# Characterization and Selection of _Lactobacillus_ Strains with Potential Robotic Applications
## 3 Results and Discussion
### Antimicrobial Activity of Lactobacillus Strains

Table 2: Survival rates of _Lactobacillus_ strains after exposure to different concentrations of bile salts at the 4 th, 8 th and 24 th hour of cultivation at 37 \({}^{\text{\,\The results obtained (Figure 5) demonstrated that the neutralized cell-free supernatant (NCFS) to pH = 7.0 in all of the tested _Lactobacillus_ strains completely lost its inhibitory effect, indicating that one of the reasons for their antimicrobial activity is the production of lactic acid in the culture medium. On the other hand, the highest lactic acid production was not always associated with the highest antimicrobial activity as in the case of _L. casei_ ATCC 393 (Figure 2A,B and Figure 5). Consequently, the antagonistic activity was also due to the presence of cell-associated components possessing an antimicrobial effect. [PERSON] et al. [37] investigated the antimicrobial activity of five _L. casei_ strains isolated from camel milk from Pakistan and determined that the strains inhibited the growth of the multidrug-resistant _E. coli_ AZ1 (diameter of IZ from 13.67 to 15.33 mm) and methicillin-resistant _S. aureus_ Saba-1 (IZ from 15 to 16.33 mm). [PERSON] et al. [42] investigated seven _Lactobacillus_ strains, namely _L. brevis_ (B2 and B3), _L. acidophilus_ (B14, B15 and B17), _L. plantarum_ (B20) and _L. casei_ (B22) isolated from Iranian cheese, as well as _L. rhamn_ GG as a reference strain. The authors reported that the neutral cell-free supernatant (NCFS) of the first seven strains inhibited the growth of test bacterial strains--_E. coli_, _S. aureus_, _P. aeruginosa_ and _Salmonella typhimurium_ at varying degrees. The strain _L. acidophilus_ B14 showed the highest inhibitory activity against the studied pathogens, with an IZ ranging from 14.6 to 23.2 mm, while the strain _L. casei_ B22 exhibited the lowest inhibitory activity, with an IZ ranging between 7.2 and 16.5 mm. [PERSON] et al. [43] studied the efficacy of cell-free supernatant (CFS) obtained from _L. acidophilus_ ATCC 314 and determined that the inhibitory activity of concentrated CFS (dialyzed with 5 M sucrose solution at 4 \({}^{\circ}\)C) was most pronounced against _S. aureus_ (IZ = 12.85 mm), followed by _E. coli_ (IZ = 8.15 mm), _A. niger_ (IZ = 6.98 mm) and _Aspergillus flavus_ (IZ = 5.6 mm). The untreated and precipitated (with 4 \({}^{\circ}\)C acetone) CFSs showed lower antimicrobial activity. Using the agar well diffusion assay, [PERSON] et al. [44] examined the antimicrobial activity of CFSs of _Lactobacillus_ strains isolated from traditional fermented dairy products and determined that _L. acidophilus_ (LAB  
Figure 5: Heat map analysis of the antimicrobial activity of the _Lactobacillus_ strains. The different colors represent the diameter of the inhibition zones (IZs), with green indicating the absence or the smallest diameter and red indicating the largest. The transition from green to red illustrates the increase in the diameter of the IZs. LC—whole _Lactobacillus_ culture; CB—cell biomass; CFS—cell-free supernatant; NCFS—neutralized cell-free supernatant. 2) and _L. rhamnosus_ (LAB 5) inhibited the growth of test bacteria _P. aeruginosa_ (IZs = 15.7 and 15.6 mm), _E. coli_ (IZs = 15.3 and 16.9 mm), _E. coli_ MC1400 (IZs = 14.5 and 15.5 mm), _S. aureus_ (IZs = 15.3 and 17.7 mm) and _Listeria Ivanovii_ (IZs = 11.3 and 12.4 mm). In contrast to our results regarding antifungal activity, the CFSs of the two strains exhibited inhibitory effect on the yeasts _C. albicans_ (IZs = 14.7 and 14.3 mm) and fungi _A. niger_, _A. flavus_, _A. Aspergillus fumigatus_ and _P. chrysogenum_. A study conducted by [PERSON] et al. [45] demonstrated that _L. rhamnosus_ ATCC 7469 effectively inhibited the growth of _E. faecalis_ ATCC 29212 and _C. albicans_ ATCC 10231 (used as experimental models of endodontic pathogens) as the tested strain exhibited IZs of 19.03-19.77 mm and 18.52-19.48 mm, respectively; these values were higher in comparison with the results for our _L. rhamnosus_ RC-10 strain.