Viability assessment of lactic acid bacteria in commercial dairy products stored at 4 oC using LIVE/DEADR BacLightTM staining and conventional plate counts

Specific cultivation-independent enumeration of viable cells in probiotic products using a combination of fluorescence in situ hybridization and flow cytometry

This study introduces an optimized integration of flow cytometry and fluorescence in situ hybridization (Flow-FISH) as an approach for the specific enumeration of gram-positive bacteria in probiotic products, overcoming the limitations of conventional methods. The enhanced Flow-FISH technique synergizes the rapid and automated capabilities of flow cytometry with the high specificity of FISH, facilitating the differentiation of viable cells at the species level within probiotic blends. By analyzing lyophilized samples of Lacticaseibacillus rhamnosus, Lactiplantibacillus plantarum, and Bifidobacterium animalis subsp. lactis, and a commercial product, the study highlights the optimized Flow-FISH protocol's advantages, including reduced hybridization times to 1.5 h and elimination of centrifugation steps. Comparative evaluations with the widely accepted enumeration methods plate count and Live/Dead (L/D) staining were conducted. The study revealed that Flow-FISH produces higher viable cell counts than plate count, thereby challenging the traditional "gold standard" by highlighting its predisposition to underestimate actual viable cell numbers. Against L/D staining, Flow-FISH achieved comparable results, which, despite the different foundational premises of each technique, confirms the accuracy and reliability of our method. In conclusion, the optimized Flow-FISH protocol represents a significant leap forward in probiotic research and quality control. This method provides a rapid, robust, and highly specific alternative for the enumeration of probiotic bacteria, surpassing traditional methodologies. Its ability to enable a more detailed and reliable analysis of probiotic products paves the way for precise quality control and research insights, underscoring its potential to improve the field significantly.

Optimal combination of cow and quinoa milk for manufacturing of functional fermented milk with high levels of antioxidant, essential amino acids and probiotics

The aim of this research was to produce Rayeb milk, a bio-fermented milk product that has important benefits for health and nutrition. The Rayeb milk was divided into five different treatments: T1 from cow milk, T2 from quinoa milk, T3 from a mixture of cow and quinoa milk (50%:50%), T4 from a mixture of cow and quinoa milk (75%:25%), and T5 from a mixture of cow and quinoa milk (25%:75%). As a starting culture, ABT-5 culture was used. The results demonstrated that blending quinoa milk with cow milk increased the total solids, fat, total protein, pH, acetaldehyde, and diacetyl values of the resulting Rayeb milk. Additionally, the total phenolic content, antioxidant activity, minerals, and amino acids-particularly important amino acids-in Rayeb milk with quinoa milk were higher. In Rayeb milk prepared from a cow and quinoa milk mixture, Lactobacillus acidophilus and Bifidobacterium bifidum were highly stimulated. All Rayeb milk samples, particularly those that contained quinoa milk, possessed more bifidobacteria than the recommended count of 106 cfu g-1 for use as a probiotic. Based on the sensory evaluation results, it is possible to manufacture a bio-Rayeb milk acceptable to the consumer and has a high nutritional and health values using a mixture of cow milk and quinoa milk (75%:25% or 50%:50%) and ABT-5 culture.

Supplementation of Labneh with Passion Fruit Peel Enhanced Survival of E. coli Nissle 1917 during Simulated Gastrointestinal Digestion and Adhesion to Caco-2 Cells

Passion fruit peel powder (PFPP) was used to supplement the probiotic labneh to increase the activity of Escherichia coli Nissle 1917 (EcN) during production and storage. Labneh was manufactured with PFPP (0.5% and 1%) and analyzed at 0, 7, and 15 days of cold storage for postacidification and sensory properties and viability of EcN, survival of EcN to simulated gastrointestinal tract stress, and adhesion potential of EcN to Caco-2 cells. Acidification kinetics during fermentation showed that supplementation with PFPP reduced the time needed to decrease pH and reach the maximum acidification rate. PFPP addition contributed to postacidification of labneh during storage. PFPP had a beneficial effect (p < 0.05) on counts of EcN in labneh during different storage periods. Consumer preference expectations for labneh enriched with PFPP (0.5% and 1%) were higher than those for the control. PFPP provided a significant protective action for EcN during simulated gastrointestinal transit and had a positive effect on EcN adhesion to Caco-2 cells in vitro, although this decreased during storage with labneh. Labneh supplementation with PFPP can be recommended because of the positive effect on EcN viability and the high nutritional value, which may increase the appeal of the product to consumers.

