Evidence on the role of protein biosynthesis in the induction of heat tolerance of Lactobacillus rhamnosus GG by pressure pre-treatment

Biomaterials and Encapsulation Techniques for Probiotics: Current Status and Future Prospects in Biomedical Applications

Probiotics have garnered significant attention in recent years due to their potential advantages in diverse biomedical applications, such as acting as antimicrobial agents, aiding in tissue repair, and treating diseases. These live bacteria must exist in appropriate quantities and precise locations to exert beneficial effects. However, their viability and activity can be significantly impacted by the surrounding tissue, posing a challenge to maintain their stability in the target location for an extended duration. To counter this, researchers have formulated various strategies that enhance the activity and stability of probiotics by encapsulating them within biomaterials. This approach enables site-specific release, overcoming technical impediments encountered during the processing and application of probiotics. A range of materials can be utilized for encapsulating probiotics, and several methods can be employed for this encapsulation process. This article reviews the recent advancements in probiotics encapsulated within biomaterials, examining the materials, methods, and effects of encapsulation. It also provides an overview of the hurdles faced by currently available biomaterial-based probiotic capsules and suggests potential future research directions in this field. Despite the progress achieved to date, numerous challenges persist, such as the necessity for developing efficient, reproducible encapsulation methods that maintain the viability and activity of probiotics. Furthermore, there is a need to design more robust and targeted delivery vehicles.

Fabrication and characterization of bioprints with Lactobacillus crispatus for vaginal application

Bacterial vaginosis (BV) is characterized by low levels of lactobacilli and overgrowth of potential pathogens in the female genital tract. Current antibiotic treatments often fail to treat BV in a sustained manner, and > 50% of women experience recurrence within 6 months post-treatment. Recently, lactobacilli have shown promise for acting as probiotics by offering health benefits in BV. However, as with other active agents, probiotics often require intensive administration schedules incurring difficult user adherence. Three-dimensional (3D)-bioprinting enables fabrication of well-defined architectures with tunable release of active agents, including live mammalian cells, offering the potential for long-acting probiotic delivery. One promising bioink, gelatin alginate has been previously shown to provide structural stability, host compatibility, viable probiotic incorporation, and cellular nutrient diffusion. This study formulates and characterizes 3D-bioprinted Lactobacillus crispatus-containing gelatin alginate scaffolds for gynecologic applications. Different weight to volume (w/v) ratios of gelatin alginate were bioprinted to determine formulations with highest printing resolution, and different crosslinking reagents were evaluated for effect on scaffold integrity via mass loss and swelling measurements. Post-print viability, sustained-release, and vaginal keratinocyte cytotoxicity assays were conducted. A 10:2 (w/v) gelatin alginate formulation was selected based on line continuity and resolution, while degradation and swelling experiments demonstrated greatest structural stability with dual genipin and calcium crosslinking, showing minimal mass loss and swelling over 28 days. 3D-bioprinted L. crispatus-containing scaffolds demonstrated sustained release and proliferation of live bacteria over 28 days, without impacting viability of vaginal epithelial cells. This study provides in vitro evidence for 3D-bioprinted scaffolds as a novel strategy to sustain probiotic delivery with the ultimate goal of restoring vaginal lactobacilli following microbiological disturbances.

Bacterial survival and adhesion for formulating new oral probiotic foods

Probiotics are defined as live microorganisms, which, when administered in adequate amounts, confer health benefits to the host. Traditionally, probiotic food research has heavily focused on the genera Bifidobacteria and Lactobacilli, along with their benefits for gut health. Recently with the identification of new probiotic strains specifically intended for oral health applications, the development of probiotic foods for oral health benefits has garnered interest, with a renewed focus on identifying new food formats for delivering probiotics. The development of novel oral probiotic foods is highly complex, as the composition of a food matrix dictates: (1) bacterial viability during production and shelf life and (2) how bacteria partition with components within a food matrix and subsequently adhere to oral cavity surfaces. At present, virtually no information is available on oral probiotic strains such as Streptococcus salivarius; specifically, how orally-derived strains survive under different food parameters. Furthermore, limited information exists on the partition behavior of probiotics with food components, governed by physico-chemical interactions and adhesion phenomena. This review aspires to examine this framework by providing a foundation with existing literature related to the common probiotic genera, in order to inform and drive future attempts of designing new oral probiotic food formats.

