Gastrointestinal microbial community shifts observed following oral administration of a Lactobacillus fermentum strain to mice.

The indigenous gastrointestinal microbiota acts as an integral defense against the colonisation of orally introduced microbes. Whilst this can be important in host protection, some introduced species, including lactobacilli, can have a positive impact on existing microbial communities. The interaction of a candidate probiotic strain of Lactobacillus fermentum within the gastrointestinal tract was monitored in a mouse model and its effect on the indigenous microbiota observed. L. fermentum KLD was administered via oro-gastric doses to mice with both a specific pathogen-free (SPF) and an ampicillin-depleted gut microbiota, containing no detectable lactobacilli. Its persistence was monitored by detection in faecal homogenates using culturing methods and polymerase chain reaction with L. fermentum specific primers. Microbial population shifts were observed using denaturing gradient gel electrophoresis (DGGE). L. fermentum KLD was detected within the gastrointestinal tract of SPF mice for up to 36 h, and for greater than 11 days in the ampicillin-treated mice. The administration resulted in substantial changes within the host Lactobacillus levels, determined by DGGE of 16S rDNA from faecal samples. Denaturing gradient profiles, from faecal samples collected at a range of pre- and post-dose intervals of groups of 10 SPF mice, indicated that several other constituents of the gastrointestinal community also fluctuated following dosing. These included Bifidobacterium and Eubacterium, which increased following KLD administration. The indigenous microbiota affected the persistence of L. fermentum KLD and in SPF mice the administration of this strain induced significant shifts in the indigenous microbial community.