Carrier matrix effect and transcriptional analysis of genes associated to stress and probiosis in Lactobacillus plantarum WCFS1 during passage through an in vitro human gastro intestinal tract model.

FAO and WHO encourage studies that implement in vitro experimental protocols to pre-screen novel probiotics and/or attest the efficacy of claimed probiotic strains [1]. To be effective, orally-delivered probiotics should reach the human intestine in relatively high numbers and in a viable state; therefore, they have to tolerate the stresses associated to the gastro-intestinal (GI) environment. All along the different GI sections, bacteria are challenged by several sources of stress, including the action of digestive enzymes, low pH and emulsifying bile salts. Bacterial cells are naturally equipped with various defense mechanisms to enhance survival in hostile environments [2]; these include chaperones to assist the re-folding of denatured proteins and proteases which degrade irreversibly damaged proteins. The food matrix used to deliver microbes may considerably contribute to their probiotic action, e.g. by enhancing survival to stress, stimulating selective growth and favouring gut colonization. Lactobacillus plantarum (Lp) is a widespread lactic acid bacterium which is recognized as a probiotic and is traditionally employed as a food starter. The stress tolerance of Lp WCFS1 was examined in a previously developed in vitro system that simulates the human GI tract [3]. Different carrier matrices were used to assess their protective and buffering properties. Higher survival was observed for bacteria included in complex and/or nutrient-rich matrices, and when potential prebiotics were added, thus highlighting the relevance of matrix composition in shielding and growth-promoting effects. The molecular response of Lp WCFS1 to the simulated GI system was analysed by studying the transcriptional pattern of bacterial genes involved both in stress response (i.e. chaperones, shsp, proteases) and in exerting beneficial effects on the host (i.e. bacteriocins, adhesion factors). Transcription of bacterial stress-related genes remarkably matched the extent of stress during the GI transit, as revealed by the observed survival rate. Indeed, the GI steps of higher mortality corresponded to major induction of typical stress genes, thus implying their involvement in the mechanisms of cellular adaptation to GI stress. GI environment consistently up-regulated probiosis-associated genes. Data obtained with the different vehicle matrices may be valuable for the development of protective and host/bacteria-friendly carriers in the design of functional food. Transcriptional analysis paves the way to the use of some bacterial genes as molecular markers for the screening of strains with potential probiotic applications. Our results also suggest cues to improve reliability and performance of in vitro GI simulators. References 1. FAO/WHO (2002) ftp://ftp.fao.org/es/esn/food/wgreport2.pdf. 2. van de Guchte M. et al. (2002) Antonie Van Leeuwenhoek 82, 187 - 216. 3. Bove P. et al. (2012) Appl. Microb. Biotechnol. DOI 10.1007/s00253-012-4031-2.