High-Pressure-Induced Sublethal Injuries of Food Pathogens-Microscopic Assessment

High Hydrostatic Pressure (HHP) technology is considered an alternative method of food preservation. Nevertheless, the current dogma is that HHP might be insufficient to preserve food lastingly against some pathogens. Incompletely damaged cells can resuscitate under favorable conditions, and they may proliferate in food during storage. This study was undertaken to characterize the extent of sublethal injuries induced by HHP (300-500 MPa) on Escherichia coli and Listeria inncua strains. The morphological changes were evaluated using microscopy methods such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Epifluorescence Microscopy (EFM). The overall assessment of the physiological state of tested bacteria through TEM and SEM showed that the action of pressure on the structure of the bacterial membrane was almost minor or unnoticeable, beyond the L. innocua wild-type strain. However, alterations were observed in subcellular structures such as the cytoplasm and nucleoid for both L. innocua and E. coli strains. More significant changes after the HHP of internal structures were reported in the case of wild-type strains isolated from raw juice. Extreme condensation of the cytoplasm was observed, while the outline of cells was intact. The percentage ratio between alive and injured cells in the population was assessed by fluorescent microscopy. The results of HHP-treated samples showed a heterogeneous population, and red cell aggregates were observed. The percentage ratio of live and dead cells (L/D) in the L. innocua collection strain population was higher than in the case of the wild-type strain (69%/31% and 55%/45%, respectively). In turn, E. coli populations were characterized with a similar L/D ratio. Half of the cells in the populations were distinguished as visibly fluorescing red. The results obtained in this study confirmed sublethal HHP reaction on pathogens cells.

Invited review: Characterization of new probiotics from dairy and nondairy products-Insights into acid tolerance, bile metabolism and tolerance, and adhesion capability

The selection of potential probiotic strains that possess the physiological capacity of performing successfully in the gastrointestinal tract (GIT) is a critical challenge. Probiotic microorganisms must tolerate the deleterious effects of various stresses to survive passage and function in the human GIT. Adhesion to the intestinal mucosa is also an important aspect. Recently, numerous studies have been performed concerning the selection and evaluation of novel probiotic microorganisms, mainly probiotic bacteria isolated from dairy and nondairy products. Therefore, it would be crucial to critically review the assessment methods employed to select the potential probiotics. This article aims to review and discuss the recent approaches, methods used for the selection, and outcomes of the evaluation of novel probiotic strains with the main purpose of supporting future probiotic microbial assessment studies. The findings and approaches used for assessing acid tolerance, bile metabolism and tolerance, and adhesion capability are the focus of this review. In addition, probiotic bile deconjugation and bile salt hydrolysis are explored. The selection of a new probiotic strain has mainly been based on the in vitro tolerance of physiologically related stresses including low pH and bile, to ensure that the potential probiotic microorganism can survive the harsh conditions of the GIT. However, the varied experimental conditions used in these studies (different types of media, bile, pH, and incubation time) hamper the comparison of the results of these investigations. Therefore, standardization of experimental conditions for characterizing and selecting probiotics is warranted.

Germinated black soybean fermented with Lactobacillus pentosus SC65 alleviates DNFB-induced delayed-type hypersensitivity in C57BL/6N mice

ETHNOPHARMACOLOGICAL RELEVANCE

Rhynchosia nulubilis (black soybean) has many applications in oriental medicine. It is traditionally used to treat disease related with high blood pressure, diabetes, inflammation, and osteoporosis. Furthermore, fermented soybean foods have traditionally been used for immunity enhancement in East Asia. However, the anti-inflammatory effects of germinated R. nulubilis (GR) against delayed-type hypersensitivity (DTH) are not fully understood.

AIM OF STUDY

This study aimed to investigate the anti-inflammatory effects of germinated Rhynchosia nulubilis (GR) fermented with the lactic acid bacterium Lactobacillus pentosus SC65 (GR-SC65) isolated from pickled burdock.

