METHOD FOR SCREENING PROBIOTIC STRAINS OF THE GENUS BIFIDOBACTERIUM

Abstract: The present invention relates to a method for screening bacteria which are beneficial to human health, and to specific strains selected using the method. In specific, the invention provides a method for screening probiotic strains of bifidobacteria, which can be used in production of cereal-based functional and clinical food products or dietary supplements.

Description: Method for screen i ng prob i ot i c st ra i ns of the genus B i f i dobacter i um . Field of the invention The present invention relates to a method for screening bacteria which are beneficial to human health, and to specific strains selected using the method. In specific, the invention provides a method for screening probiotic strains of bifidobacteria, which can be used in production of functional and clinical food products or dietary supplements. Background of the Invention Probiotics are viable bacteria, or their inactivated cells or cell wall components, that have a beneficial effect on human health [Salminen et al. (1999) Trends in Food Science and Technology 10:107-110]. Probiotics are most commonly viable Lactobacillus preparations, but recently also bifidobacteria and other microbes have been shown to have probiotic properties. The importance of human intestinal microflora for the well-being of the human host, and the importance of the development of intestinal microflora after birth, during childhood, during adult ages and during the old age is in the background of the present invention. At birth the newborn is practically sterile and is colonised by the microbes present in the birth channel of the mother and the environment. Bifidobacteria soon colonise a healthy infant and can be detected in the faeces from the 2 nd or 3 rd day after birth. The growth of bifidobacteria is promoted by breast feeding. Besides bifidobacteria, lactobacilli are among the first colonisers of the intestinal tract following the birth of a human being. These two genera soon form the major basis of the intestinal microflora in health, preventing diseases in the early childhood. During growth and ageing the microflora becomes more diverse, but the role of lactobacilli and bifidobacteria remains important. Especially in Japanese studies it has been shown that bifidobacteria decrease and lactobacilli increase in numbers, and the diversity of strains present in the intestinal tract of the elderly are less than in adults or infants [Mitsuoka et al, (1974) Zbl. Bakt. Hyg. I Abt. Orig. A 266:469-478]. Consequently, it has been suggested that the Lactobacillus flora and the Bifidobacterium flora are important factors in promoting health and preventing or reducing the risk of disease. Supplementation of the microflora with selected strains from the genera Lactobacillus and Bifidobacterium may therefore improve the health and well-being of the host. The strains to be used for this purpose are to possess several advantageous properties in order to be potentially successful probiotic strains [Ouwehand et al. (1999), Int. Dairy I 9:43-52]. The types of bifidobacteria present in the intestinal contents in the elderly and in infants vary, and healthy subjects have higher bifidobacterial numbers and different Bifidobacterium species. Especially bifidobacteria appear to bind less to the intestinal mucus of the elderly subjects but they may be more abundant in healthy very old subjects. Similarly, different strains of bifidobacteria colonise subjects from different age groups and patient populations. On the other hand, there are specific strains of bifidobacteria that have documented health effects and these include prevention and treatment of diarrhoea in children and alleviation of food allergy symptoms in children. Summary of the invention The present invention is based on the inventors' observation that bifidobacteria exhibit differential binding, not only on human intestinal mucus preparations of subjects from different age groups, but especially on whole human intestinal mucosa (ex vivo) of such groups. On the basis of said observation a method for screening probiotic strains of bifidobacteria has been developed. The probiotic strains so obtained have desired properties and can be used in producing functional and clinical food products or dietary supplements. The main object of the present invention is thus a method for screening probiotic strains of the genus Bifidobacterium, comprising isolating bifidobacteria from faecal specimens of healthy elderly human subjects, and by screening for their age- and disease- specific properties by screening for their adhesion to intestinal mucus glycoproteins (in vitro) and to whole human intestinal mucosa (ex vivo) and, optionally, further subjecting the bacteria to the specific screening or selection steps as defined