First Insight into the Probiotic Properties of Ten Streptococcus thermophilus Strains Based on In Vitro Conditions

Identification of novel probiotic lactic acid bacteria from soymilk waste using the 16s rRNA gene for potential use in poultry

Background and Aim

In-feed antibiotics have been used as antibiotic growth promoters (AGPs) to enhance the genetic potential of poultry. However, the long-term use of AGPs is known to lead to bacterial resistance and antibiotic residues in poultry meat and eggs. To address these concerns, alternatives to AGPs are needed, one of which is probiotics, which can promote the health of livestock without having any negative effects. In vitro probiotic screening was performed to determine the ability of lactic acid bacteria (LAB) isolated from soymilk waste to be used as a probiotic for livestock.

Materials and Methods

Four LAB isolates (designated F4, F6, F9, and F11) isolated from soymilk waste were used in this study. In vitro testing was performed on LAB isolates to determine their resistance to temperatures of 42°C, acidic pH, bile salts, hydrophobicity to the intestine, and ability to inhibit pathogenic bacteria. A promising isolate was identified using the 16S rRNA gene.

Result

All LAB isolates used in this study have the potential to be used as probiotics. On the basis of the results of in vitro testing, all isolates showed resistance to temperatures of 42°C and low pH (2.5) for 3 h (79.87%-94.44%) and 6 h (76.29%-83.39%), respectively. The survival rate at a bile salt concentration of 0.3% ranged from 73.24% to 90.39%, whereas the survival rate at a bile salt concentration of 0.5% ranged from 56.28% to 81.96%. All isolates showed the ability to attach and colonize the digestive tract with a hydrophobicity of 87.58%-91.88%. Inhibitory zones of LAB against pathogens ranged from 4.80-15.15 mm against Staphylococcus aureus, 8.85-14.50 mm against Salmonella enteritidis, and 6.75-22.25 mm against Escherichia coli. Although all isolates showed good ability as probiotics, isolate F4 showed the best probiotic ability. This isolate was identified as Lactobacillus casei strain T22 (JQ412731.1) using the 16S rRNA gene.

Conclusion

All isolates in this study have the potential to be used as probiotics. However, isolate F4 has the best probiotic properties and is considered to be the most promising novel probiotic for poultry.

Unveiling the Probiotic Potential of Streptococcus thermophilus MCC0200: Insights from In Vitro Studies Corroborated with Genome Analysis

Streptococcus thermophilus is widely used as a starter culture in the dairy industry and has garnered attention as a beneficial bacterium owing to its health-promoting functionalities in humans. In this study, the probiotic potential of S. thermophilus MCC0200 isolated from a dairy product was investigated through a combinatorial approach of in vitro and in silico studies. MCC0200 demonstrated the ability to survive harsh gastrointestinal (GI) transit, adhere to intestinal mucosa and exert health-promoting traits in in vitro studies. These findings were corroborated with in silico evidence, wherein, MCC0200 genome harboured genes associated with tolerance to GI conditions, intestinal adhesion and colonization. Genome mapping also highlighted the ability of MCC0200 to produce compounds advantageous for the host (folate, bacteriocins), to release antioxidant enzymes that can quench the free radicals (superoxide dismutase, NADH peroxidase), and to metabolize food components that can be harmful to sensitive people (lactose). MCC0200 also demonstrated a positive effect on reducing cholesterol levels, proving to be a potential candidate for food and pharmaceutical applications. The absence of transmissible antibiotic resistance genes and virulence genes underscored the generally regarded as safe (GRAS) nature of MCC0200. This study explored the potential of Streptococcus thermophilus for its probable applications as a probiotic beyond the dairy industry.