MATERIALS AND METHODS

We investigated the effects of GR-SC65 (300 mg/kg/day) on ear thickness and immune cell infiltration in DNFB-induced DTH in mice. We used dexamethasone (3 mg/kg) as a reference drug. Changes in infiltration of CD4+ and CD8+ T cells and NK cells were examined by immunohistochemistry. In addition, we investigated cytokine and chemokine production related to DTH using reverse transcription-polymerase chain reaction. We also investigated DTH-related cytokine production using lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells.

RESULTS

Two lactic acid bacterial strains (Lactobacillus pentosus SC65 and Pediococcus pentosaceus ON81A) were selected for fermenting GR due to their high 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity. The total polyphenol contents (TPCs) in GR-SC65 and GR-ON81A were higher than that in unfermented GR (∗∗∗P < 0.001 vs. GR). Content of daidzein, glycitein, and genistein, the deglycosylated form of isoflavonoids, was higher in GR-SC65 than in unfermented GR. The ethanol extracts of GR-SC65 exerted a stronger anti-inflammatory activity than GR by inhibiting pro-inflammatory cytokines, such as tumor necrosis factor (TNF), interleukin-6 (IL-6), and interleukin-1β (IL-1β) in LPS-induced RAW264.7 macrophages. GR-SC65 reduced 1-fluoro-2,4-dinitrofluorobenzene (DNFB)-induced ear swelling and hyperplasia as well as vascular permeability. Fewer infiltrated CD4+ and CD8+ T cells were observed in the ear tissue of the GR-SC65-treated mice than those of the unfermented GR-treated mice. Furthermore, fewer infiltrated NK cells were observed in the GR-SC65 treated mice, than in the GR-treated mice. GR-SC65 significantly diminished the levels of CCL5 and COX-2 mRNAs and increased the level of IL-10 mRNA.

CONCLUSIONS

These data suggest that GR-SC65 can be used as a health supplement or a prophylactic against delayed-type hypersensitive inflammatory disease.

Three Types of Beetroot Products Enriched with Lactic Acid Bacteria

Beetroot (Beta vulgaris L.) represents a very rich source of bioactive compounds such as phenolic compounds and carotenoids, among which the most important being betalains, mainly betacyanins and betaxanthins. The beetroot matrix was used in a fresh or dried form or as lyophilized powder. A 10¹² CFU/g inoculum of Lactobacillus plantarum MIUG BL3 culture was sprayed on the vegetal tissue. The lactic acid bacteria (LAB) viability for all the products was evaluated over 21 days, by microbiological culture methods. The antioxidant activity of the obtained food products was correlated to the betalains content and the viability of LAB. The content of polyphenolic compounds varied between 225.7 and 1314.7 mg L⁻¹, hence revealing a high content of bioactive compounds. Through the confocal laser scanning microscopy analysis, a large number of viable probiotic cells were observed in all the variants but especially in the fresh red beet cubes. After 21 days of refrigeration, the high content of Lb. plantarum (CFU per gram) of the food products was attributed to the biocompounds and the nutrients of the vegetal matrix that somehow protected the bacterial cells, and thus maintained their viability. The obtained food products enriched with probiotic LAB can be regarded as new functional food products due to the beneficial properties they possessed throughout the undertaken experiments.

Viability assessment of Bifidobacterium longum ATCC 15707 on non-dairy foods using quantitative fluorescence microscopy

This study demonstrates an effective technique for separating and purifying viable bacteria from samples that interfere with viability staining. The viability of Bifidobacterium longum ATCC 15707 was assessed using Percoll Buoyant Density Gradient Centrifugation (PBDC) to separate bacteria from complex non-dairy food matrices and Quantitative Fluorescence Microscopy (QFM) to determine individual cells using LIVE/DEAD BacLight bacterial viability staining. Water agar (3%) was used to retain cells of B. longum and offered a lower fluorescence background with BacLight viability staining, compared with fixation on polycarbonate (PC) black membrane. The effect of drying temperatures and non-dairy foods on viability of B. longum was assessed. B. longum coated on oat, peanut or raisin was separated by filtration, low- and high-speed centrifugation, flotation and sedimentation buoyant density centrifugation. Purified cells were subsequently deposited on water agar for rehydration followed by LIVE/DEAD BacLight viability staining and enumeration. Conventional plate counting was also conducted to compare viability results. Finally, this method was applied to assess cell membrane damages of B. longum incorporated onto non-dairy foods during 24 h drying. Furthermore, viability assessment of B. longum coated onto oat, peanut, or raisin was much lower by plate counting compared to viability staining. Drying appeared to have a greater impact when viability was assessed by plate counting compared to viability staining. IMPORTANCE: Enumeration of viable beneficial bacteria from function foods presents a significant bottleneck for product development and quality control. Interference with microscopic and/or fluorescent techniques by ingredients, time required to incubate plated microbes, and the transient nature of the colony forming unit make rapid assessment of viable bacteria difficult. Viability assessment of Bifidobacterium longum ATCC 15707 by Percoll Buoyant Density Gradient Centrifugation with LIVE/DEAD BacLight viability staining on water agar (3%) was in agreement with serial dilution enumeration. Without the need for incubation viability assessment by staining provided a more rapid means to assess the impact of drying on the viability of B. longum coated onto oat, peanut or raisin.

