**5. Conclusions**

Results of our study show that among all analyzed probiotic bacteria from commercial preparations avaliable on Polish market, the Lb. plantarum was the most resistant to the applied conditions of the experiment. It showed a noticeable growth under both in vitro gastric conditions at pH 4.0 and 5.0, as well as in vitro intestinal conditions at all tested concentrations of bile salts. Interestingly, its preparations did not contain a prebiotic. In turn, preparation 2 (Bifidobacterium BB-12) contained FOS, which could affect its capability to grow under simulated conditions of the gastric passage (pH 4.0 and 5.0) and of the gastrointestinal passage at bile salts concentration of 10 gL−1. The remaining preparations (preparation 3 – Lb. casei and preparation 4 – Lb. acidophilus) contained inulin which, however, didn't influence their cell proliferation capability during incubation under experimental conditions.

No growth of the tested commercial probiotics under the assumed experimental conditions does not have to indicate their incapability for surviving the in vivo gastrointestinal passage. However, study results show clearly that the Lb. plantarum strain had the best capability for growth, which suggests it could proliferate in intestines also under in vivo conditions. It is a valuable piece of information, considering that exogenous probiotics share a limited capability for adhesion to cells of the intestinal epithelium and that their major part is excreted with feces.

**Author Contributions:** Conceptualization, L.S.-R. and A.B.-P.; funding acquisition, L.S.-R., A.B.-P., A.S.P. and M.G.; investigation, L.S.-R.; Methodology, L.S.-R. and A.B.-P.; statistical analysis, M.G.; result interpretations, L.S.-R., A.B.-P., A.S.P., K.D. and M.G.; Writing—Original draft, L.S.-R.; Writing— Review and editing, L.S.-R., A.B.-P., A.S.P., K.D. and M.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work had no financial support from any sponsors. This research did not receive any specific gran<sup>t</sup> from funding agencies in the public, commercial or not-for-profit sectors. Funds received to cover publication costs come from scientific institutions in which the authors work.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
