Innovative Journal of Medical and Health Science 2: 4 July – Aug (2012) 59 – 62. Contents lists available at www.innovativejournal.in INNOVATIVE JOURNAL OF MEDICAL AND HEALTH SCIENCE Journal homepage: http://www.innovativejournal.in/index.php/ijmhs 59 EVALUATION OF THE EXPRESSION OF LUXS GENE IN CLINICAL ISOLATES OF STAPHYLOCOCCUS EPIDERMIDIS FROM BLOODSTREAM INFECTIONS Tracevska T. 1 *, Liduma 1 I., Bers U 2 ., Riekstina U. 1 , Zilevica A. 1 1 Faculty of Medicine, University of Latvia, Riga, Latvia. 2 Faculty of Biology, Bioanalytical Research and Methods Laboratory, University of Latvia, Riga, Latvia. ARTICLE INFO ABSTRACT Corresponding Author: Tracevska T Faculty of Medicine, University of Latvia, Riga, Latvia. Staphylococcus epidermidis is a common, nosocomial bacteria causing bloodstream infections. There is an urgent need to develop techniques which assist for differentiating between invasive and contaminating strains. Phenol-soluble modulin (PSM) peptides important for biofilm formation of S.epidermidis are regulated by the luxS/Autoinducer-2. To evaluate the expression of luxS gene for diagnostic purpose, we analysed changes in gene expression in vitro in S.epidermidis specimens isolated from bloodstream infections (n = 43) and in those from a control group (n = 35) produced by quantitative PCR. The mean expression of luxS gene was not significantly different between the clinical and control groups. We also studied correlation of the expression of luxS gene with previously described icaADBC operon. The presence of icaADBC operon regulating polysaccharide intercellular adhesin (PIA) production was detected by amplification of icaA gene fragment in all isolates. S.epidermidis isolates from patients with bloodstream infections were not different in presence of icaA gene from the nasal flora of healthy volunteers. In the clinical group, the mean expression of luxS gene was significantly higher (p = 0,0026) in isolates positive for icaA (icaA + ) then in isolates negative for icaA (icaA - ) gene (21,3% and 8,3%, respectively). The results of our study show that the capacity to form biofilm in vivo is strongly influenced by many environmental factors independent of luxS expression and the icaADBC products. ©2012, IJMHS, All Right Reserved. Keywords: S.epidermidis, bloodstream infections, biofilm, luxS, icaADBC. INTRODUCTION Coagulase negative Staphylococci (CoNS), particularly, Staphylococcus epidermidis, have emerged as important cause of nosocomial infections in recent twenty years 1 . S.epidermidis is the opportunistic pathogen which colonises and infects both hospitalised patients with decreased host response and healthy, immuno-competent people in the community. Given the epidermal origin of CoNS, it is often difficult to differentiate S.epidermidis strain isolated from a single blood culture as a contaminating or an infecting strain. The pathogenity of S.epidermidis is mainly due to the ability to form biofilms on indwelling medical devices 2, 3 . Many candidate genes have been explored as potential virulence markers 4, 5, 6, 7 , however, the molecular basis of virulence in S.epidermidis is not completely understood. Biofilm formation in S.epidermidis involves a bacterial intercommunication system called quorum sensing. S.epidermidis has a well known quorum-sensing (QS) system termed agr for accessory gene regulator 8 . A recent novel QS system described luxS in staphylococci 9 . Gene luxS was shown in vitro as playing a major role in biofilm formation. QS system controls the expression of several genes using small signalling molecules called autoinducers (AIs). A gene called luxS is required for the synthesis of autoinducers, particularly, for AI-2 10 . It is known that AI-2 has a signalling function in S.epidermidis, among other genes (e.g. from agr QS system) involving regulation of virulence-associated genes coding for the proinflammatory phenol-soluble modulin (PSM) peptides 11 . It was shown, that the deletion of luxS in S.epidermidis increased pathogen success during a biofilm–associated infection in a rat model by causing more severe bacteraemia 9 . However, there are no clinical studies indicating the role of luxS in biofilm formation during bloodstream infections. The goal of the present study was to evaluate the expression level in vitro of luxS gene in clinical isolates. The expression of luxS was measured by real-time PCR and compared between S.epidermidis isolates recovered from patients in cases of life-threatening infections such as bacteraemia and sepsis, and those from healthy people. This is the first study determining the expression of luxS gene in S.epidermidis isolates from patients with bloodstream infections. Also, we evaluated the functional correlation of luxS and the presence of well-known icaADBC operon, which is important for biofilm formation in