Differential enumeration of subpopulations in concentrated frozen and lyophilized cultures of Lactobacillus delbrueckii ssp. bulgaricus

Differential enumeration of subpopulations in concentrated frozen and lyophilized cultures of Lactobacillus delbrueckii ssp. bulgaricus ND02 derived from 2 propagation procedures was determined. The subpopulations consisted of 3 categories (physiological states): viable cells capable of forming colonies on agar plates (VC+), viable cells incapable of forming colonies on agar plates (VC-), widely referred to as viable but nonculturable (VBNC) cells, and nonviable or dead cells (NVC). Counts of VC+ were recorded using a conventional plate count procedure. A fluorescent vital staining procedure that discriminates between viable (VC+ and VC-) and NVC cells was used to determine the number of viable and nonviable cells. Both propagation procedures had 2 variables: in procedure (P)1, the propagation medium was rich in yeast extract (4.0%) and the pH was maintained at 5.7; in P2, the medium was devoid of yeast extract and the pH was maintained at 5.1. The results showed that post-propagation operations-concentration of cells by centrifugation and subsequent freezing or lyophilization of cell concentrate-induced different degrees of transience from VC+ to VC- states in cells derived from P1 and P2. Compared with cells derived from P2, cells from P1 were more labile to stress associated with centrifugation, freezing, and lyophilization, as revealed by differential counting.

Raman spectroscopic analysis of Lactobacillus rhamnosus GG in response to dehydration reveals DNA conformation changes

Dehydration of bacterial cells elicits cellular stress responses in bacteria. Microencapsulation has been used to protect cells against the environmental stress. In this study, Confocal Raman Spectroscopy was used to examine DNA changes in the chemical composition of non-encapsulated and microencapsulated Lactobacillus rhamnosus GG and the reversibility of these changes upon freeze drying and rehydration. The viability of cells upon freeze drying was also enumerated using culture methods and membrane integrity was measured using BacLight Live/Dead staining. Raman analyses show changes in the spectral features associated with various biochemical compounds, which are interpreted as the result of detrimental freeze drying effects on the bacterial cells. Specifically, analyses based on Principal Components Analysis (PCA) of Raman spectra, confirm that microencapsulation protects cells from environmental stress. The results also reveal a B- to A-like DNA conformation change in dormant cells that provided insights into the extent of reversibility of this transition upon rehydration. The extent of this reversibility is less in non-encapsulated than in microencapsulated cells. These findings indicate the potential application of Raman spectroscopy in rapid sensing of microbial dehydration stress responses.

Effect of Drying Methods on Protein and DNA Conformation Changes in Lactobacillus rhamnosus GG Cells by Fourier Transform Infrared Spectroscopy

Microencapsulation protects cells against environmental stress encountered during the production of probiotics, which are used as live microbial food ingredients. Freeze-drying and spray-drying are used in the preparation of powdered microencapsulated probiotics. This study examines the ability of Fourier transform infrared (FTIR) spectroscopy to detect differences in cells exposed to freeze-drying and spray-drying of encapsulated Lactobacillus rhamnosus GG cells. The FTIR analysis clearly demonstrated there were more significant molecular changes in lipid, fatty acid content, protein, and DNA conformation of nonencapsulated compared to encapsulated bacterial cells. The technique was also able to differentiate between spray-dried and freeze-dried cells. The results also revealed the extent of protection from a protein-carbohydrate-based encapsulant matrix on the cells depending on the type drying process. The extent of this protection to the dehydration stress was shown to be less in spray-dried cells than in freeze-dried cells. This suggests that FTIR could be used as a rapid, noninvasive, and real-time measurement technique to detect detrimental drying effects on cells.