hereinafter, to obtain bacterial strains having specific probiotic properties. Specific bifidobacterial strains obtained by the screening method are further objects of the invention. Such strains preferably show e.g. age-specific or disease-specific properties and, consequently, can be used in preparing functional foods for target populations, in specific, elderly people, or disease-specific functional foods for the reduction of risk of diseases, respectively. Detailed Description of the Invention Our in vitro studies have shown that the adhesive properties of most bifidobacteria used commercially are lower in the elderly, and that in humans the types of bifidobacteria change in different age groups with decreasing adherence along with old age. Furthermore, our ex vivo studies with whole human intestinal mucosa, obtained from surgically removed colonic tissue, have shown similar adherence variation in different groups. Consequently, besides showing that the types of bifidobacteria are specific for certain age groups, we have shown that adherence in the elderly can be used as a selection criterion for strains applicable to the intestinal conditions of the elderly. We have isolated bifidobacteria from the faeces of healthy elderly human subjects and shown that these strains exhibit different binding properties in vitro and ex vivo. We have noticed that among the healthy and old individuals there is a population of bifidobacteria which shows good adherence on these subjects and thus increase the possibility of intestinal colonisation in such subjects with health-promoting effects on intestinal microflora and function. It should also be noted that the screening method of the invention can also be applied to bacteria from faecal specimens from any appropriate animals, not only human beings. In this specification the term "elderly", e.g. in the expression 'elderly human subjects' refers to individuals of about 60 years of age or older. On the other hand, the term "very old", e.g. in the connection of the expression 'very old human subjects' refers to individuals of about 80 years of age, or older. The microbes are isolated from healthy individuals from freshly voided faecal specimens using specific media for isolating bifidobacteria. The isolated bacteria are selected following the described selection criteria and procedure. In vitro adhesion of probiotics is generally assessed using enterocyte-like tissue culture cells or human intestinal mucus. The mucus used is usually isolated from fecal samples. Although these methods are well established, they take into account only one part of the intestinal mucosa; i.e. either the enterocytes or the overlying mucus layer. None of the currently used models takes into account the presence of the normal intestinal microflora. The bifidobacteria described in this application have, in addition, been assessed for their adhesive ability to whole human intestinal mucosa, obtained from surgically removed colonic tissue. This new ex vivo model takes into account the interaction of the bifidobacteria with both the intestinal mucus and the enterocytes, and also the normal intestinal microflora. This provides more accurate knowledge on the adhesive abilities of the bifidobacteria than earlier models. Consequently, specific bacteria are subjected to a test using whole human intestinal mucosa, and their age- and disease-dependent samples to select for specific bacteria adhering to the mucosa of very old healthy subjects. This screens for age-specific adhesion properties for the elderly. Whole mucosa from subjects with colon cancer, inflammatory bowel disease or other intestinal dysfunctions can be used to screen for disease-specific probiotic bifidobacteria. In a preferred embodiment specific bacteria are subjected to a test using human intestinal mucus glycoproteins and their age- and disease-dependent samples to select for specific bacteria adhering to the mucus of very old healthy subjects. This also screens for age-specific properties for the elderly. Mucus from subjects with rotavirus diarrhoea or other intestinal dysfunctions can be used to screen for disease-specificity. The screening for toxin binding is carried out by using mycotoxin and/or bacterial toxin binding as a model for intestinal toxin binding. Preferably the binding should be extensive, so that the adhering strains lose their adherence when toxin is bound. Promising strains will be tested for their relative resistance to bile and low pH with the help of flow cytometry to select for strains that are likely to survive the passage through the intestinal tract. The ability of the strains to grow on certain cereal-based substrates will be determined. Useful cereals are oat, rye, barley, wheat and rice. Mixtures of them or fractions of them can be used as well. Most preferred for the purposes