Probiotics in Food Systems: Significance and Emerging Strategies Towards Improved Viability and Delivery of Enhanced Beneficial Value

Preserving the efficacy of probiotic bacteria exhibits paramount challenges that need to be addressed during the development of functional food products. Several factors have been claimed to be responsible for reducing the viability of probiotics including matrix acidity, level of oxygen in products, presence of other lactic acid bacteria, and sensitivity to metabolites produced by other competing bacteria. Several approaches are undertaken to improve and sustain microbial cell viability, like strain selection, immobilization technologies, synbiotics development etc. Among them, cell immobilization in various carriers, including composite carrier matrix systems has recently attracted interest targeting to protect probiotics from different types of environmental stress (e.g., pH and heat treatments). Likewise, to successfully deliver the probiotics in the large intestine, cells must survive food processing and storage, and withstand the stress conditions encountered in the upper gastrointestinal tract. Hence, the appropriate selection of probiotics and their effective delivery remains a technological challenge with special focus on sustaining the viability of the probiotic culture in the formulated product. Development of synbiotic combinations exhibits another approach of functional food to stimulate the growth of probiotics. The aim of the current review is to summarize the strategies and the novel techniques adopted to enhance the viability of probiotics.

In vitro characterisation of two Lactobacillus strains and evaluation of their suitability as probiotics for growing-finishing pigs

In this study, we evaluated the probiotic properties of two strains Lactobacillus reuteri ZLR003 and Lactobacillus salivarius ZLS006. The two strains displayed tolerance of acid and heat, and demonstrated antimicrobial ability in vitro. Furthermore, their potential functions in vivo were also tested. A total of 120 crossbred (Landrace × Large White) growing pigs were divided into three groups: a control diet, the same diet supplemented with L. reuteri ZLR003 (2.0 × 109 cfu/kg of diet) or L. salivarius ZLS006 (3.50 × 109 cfu/kg of diet). The results showed that the average daily gain and feed conversion ratio were significantly improved in L. reuteri ZLR003- (1–5 weeks and 1–9 weeks) (P < 0.05) and L. salivarius ZLS006-treated pigs (1–5 weeks, 6–9 weeks and 1–9 weeks) (P < 0.05) compared with the control group. Dietary supplementation with L. salivarius ZLS006 increased the apparent digestibility of nitrogen at Week 9 (P < 0.05). The faecal Lactobacillus populations increased at the end of experiment, and the Escherichia coli and Staphylococcus aureus in faeces decreased in the two Lactobacillus treatments compared with the control at Week 5 (P < 0.05) and Week 9 (P < 0.05), respectively. Furthermore, the total cholesterol, alanine transferase, aspartate transferase, blood urea nitrogen and haptoglobin levels in serum were significantly decreased following L. reuteri ZLR003 and L. salivarius ZLS006 treatments (P < 0.05). In conclusion, these data suggest that the two Lactobacillus strains may be promising candidates for probiotic products in growing-finishing pigs.

Adaptation of Saccharomyces cerevisiae to high pressure (15, 25 and 35 MPa) to enhance the production of bioethanol

Saccharomyces cerevisiae is a yeast of great importance in many industries and it has been frequently used to produce food products and beverages. More recently, other uses have also been described for this microorganism, such as the production of bioethanol, as a clean, renewable and sustainable alternative fuel. High pressure processing (HPP) is a technology that has attracted a lot of interest and is increasingly being used in the food industry as a non-thermal method of food processing. However, other applications of high pressure (HP) are being studied with this technology in different areas, for example, for fermentation processes, because microbial cells can resist to pressure sub-lethal levels, due to the development of different adaptation mechanisms. The present work intended to study the adaptation of S. cerevisiae to high pressure, using consecutive cycles of fermentation under pressure (at sub-lethal levels), in an attempt to enhance the production of bioethanol. In this context, three pressure levels (15, 25 and 35 MPa) were tested, with each of them showing different effects on S. cerevisiae fermentation behavior. After each cycle at 15 and 25 MPa, both cell growth and ethanol production showed a tendency to increase, suggesting the adaptation of S. cerevisiae to these pressure levels. In fact, at the end of the 4th cycle, the ethanol production was higher under pressure than at atmospheric pressure (0.1 MPa) (8.75 g.L^-1 and 10.69 g.L^-1 at 15 and 25 MPa, respectively, compared to 8.02 g.L^-1 at atmospheric pressure). However, when the pressure was increased to 35 MPa, cell growth and bioethanol production decreased, with minimal production after the 4 consecutive fermentation cycles. In general, the results of this work suggest that consecutive cycles of fermentation under sub-lethal pressure conditions (15 and 25 MPa) can stimulate adaptation to pressure and improve the bioethanol production capacity by S. cerevisiae; hence, this technology can be used to increase rates, yields and productivities of alcoholic fermentation.

