Flow cytometric assessment of the protectants for enhanced in vitro survival of probiotic lactic acid bacteria through simulated human gastro-intestinal stresses

Effects of Simulated Gastrointestinal Conditions on Combined Potentially Probiotic Limosilactobacillus fermentum 296, Quercetin, and/or Resveratrol as Bioactive Components of Novel Nutraceuticals

This study evaluated the effects of simulated gastrointestinal conditions (SGIC) on combined potentially probiotic Limosilactobacillus fermentum 296 (~ 10 log CFU/mL), quercetin (QUE, 160 mg), and/or resveratrol (RES, 150 mg) as the bioactive components of novel nutraceuticals. Four different nutraceuticals were evaluated during exposure to SGIC and analyzed the plate counts and physiological status of L. fermentum 296, contents and bioaccessibility of QUE and RES, and antioxidant capacity. Nutraceuticals with QUE and RES had the highest plate counts (4.94 ± 0.32 log CFU/mL) and sizes of live cell subpopulations (28.40 ± 0.28%) of L. fermentum 296 after SGIC exposure. An index of injured cells (Gmean index, arbitrary unit defined as above 0.5) indicated that part of L. fermentum 296 cells could be entered the viable but nonculturable state when the nutraceuticals were exposed to gastric and intestinal conditions while maintaining vitality. The nutraceuticals maintained high contents (QUE ~ 29.17 ± 0.62 and RES ~ 23.05 mg/100 g) and bioaccessibility (QUE ~ 41.0 ± 0.09% and RES ~ 67.4 ± 0.17%) of QUE and RES, as well as high antioxidant capacity (ABTS assay ~ 88.18 ± 1.16% and DPPH assay 75.54 ± 0.65%) during SGIC exposure, which could be linked to the protective effects on L. fermentum 296 cells. The developed nutraceuticals could cross along the gastrointestinal tract with high concentrations of functioning potentially probiotic cells and bioavailable phenolic compounds to exert their beneficial impacts on consumer health, being an innovative strategy for the co-ingestion of these bioactive components.

Co-encapsulation of probiotics with acylglycerols in gelatin-gum arabic complex coacervates: Stability evaluation under adverse conditions

Co-encapsulation of acylglycerols and probiotics may improve the resistance of probiotics to adverse conditions. In this study, three probiotic microcapsule models were constructed using gelatin (GE)-gum arabic (GA) complex coacervate as wall material: microcapsules containing only probiotics (GE-GA), microcapsules containing triacylglycerol (TAG) oil and probiotics (GE-T-GA) and microcapsules containing diacylglycerol (DAG) oil and probiotics (GE-D-GA). The protective effects of three microcapsules on probiotic cells under environmental stresses (freeze-drying, heat treatment, simulated digestive fluid and storage) were evaluated. The results of cell membrane fatty acid composition and Fourier transform infrared (FTIR) spectroscopy revealed that GE-D-GA could improve the fluidity of cell membrane, maintain the stability of protein and nucleic acid structure, and decrease the damage of cell membrane. These characteristics supported the high freeze-dried survival rate (96.24 %) of GE-D-GA. Furthermore, regardless of thermotolerance or storage, GE-D-GA showed the best cell viability retention. More importantly, GE-D-GA provided the best protection for probiotics under simulated gastrointestinal conditions, as the presence of DAG reduced cell damage during freeze-drying and the degree of contact between probiotics and digestive fluids. Therefore, co-microencapsulation of DAG oil and probiotics is a promising strategy to resist adverse conditions.

Soy lecithin increases the stability and lipolysis of encapsulated algal oil and probiotics complex coacervates

BACKGROUND

Co-encapsulation of probiotics and omega-3 oil using complex coacervation is an effective method for enhancing the tolerance of probiotics under adverse conditions, whereas complex coacervation of omega-3 oil was found to have low lipid digestibility. In the present study, gelatin (GE, 30 g kg^-1 ) and gum arabic (GA, 30 g kg^-1 ) were used to encapsulate Lactobacillus plantarum WCFS1 and algal oil by complex coacervation to produce microcapsules containing probiotics (GE-P-GA) and co-microcapsules containing probiotics and algal oil (GE-P-O-GA), and soy lecithin (SL) was added to probiotics-algal oil complex coacervates [GE-P-O(SL)-GA] to enhance its stability and lipolysis. Then, we evaluated the viability of different microencapsulated probiotics exposed to freeze-drying and long-term storage, as well as the survival rate and release performance of encapsulated probiotics and algal oil during in vitro digestion.

