Investigation of acid and bile tolerance of native lactobacilli isolated from fecal samples and commercial probiotics by growth and survival studies

This study aimed at applying both growth and survival approaches to compare three native strains of lactobacilli, belonging to Lactobacillus plantarum, Lactobacillus rhamnosus and Lactobacillus acidophilus species, with two commercial probiotic strains in their tolerance to acid and bile. The association between the data obtained from the methods was studied. The results of the different methods applied in this study, did not confirm each other for all the examined strains. However, the native strain of L. plantarum and the commercial strain of L. acidophilus repeatedly demonstrated the most and least bile resistances, respectively. The former excelled in all growth approaches but showed moderate acid resistance in the survival studies. Bile stress seemed to have more detrimental effects on all examined strains. The overall results suggest that the growth-rate designed studies and survival studies evaluating transit tolerance, might bring up different results when the examined strains belong to different species of lactobacilli showing different growth and metabolic activities. The strain of L. plantarum examined here could thus be considered as a potential probiotic, regarding its overall resistance to acid and bile

Identification of lactobacilli from fecal flora of some Iranian infants

During the past 20 years identification of lactobacilli isolated from normal flora has received great interest due to their health promoting effects. This study has aimed at characterizing the lactobacillus strains isolated from the fecal flora of Iranian infants based on phenotypic oriented methods. Moreover, the diversity of identified species among tested infants has been looked into. Thirty two strains of lactobacilli were included in this study. The given strains were previously isolated from the fecal samples of 6 infants between 1-19 months of age. They are examined through 14 carbohydrate fermentation tests, growth ability at different temperatures and different concentrations of NaCl. Cell and colony morphology were assessed as well. The examined strains were identified as L. acidophilus [12 strains], L. plantarum [9 strains], L. rhamnosus [7 strains], L. paracasei [3 strains] and L. fermentum [1 strain]; 2 strains remained unidentified. Accordingly L. acidophiluswas the most predominant species among tested samples. Some biochemical differences were obtained among the strains of L. acidophilus group and some morphological peculiarities were observed among the strains of L. paracasei and L. rhamnosus in comparison to the typical strains of L. casei group. These differences revealed the necessity of application of complementary molecular methods for clear identification of examined Lactobacillus strains