Compatibility balanced antibacterial modification based on vapor-deposited parylene coatings for biomaterials

An advanced antibacterial modification technique is conducted by immobilizing antibacterial agents to reduce bacterial attachment and show balanced biocompatibility.

Total viable bacterial count using a real time all-fibre spectroscopic system

Rapid, accurate and sensitive enumeration of bacterial populations in the natural environment is an essential task for many research fields. Widely used standard methods for counting bacteria such as heterotrophic plate count require 1 to 8 days of incubation time for limited accuracy, while more accurate and rapid techniques are often expensive and may require bulky equipment. In the present study, we have developed a computerized optical prototype for bacterial detection. The goal of this research was to estimate the potential of this optical system for Total Viable Bacterial Count in water. For this purpose, we tested water batches with different microbiological content. Bacterial detection was based on fluorescence enhanced by nucleic acid staining. High sensitivity was achieved by a stable diode pumped solid state laser, sensitive CCD spectrometer and in situ excitation and signal collection. The results have shown that the bacterial count from different water origins using our optical setup along with multivariate analysis presents a higher accuracy and a shorter detection time compared to standard methods. For example, in a case where the fluorescence signal is calibrated to the water batch regression line, the relative standard deviation of the optical system enumeration varies between 21 and 36%, while that of the heterotropic plate count counterpart varies between 41 and 59%. In summary, we conclude that the all-fibre optical system may offer the following advantages over conventional methods: near real time examinations, portability, sensitivity, accuracy and ability to detect 10(2) to 10(8) CFU per ml bacterial concentrations.

Recommendations for the viability assessment of probiotics as concentrated cultures and in food matrices

Due to the fact that probiotic cells need to be alive when they are consumed, culture-based analysis (plate count) is critical in ascertaining the quality (numbers of viable cells) of probiotic products. Since probiotic cells are typically stressed, due to various factors related to their production, processing and formulation, the standard methodology for total plate counts tends to underestimate the cell numbers of these products. Furthermore, products such as microencapsulated cultures require modifications in the release and sampling procedure in order to correctly estimate viable counts. This review examines the enumeration of probiotic bacteria in the following commercial products: powders, microencapsulated cultures, frozen concentrates, capsules, foods and beverages. The parameters which are specifically examined include: sample preparation (rehydration, thawing), dilutions (homogenization, media) and plating (media, incubation) procedures. Recommendations are provided for each of these analytical steps to improve the accuracy of the analysis. Although the recommendations specifically target the analysis of probiotics, many will apply to the analysis of commercial lactic starter cultures used in food fermentations as well.

Bioactive compounds and prebiotic activity in Thailand-grown red and white guava fruit (Psidium guajava L.)

This research involves the comparison of bioactive compounds, volatile compounds and prebiotic activity of white guava (Psidium guajava L.) cv. Pansithong and red guava cv. Samsi. The antioxidant activity values determined by 2-diphenyl-1-picryhydrazyl (DPPH) free radical scavenging and ferric reducing antioxidant power (FRAP) assays were 10.28 µg fresh weight (fw)/µg DPPH and 78.56 µg Trolox equivalent (TE)/g fw for white guava and 7.82 µg/µg DPPH, fw and 111.06 µM TE/g fw for red guava. Ascorbic acid contents were 130 and 112mg/100g fw total phenolics contents 145.52 and 163.36 mg gallic acid equivalents (GAE)/100 g fw and total flavonoids contents 19.06 and 35.85 mg catechin equivalents (CE)/100 g fw, in white and red guava, respectively. Volatile compounds in guava were analyzed by the solid-phase microextraction (SPME)/gas chromatography (GC)/mass spectrometry (MS) method. The major constituents identified in white and red guavas were cinnamyl alcohol, ethyl benzoate, ß-caryophyllene, (E)-3-hexenyl acetate and α-bisabolene. Prebiotic activity scores for Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12 were 0.12 and 0.28 in white guava, respectively, and 0.13 and 0.29 in red guava, respectively.