Enhanced electric field and charge polarity modulate the microencapsulation and stability of electrosprayed probiotic cells (Streptococcus thermophilus, ST44)

The effect of the polarity of the direct current electric field on the "organization" of Streptococcus thermophilus (ST44) probiotic cells within electrosprayed maltodextrin microcapsules was investigated. The generated electrostatic forces between the negatively surface-charged probiotic cells and the applied negative polarity on the electrospray nozzle, allowed to control the location of the cells towards the core of the electrosprayed microcapsules. This "organization" of the cells increased the evaporation of the solvent (water) and successively the glass transition temperature (Tg) of the electrosprayed microcapsules. Moreover, the utilization of auxiliary ring-shaped electrodes between the nozzle and the collector, enhanced the electric field strength and contributed further to the increase of the Tg. Numerical simulation, through Finite Element Method (FEM), shed light to the effects of the additional ring-electrode on the electric field strength, potential distribution, and controlled deposition of the capsules on the collector. Furthermore, when the cells were located at the core of the microcapsules their viability was significantly improved for up to 2 weeks of storage at 25 °C and 35% RH, compared to the case where the probiotics were distributed towards the surface. Overall, this study reports a method to manipulate the encapsulation of the surface charged probiotic cells within electrosprayed microcapsules, utilizing the polarity of the electric field and additional ring-electrodes.

Attributes of Culture Bacteria as Influenced by Ingredients That Help Treat Leaky Gut

Consumers are becoming aware of functional ingredients such as medicinal herbs, polyphenols, mushrooms, amino acids, proteins, and probiotics more than ever before. Like yogurt and its probiotics, L-glutamine, quercetin, slippery elm bark, marshmallow root, N-acetyl-D-glucosamine, licorice root, maitake mushrooms, and zinc orotate have demonstrated health benefits through gut microbiota. The impact of these ingredients on yogurt starter culture bacteria characteristics is not well known. The objective of this study was to determine the influence of these ingredients on the probiotic characteristics, tolerance to gastric juices and lysozyme, protease activity, and viability of Streptococcus thermophilus STI-06 and Lactobacillus bulgaricus LB-12. Acid tolerance was determined at 0, 30, 60, 90, and 120 min of incubation, whereas bile tolerance was analyzed at 0, 4, and 8 h. The microbial growth was determined at 0, 2, 4, 6, 8, 10, 12, 14, and 16 h of incubation, while protease activity was evaluated at 0, 12, and 24 h. The application of marshmallow root, licorice root, and slippery elm bark improved bile tolerance and acid tolerance of S. thermophilus. These ingredients did not impact the bile tolerance, acid tolerance, and simulated gastric juice tolerance characteristics of L. bulgaricus over 8 h and 120 min (respectively) of incubation. Similarly, the growth of S. thermophilus and L. bulgaricus was not affected by any of these functional ingredients. The application of marshmallow root, N-acetyl-D-glucosamine, and maitake mushroom significantly increased the protease activity of S. thermophilus, whereas the protease activity of L. bulgaricus was not affected by any ingredient. Compared to the control, marshmallow root and quercetin samples had higher mean log counts and log counts for S. thermophilus on the simulated gastric juice and lysozyme resistance in vitro test, respectively. For L. bulgaricus, licorice root, quercetin, marshmallow root, and slippery elm bark samples had higher log counts than the control samples.

Effect of Cellulose–Chitosan Hybrid-Based Encapsulation on the Viability and Stability of Probiotics under Simulated Gastric Transit and in Kefir

Encapsulation comprises a promising potential for the targeted delivery of entrapped sensitive agents into the food system. A unique combination of cellulose/chitosan (Cl-Ch)-based hybrid wall material was employed to encapsulate L. plantarum by emulsion technique. The developed beads were further subjected to morphological and in vitro studies. The viability of free and encapsulated probiotics was also evaluated in kefir during storage. The developed beads presented porous spherical structures with a rough surface. A 1.58 ± 0.02 log CFU/mL, 1.26 ± 0.01 log CFU/mL, and 1.82 ± 0.01 log CFU/mL reduction were noticed for Cl-Ch hybrid cells under simulated gastro-intestinal and thermal conditions, respectively. The encapsulated cells were found to be acidic and thermally resistant compared to the free cells. Similarly, encapsulated probiotics showed better viability in kefir at the end of the storage period compared to free cells. In short, the newly developed Cl-Ch hybrid-based encapsulation has a promising potential for the targeted delivery of probiotics, as career agents, in gastric transit, and in foods.