Biofilm-like Lactobacillus rhamnosus probiotics encapsulated in alginate and carrageenan microcapsules exhibiting enhanced thermotolerance and freeze-drying resistance

Microcapsules containing high-density biofilm-like Lactobacillus rhamnosus probiotics, in place of planktonic cells, are developed in order to enhance the cell viability upon exposures to stresses commonly encountered during food lifecycle (i.e., heating, freeze-drying, refrigerated storage, and acid). The high-density (HD) capsules are prepared by in situ cultivation of the planktonic cells in the confined space of polysaccharide-based capsules (i.e., chitosan-coated alginate and carrageenan capsules). Compared to their planktonic counterparts, the HD capsules exhibit higher freeze-drying resistance (~40×) and higher thermotolerance upon prolonged wet heat exposures at 60 and 70 °C (~12-8000×), but not at higher temperatures even for short exposures (i.e., 80 and 100 °C). The enhanced viability of the HD capsules, however, is not observed during the refrigerated storage and exposure to the simulated gastric juice. The alginate capsules are superior to carrageenan owed to their better cell release profile in the simulated intestinal juice and storage viability.

Microorganisms under high pressure--adaptation, growth and biotechnological potential

Hydrostatic pressure is a well-known physical parameter which is now considered an important variable of life, since organisms have the ability to adapt to pressure changes, by the development of resistance against this variable. In the past decades a huge interest in high hydrostatic pressure (HHP) technology is increasingly emerging among food and biosciences researchers. Microbial specific stress responses to HHP are currently being investigated, through the evaluation of pressure effects on biomolecules, cell structure, metabolic behavior, growth and viability. The knowledge development in this field allows a better comprehension of pressure resistance mechanisms acquired at sub-lethal pressures. In addition, new applications of HHP could arise from these studies, particularly in what concerns to biotechnology. For instance, the modulation of microbial metabolic pathways, as a response to different pressure conditions, may lead to the production of novel compounds with potential biotechnological and industrial applications. Considering pressure as an extreme life condition, this review intends to present the main findings so far reported in the scientific literature, focusing on microorganisms with the ability to withstand and to grow in high pressure conditions, whether they have innated or acquired resistance, and show the potential of the application of HHP technology for microbial biotechnology.

Assessment of the effect of stress-tolerance acquisition on some basic characteristics of specific probiotics

The production of viable functional probiotics presupposes stability of strain features in the final product. We evaluated the impact of acquisition of heat-tolerance and subsequent freeze-drying on the adhesion properties of Lactobacillus rhamnosus GG, Lactobacillus casei Shirota, Bifidobacterium lactis Bb-12 and Bifidobacterium animalis IF20/1 and on their ability to inhibit the adhesion of pathogens in a mucus model. Both fresh and freeze-dried cultures were evaluated. Significant differences were observed between fresh, freeze dried, fresh heat-tolerant and freeze dried heat-tolerant strains, especially in the ability of the freeze dried probiotics to exclude, displace or outcompete pathogens. Based on our study characterizing probiotic properties such as adhesion and competitive exclusion, it seems possible to adapt probiotics to processing stresses, such as heat, without significantly changing the probiotic properties of the strains assessed. This may provide new options for future probiotic production technology. However, our results also emphasize that the properties of the stress-adapted strains, as well as the effect of the production processes should always be assessed as these are strain-specific.

