Lactobacilli in the porcine intestine: from composition to functionality

Monogastric animals including pigs coexist with a diverse and dense commensal microbiota in their gastrointestinal (GI) tract. Most of these microbes are beneficial and provide the necessary nutrients or protection against harmful pathogens for the host. The microbial colonization of the porcine intestine begins after birth and follows a rapid succession during the neonatal and weaning period. In the immediate post-weaning period, the balance between the development of beneficial microbiota or the establishment of bacterial intestinal pathogens can be easily tipped toward disease expression. In order to enhance the animal growth and suppress the activity of the gut microbiota , antimicrobial compounds have been fed to weaning piglets for more than four decades. Nowadays, however, the emergence of antibiotic resistance in the human commensal bacteria has raised concerns about the impact of antimicrobial compounds for agricultural use, and accelerated the search for alternative nutritional strategies, such as the addition of probiotics and prebiotics . The aim of the current study was to understand the i nteractions between the intestinal microbiota , feed components and the host in the porcine GI tract and to validate some novel dietary strategies in vivo and in vitro . The porcine intestinal microbiota development was analysed by 16S ribosomal RNA gene ( rRNA ) targeted approaches in relation to differences in nutritional strategies, age and pathogenic challenge. The GI tract microbial diversity was assessed using PCR-analysis of 16S rRNA genes by cloning and denaturing gradient gel electrophoresis. In addition, methods such as real-time PCR and fluorescent in situ hybridisation were applied to quantify the predominant bacterial community and the major Lactobacillus populations. Furthermore, we developed a novel strain detection system based on isolation of specific genomic fragments by representative difference analysis and their further quantification by real-time PCR. The data obtained during the course of the study indicated that a stable and complex commensal bacterial community might be considered as prerequisite of a healthy intestinal ecosystem. Moreover, the addition of fermentable carbohydrates to the diet of weaning piglets was found to enhance the stability and diversity of the microbiota in the large intestine of piglets, and to stimulate the growth of strains closely related to Lactobacillus amylovorus . The phenotypic and molecular taxonomic characterization of these strains, however, revealed significant differences with the type strain of L. amylovorus (DSMZ 20531 T ) and the name Lactobacillus sobrius sp. nov . was proposed. L. sobrius strain 001 T was found to exert a significant protective effect against the enterotoxigenic Escherichia coli K88 promoted intestinal damages in vitro using porcine intestinal cell cultures. Furthermore, when L. sobrius was dietary fed to piglets subjected to E. coli K88 challenge, improved daily weight gain (+ 74%, P total secretory IgA , and reduced E. coli K88 intestinal levels were observed. The data indicate that L. sobrius exerts a protective effect against specific intestinal challenges while improving the weight gain and immunity of weaning piglets. Hence, the finding of this beneficial member of the porcine Lactobacillus community may have further implications for new dietary strategies aiming to improve the animal health during weaning.