Identification, Biochemical Characterization, and Safety Attributes of Locally Isolated Lactobacillus fermentum from Bubalus bubalis (buffalo) Milk as a Probiotic

The demand of functional foods is on the rise, and researchers are trying to develop nutritious dairy products by using well-characterized strains of bacteria. In this study, we identified locally isolated strains of Lactobacillus fermentum from Bubalus bubalis (Nilli Ravi buffalo) milk and evaluated their potential as probiotics in food products like fermented milk. Fifteen Lactobacillus strains were initially isolated, and only four strains (NMCC-2, NMCC-14, NMCC-17, and NMCC-27) were examined for morphological and biochemical characterizations due to their ability of gas production in Durham tubes. Moreover, these strains were selected for further probiotic characterizations due to their extreme morphological resemblance with lactic acid bacteria for their antimicrobial activity, enzymatic potential, autoaggregation capability, hydrophobicity, and acid and bile tolerance. All selected isolates showed significant probiotic potential. However, NMCC-14 and NMCC-17 strains showed maximum probiotic potential. The isolates (NMCC-2, NMCC-14, NMCC-17, and NMCC-27) were identified as Lactobacillus fermentum utilizing 16S rRNA gene sequencing. The in vivo safety study of NMCC-14 (dose: 1010 CFU/day/mice; 21 days, orally) showed no histological dysfunctions in a mouse model. Pathogenic bacterial enzymes reduced the beneficial bacterial load in the host gastrointestinal tract. These results suggest that the NMCC-14 strain is safe and can be potentially used as a probiotic. Moreover, fermented milk was prepared by using the NMCC-14 strain. The results revealed that NMCC-14 strain-based fermented milk had significantly (p < 0.05) higher protein content (4.4 ± 0.06), water-holding capacity (WHC), and dynamic viscosity as compared to non-fermented milk. The results suggest that L. fermentum NMCC-14 is safe and nontoxic; hence, it can be a beneficial supplement to be used for the development of dairy products to be subjected to further clinical testing.

Site-directed mutation of β-galactosidase from Streptococcus thermophilus for galactooligosaccharide-enriched yogurt making

β-Galactosidase is one of the most important enzymes used in dairy processing. It converts lactose into glucose and galactose, and also catalyzes galactose to form galactooligosaccharides (GOS), so-called prebiotics. However, most of the β-galactosidases from the starter cultures have low transgalactosylation activities, the process that results in galactose accumulation in yogurt. Here, a site-directed mutation strategy was attempted, to genetically modify β-galactosidase from Streptococcus thermophilus. Out of 28 Strep. thermophilus strains, a β-galactosidase gene named bgaQ, encoded for high β-galactosidase hydrolysis activity (BgaQ), was cloned from the strain Strep. thermophilus SDMCC050237. It was 3,081 bp in size, with 1,027 deduced amino acid residuals, which belonged to the GH2 family. After replacing the Tyr⁸⁰¹ and Pro⁸⁰² around the active sites of BgaQ with His⁸⁰¹ and Gly⁸⁰², the GOS synthesis of the generated mutant protein BgaQ-8012 increased from 20.5% to 26.7% at 5% lactose, and no hydrolysis activity altered obviously. Subsequently, the purified BgaQ or BgaQ-8012 was added to sterilized milk inoculated with 2 starters from Strep. thermophilus SDMCC050237 and Lactobacillus delbrueckii ssp. bulgaricus ATCC11842. The GOS yields with added BgaQ or BgaQ-8012 rose to 5.8 and 8.3 g/L, respectively, compared with a yield of 3.7 g/L without enzymes added. Meanwhile, the addition of the BgaQ or BgaQ-8012 reduced the lactose content by 49.3% and 54.4% in the fermented yogurt and shortened the curd time. Therefore, this study provided a site-directed mutation strategy for improvement of the transgalactosylation activity of β-galactosidase from Strep. thermophilus for GOS-enriched yogurt making.