of this invention is oat. Substrates of interest include cereal components like carbohydrates (starch, oligosaccharides, β-glucans) and protein or other fermentable components. Oat oligosaccharides or, in specific, oat fractions enriched in β-glucan, protein or starch are most preferable. This is important for functional food applications and health effects. To allow for food technology and industrial processes, screening for relatively aerotolerant strains is needed. Said screening is effected by culturing the strains on blood liver agar plates in an atmosphere with reduced oxygen pressure. Strains of interest will be subjected to competitive exclusion of model pathogens such as pathogenic E. coli strains, Yersinia enterocolitica, Salmonella typhimurium or S. enteritidis, to select for the most effective strains that inhibit common intestinal pathogens. Host-microbe interactions are tested for the influence of the host microflora on mucus binding properties of the selected strains. The aim is to use the specific target group's own microflora as a selection criterion for well adhering strains in age-specific and disease-specific populations. Age- and disease-specificity are used as criteria for selecting strains. Disease-specific and age-specific intestinal segments received from surgical procedures are used for screening. The samples are used immediately following surgery. Specificity has been demonstrated for commercial strains in terms of age of the subjects and diseases. A specific object of the present invention is thus a method for screening probiotic strains of the genus Bifidobacterium, comprising isolating bifidobacteria from faecal specimens of healthy elderly human subjects, and screening for their age- and disease-specific properties by screening for their adhesion to intestinal mucus glycoproteins and to whole intestinal mucosa and, optionally, subjecting the bacteria to the steps of: a) selecting for strains which, when binding intestinal toxins lose their adherence to the mucus, b) selecting for strains likely to survive the passage through the intestinal tract, c) screening for the ability of the strains to grow on cereal-based substrates, d) screening for the aerotolerance of the strains, and isolating and identifying the strains showing an appropriate selection of the above-indicated properties. A specific set of Bifidobacterium strains has been characterised with such properties and will be described hereinafter. Some strains may indeed have these properties, while others will have only some of the mentioned properties. For instance, some strains bind aflatoxin best when boiled. Obviously, bile and acid resistance is not relevant for these organisms if they are used that way. The following strains A to H, which form a further object of this invention, were isolated from faecal specimens from very old, healthy Japanese men. The strains were selected using the above-indicated selection criteria. Strain A: Bifidobacterium adolescentis 5 shows good adhesion to resected colonic tissue. The strain also has high Aflatoxin Bl binding capacity both when viable and when heat-treated. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 24, 2000 with the accession number DSM 13797. Strain B: Bifidobacterium adolescentis 15 shows good adhesion to resected colonic tissue and has high Aflatoxin Bl binding capacity both when viable and when heat-treated. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 24, 2000 with the accession number DSM 13798. Strain C: Bifidobacterium adolescentis 19 has good adherence to intestinal mucus and good resistance to bile. It also has high Aflatoxin Bl binding capacity both when viable and when heat-treated. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 24, 2000 with the accession number DSM 13799. Strain D: Bifidobacterium adolescentis 34 has high Aflatoxin Bl binding capacity when heat- treated and has good acidification, growth and survival in oat-based media. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 24, 2000 with the accession number DSM 13800. Strain E: Bifidobacterium longum 56 has high Aflatoxin Bl binding capacity after heat- treatment and exhibits some tolerance to low (2.5) pH. The strain also shows good adhesion to resected colonic tissue. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 24, 2000 with the accession number DSM 13801. Strain F: Bifidobacterium breve 134 has good resistance to bile and low pH and exhibits fast growth in conventional laboratory media. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 24, 2000 with the accession number DSM 13802. Strain G: Bifidobacterium longum 46 has good resistance to bile and oxygen. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 15, 2001 with the accession number DSM 14583. Strain H: Bifidobacterium longum 51 has good adhesion to intestinal mucus and good resistance to oxygen. