Lactobacilli in the porcine intestine: from composition to functionality

Monogastricanimals including pigs coexist with a diverse and densecommensalmicrobiotain 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 beneficialmicrobiotaorthe 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 gutmicrobiota, antimicrobial compounds have been fed to weaning piglets for more than four decades. Nowadays, however, the emergence of antibiotic resistance in the humancommensalbacteria has raised concerns about the impact of antimicrobial compounds for agricultural use, and accelerated the search for alternative nutritional strategies, such as the addition ofprobioticsandprebiotics. The aim of the current study was to understand the interactions between the intestinalmicrobiota, feed components and the host in the porcine GI tract and to validate some novel dietary strategiesin vivoandin vitro.The porcine intestinalmicrobiotadevelopment wasanalysedby 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 16SrRNAgenes by cloning and denaturing gradient gel electrophoresis. In addition, methods such as real-time PCR and fluorescent in situhybridisationwere 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 complexcommensalbacterial 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 themicrobiotain the large intestine of piglets, and to stimulate the growth of strainsclosely related to Lactobacillusamylovorus. 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 Lactobacillussobrius sp.nov.wasproposed. L.sobrius strain 001 T was found to exert a significant protective effect against theenterotoxigenicEscherichia 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