RESULTS

GE-P-O(SL)-GA had a smaller particle size (51.20 μm), as well as higher freeze-drying survival (90.06%) of probiotics and encapsulation efficiency of algal oil (75.74%). Moreover, GE-P-O(SL)-GA showed a higher algal oil release rate (79.54%), lipolysis degree (74.63%) and docosahexaenoic acid lipolysis efficiency (64.8%) in the in vitro digestion model. The viability of microencapsulated probiotics after simulated digestion and long-term storage at -18,4 and 25 °C was in the order: GE-P-O(SL)-GA > GE-P-O-GA > GE-P-GA.

CONCLUSION

As a result of its amphiphilic properties, SL strongly affected the physicochemical properties of probiotics and algal oil complex coacervates, resulting in higher stability and more effective lipolysis. Thus, the GE-P-O(SL)-GA can more effectively deliver probiotics and docosahexaenoic acid to the intestine, which provides a reference for the preparation of high-viability and high-lipolysis probiotics-algal oil microcapsules. © 2022 Society of Chemical Industry.

Detection of Glycolytically Active Lacticaseibacillus paracasei Strain Shirota by Flow Cytometry Targeting the Efflux Activity of Fluorescent Dye: a Potential Tool for Quality Assessment of Probiotic Cells in Milk Products

The rapid and accurate detection of viable probiotic cells in dairy products is important for assessing product quality in manufacturing. Flow cytometry is widely used for the rapid analysis of bacterial cells. However, further investigation is needed into the optimum property to use it for assessing cell viability. Here, we proposed using the efflux activity of a fluorescent dye, carboxyfluorescein (CF), as an indicator of cell viability. CF is generated from 5(6)-carboxyfluorescein diacetate as a result of cleavage by intracellular esterase. It generally accumulates in the cell, but certain bacterial species are known to extrude it. We found here that the probiotic strain Lacticaseibacillus paracasei strain Shirota (LcS) also extruded CF in the presence of energy sources, such as glucose. To investigate the mechanism of its CF-efflux activity, we screened CF-efflux-negative mutants from a random mutagenesis LcS library and examined the whole genome for genes responsible for CF efflux. We identified a base substitution in the pfkA gene in the glycolytic pathway, and we demonstrated that intact pfkA was essential for CF efflux, indicating that CF-efflux-positive cells must have uncompromised glycolytic activity. We also confirmed that there was a good correlation between the rate of CF-efflux-positive cells and that of colony-forming cells of LcS in a fermented milk product, whereas other properties, such as esterase activity and cell membrane integrity, lost their correlation with the colony-forming activity after long storage. We propose that CF-efflux activity could be an appropriate indicator of cell viability in certain probiotic strains. IMPORTANCE To our knowledge, this is the first report to demonstrate that CF efflux requires uncompromised glycolytic activity in certain lactic acid bacteria. Compared with the cell properties currently widely used for cell viability assessment, such as intracellular esterase activity and membrane integrity, CF-efflux activity enables the accurate detection of culturable cells, especially in products stored for long periods at cold temperatures. These results indicate strongly that CF-efflux activity can be an adequate cell-viability indicator and that flow cytometric quantification could be an alternative to conventional CFU counting. Our findings should be especially informative for dairy/probiotic product manufacturing.

Insights into the enumeration of mixtures of probiotic bacteria by flow cytometry

The use of flow cytometry to enumerate microorganisms is gaining traction over the traditional plate count technique on the basis of superior accuracy, precision and time-to-result. Here, we assessed the suitability of live/dead flow cytometry for the enumeration of mixed populations of probiotic bacteria (L. acidophilus, L. paracasei, L. plantarum, L. salivarius, B. lactis and B. bifidum) whilst comparing outcomes with plate counting. Using a novel gating strategy designed specifically for the enumeration of mixed populations, the application of flow cytometry resulted in the detection of higher numbers of viable bacteria with a greater level of repeatability than plate counting (RSD of 6.82 and 13.14% respectively). Across all multi-species blends tested, viable cell input was more accurately recovered by flow cytometry (101.8 ± 6.95%) than plate counts (81.37 ± 16.03%). However, when certain probiotic mixtures contained preparations with high numbers of non-viable cells in their total population, flow cytometry had the potential for overestimation of the viable population. Nevertheless, the comparative plate counts of these mixtures were low and variable, thus supporting the use of flow cytometry for the enumeration of viable bacteria in mixed populations.