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 15, 2001 with the accession number DSM 14584. The following strains I to L, which form a still further object of this invention, were isolated from faecal specimens from very old, healthy Finnish women and men. The strains were selected using the above indicated selection criteria. Strain I: Bifidobacterium adolescentis 2C exhibits good adhesion both to intestinal mucus and to whole intestinal mucosa. It has good acidification, growth and survival in oat-based media. The strain also has good resistance to oxygen. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 15, 2001 with the accession number DSM 14579. Strain J: Bifidobacterium longum 3A exhibits good adhesion and has good resistance to bile and oxygen. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 15, 2001 with the accession number DSM 14580. Strain K: Bifidobacterium longum 6 exhibits good adhesion and has good resistance to bile and oxygen. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 15, 2001 with the accession number DSM 14581. Strain L: Bifidobacterium adolescentis 9J has good acidification, growth and survival in oat- based media. This strain has been deposited according to the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany, on October 15, 2001 with the accession number DSM 14582. All the above strains are non-spore forming Gram-positive anaerobes with rod or 'Y'-shaped cell morphology. Their shape and colony morphology on BL-agar is typical to bifidobacteria (round, smooth, brown). All the strains ferment ribose, glucose, fructose, galactose, sucrose, maltose, cellobiose, lactose, melibiose, sorbitol (A only weakly) and raffinose, but none of them ferment melezitose or inositol. The strains show mutual differences in the fermentation of arabinose and xylose [strain F (-), others (+)] , mannose [A, E, G, H, J, K and L (-), F unknown, others (+)], trehalose [A, F, G, H, I, J, K and L (-), others (+)], starch [D, G, H, I, J, K (-), others (+)], inulin [A and E (+), others (-)], glycogen [D, G, H, I, J, K, L (-), others (+)] and mannitol [E, G, H, I, J, K, L (-), others (+)]. Further strains can be isolated in a similar way to contain all or some of the above-mentioned properties, for use in disease-specific functional foods and foods for the reduction of risk of diseases such as intestinal cancers. The resulting strains can be specifically applied for the target populations, especially elderly people, to produce functional foods for such populations. For instance, the strains B. adolescentis 5, B. adolescentis 15 and -5. longum 56, isolated from healthy elderly Japanese men, where found to adhere to the intestinal mucosa of colon cancer patients. Table 1 below shows advantageous properties of e Bifidobacterium strains of the invention as compared to the probiotic prior art strain Bifidobacterium lactis Bbl2. Table 1. Adh. mucus Adhesion to mucus from elderly Adh. tissue Adhesion to intestinal tissue (whole intestinal mucosa) Adh. tissue + oat Adhesion to intestinal tissue after exposure to oat 'milk' AF live Binding of aflatoxin b1 by live bacteria AF dead Binding of aflatoxin b1 by dead bacteria Marked In grey are the properties that are better than B. lactis Bb12 EXPERIMENTAL Isolating bifidobacteria from faecal specimens The collected faecal samples were kept at 4°C and analysed within 6 hours. Fecal bifido- bacteria were isolated and identified using the methods reported by Mitsuoka [(1980) A color atlas of anaerobic bacteria. Sobunsya, Tokyo, pp. 341]. In brief, the fecal samples were homogenised, and a 10-fold serial dilution was prepared with an anaerobic buffer solution. Fifty microliters of appropriate dilutions were plated on the Blood Liver agar (BL agar; Nissui Seiyaku Co., Tokyo, Japan). The inoculum was incubated under anaerobic conditions at 37°C for 72h. The characteristic brown colonies formed on BL agar were randomly picked as potential bifidobacteria and further confirmed by Gram stain, cell morphology, absence of growth under aerobic conditions and spore formation. The strains were identified to species level based on their sugar fermentation pattern, as described by Mitsuoka [(1980) A color atlas of anaerobic bacteria. Sobunsya, Tokyo, pp. 341]. Isolated bifidobacteria were stored at -75°C in 50% glycerol until use. Screening for adhesion properties by in vitro adhesion assay using isolated intestinal mucus Mucus was isolated from the faeces by extraction and dual ethanol precipitation [Kirjavainen et al. (1998) FEMS Microbiol. Lett. 167: 185-189; Millerand & Hoskins (1981) Gastro- enterology 81 :759-765]. In short, faeces from healthy elderly volunteers were suspended in ice-cold PBS containing protease inhibitors and sodium azide. Fecal extracts were prepared by centrifuging the