# Characterization and Selection of _Lactobacillus_ Strains with Potential Robotic Applications
## 3 Results and Discussion
### Resistance of Lactobacillus Strains to Bile Salts  
Similar to that through the stomach, the passage of probiotics through the small intestine can result in a significant decrease in viable cells due to the presence of bile acids, salts and pancreatic enzymes, while the neutral pH (6.1 to 7.8) does not possess an inhibitory effect. Bile acids (derivatives of cholic acid) attend in the dispersion and absorption of lipids, thus playing an important role in fat digestion and microbial ecology in humans' small and large intestines. It has been found that bile acids are secreted by the liver, whereas bile salts (bile acid conjugates with glycine or taurine) are produced in the duodenum [21; 32]. Although tolerance to intestinal juice is a strain-dependent property, it has been reported that lactobacillus can progressively adapt to the presence of bile salts and other components of the intestinal juice due to global cellular responses such as preservation of internal pH, cell membrane integrity, and activation of bile salt efflux pumps [33]. The results presented in Table 2 and Figure 4A-D showed that the survival rates of the _Lactobacillus_ strains decreased with increasing bile salt concentration and prolongation of the cultivation time. It is noteworthy that all of the strains retained their survival from 61.19% (_L. acidophilus_ RC-2) to 82.5% (_L. casei_ ATCC 393) at the highest bile salt concentration (1%) at the 4 th hour of incubation. All of the strains retained over 50% survival rates at the lowest bile salt concentration (0.25%) at the 24 th hour of cultivation. It should be noted here that the average concentration of bile salts in duodenal juice during the fasted state is up to 0.15 mM (approximately 0.6-0.7%) [34]. On the other hand, the time required for food to pass through the upper gastrointestinal tract (including small intestines--duodenum, jejunum and ileum) varies between 1.5 and 9 h, depending on the nature of the food [35]. Based on the results obtained and the above-mentioned physiological points, it can be concluded that the investigated strains possess probiotic potential. Figure 4: _Cont._  
As previously noted, the resistance of LAB to bile salts is a feature depending on the species, strain and even the experimental conditions. A study conducted by [PERSON] et al. [22] demonstrated that the viability of _L. casei_ SB71 reduced in the presence of 0.5% bile salts, compared to the control, whereas _L. casei_ SB73 and _L. casei_ SB93 at the same concentration remained unaffected (_L. casei_ SB93 exhibited 100% survival). In the presence of 1% bile salts, the authors observed a significant reduction in the survival rate of _L. casei_ SB73 compared to the control. Although _L. casei_ SB93 tolerated up to 1.8% bile, its survival was significantly reduced. [PERSON] et al. [36] observed an insignificant reduction in viable cells of the strains _L. casei_ BgShn3, _L. casei_ Dwan5, _L. casei_ MSJ1, _L. casei_ Masalam7, _L. acidophilus_ Hadhramaut4 and _L. acidophilus_ Musalam2 isolated from raw and fermented milk from Saudi Arabia after treatment with 0.5% bile for 4 h. The results showed that survival rates ranged between 97.4% and 99.3% for the _L. casei_ strains and between 90.7% and 99.45% for the _L. acidophilus_ strains; these values were higher in comparison with our results for the same hour of cultivation and the same bile salt concentration. [PERSON] et al. [37] investigated the probiotic properties of five _L. casei_ strains isolated from camel milk from Pakistan and determined that the strains tolerated a concentration of 1.5% bile salts (exposure of 5-7 h) with survival rates varying between 77.78% and 81.35%. The strain _L. acidophilus_ SAM1, isolated from human breast milk, showed a viability rate of 67.4% after 24 h of incubation  
Figure 4: Growth of _L. casei_ ATCC 393 (**A**), _L. casei_ RC-1 (**B**), _L. acidophilus_ RC-2 (**C**), _L.