Quorum Sensing in Aeromonas Species Isolated from Patients in Malaysia Kok-Gan Chan • Savithri D. Puthucheary • Xin-Yue Chan • Wai-Fong Yin • Cheng-Siang Wong • Wah-Seng See Too • Kek-Heng Chua Received: 18 March 2010 / Accepted: 20 May 2010 / Published online: 11 June 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Bacterial quorum sensing signal molecules called N-acylhomoserine lactone (AHL) controls the expression of virulence determinants in many Gram-neg- ative bacteria. We determined AHL production in 22 Aeromonas strains isolated from various infected sites from patients (bile, blood, peritoneal fluid, pus, stool and urine). All isolates produced the two principal AHLs, N-buta- noylhomoserine lactone (C4-HSL) and N-hexanoyl homo- serine lactone (C6-HSL). Ten isolates also produced additional AHLs. This report is the first documentation of Aeromonas sobria producing C6-HSL and two additional AHLs with N-acyl side chain longer than C 6 . Our data provides a better understanding of the mechanism(s) of this environmental bacterium emerging as a human pathogen. Introduction Members of the genus Aeromonas have a broad pathogenic range in nature, infecting not only humans but also a variety of other animals. The natural habitat of Aeromonas is aquatic; they can multiply in fresh and drinking water and can infect fish, turtles, alligators and other fresh water animals [11]. Members of Aeromonas pose a threat to aquaculture as Aeromonas salmonicida principally attacks salmonid fish [10]. More importantly, A. hydrophila has been implicated not only as a gastrointestinal pathogen of humans affecting all age groups but in Malaysia it also gives rise to extra-intestinal infections such as septicaemia, peritonitis, osteomyelitis and soft tissue infections [5, 18]. The range of extra-intestinal infections is from traumatic introduction of the microorganism with resultant necrotiz- ing cellulitis, to opportunistic systemic infections in immunocompromised patients [18, 19]. A number of secreted virulence factors are responsible for host tissue destruction during initiation of the infectious process by Aeromonas sp. These pathogenicity determi- nants include surface associated factors such as adhesions, siderophore secretion, S-layer, lipopolysaccharide, exo- toxins, enterotoxins, lipases and exoprotease [1, 10, 12, 13, 16, 17]. Many Gram-negative bacteria produce N-acylhomoser- ine lactone (AHL) signal molecules to monitor their own population density in a process known as ‘quorum sensing’ (QS) [20]. AHL molecules produced by LuxI synthase bind to its cognate receptor (LuxR) which in turn will regulate gene expression. As a consequence, expression of certain functions, often virulence factors required for pathogenesis, are triggered at high population densities in a coordinated manner. It has been suggested that this form of gene reg- ulation ensures that the bacteria remain invisible to the immune system of the host until they have reached a suf- ficiently high density to overwhelm host defences to establish infection [3]. Reported work on QS system in A. hydrophila and A. salmonicida has led to the identification of the luxR/luxI homologues ahyRI and asaRI, respectively [15]. A number K.-G. Chan (&) Á X.-Y. Chan Á W.-F. Yin Á C.-S. Wong Á W.-S. S. Too Institute of Biological Sciences (Division of Genetics and Molecular Biology), Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia e-mail: kokgan@um.edu.my S. D. Puthucheary Department of Medical Microbiology, University of Malaya, 50603 Kuala Lumpur, Malaysia K.-H. Chua Department of Molecular Medicine, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia 123 Curr Microbiol (2011) 62:167–172 DOI 10.1007/s00284-010-9689-z