Enhancing probiotic stability in industrial processes

Background

Manufacture of probiotic products involves industrial processes that reduce the viability of the strains. This lost of viability constitutes an economic burden for manufacturers, compromising the efficacy of the product and preventing the inclusion of probiotics in many product categories. Different strategies have been used to improve probiotic stability during industrial processes. These include technological approaches, such as the modification of production parameters or the reformulation of products, as well as microbiological approaches focused on the strain intrinsic resistance. Among the later, both selection of natural strains with the desired properties and stress-adaptation of strains have been widely used.

Conclusion

During recent years, the knowledge acquired on the molecular basis of stress-tolerance of probiotics has increased our understanding on their responses to industrial stresses. This knowledge on stress-response may nowadays be used for the selection of the best strains and industrial conditions in terms of probiotic stability in the final product.

How do bifidobacteria counteract environmental challenges? Mechanisms involved and physiological consequences

An effective response to stress is of paramount importance for probiotic bifidobacteria administered in foods, since it determines their performance as beneficial microorganisms. Firstly, bifidobacteria have to be resistant to the stress sources typical in manufacturing, including heating, exposure to low water activities, osmotic shock and presence of oxygen. Secondly, and once they are orally ingested, bifidobacteria have to overcome physiological barriers in order to arrive in the large intestine biologically active. These barriers are mainly the acid pH in the stomach and the presence of high bile salt concentrations in the small intestine. In addition, the large intestine is, in terms of microbial amounts, a densely populated environment in which there is an extreme variability in carbon source availability. For this reason, bifidobacteria harbours a wide molecular machinery allowing the degradation of a wide variety of otherwise non-digestible sugars. In this review, the molecular mechanisms allowing this bacterial group to favourably react to the presence of different stress sources are presented and discussed.

Inhibition of Bacillus anthracis spore outgrowth by nisin

The lantibiotic nisin has previously been reported to inhibit the outgrowth of spores from several Bacillus species. However, the mode of action of nisin responsible for outgrowth inhibition is poorly understood. By using B. anthracis Sterne 7702 as a model, nisin acted against spores with a 50% inhibitory concentration (IC(50)) and an IC(90) of 0.57 microM and 0.90 microM, respectively. Viable B. anthracis organisms were not recoverable from cultures containing concentrations of nisin greater than the IC(90). These studies demonstrated that spores lose heat resistance and become hydrated in the presence of nisin, thereby ruling out a possible mechanism of inhibition in which nisin acts to block germination initiation. Rather, germination initiation is requisite for the action of nisin. This study also revealed that nisin rapidly and irreversibly inhibits growth by preventing the establishment of oxidative metabolism and the membrane potential in germinating spores. On the other hand, nisin had no detectable effects on the typical changes associated with the dissolution of the outer spore structures (e.g., the spore coats, cortex, and exosporium). Thus, the action of nisin results in the uncoupling of two critical sequences of events necessary for the outgrowth of spores: the establishment of metabolism and the shedding of the external spore structures.

Evaluation of the response of Lactobacillus rhamnosus VTT E-97800 to sucrose-induced osmotic stress

Environmental osmotic changes are one of the stresses live probiotics may encounter either in their natural habitats or as a result of usage in food formulations and processing. Response to osmotic stress, induced by sucrose, of the probiotic strain Lactobacillus rhamnosus VTT E-97800 (E800) was investigated. The fluorescence-based approach used, by combined staining with caboxyfluorescein (cFDA) and propidium iodide (PI) could give insights on the osmotic-induced changes of microbial esterase activity and membrane integrity; also the extrusion of intracellular accumulated carboxyfluorescein (cF) upon energizing with glucose. Comparison of the flowcytometric viability assessment with the conventional culture techniques revealed that sucrose-stressed cells had a slight loss of culturability (logN/N(0) approximately -0.3) at 1.2 and 1.5M sucrose concentration though they could perform an enzymatic conversion of cFDA into cF. The presence of such metabolically active bacteria in food might be critical as they may excrete toxic or food spoilage metabolites. Moreover, the perturbation of cF extrusion activities became a limiting factor for reproductive capacities. There was no change in the cell morphology. These results proved the ability of the strain of study to tolerate sucrose, even at extreme concentrations and these must be taken into consideration for its usage in the formulation/processing of sugar-based foods, e.g. jams, candies, etc.