Cultureless enumeration of live bacteria in urinary tract infection by single-cell Raman spectroscopy

Urinary tract infections (UTIs) are the most common outpatient infections. Obtaining the concentration of live pathogens in the sample is crucial for the treatment. Still, the enumeration depends on urine culture and plate counting, which requires days of turn-around time (TAT). Single-cell Raman spectra combined with deuterium isotope probing (Raman-DIP) has been proven to identify the metabolic-active bacteria with high accuracy but is not able to reveal the number of live pathogens due to bacteria replication during the Raman-DIP process. In this study, we established a new approach of using sodium acetate to inhibit the replication of the pathogen and applying Raman-DIP to identify the active single cells. By combining microscopic image stitching and recognition, we could further improve the efficiency of the new method. Validation of the new method on nine artificial urine samples indicated that the exact number of live pathogens obtained with Raman-DIP is consistent with plate-counting while shortening the TAT from 18 h to within 3 h, and the potential of applying Raman-DIP for pathogen enumeration in clinics is promising.

Recent Advances in Lactic Acid Production by Lactic Acid Bacteria

Lactic acid can synthesize high value-added chemicals such as poly lactic acid. In order to further minimize the cost of lactic acid production, some effective strategies (e.g., effective mutagenesis and metabolic engineering) have been applied to increase productive capacity of lactic acid bacteria. In addition, low-cost cheap raw materials (e.g., cheap carbon source and cheap nitrogen source) are also used to reduce the cost of lactic acid production. In this review, we summarized the recent developments in lactic acid production, including efficient strain modification technology (high-efficiency mutagenesis means, adaptive laboratory evolution, and metabolic engineering), the use of low-cost cheap raw materials, and also discussed the future prospects of this field, which could promote the development of lactic acid industry.

Factors that influence clinical efficacy of live biotherapeutic products

Traditional probiotics are increasingly being used in a medical context. The use of these products as drugs is considerably different from the traditional use as food or food supplements, as, obviously, the target population is different (diseased versus healthy or at risk population). Besides the target population, also the regulatory context is different, mainly with respect to production, administration regime and type of clinical studies required. In this paper we will, besides the regulatory differences, focus on aspects that may impact the efficacy of a live biotherapeutic product (drug), especially in a clinical setting. The impact of the dosage seems to depend on the strain and the application and may follow some rationale. In contrast, information on the impact of the time of administration or diet, is often still lacking. The matrix and the use of protective measures may clearly have an impact on the survival and efficacy of the strain.

Polymeric carriers for enhanced delivery of probiotics

Probiotics are live microorganisms (usually bacteria), which are defined by their ability to confer health benefits to the host, if administered adequately. Probiotics are not only used as health supplements but have also been applied in various attempts to prevent and treat gastrointestinal (GI) and non-gastrointestinal diseases such as diarrhea, colon cancer, obesity, diabetes, and inflammation. One of the challenges in the use of probiotics is putative loss of viability by the time of administration. It can be due to procedures that the probiotic products go through during fabrication, storage, or administration. Biocompatible and biodegradable polymers with specific moieties or pH/enzyme sensitivity have shown great potential as carriers of the bacteria for 1) better viability, 2) longer storage times, 3) preservation from the aggressive environment in the stomach and 4) topographically targeted delivery of probiotics. In this review, we focus on polymeric carriers and the procedures applied for encapsulation of the probiotics into them. At the end, some novel methods for specific probiotic delivery, possibilities to improve the targeted delivery of probiotics and some challenges are discussed.

Flow cytometry: a versatile technology for specific quantification and viability assessment of micro-organisms in multistrain probiotic products

AIMS

Classical microbiology techniques are the gold standard for probiotic enumeration. However, these techniques are limited by parameters of time, specificity and incapacity to detect viable but nonculturable (VBNC) micro-organisms and nonviable cells. The aim of the study was to evaluate flow cytometry as a novel method for the specific quantification of viable and nonviable probiotics in multistrain products.

METHODS AND RESULTS

Custom polyclonal antibodies were produced against five probiotic strains from different species (Bifidobacterium bifidum R0071, Bifidobacterium longum ssp. infantis R0033, Bifidobacterium longum ssp. longum R0175, Lactobacillus helveticus R0052 and Lactobacillus rhamnosus R0011). Evaluation of specificity confirmed that all antibodies were specific at least at the subspecies level. A flow cytometry method combining specific antibodies and viability assessment with SYTO^® 24 and propidium iodide was applied to quantify these strains in three commercial products. Analyses were conducted on two flow cytometry instruments by two operators and compared with classical microbiology using selective media. Results indicated that flow cytometry provides higher cell counts than classical microbiology (P < 0·05) in 73% of cases highlighting the possible presence of VBNC. Equivalent performances (repeatability and reproducibility) were obtained for both methods.

