APPLIED MICROBIAL AND CELL PHYSIOLOGY Implication of sortase-dependent proteins of Streptococcus thermophilus in adhesion to human intestinal epithelial cell lines and bile salt tolerance Mounira Kebouchi 1,2 & Wessam Galia 1,2 & Magali Genay 1,2 & Claire Soligot 1,2 & Xavier Lecomte 1,2 & Ahoefa Ablavi Awussi 1,2 & Clarisse Perrin 1,2 & Emeline Roux 1,2 & Annie Dary-Mourot 1,2 & Yves Le Roux 1,2 Received: 4 November 2015 /Revised: 10 January 2016 /Accepted: 13 January 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Streptococcus thermophilus (ST) is a lactic acid bacterium widely used in dairy industry and displays several properties which could be beneficial for host. The objective of this study was to investigate, in vitro, the implication of sortase A (SrtA) and sortase-dependent proteins (SDPs) in the adhesion of ST LMD-9 strain to intestinal epithelial cells (IECs) and resistance to bile salt mixture (BSM; taurocholoate, deoxycholate, and cholate). The effect of mu- tations in prtS (protease), mucBP (MUCin-Binding Protein), and srtA genes in ST LMD-9 in these mechanisms were ex- amined. The HT29-MTX, HT29-CL.16E, and Caco-2 TC7 cell lines were used. HT29-MTX and HT29-CL.16E cells express different mucins found in the gastro intestinal tract; whereas, Caco-2 TC7 express cell surface proteins found in the small intestine. All mutants showed different adhesion profiles depending on cell lines. The mutation in genes srtA and mucBP leads to a significant decrease in LMD-9 adhesion capacity to Caco-2 TC7 cells. A mutation in mucBP gene has also shown a significant decrease in LMD-9 adhesion capacity to HT29-CL.16E cells. However, no difference was observed using HT29-MTX cells. Furthermore, ST LMD-9 and srtA mutant were resistant to BSM up to 3 mM. Contrariwise, no viable bacteria were detected for prtS and mucBP mutants at this concentration. Two conclusions could be drawn. First, SDPs could be involved in the LMD-9 adhesion depending on the cell lines indicating the importance of eukaryotic-cell surface components in adherence. Second, SDPs could con- tribute to resistance to bile salts probably by maintaining the cell membrane integrity. Keyword S. thermophilus . Sortase-dependent proteins (SDPs) . Adhesion . Intestinal epithelial cells . Bile salt stress Introduction Lactic acid bacteria (LAB), a clade of Gram-positive bacteria, are widely used in the manufacture of dairy products. Once consumed, most of them have been shown to promote health benefits on the host and therefore are considered as probiotics (Veiga et al. 2010; Pagnini et al. 2010). The probiotic defini- tion adopted in 2002 (live microorganisms which conferred a health benefit when administrated in adequate amount) im- plies that to be recognized as a probiotic, a bacterium has to remain alive in the digestive tract, especially able to resist to bile salts in gastro intestinal tract (GIT), and confer a health benefit. As several health effects require that the probiotic adheres, even transiently, to the mucus and/or intestinal epi- thelial cells (IECs), this property is often sought. Streptococcus thermophilus (ST) belongs to the LAB group and is recognized as safe since it has obtained the Generally Recognized as Safe (GRAS) status from the American Food and Drug Administration (FDA 2002; FDA 2012) and the Qualified Presumption of Safety (QPS) status from the European Food Safety Authority (EFSA). Due to its high capability of fermenting milk and flavor producing char- acteristics, this bacterium is massively used as a starter in dairy * Magali Genay magali.genay@univ-lorraine.fr 1 Université de Lorraine, Unité de Recherche « Animal et Fonctionnalités des Produits Animaux» (UR AFPA), Équipe « Protéolyse et Biofonctionnalités des Protéines et des Peptides » (PB2P), Vandœuvre-lès-Nancy 54506, France 2 INRA, Unité de Recherche « Animal et Fonctionnalités des Produits Animaux » (UR AFPA), Unité Sous Contrat 340, Vandœuvre-lès-Nancy 54506, France Appl Microbiol Biotechnol DOI 10.1007/s00253-016-7322-1