Nutridynamics--studying the dynamics of food components in products and in the consumer

The concentrations and biological effects of nutrients, antinutrients and bioactive compounds, including microbes and their constituents, are affected by production and processing steps, the food matrix in which they reside, the way they are digested and metabolized in the human body, and whether or not and in what form they subsequently reach their target site. A new scientific concept, denoted here as 'nutridynamics', aims to unravel the dynamics of these processes by using a systematic approach to study how a food component is affected by the food matrix itself and what it does in the body. This holistic concept has potential synergy with the areas of food technology and nutrigenomics, and provides a link between food production and the mechanistic effects of bioactive ingredients.

Comparative proteome approach to characterize the high-pressure stress response ofLactobacillus sanfranciscensis DSM 20451T

High hydrostatic pressure (HHP) exerts diverse effects on microorganisms, leading to stress response and cell death. While inactivation of microorganisms by lethal HHP is well investigated in the context of food preservation and the hygienic safety of minimal food processes, sublethal HHP stress response and its effect on adaptation and cross-protection is less understood. In this study, the HHP stress response of Lactobacillus sanfranciscensis was characterized and compared with cold, heat, salt, acid and starvation stress at the proteome level by using 2-DE so as to provide insight into general versus specific stress responses. Sixteen proteins were found to be affected by HHP and were identified by using N-terminal amino acid sequencing and MS. Only one slightly increased protein was specific to the HHP response and showed homology to a clp protease. The other proteins were influenced by most of the investigated stresses in a similar way as HHP. The highest similarity in the HHP proteome was found to be with cold- and NaCl-stressed cells, with 11 overlapping proteins. At the proteome level, L. sanfranciscensis appears to use overlapping subsets of stress-inducible proteins rather than stereotype responses. Our data suggest that a specific pressure response does not exist in this bacteria.

Application of a microplate scale fluorochrome staining assay for the assessment of viability of probiotic preparations

Cell viability in probiotic preparations is traditionally assessed by the plate count technique. Additionally, fluorescent staining combined with epifluorescence microscopy or flow cytometry has been developed for the viability assessment, but the currently available assays are either laborious or require highly sophisticated equipment. The aim of this study was to investigate the applicability of a microplate scale fluorochrome assay for predicting the cell state of freeze-dried Lactobacillus rhamnosus and Bifidobacterium animalis subsp. lactis preparations. In addition to viability assessment with LIVE/DEAD BacLight Bacterial Viability Kit, DiBAC(4)3 stain was used for the kinetic measurement of changes in bifidobacterial cell membrane functions during exposure to low pH. The microplate scale fluorochrome assay results on the viability and cell numbers of probiotic preparations correlated well with the results obtained with the culture-based technique and (with few exceptions) with epifluorescence microscopy. The assay was applicable also for the viability assessment of stressed (acid-treated) cells provided that the cell density in treatments was adjusted to the optimal measurement level of the fluorometer. The microplate scale fluorochrome assay offers a rapid and robust tool for the viability assessment of probiotic preparations, and enables also kinetic measurements.

Induction of oxidative stress by high hydrostatic pressure in Escherichia coli

Using leaderless alkaline phosphatase as a probe, it was demonstrated that pressure treatment induces endogenous intracellular oxidative stress in Escherichia coli MG1655. In stationary-phase cells, this oxidative stress increased with the applied pressure at least up to 400 MPa, which is well beyond the pressure at which the cells started to become inactivated (200 MPa). In exponential-phase cells, in contrast, oxidative stress increased with pressure treatment up to 150 MPa and then decreased again, together with the cell counts. Anaerobic incubation after pressure treatment significantly supported the recovery of MG1655, while mutants with increased intrinsic sensitivity toward oxidative stress (katE, katF, oxyR, sodAB, and soxS) were found to be more pressure sensitive than wild-type MG1655. Furthermore, mild pressure treatment strongly sensitized E. coli toward t-butylhydroperoxide and the superoxide generator plumbagin. Finally, previously described pressure-resistant mutants of E. coli MG1655 displayed enhanced resistance toward plumbagin. In one of these mutants, the induction of endogenous oxidative stress upon high hydrostatic pressure treatment was also investigated and found to be much lower than in MG1655. These results suggest that, at least under some conditions, the inactivation of E. coli by high hydrostatic pressure treatment is the consequence of a suicide mechanism involving the induction of an endogenous oxidative burst.