Identification of isolated or mixed strains from long reads: a challenge met on Streptococcus thermophilus using a MinION sequencer

This study aimed to provide efficient recognition of bacterial strains on personal computers from MinION (Nanopore) long read data. Thanks to the fall in sequencing costs, the identification of bacteria can now proceed by whole genome sequencing. MinION is a fast, but highly error-prone sequencing device and it is a challenge to successfully identify the strain content of unknown simple or complex microbial samples. It is heavily constrained by memory management and fast access to the read and genome fragments. Our strategy involves three steps: indexing of known genomic sequences for a given or several bacterial species; a request process to assign a read to a strain by matching it to the closest reference genomes; and a final step looking for a minimum set of strains that best explains the observed reads. We have applied our method, called ORI, on 77 strains of Streptococcus thermophilus. We worked on several genomic distances and obtained a detailed classification of the strains, together with a criterion that allows merging of what we termed 'sibling' strains, only separated by a few mutations. Overall, isolated strains can be safely recognized from MinION data. For mixtures of several non-sibling strains, results depend on strain abundance.

Protective Effect of Fermented Camel Milk Containing Bifidobacterium longum BB536 on Blood Lipid Profile in Hypercholesterolemic Rats

The present study aimed to investigate synergistic health effects of camel milk and Bif. longum BB536 in rats with diet-induced obesity, impaired lipid profile, and hypercholesterolemia. Wistar rats received a high-fat (HF) diet plus 2 ml/day of either cow's milk fermented with yogurt culture (CT), camel milk fermented with yogurt culture (CAT), camel milk fermented with Bif. longum BB536 (CAP), mixed cow's and camel milk fermented with yogurt culture (CCAT), or cow's milk and camel milk fermented with Bif. longum (CCAP). All fermented milk products significantly reduced HDL, albumin, and total protein. The percentage change in body weight gain was between −40% (CAP) and −24% (CT) and in serum triglycerides between −54% (CCAP) and −37% (CT); for the other parameters, changes caused by CCAP/CT were −40%/−22% (total cholesterol), +29%/+8% (HDL), −73%/−54% (LDL), −54%/−37% (VLDL), −52%/−14% (AST), −53%/−31% (ALT), +43%/+25% (albumin), +37%/+25% (total protein), −48%/−27% (urea), and −34%/−16% (creatinine). Camel or cow's milk fermented with yogurt culture or Bif. longum significantly improved negative effects of the HF diet on body weight, blood lipid profile, serum proteins, liver and kidney markers, and severity of the metabolic syndrome. Milk and fermentation culture acted synergistically with camel milk and Bif. longum generally showed stronger positive effects./

Identification of Streptococcus thermophilus Genes Specifically Expressed under Simulated Human Digestive Conditions Using R-IVET Technology

Despite promising health effects, the probiotic status of Streptococcus thermophilus, a lactic acid bacterium widely used in dairy industry, requires further documentation of its physiological status during human gastrointestinal passage. This study aimed to apply recombinant-based in vivo technology (R-IVET) to identify genes triggered in a S. thermophilus LMD-9 reference strain under simulated digestive conditions. First, the R-IVET chromosomal cassette and plasmid genomic library were designed to positively select activated genes. Second, recombinant clones were introduced into complementary models mimicking the human gut, the Netherlands Organization for Applied Scientific Research (TNO) gastrointestinal model imitating the human stomach and small intestine, the Caco-2 TC7 cell line as a model of intestinal epithelium, and anaerobic batch cultures of human feces as a colon model. All inserts of activated clones displayed a promoter activity that differed from one digestive condition to another. Our results also showed that S. thermophilus adapted its metabolism to stressful conditions found in the gastric and colonic competitive environment and modified its surface proteins during adhesion to Caco-2 TC7 cells. Activated genes were investigated in a collection of S. thermophilus strains showing various resistance levels to gastrointestinal stresses, a first stage in the identification of gut resistance markers and a key step in probiotic selection.

