is not at present fully understood.Quorum sensing inhibitors (QSIs) are compounds that antagonise bacterial QS systems without affecting growth of the bacteria (Smith et al. 2003, Castang et al. 2004, Rasmussen et al. 2005a. QSIs reduce production of toxin from Vibrio harveyi (Manefield et al. 2000) and treatment with a QSI, the halogenated furanone C-30, reduced accumulated mortality in rainbow trout infected with V. anguillarum (Rasch et al. 2004). However higher concentrations of furanone C-30 resulted in rapid fish death (Rasch et al. 2004), which stressed the need to explore less toxic QSI compounds for treatment. Sulfonated analogues of AHL compounds are such less toxic compounds ) and can inhibit several QS systems (Koch et al. 2005). In the present study, we address the possible involvement of QS systems in expression of virulence factors of Aeromonas salmonicida and determine to what extent QSI compounds affect production of virulence factors.Aeromonas salmonicida is the bacterial agent associated with ...

The Social Life of Aeromonas through Biofilm and Quorum Sensing Systems

“…Consistently, the 3-oxo-C10-HSL produced by Vibrio anguillarum inhibits protease activities from A. salmonicida and A. hydrophila (Rasch et al, 2007). Similarly, the synthetic 2(5H)-furanone derived from the competitive inhibitor of AHL produced by the marine algae Delisea pulchra , exhibited QS inhibition activity against C4-HSL and C6-HSL, molecules usually produced by aeromonads (Ponnusamy et al, 2010).…”

An Insertion Sequence-Dependent Plasmid Rearrangement in Aeromonas salmonicida Causes the Loss of the Type Three Secretion System

“…A. salmonicida possesses a wide variety of virulence factors, including extracellular proteases, lipases, and a functional type three secretion system (TTSS) [3], [4]. The TTSS, a virulence system shared by many Gram-negative bacteria, can translocate effector proteins into host cells where they can disrupt cell processes and disturb immune responses [5], [6].…”

Biological approaches for controlling shellfish-associated pathogens

“…On the contrary, mutational inactivation of the genes involved in AHL-mediated signaling in Vibrio anguillarum and Aeromonas spp. decreased expression of virulence-related traits [45][46][47][48], but did not correspond to a decreased virulence in brine shrimp [49 ] or trout [48]. While outcomes of mutational inactivation and chemical blockage of QS appear to be different, it is worth noting that QS in most bacteria consists of overlapping partially redundant signaling circuits (e.g.…”