Patterns of survival and volatile metabolites of selected Lactobacillus strains during long-term incubation in milk

The focus of this study was to monitor the survival of populations and the volatile compound profiles of selected Lactobacillus strains during long-term incubation in milk. The enumeration of cells was determined by both the Direct Epifluorescent Filter Technique using carboxyfluorescein diacetate (CFDA) staining and the plate method. Volatile compounds were analysed by the gas-chromatography technique. All strains exhibited good survival in cultured milks, but Lactobacillus crispatus L800 was the only strain with comparable growth and viability in milk, assessed by plate and epifluorescence methods. The significant differences in cell numbers between plate and microscopic counts were obtained for L. acidophilus strains. The investigated strains exhibited different metabolic profiles. Depending on the strain used, 3 to 8 compounds were produced. The strains produced significantly higher concentrations of acetic acid, compared to other volatiles. Lactobacillus strains differed from one another in number and contents of the volatile compounds.

Effect of glucose in removal of microcystin-LR by viable commercial probiotic strains and strains isolated from dadih fermented milk

The removal of the cyanobacterial peptide toxin microcystin-LR at 4 and 37 degrees C by six commercial probiotic strains and Lactobacillus plantarum strains IS-10506 and IS-20506 isolated from dadih, Indonesian traditional fermented milk, was assessed in this study. The aim was to evaluate the main factors influencing the viability and metabolic activity of the probiotic strains, as well as their capacity to remove microcystin-LR. Both L. plantarum strains isolated from dadih, as well as Bifidobacterium lactis strains Bb12 and 420, were shown to be more resistant, and >85% remained viable in phosphate-buffered saline (PBS) solution for 48 h of incubation at either temperature, while the viability of the other four commercial bacteria decreased markedly over time. The effect of glucose on viability and removal of toxin was shown to be a strain-specific and strain-dependent property, but in general, the efficiency of microcystin-LR removal increased when glucose was added to the solution. A maximum removal of 95% was observed for L. plantarum strain IS-20506 (37 degrees C, 10 (11) colony-forming units mL(-1)) with 1-2% glucose supplementation and 75% in PBS alone.

Induction of acid resistance in Bifidobacterium: a mechanism for improving desirable traits of potentially probiotic strains

AIMS

To generate stable acid-resistant Bifidobacterium strains isolated from human subjects and characterize the phenotypic changes of the acid-resistant derivatives.

METHODS AND RESULTS

The ability of 20 Bifidobacterium strains isolated from human faeces to survive to simulated gastrointestinal transit was evaluated, showing major reductions in viability (0.25-5.8 logarithmic units) because of gastric stress conditions. Six acid-sensitive strains belonging to the species Bifidobacterium longum and Bifidobacterium catenulatum were submitted to prolonged incubation at pH 2.0 to generate acid-resistant strains. The acid-sensitive and acid-resistant derivative strains were characterized to determine the changes associated with the acquisition of an acid-tolerant phenotype. The acid-resistant derivatives showed better ability to grow in the presence of bile salt (1-3%) and NaCl (6-10%) and higher resistance at elevated temperatures (60-70 degrees C, 10 min) than the parental strains. The acid-resistant derivatives displayed higher fermentative ability, and enzymatic activities. These strains also showed higher sensitivity to most of the tested antibiotics than the parental strains.

CONCLUSIONS

The stress tolerance of B. longum and B. catenulatum strains was improved by prolonged exposure to acid stress conditions. Some of the generated strains also seemed to have enhanced metabolic properties of relevance for probiotic applications.

SIGNIFICANCE AND IMPACT OF THE STUDY

The successful use of prolonged exposures to acid stress to improve the stability of human bifidobacteria indicates that this strategy could be useful for the production of robust probiotic strains, but involves other phenotypic changes that required an individual characterization.

Method for direct selection of potentially probiotic Bifidobacterium strains from human feces based on their acid-adaptation ability

A method for direct selection of acid-resistant Bifidobacterium strains was developed by prolonged exposure of human feces to homologous lethal stress conditions. The recovered strains were intrinsically resistant to acidic gastric conditions (pH 2.0) and also showed good tolerance to high concentrations of bile salts and NaCl. Bifidobacterium breve and Bifidobacterium adolescentis were, respectively, the infant- and adult-type bifidobacterial species showing the highest ability to develop an acid-tolerant phenotype. Therefore, this procedure could be applicable to the direct selection of Bifidobacterium strains with improved stability in adverse environments and, probably, contribute to expand the spectra of probiotic species of human origin currently marketed.