# Exploring the Probiotic Potential of Dairy Industrial-Relevant Lactobacillus
## 4 Discussion  
This work aimed to investigate further beneficial properties of lactobacillus that are already commercialised and employed in the dairy sector. Specifically, we investigated the antimicrobial potential and the _in vitro_ probiotic properties of four strains belonging to two different LAB species to make them even more attractive and versatile both from  
Figure 4: Relative transcriptional level of TNF-\(\alpha\) (**A**) and IL-8 genes (**B**) in LPS-stimulated macrophages without or with pre-incubation with 5% CFS from _L. plantarum_ (PLA or PLA2), 10% CFS from _L. rhamnus_ (RHM or PAR4). Relative gene expression values were obtained by qRT-PCR after 3.5 h of LPS treatment. Relative mRNA level was obtained by normalising to the transcriptional level observed in unstimulated macrophages (gene expression = 1), and \(\beta\)-actin gene was used as an internal control: LPS-stimulated macrophages, LPS (positive control). Values represent the mean \(\pm\) SD of at least two different experiments. Statistical analyses were carried out by ANOVA test (\(p<0.05\)). the technological and functional points of view. Ideally, dietary probiotics should fulfil all those actions that can contribute to preserving the balance of the host gut microbiota and prevent dysbiosis [39]. The beneficial effects of probiotics, including lactobacilli, are strain-dependent and not universal; therefore, the investigation of the probiotic criteria is crucial to ascertain health-promoting potential and develop any probiotic product. With this regard, we started to analyse one of the main criteria to select potential probiotic microbes, namely their capability to survive the transit along the gastrointestinal tract, in order to reach and colonise the host intestine [20]. All the tested strains well tolerated the first two steps of the OGT, especially _L. plantarum_ PLA and PLA2, whose viability seemed not affected by exposure to oral stress; further, they did not show any significantly decreased viability to the first exposure to gastric conditions, compared to RHM and PAR4. The good survival of _L. plantarum_ under oral stress is in agreement with previous studies [40; 41]. Even for _L. rhamnusus_, the literature confirms its tolerance to stressors typical of the mouth when studied under similar simulated gastrointestinal condition [41; 42]. Persistent exposure to lower pH caused a drop in viability for all lactobacilli, although _L. plantarum_ strains, especially PLA2, were much more viable under intestinal conditions, which could be attributed to a higher resistance of this species to acids and bile, compared to the other lactobacilli. A major resistance of _L. plantarum_ with respect to _L. rhamnus_ is in accordance with past and recent works that compared probiotic strains' survival upon simulated gastric and intestinal digestion [43; 44]. The ability to produce riboflavin is a microbial feature of increasing interest for in situ nutritional status improvements. This phenotype, considered an emerging trait that can be profitably exploited in probiotic strains [45; 46], is associated with the capacity to grow in the absence of vitamin B2. A growth under such conditions was registered for all the tested strains, except for _L. rhamnus_ PAR4. This is in accordance with the literature, considering that riboflavin biosynthesis is known to be a strain-specific character within the two investigated species [45; 47; 48]. Considering the antibacterial potential, _L. plantarum_ PLA, along with _L. rhamnus_ PAR4, showed the strongest activity against all the tested harmful bacteria compared to _L. rhamnus_ RHM, which, on the contrary, exhibited strong antagonistic activity only against _E. coli_. The findings confirmed the generally good antimicrobial spectrum observed for _L. plantarum_ probiotic strains [49; 50; 51]. Notably, PLA and PAR4 strongly inhibited _S.