ORIGINAL PAPER Pseudomonas fluorescens can induce and divert the human b-defensin-2 secretion in intestinal epithelial cells to enhance its virulence Amar Madi • Ziad Alnabhani • Charle `ne Leneveu • Lily Mijouin • Marc Feuilloley • Nathalie Connil Received: 10 July 2012 / Revised: 17 December 2012 / Accepted: 20 December 2012 / Published online: 10 January 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract The effect of intestinal molecules produced by the host on the virulence of Pseudomonas fluorescens is poorly documented. In the present work, we evaluated the secretion of human b-defensin-2 (hBD-2) by enterocytes after infection with P. fluorescens (a species previously suggested to be involved in inflammatory bowel disease) and investigated the effect of this host-defense peptide on the bacterial virulence. The results showed that P. fluo- rescens can induce hBD-2 production in Caco-2/TC7 cells via P38 and ERK MAPK-dependent pathways. Surpris- ingly, the exposure of P. fluorescens to low doses of the antimicrobial peptide was found to enhance its cytotoxic and proinflammatory effects suggesting a potential feed- back mechanism in the dialog between bacteria and the host. Keywords P. fluorescens Á Caco-2/TC7 Á hBD-2 Á NF-jB Á MAPK Á Virulence Introduction The intestinal epithelium contains a great diversity of cell types, including disseminated neuroendocrine and defense cells. These cells are the source of a multitude of signal molecules and antibacterial substances. Among these fac- tors are defensins, inducible or constitutive antimicrobial peptides, expressed by various cell types (Selsted and Ouellette 2005; Nuding et al. 2009). These small (3–5 kDa) cationic peptides are classified as a-, b-, or h-defensins, on the basis of the position of their intramo- lecular disulfide bridges. An alteration of defensin production should participate in the pathogenesis of inflammatory bowel disease (IBD). In CD, reduced a-de- fensin levels have been seen in patients with ileal inflam- mation, whereas reduced b-defensin levels were measured in those with colonic involvement (Ramasundara et al. 2009; Chamaillard and Dessein 2011). An attenuated expression of defensins, such as human b-defensin-2 (hBD- 2), could compromise host immunity and alter the balance between protection from pathogens and tolerance to the normal flora (Ramasundara et al. 2009). hBD-2 is an antimicrobial peptide having a broad antibiotic spectrum against gram-negative and gram-positive bacteria, as well as against fungi and viruses (Ganz 2005). It is induced by cytokines or in response to inflammatory stimuli such as bacterial infections (Yoon et al. 2010). Activation of AP-1 (activator protein 1) and/or NF-jB (nuclear factor jB) transcription factors via the MAPK (mitogen-activated protein kinases) including P38, JNK (c-jun N-terminal kinase), and ERK1/2 (extracellular signal-regulated protein kinases), via the MAPK/I-jB kinase (IKK)/NF-jB, or via JNK/NF-jB pathways are known to be important for the induction of defensins and proinflammatory factors in sev- eral cell lines (Wehkamp et al. 2004; Schneider et al. 2005; Wehkamp et al. 2006; Yoon et al. 2010; Jung et al. 2012). Unlike P. aeruginosa which is largely described as an opportunistic pathogen (Okuda et al. 2010), the virulence of P. fluorescens has often been underestimated. This bacterium Communicated by Djamel Drider. A. Madi Á C. Leneveu Á L. Mijouin Á M. Feuilloley Á N. Connil (&) Laboratoire de Microbiologie Signaux et Microenvironnement (LMSM), EA4312, Universite ´ de Rouen, 55 rue Saint Germain, 27000 Evreux, France e-mail: nathalie.connil@univ-rouen.fr Z. Alnabhani Faculte ´ de me ´decine de Bichat, INSERM, U843, Universite ´ Paris-Diderot, 16 rue Huchard, 75018 Paris, France 123 Arch Microbiol (2013) 195:189–195 DOI 10.1007/s00203-012-0865-3