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Most probiotic strains commercially available today are lactic acid bacteria. Within this functional group, Streptococcus thermophilus is a thermophilic species widely used as starter culture for a huge number of dairy products. Besides being rapid acidifiers, many S. thermophilus strains are able to produce and release folate during growth but, unfortunately, they are seriously impaired during passage through the human gastrointestinal tract. In this work, we studied eight S. thermophilus strains isolated from dairy environments in Italy, which already had shown good technological properties, to evaluate their possible probiotic potential and cytotoxicity against cancer cells in vitro. All strains were also evaluated for some health-related properties such as susceptibility to most common antibiotics, hemolytic activity, resistance to simulated gastrointestinal conditions, bile salts hydrolytic activity, production of folate, adhesion to HT-29 human colorectal adenocarcinoma cells and cytotoxic activity against cancer cells and production of biogenic amines. Results revealed that two fast acidifying S. thermophilus strains were found to possess in vitro probiotic properties along with anticancer activity and production of folate. These properties resulted similar and, in some cases, superior to those of Lactobacillus rhamnosus GG, a well-known commercial probiotic strain. These findings encourage further in vivo studies to evaluate the actual health benefits of these strains on the human host.

Streptococcus thermophilus is considered one of the most important species for the dairy industry. Due to their diffusion in dairy environments, bacteriophages can represent a threat to this widely used bacterial species. Despite the presence of a CRISPR-Cas system in the S. thermophilus genome, some lysogenic strains harbor cryptic prophages that can increase the phage-host resistance defense. This characteristic was identified in the dairy strain S. thermophilus M17PTZA496, which contains two integrated prophages 51.8 and 28.3 Kb long, respectively. In the present study, defense mechanisms, such as a lipoprotein-encoding gene and Siphovirus Gp157, the last associated to the presence of a noncoding viral DNA element, were identified in the prophage M17PTZA496 genome. The ability to overexpress genes involved in these defense mechanisms under specific stressful conditions, such as phage attack, has been demonstrated. Despite the addition of increasing amounts of Mitomycin C, M17PTZA496 was found to be non-inducible. However, the transcriptional activity of the phage terminase large subunit was detected in the presence of the antagonist phage vB_SthS-VA460 and of Mitomycin C. The discovery of an additional immune mechanism, associated with bacteriophage-insensitive strains, is of utmost importance, for technological applications and industrial processes. To our knowledge, this is the first study reporting the capability of a prophage integrated into the S. thermophilus genome expressing different phage defense mechanisms. Bacteriophages are widespread entities that constantly threaten starter cultures in the dairy industry. In cheese and yogurt manufacturing, the lysis of Streptococcus thermophilus cultures by viral attacks can lead to huge economic losses. Nowadays S. thermophilus is considered a well-stablished model organism for the study of natural adaptive immunity (CRISPR-Cas) against phage and plasmids, however, the identification of novel bacteriophage-resistance mechanisms, in this species, is strongly desirable. Here, we demonstrated that the presence of a non-inducible prophage confers phage-immunity to an S. thermophilus strain, by the presence of ltp and a viral noncoding region. S. thermophilus M17PTZA496 arises as an unconventional model to study phage resistance and potentially represents an alternative starter strain for dairy productions.

Streptococcus thermophilus is a species widely used in the dairy industry for its capability to rapidly ferment lactose and lower the pH. The capability to use galactose produced from lactose hydrolysis is strain dependent and most of commercial S. thermophilus strains are galactose-negative (Gal−), although galactose-positive (Gal+) would be more technologically advantageous because this feature could provide additional metabolic products and prevent galactose accumulation in foods. In this study, a next generation sequencing transcriptome approach was used to compare for the first time a Gal+ and a Gal− strain to characterize their whole metabolism and shed light on their different properties, metabolic performance and gene regulation. Transcriptome analysis revealed that all genes of the gal operon were expressed very differently in Gal+ and in the Gal− strains. The expression of several genes involved in mixed acid fermentation, PTS sugars transporter and stress response were found enhanced in Gal+. Conversely, genes related to amino acids, proteins metabolism and CRISPR associated proteins were under-expressed. In addition, the strains showed a diverse series of predicted genes controlled by the transcriptional factor catabolite control protein A (CcpA). Overall, transcriptomic analysis suggests that the Gal+ strain underwent a metabolic remodeling to cope with the changed environmental conditions.