suspensions at 15000 x g at 4°C. Mucus was isolated from the fecal extract by dual ethanol precipitation. The pooled mucus was dissolved in HEPES (N-(2- hydroxyethyl)piperazine N-2(ethane sulfonic acid) buffered Hanks' balanced salt solution (HH; 10 mM HEPES; pH 7.4) at a concentration of 1 mg ml "1 . Any particulate material was removed from the suspension by centrifugation (2000 x g for 10 min). The tested bacteria were grown in 1 ml of GAM broth (Nissui Seiyaku Co., Tokyo, Japan) from frozen stocks. To metabolically radiolabel the bacteria, 20 μl (methyl-1, 2- 3 TX) thymidine, (117 Ci m ol -1 ) was added to the medium. After approximately 36 h of anaerobic growth at 37°C, the bacteria were harvested by centrifugation (2000 x g, 7 min), washed twice and resuspended in HH buffer. The absorbance at 600 nm was adjusted to 0.25 ± 0.01 in order to standardise the number of bacteria (approximately 10 7 CFU ml "1 ). The adhesion assay was performed essentially as reported earlier [Kirjavainen et al. (1998) FEMS Microbiol. Lett. 167, 185-189; Ouwehand (1999) FEMS Microbiol. Lett. 172, 61-64]. In short, the intestinal mucus was passively immobilised on polystyrene microtitre plate wells by overnight incubation at 4°C. The wells were washed with HH buffer and the radioactively labelled bacteria were added. After 1.5 h incubation at 37°C, the wells were washed and the adhered bacteria were lysed with 1% SDS in 0J M NaOH at 60°C for lh. The radioactivity of the lysed bacteria was assessed by liquid scintillation. Adhesion is expressed as the percentage of radioactivity recovered from the wells compared to radioactivity added to the wells. Screening for adhesion properties by ex vivo adhesion assay using resected intestinal tissue Colonic tissue was resected from colon cancer patients by surgery. The diseased part of the resected tissue was used for adhesion studies to study disease-specificity and the healthy part for studying adhesion to healthy human mucosa. The resected material was collected on ice within 20 min after resection and processed immediately. The intestine was cut open and possible contents were removed. Subsequently, the tissue was gently washed in PBS containing 0.01% gelatin until no contents were visible. From the tissue 9 mm circular pieces (64 mm 2 ) were stamped. The pieces were stored at -70°C in PBS with 40% glycerol until use. For the adhesion to the human colonic tissue a method modified after Henriksson et al. [(1991) Appl. Environ. Microbiol. 57:499-502] was used. The tissue pieces were thawed and gently washed in HH. The pieces were then placed in wells of 24-well tissue culture plates, mucosal side up. To the wells 0.5 ml of radioactively labelled bacteria were added, to cover the tissue. The plates were incubated for 1 h in a 37°C water bath. Subsequently, each well was washed twice with 1 ml of PBS and the tissue pieces were fixed with 3% glutaraldehyde in PBS for 45 min at room temperature. The mucosa was then separated from the muscle tissue with a scalpel and digested overnight with 300 μl of 30% H 2 O 2 and 150 μl of 70% perchloric acid in glass scintillation vials at 60-70°C. After digestion, 4 ml of scintillant was added and the radioactivity determined by liquid scintillation. The percentage adhesion was determined from the radioactivity in 0.5 ml of the original bacterial suspension as mentioned above for colonic mucus. Selecting strains which, when binding intestinal toxins lose their adherence to the mucus Bacteria were grown in GAM broth (Nissui Seiyaku Co., Tokyo, Japan) overnight under anaerobic conditions. The bacteria were washed twice with phosphate buffered saline (PBS) and the concentration was adjusted to lxl 0 8 CFU/ml using the method described by Virta and co-workers [(1998) Appl. Environ. Microbiol. 2:515-519]. Aflatoxin Bl (5 μg/ml) in PBS was added, the mixture was incubated at 37°C for 4 h and supernatants analysed with HPLC as previously described [El-Nezami et al. (1996) Nutr. Today 31:41-42]. The adhesion assay to intestinal mucus was performed as described above, with aflatoxin Bl-preincubated as well as non-treated bacterial suspensions. Influence of the food matrix on tissue adhesion The influence of the food matrix on the adhesion of microorganisms has been investigated only marginally for milk. It was observed that milk significantly inhibited the adhesion of all tested probiotic microorganisms. Using the new whole intestinal mucosa model, the effect of cereal substrates, especially oats, on the adhesion of the bifidobacteria was investigated. In contrast to the observations for milk (Ouwehand et al. 2001, Int. J. Food Microbiol. 