# Characterization and Selection of _Lactobacillus_ Strains with Potential Robotic Applications
## 3 Results and Discussion
### Antibiotic Susceptibility of Lactobacillus Strains  
Antibiotic resistance is accepted as a main characteristic of probiotic bacteria. Therefore, an important step in the design of successful technological schemes for manufacturing various probiotic products and functional foods is the selection of suitable _Lactobacillus_ strains that are resistant to the conventional antibiotics used in medical/clinical practice.  
The investigated _Lactobacillus_ strains were sensitive, moderately sensitive or resistant to the 23 antibiotics used in the study (Figure 6). The antibiotics used belonged to three main groups depending on their mechanism of action, namely inhibitors of the cell wall synthesis (bacitracin, piperacillin, penicillin, ampicillin, oxacillin, vancomycin, cefturoxime), inhibitors of the protein synthesis (tetracycline, doxycycline, gentamicin, amikacin, rifampin, limomycin, tobramycin, erythromycinycin, clarithromycin, chloramphenicol) and inhibitors of the DNA synthesis or cell division (novobiocin, ciprofloxacin, norfloxacin, levofloxacin, nalidixic acid, sulfamethoxazole/trimethoprim).  
According to data existing in the literature [49], Lactobacillus species are generally sensitive to inhibitors of protein synthesis (chloramphenicol, erythromycinycin, clindamycin, tetracycline and others) and resistant to the antibiotics belonging to the aminoglycos group, such as neomycin, kanamycin, streptomycin, gentamicin and others. However, our results were partially consistent with these findings because three of the strains (_L. casei_ ATCC 393, _L. casei_ RC-1 and _L. rhamnosus_ RC-10) were resistant to chloramphenicol; _L. casei_ ATCC 393 was resistant to erythromycinycin; _L. acidophilus_ RC-2 and _L. rhamnosus_ RC-10 were determined as moderately susceptible (SR) to tetracycline; and all of the studied strains were moderately susceptible to gentamicin.  
The degree of antibiotic susceptibility is a feature depending on the origin of the strains. [PERSON] and [PERSON] [50] examined the antibiotic susceptibility of 20 _Lactobacillus_ strains and stated that _L. rhamn_s B-8238 was resistant to vancomycin, amikacin, kanamycin, streptomycin and gentamicin. Similar results were reported by [PERSON] et al. [51], who investigated the probiotic potential of twelve _L. casei_ strains (SJRP38, SJRP39, SJRP48, SJRP135, SJRP136, SJRP143, SJRP144, SJRP147, SJRP148, SJRP150, SJRP151 and SJRP166) isolated from water buffalo mozzarella cheese, and determined that all of the strains were resistant to vancomycin and moderately susceptible to gentamicin. Ten of these isolates were resistant to kanamycin, while the other two were moderately susceptible to this antibiotic. The strain _L. rhamn_ isolated from commercial dietary supplements was resistant to erythromycincin and ceftazidime, while the strain _L. acidophilus_ (isolated from the same sources) was resistant only to ceftazidime out of the total of five antibiotics tested [52]. [PERSON] et al. [53] investigated the antibiotic susceptibility of 17 _L. casei_ isolates from fermented cow's and yak's milk from Tibet and stated the number of resistant strains as follows: all of these were resistant to vancomycin, 12 of these to chloramphenicol, 10 of these to streptomycin, 4 of these to kanamycin, 1 of these to neomycin and 1 of these to tetracycline.  
Figure 6: Heat map analysis of the antibiotic susceptibility of the _Lactobacillus_ strains. The different colors represent the diameter of the inhibition zones (IZs), with green indicating the absence or the smallest diameter (resistant), yellow indicating IZ = 7–16 mm (moderately resistant) and red indicating the largest IZ > 16 mm (sensitive).