Genomic and in vitro properties of the dairy Streptococcus thermophilus SMQ-301 strain against selected pathogens

Cumulative studies have suggested that probiotic bacterial strains could be an effective alternative in inhibiting conditions caused by foodborne and vaginal pathogens. The use of genomic techniques is becoming highly useful in understanding the potential of these beneficial microorganisms. This study presents some genomic and in vitro properties of the Streptococcus thermophilus SMQ-301 strain against foodborne and vaginal pathogens (Staphylococcus aureus, Escherichia coli, and Gardnerella vaginalis) to validate its use in dairy food formulations. Genomic analyses include bacteriocin production, stress response systems, antioxidant capability, and RAST-based functional annotation. In vitro investigations focused on the antimicrobial effects of the S. thermophilus SMQ-301 cell-free solution (CFS) against the selected pathogens after enzymatic actions and pH treatments, assessment of cytotoxic effects using murine RAW264.7 cells, and assessment of organic acid production levels using supplementary carbon sources. The results show that the S. thermophilus SMQ-301 genome possesses essential pathways for stress management, antioxidant activities, and bacteriocin production. For the first time, the bacteriocin-producing peptides of S. thermophilus SMQ-301 are reported, which gives an insight into its inhibitory potential. In vitro, the CFS of S. thermophilus SMQ-301 had significant (P < 0.05) antimicrobial effects on the selected pathogens, with S. aureus ATCC25923 being the most resistant. All antimicrobial activities of the CFS against the selected pathogens were eliminated at pH 6.5 and 7.0. S. thermophilus SMQ-301 CFS yielded the highest lactic (25.58 ± 0.24 mg mL-1) and acetic (5.53 ± 0.12 mg mL-1) acid production levels, with 1% fructooligosaccharide (P < 0.05). The S. thermophilus SMQ-301 strain also lowered murine RAW264.7 cell activities from 101.77% (control) to 80.16% (T5 - RAW264.7 cells + 1 × 109 CFU mL-1 cells) (P < 0.05). This study showed that although the S. thermophilus SMQ-301 strain had excellent genomic characteristics, the in vitro effects varied markedly against all three pathogens. In all, the S. thermophilus SMQ-301 strain has promising applications as a potential probiotic in the food and allied industries.

Regulation of c-di-GMP in Biofilm Formation of Klebsiella pneumoniae in Response to Antibiotics and Probiotic Supernatant in a Chemostat System

The resistance of bacteria to antibiotics is a major public health issue. Klebsiella pneumoniae is a type exemplification of multi-resistant enterobacteria. Its high biofilm forming capacity is a major factor in the recurrent infection of the intestinal tract. In this study, the intrinsic mechanism of secondary growth of K. pneumoniae in response to antibiotics and the inhibition effect of probiotic supernatant on biofilm formation after antibiotic treatment were investigated in a polyester nonwoven chemostat bioreactor. The experimental results showed that the c-di-GMP content in the cells increased after treatment with levofloxacin, leading to the formation of a thick biofilm due to an increase in the production of extracellular polymer substance (EPS) and type 3 fimbriae. Biofilm prevents the mass transfer of levofloxacin and protects K. pneumoniae cells from being killed by levofloxacin. Under suitable conditions, K. pneumoniae cells on the biofilm enter into the suspension for secondary growth. Moreover, the inhibition of probiotic supernatant on the biofilm formation was mainly due to the reduced expression of yfiN and mrkJ genes, and the decreased concentration of c-di-GMP in cells, as well as the less secretion of EPS. At the same time, the decrease in the concentration of c-di-GMP also reduced the expression of the mrkABCDF gene and prevented the synthesis of the type 3 fimbriae. The results would help to understand the mechanism of antibiotic resistance of pathogenic bacteria and to provide evidence to address this problem through the use of probiotics.

Draft Genome Sequence of Streptococcus thermophilus Strain CBC-S77, Isolated from Homemade Dairy Foods in Bulgaria

Here, we report the draft genome sequence of Streptococcus thermophilus strain CBC-S77. The strain was originally isolated from naturally processed, homemade dairy foods in West Rhode Mountain, Bulgaria. The genome was assembled in 148 contigs with a total length of 1,707,130 bp, with 1,563 coding genes and a GC content of 39.11%.

Here, we report the draft genome sequence of Streptococcus thermophilus strain CBC-S77. The strain was originally isolated from naturally processed, homemade dairy foods in West Rhode Mountain, Bulgaria. The genome was assembled in 148 contigs with a total length of 1,707,130 bp, with 1,563 coding genes and a GC content of 39.11%.