Abstract:

Totally 75 suspected bifidobacterium were obtained in modified MRSC broth with 60 mg/mL X-Gal. Of these
strains, 11 with high viability were screened by simulating the micro-environment of the human gastrointestinal tract using
MRSC broth (pH 3.0) and then MRSC with 3 mg/mL bile salt for 20 h. Physiological and biochemical tests were conducted
on NCU712, NCU701, and NCU708. They were all identified as B. longum via 16S rDNA sequencing. NCU712 was in line
with the characteristics of B. longum. Preliminary study on its tolerance to the human digestive environment was conducted.
The results showed that the viable count rose slightly with increasing incubation time when the pH of artificial gastric
fluid equaled or exceeded 3.5. The death value (the time it takes to kill 90% of cells) of NCU712 was 92.97 min and 30.42
min in artificial gastric fluid at pH 2.5 and pH 3.0, respectively. The number of viable NCU712 cells remained more than
107 CFU/mL after 2.5 h. The number of living bacterium remained above 108 CFU/mL after 4.0 h in artificial intestinal fluid.
The number of viable NCU712 cells was reduced by one order of magnitude after being incubated in MRSC with 3 mg/mL
bile salt for 24 h. In summary, B. longum NCU712 has excellent tolerance to the human gastrointestinal tract and may be
regarded as functional probiotic with great application potential.

Key words: Bifidobacterium, screening and identification, gastrointestinal tract, tolerance