64: 119- 126), oat substrate was observed to more than double the adhesion to the whole intestinal mucosa (ex vivo) of selected B. adolescentis strains. Other tested strains were not affected in their (ex vivo) adhesion. This suggests that a cereal substrate, especially oat substrate has a positive or no effect on the adhesion of probiotic bacteria, while milk has a strong negative effect on the adhesion of probiotics (Ouwehand et al. 2001 Int. J. Food Mcrobiol. 64: 119- 126). The effect of ash, protein and fibre content was investigated using different mill fractionated cereals; oats, rye and barley. Bifidobacterium strains showed to grow in all fractions but the best was oats, and oats also increased the tissue adhesion. Selecting strains likely to survive the passage through the intestinal tract Bacteria were grown in GAM broth (Nissui Seiyaku Co., Tokyo, Japan) overnight under anaerobic conditions. The bacteria were washed twice with phosphate buffered saline (PBS) and the concentration was adjusted to approximately 10 8 CFU/ml by adjusting the absorbance at 600 nm to 0.5. The bacteria were centrifuged, resuspended in PBS, PBS+0.3% Oxgall or PBS at pH 2.5 and incubated for 60 min at 37°C. Viability in the different incubations was assessed by plate counting on BL-agar and compared to the PBS incubation. Screening strains with the ability to grow on cereal oligosaccharides Flour fractions enriched in oat starch or oat β-glucan were produced. From these fractions and whole oat flour, a stable slurry was produced to obtain an oat-drink. Strains were inoculated in this drink, and their growth (determined as CFU/ml on BL-agar) and ability to acidify the substrate were assessed. Screening for the aerotolerance of the bacteria Bacteria were grown in GAM broth (Nissui Seiyaku Co., Tokyo, Japan) overnight under anaerobic conditions. The bacteria were spread on BL-agar and incubated under strict anaerobic conditions (control), under aerobic conditions and under conditions with 3-5% oxygen. Possible growth on the latter two was compared to growth on the control. Screening for the most effective strains that inhibit the growth of common intestinal pathogens Bacteria were grown in GAM broth (Nissui Seiyaku Co., Tokyo, Japan) overnight under anaerobic conditions. The bacteria were removed from the broth by centrifugation. The spent culture liquid was neutralised to pH 7.0 by the addition of 1M NaOH and filter-sterilised. Intestinal pathogens were grown overnight at 37° in an appropriate medium (Luria-Bertani- broth; LB-broth). Neutralised spent culture liquid was mixed in 1:1 ratio with double concentrated LB-broth and inoculated with intestinal pathogens. The growth of the pathogens was assessed by determining the absorbance at 600 nm at regular intervals. The results were compared to growth in fresh GAM broth mixed with double concentrated LB-broth as control. Screening for the most effective strains that inhibit the adhesion of common intestinal pathogens Mucus was isolated from the faeces by extraction and dual ethanol precipitation as described above. In vitro adhesion assay The tested bacteria were grown in 1 ml GAM broth (Nissui Seiyaku Co., Tokyo, Japan) from frozen stocks. After approximately 36 h of anaerobic growth at 37°C, the bacteria were harvested by centrifugation (2000 x g, 7 min), washed twice and resuspended in HH buffer. The absorbance at 600 nm was adjusted to 0.25 ± 0.01 in order to standardise the number of bacteria (approximately 10 7 CFU ml "1 ). The intestinal pathogens were grown in LB-broth and metabolically radiolabeled with 10 μl (methyl-l,2- 3 Η.) thymidine (117 Ci mmol -1 ) in the medium. After overnight growth at 37°C, the bacteria were harvested by centrifugation (2000 x g, 7 min), washed twice and resus- pended in HH buffer. The absorbance at 600 nm was adjusted to 0.25 ± 0.01 in order to standardise the number of bacteria (approximately 10 7 CFU ml "1 ). The adhesion assay was performed essentially as reported earlier [Kirjavainen et al. (1998) FEMS Microbiol. Lett. 167, 185-189; Ouwehand et al. (1999) FEMS Microbiol. Lett. 172, 61-64]. In short, the intestinal mucus was passively immobilised on polystyrene microtitre plate wells by overnight incubation at 4°C. The wells were washed with HH buffer and the bacteria to be assessed were added. After 1 h incubation at 37°C, the wells were washed and the radiolabelled intestinal pathogens were added and incubated again for lh at 37°C. As a control, intestinal pathogens were also allowed to adhere to immobilised intestinal mucus not pre-treated with the test bacteria. The adhered bacteria were lysed with 1% SDS in 0J M NaOH at 60°C for lh. The radioactivity of the lysed bacteria was assessed by liquid scintillation. The effect of the test bacteria on the adhesion of the intestinal pathogens was expressed as the percentage of radioactivity recovered from the wells pre-treated with test bacteria, compared to radioactivity recovered from the wells without test bacteria. Determining the absorption of aflatoxin Bl and other mycotoxins to viable and heat- killed strains Bacteria were grown in GAM broth (Nissui Seiyaku Co., Tokyo, Japan) overnight under anaerobic conditions. The bacteria were washed twice with phosphate buffered saline (PBS) and the concentration was adjusted to lxl 0 10 CFU/ml using the method described by Nirta and co-workers [(1998) Appl. Environ. Microbiol. 