CONCLUSIONS

This study showed that flow cytometry methods can be applied to probiotic enumeration and viability assessment. Combination with polyclonal antibodies can achieve sufficient specificity to differentiate closely related strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Flow cytometry provides absolute and specific quantification of viable and nonviable probiotic strains in a very short time (<2 h) compared with classical techniques (>48 h), bringing efficient tools for research and development and quality control.

In vitro and in vivo evaluation of the probiotic attributes of Lactobacillus kefiranofaciens XL10 isolated from Tibetan kefir grain

Lactobacillus kefiranofaciens XL10, with a high yield of extracellular polysaccharide (EPS), is isolated from Tibetan kefir grain and benefits the health of human beings and has been considered to exhibit probiotic potential in vitro and in vivo. The probiotic function of the strain was studied extensively, viz., acid and bile salt tolerances, cell surface hydrophobicity and autoaggregation, the modulation of gut microbiota, and the distribution and colonization of XL10 in the mouse intestinal tract after oral administration. XL10 could survive 3-h incubation at pH 3.5 and exhibited cell surface hydrophobicity of ∼79.9% and autoaggregation of ∼27.8%. After continuous oral administration of XL10 for 2 weeks, the Bifidobacteriaceae family increased, accompanied by an observable decline in Proteobacteria phyla in the tested mice. Butyrivibrio and Pseudobutyrivibrio, recognized as butyric acid-producing bacteria, could also be detected at day 7 and day 14, respectively. The most abundant community in the mouse gut had formed by day 14. Additionally, we found that XL10 successfully adhered to the mucous tissue and colonized the ileum of the mice based on fluorescence imaging, flow cytometry, and qPCR. Our results suggested that XL10 has excellent probiotic properties and represents an alternative for exploitation in the development of novel functional foods.

Reevaluating multicolor flow cytometry to assess microbial viability

Flow cytometry is a rapid and quantitative method to determine bacterial viability. Although different stains can be used to establish viability, staining protocols are inconsistent and lack a general optimization approach. Very few "true" multicolor protocols, where dyes are combined in one sample, have been developed for microbiological applications. In this mini-review, the discrepancy between protocols for cell-permeant nucleic acid and functional stains are discussed as well as their use as viability dyes. Furthermore, optimization of staining protocols for a specific setup are described. Original data using the red-excitable SYTO dyes SYTO 59 to 64 and SYTO 17, combined with functional stains, for double and triple staining applications is also included. As each dye and dye combination behaves differently within a certain combination of medium matrix, microorganism, and instrument, protocols need to be tuned to obtain reproducible results. Therefore, single, double, and triple stains are reviewed, including the different parameters that influence staining such as stain kinetics, optimal stain concentration, and the effect of the chelator EDTA as membrane permeabilizer. In the last section, we highlight the need to investigate the stability of multicolor assays to ensure correct results as multiwell autoloaders are now commonly used.

Repeated exposures to blue light-activated eosin Y enhance inactivation of E. faecalis biofilms, in vitro

BACKGROUND

In dentistry, antibacterial photodynamic therapy (a-PDT) has shown promising results for inactivating bacterial biofilms causing carious, endodontic and periodontal diseases. In the current study, we assessed the ability of eosin Y exposed to 3 irradiation protocols at inactivating Enterococcus faecalis biofilms, in vitro.

METHODS

E. faecalis biofilms formed on hydroxyapatite disks were incubated with eosin Y (10-80μM), then activated with blue light using different irradiation protocols. Biofilms exposed to continuous exposure were incubated for 40min before being light-activated for 960 s. For the intermittent exposure, biofilms were exposed 4 times to the light/photosensitizer combination (960 s total) without renewing the photosensitizer. For repeated a-PDT, the same light dose was delivered in a series of 4 irradiation periods separated by dark periods; fresh photosensitizer was added between each light irradiation. After treatment, bacteria were immediately labeled with LIVE/DEAD BacLight Bacterial Viability kit and viability was assessed by flow cytometry (FCM). Results were statistically analyzed using one-way ANOVA and Tukey multiple comparison intervals (α=0.05).

RESULTS

The viability of E. faecalis biofilms exposed to 10μM eosin Y, was significantly reduced compared to controls (light only-eosin Y only). After a second exposure to blue light-activated eosin Y, viability significantly decreased from 58% to 12% whereas 6.5% of the bacterial biofilm remained live after a third exposure (p<0.05). Only 3.5% of the bacterial population survived after the fourth exposure.

CONCLUSIONS

The results of this study indicate that blue light-activated eosin Y can photoinactivate E. faecalis biofilms grown on hydroxyapatite disks. Also, repeated exposures to blue light-activated eosin Y were shown to significantly improve efficacy. Further studies seem warranted to optimize the antibacterial activity of blue light-activated eosin Y on major oral pathogens.