In vitro and in vivo gastrointestinal survival, antibiotic susceptibility and genetic identification of Propionibacterium freudenreichii ssp. shermanii JS

The in vitro tolerance of Propionibacterium freudenreichii strains to low pH and high bile concentration, their antibiotic susceptibility and enzyme activity profiles were assessed. The gastrointestinal survival of the P. freudenreichii ssp. shermanii JS strain was also examined when administered to healthy adult volunteers in whey-based fruit juice. For tracking the strain JS in faecal samples, a genetic identification method for the strain was developed. No loss of viability was observed in any of the P. freudenreichii strains during the three-hour treatment at pH 4 or 3, whereas at pH 2 the cell counts of all strains decreased remarkably. Bile salt at 0.5% concentration had no apparent effect on the viability of the strains. No atypical antibiotic resistance was detected. P. freudenreichii ssp. shermanii JS strain was recovered in high numbers in faecal samples during the consumption of whey-based fruit juice enriched with the JS strain, and with few exceptions, it was not detected after the 2-week follow-up period.