2:515-519]. Aflatoxin Bl (5 μg/ml) in PBS was added, the mixture was incubated at 37°C for 4 h and supernatants analysed with HPLC as previously described [El-Νezami et al. (1996) Νutr. Today 31:41-42]. The tested bacteria were heat killed by boiling for lh. Determining the influence of the host microflora on their mucus-binding properties, using the specific target group's own microflora as a selection criterion Mucus was isolated as described above. The adhesion assay was modified from the description under the paragraph 'Screening for adhesion properties by in vitro adhesion assay... '. In short, intestinal mucus was immobilised on polystyrene microtitre plate wells by overnight incubation at 4°C. The wells were washed with HH. To the wells, 100 μl PBS, faecal extract, faecal bacteria or washed faecal bacteria were added and incubated for 1 h at 37°C. The wells were subsequently washed and 100 μl radiolabelled probiotic bacteria were added. After lh incubation at 37°C, the wells were washed and the adhered bacteria were lysed with 1% SDS in 0J M NaOH. The radioactivity of the lysed bacteria was assessed by liquid scintillation. Adhesion is expressed as the percentage of radioactivity recovered from the wells compared to the the radioactivity added to the wells. Preparing of food products and dietary supplements Example 1. Cold Oat Meal with Bifidobacteria One or more of the strains Bifidobacterium adolescentis 5, 15, 19, 34, 2C, 9J, Bifidobacterium longum 51, 56, 46, 3 A, 6 ox Bifidobacterium breve 134 were cultivated in a medium: Trypticase peptone 8 g/l Phytone peptone 3 g/l Yeast extract 5 g/l K 2 HPO 4 g/l KH 2 PO 4 3 g/l MgCl 2 .6H 2 O 0.5 g/1 FeSO 4 JH 2 O lO mg/1 Propionate 50 mg/1 Glucose 20 g/1 L-cysteine-HCl 0.5 g/1 Growth conditions: pH controlled: 6.5; Temp: 37°C; Incubation time: approx. 2 days (until consumption of NaOH, to neutralise the medium, has stopped); N 2 -atmosphere. The bacterial cells were separated and freeze-dried. The cold oat meal was produced by mixing the dry cereal and berry ingredients with the powder of Bifidobacterium strain or strains as follows: Instant oat flakes 75 % Dry berry or fruit powder 10 % (blackberries, strawberries, banana, apple) Sugar 14 % Freeze-dried strain or strains of bifidobacteria 0,05 % ( containing 10 12 -10 13 cells/g) The product was immediately gas-packed in nitrogen atmosphere in one-serving aluminium foil packages. The size of one serving is 35 g and it contains at least 10 8 — 10 9 bifidobacterial cells per serving. One serving of a dry meal is mixed with 3/4-1 dl of cold or lukewarm milk. Example 2. Fermented oat material The following ingredients were mixed in a container suitable for heat treatment: 9.5 % oat flour 2.6 %> resistant starch or oat starch 3.0 % oligofructose 84.9 % water The mixture, being first gelatinised by steam heating to reach the temperature of 131°C and further kept at that temperature for 2-3 minutes, was mechanically homogenised and finally cooled at approximately 37°C. The slurry obtained was then transferred into a fermentation tank, and inoculated with one of the strains, or with a mixture of strains of Bifidobacterium species selected from Bifidobacterium adolescentis 5, 15, 19, 34, 2C, 9J, Bifidobacterium longum 56, 51, 46, 3 A, 6 or Bifidobacterium breve 134. Freeze-dried strain or strains of bifidobacteria contained 10 12 - 10 13 colony forming units per gram. The concentration of the bacteria added into the slurry was 0.05 - 0J % calculated from the weight of the batch. The fermentation took place at 37°C for 18-24 hours affording to fermented material, which was characterised as follows; pH 4.2- 4.8, colony forming units of bifidobacteria per gram: 10 8 - 10 9 , a total acidity of about 0.2-0.4 weight-%, expressed as lactose acid content. The fermented cereal material can be stored under 8°C up to 2 days before using, or pasteurised for long-term storage. This material is suitable for the preparation of fruit desserts, fresh cheese, yoghurts, beverages etc. Dosage, means of insertion and finishing treatment are determined by the desired product. Example 3. Fermented material with oat and rice The following ingredients were mixed in a container suitable for heat treatment: 6 % oat flour 1.5 % oat starch 3.0 % rice flour 1.5 % isolated soy proteinate 3.0 % oligofructo se 1.0 % glucose 1.0 % casein hydrolysate 83 % water The mixture was treated as described in Example 2 to obtain a corresponding product.

