Selection of Lactobacillus fermentum strains able to durably colonize the digestive tract of mice harboring a complex human flora

Sixteen Lactobacillus fermentum strains were isolated from the fecal microflora of pigs. They were challenged in vivo, in gnotobiotic mice harboring a porcine flora devoid of lactobacilli. Some of the strains were able to colonize the digestive tract of the mice at high population levels, whilst other strains were eliminated. Chromosomal DNA restriction analysis performed on both colonizing (C-type) and non-colonizing (NC-type) strains were analyzed by pulsed-field gel electrophoresis. Strains LEMPL9 (C-type) and LEM1.16A (NC-type) exhibited a high degree of homology. When challenged in mice harboring a simplified anaerobic flora, LEMPL9 was able to colonize the digestive tract of the animals whereas LEM1.16A was again eliminated. Mutagenesis performed on LEM1.16A allowed the isolation of a mutant able to colonize the gut of mice harboring the simplified anaerobic flora or a complex human flora, suggesting that genes involved in colonization process might have been affected to enhance the bacterium's colonization ability.