Streptococcus thermophilus and S. macedonicus are the only two species of the genus related to food productions so far known. In the present study, eight S. thermophilus and seven S. macedonicus strains isolated from dairy environments in Italy were compared in order to evidence possible species-specific technological characteristics. Their capability to use lactose, galactose, fructose, and glucose, sugars commonly present in foods and two carbohydrates considered as prebiotics, xylose and inulin, along with the respective growth kinetics were studied. Results showed a luxuriant growth on lactose and different behaviors on galactose, glucose, and fructose. No growth on inulin and xylose was recorded, which is a positive feature for strains intended to be used as starter cultures. Growth parameters, namely, λ, µ, and N, were estimated by using the Gompertz model. Antibiotic resistance to 14 drugs revealed an overall similar behavior between the two species with only a marked difference regarding gentamycin. Antimicrobial activity was also tested against six deleterious bacterial strains, but none of the strains evidenced inhibitory capabilities. The results presented here could be helpful to compare technological potentialities of the two species and to choose strains of the most suitable species for selected microbiological food transformations.

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Aims: In-vitro/In-vivo evaluation of cholesterol-lowering probiotic strain Lactobacillus paracasei DTA81 and the possible connection with the gut microbiota modulation. Methods and Results: In the present study, strain DTA81 has been evaluated for the possible influence on blood lipid and glucose concentrations, modulation of the immune system, gastrointestinal survivability and modulation of gut microbiota in BALB/c mice receiving a high-fat diet. After 6 weeks of treatment, a significant reduction of total cholesterol and fasting blood sugar (FBS) among animals treated with L. paracasei DTA81 has been recorded. Comparison of colon tissue levels of different cytokines revealed a significant reduction of the inflammatory cytokine interleukin-6. The comparison of gut microbiota using the 16S rRNA approach indicated that the treatment with L. paracasei DTA81 significantly increased the taxa Bacteroidetes and Coprococcus. Moreover, the genome of DTA81 was sequenced for the insilico assessment, and the analysis indicated the presence of cholesterol assimilation-related genes as well as the absence of negative traits such as transmissible antibiotic resistance genes, plasmids and prophage regions. Conclusion:The outcome of this study revealed the in-vitro and in-vivo properties of L. paracasei DTA81 and the possible mechanism between consumption of this strain, the abundance of Bacteriodetes/Coprococcus taxa, immunomodulatory activity and the subsequent reduction of cholesterol/FBS in BALB/c mice. Significance and Impact of the Study: Lactobacillus paracasei DTA81 as a nonpharmacological potential probiotic supplement can influence metabolic homeostasis in individuals, particularly those adopting high-fat diets, and it can contribute to reduce coronary heart disease.

According to FAO and WHO, probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. Most probiotic bacteria used today belong to the genera Lactobacillus and Bifidobacterium and are of animal or human origin. The fundamental characteristic routinely evaluated in potential probiotics strains is their limited viability loss during gastrointestinal transit (GIT), but to date, no studies reported whether probiotics, besides viability, still also maintain their beneficial properties intact. To study this aspect, we considered two strains, Lactobacillus rhamnosus DTA 79 and L. paracasei DTA 83, previously characterised for the presence of some probiotic properties, isolated from faeces of 7-to 21day-old babies. Here, we examined some additional properties, namely antibiotic resistance, resistance to lysozyme, presence of haemolytic activity and inhibition of pathogen biofilm formation. We then tested the effect of in vitro GIT on all these features and our results show evidence that this procedure had in some cases limited and in others no significant effects on them. Additionally, we examined the gastrointestinal resistance of the strains after skim milk fermentation and successive storage of the product for 20 and 40 days at refrigeration temperature, to see whether prolonged storage could weaken cell resistance to GIT. Our results demonstrate that a protracted refrigeration period before in vitro GIT did not affect or influenced very weakly this essential probiotic property.