Claims: Claims 1. A method for screening probiotic strains of the genus Bifidobacterium, comprising isolating bifidobacteria from faecal specimens of healthy elderly human subjects, and screening for their age- and disease-specific properties by screening for their adhesion to intestinal mucus glycoproteins and to whole intestinal mucosa and, optionally, subjecting the bacteria further to the steps of a) selecting for strains which, when binding intestinal toxins lose their adherence to the mucus, b) selecting for strains likely to survive the passage through the intestinal tract, c) screening for the ability of the strains to grow on cereal-based substrates, d) screening for the aerotolerance of the strains, and e) selecting for the most effective strains that inhibit common intestinal pathogens, and isolating and identifying the strains showing an appropriate selection of the above-indicated properties. 2. The method according to claim 1, wherein the bifidobacteria are isolated from freshly voided faecal specimens of healthy very old human subjects. 3. The method according to claim 1, wherein the screening for age-specific properties is effected by subjecting the bacteria to a test using human intestinal mucus glycoproteins and their age-dependent samples, to select for specific bacteria adhering to the mucus of very old healthy subjects. 4. The method according to claim 1, wherein the screening for disease-specific properties is effected by subjecting the bacteria to a test using human intestinal mucus glycoproteins or whole intestinal mucosa from subjects with different intestinal dysfunctions. 5. The method according to claim 1, wherein the selection for strains which, when binding intestinal toxins lose their adherence to the mucus, is effected by placing the bacteria in a test using mycotoxin and/or bacterial toxin binding as a model for intestinal toxin binding. 6. The method according to claim 1, wherein the selection of strains likely to survive the passage through the intestinal tract is effected by testing their relative resistance to bile and low pH by assessing their viability with the help of flow cytometry. 7. The method according to claim 1, wherein the ability of the strains to grow on cereal-based substrates is effected by cultivating the strains on different substrates, and selecting strains being able to grow on substrates of interest. 8. The method according to claim 7, wherein the cereal-based substrates are oat-based substrates. 9. The method according to claim 8, wherein the oat-based substrates are oat carbohydrates. 10. The method according to claim 1, wherein the screenmg for the aerotolerance of the bacteria is effected by culturing the strains on blood liver agar plates in an atmosphere with reduced oxygen pressure. 11. The method according to claim 1, wherein the selection for strains inhibiting common intestinal pathogens is effected by subjecting the bacteria to competitive exclusion of model pathogens. 12. A biologically pure culture of a probiotic Bifidobacterium strain, selected from the strains Bifidobacterium adolescentis 5, having the accession number DSM 13797, Bifidobacterium adolescentis 15, having the accession number DSM 13798, Bifidobacterium adolescentis 19, having the accession number DSM 13799, Bifidobacterium adolescentis 34, having the accession number DSM 13800, Bifidobacterium longum 56, having the accession number DSM 13801, Bifidobacterium breve 134, having the accession number DSM 13802, Bifidobacterium adolescentis 2C, having the accession number DSM 14579, Bifidobacterium longum 3 A, having the accession number DSM 14580, Bifidobacterium longum 6, having the accession number DSM 14581, Bifidobacterium adolescentis 9J, having the accession number DSM 14582, Bifidobacterium longum 46, having the accession number DSM 14583 and Bifidobacterium longum 51, having the accession number DSM 14584. 13. Use of the probiotic strains of the genus Bifidobacterium isolated according to any one of the claims 1 to 11 for producing functional or clinical food products or dietary supplements. 14. Use of the probiotic Bifidobacterium strains as defined in claim 12 for producing functional or clinical food products or dietary supplements. 15. Use according to claim 13 or 14, wherein the functional or clinical food products are age- specific or disease- specific functional or clinical food products. 16. A functional or clinical food product, comprising at least one strain of the genus Bifidobacterium being selected by the method according to any one of the claims 1-11, or at least one of the Bifidobacterium strains as defined in claim 12. 17. A dietary supplement, comprising at least one strain of the genus Bifidobacterium being selected by the method according to any one of the claims 1-11, or at least one of the Bifidobacterium strains as defined in claim 12.

Inventors: ISOLAURI ERIKA, OUWEHAND ARTHUR, SALMINEN EEVA, SALMINEN SEPPO, ISOLAURI, ERIKA, OUWEHAND, ARTHUR, SALMINEN, EEVA, SALMINEN, SEPPO
Applicants: BIOFERME OY, ISOLAURI ERIKA, OUWEHAND ARTHUR, RAISIO YHTYMAE OYJ, SALMINEN EEVA, SALMINEN SEPPO, ISOLAURI, ERIKA, OUWEHAND, ARTHUR, SALMINEN, EEVA, SALMINEN, SEPPO
Application year: 2001
Main classification: C12Q1
IPC codes: A23L1, C12Q1