Title of Invention	"ANTIMICROBIAL COMPOSITIONS CONTAINING STREPTOCOCCUS SALIVARIUS, AND USES THEREOF IN TREATING OR PREVENTING DENTAL CARIES "
Abstract	A biologically pure culture of a Streptococcus salivarius strain Mia on deposit at Deutsche Sammlung von Mikroorganismen Und Zellkulturen GmbH, Mascheroder Weg 1 b, D-38124, Braunschweig, Germany, Accession No DSM14685.

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ANTIMICROBIAL COMPOSITION FIELD OF THE INVENTION This invention relates to novel Streptococcus salivarius, compositions containing same, and use of Streptococcus salivarius strains as antimicrobial agents, particularly in the prevention or treatment of dental caries. BACKGROUND Dental caries is a disease characterised by dissolution of the mineral portion of the tooth. As caries progresses, destruction of tooth enamel and dentine occurs followed by inflammation of pulp and periapical tissues. The mutans streptococci (MS) are a cluster of acidogenic, dental plaque-inhabiting streptococcal species that are considered the principal causative agents of caries. Presently, seven different MS species (known as 5. mutans, S. rattus, S. cricetus, S. sobrinus, S.ferus, S. macacae, and S. downei) are recognised. Of these seven species it is mainly S. mutans and S. sobrinus that are of significance in terms of human caries. Over the years various methods have been developed and tried with varying results, to prevent or at least alleviate the problem of dental caries. Treatments with antibiotics such as penicillin have been suggested and are effective but indiscriminately destroy both useful and harmful bacteria in the mouth leading to microbial imbalances. In order to minimise disruption to the mouth microflora, antibiotic producing organisms have been investigated for their ability to inhibit caries. A group of organisms identified as having potential in this regard are microorganisms producing bacteriocin-like inhibitory substances (BLIS). BLIS producers of the genera Streptococcus, Staphylococcus and Enterococcus have been screened for potential application to prevention of dental caries (Balakrishnan, M. et al., Caries Res. 2001; 35:75-80). ANTIMICROBIAL COMPOSITION FIELD OF THE INVENTION This invention relates to novel Streptococcus salivarius strain Mia, compositions containing same, and use of Streptococcus salivarius strain Mia as an antimicrobial agent, particularly in the prevention or treatment of dental caries. BACKGROUND Dental caries is a disease characterised by dissolution of the mineral portion of the tooth. As caries progresses, destruction of tooth enamel and dentine occurs followed by inflammation of pulp and periapical tissues. The mutans streptococci (MS) are a cluster of acidogenic, dental plaque-inhabiting streptococcal species that are considered the principal causative agents of caries. Presently, seven different MS species (known as S. mutans, S. rattus, S. cricetus, S. sobrinus, S.ferus, S. macacae, and S, dovmei) are recognised Of these seven species it is mainly S. mutans and S. sobrinus that are of significance in terms of human caries. Over the years various methods have been developed and tried with varying results, to prevent or at least alleviate the problem of dental caries. Treatments with antibiotics such as penicillin have been suggested and are effective but indiscriminately destroy both useful and harmful bacteria in the mouth leading to microbial imbalances. In order to rninimise disruption to the mouth microflora, antibiotic producing organisms have been investigated for their ability to inhibit caries. A group of organisms identified as having potential in this regard are microorganisms producing bacteriocin-lDce inhibitory substances (BLIS). BLIS producers of the genera Streptococcus, Staphylococcus and Enterococcm have been screened for potential application to prevention of dental caries (Balakrishnan, M. et al-, Caries Res. 2001; 35:75-80). What is sought is a non-virulent analog of the disease-causing S mutans., or a so called effector strain. To serve as an effector strain in replacement therapy in bacterial infection, the microorganism must be non-virulent itself and able to compete successfully with the pathogenic microorganism either via competitive action and/or antibiotic action. S. mutans effector strains have been identified (Hillman et al., J Dent Res. 1987; 66:1092-4; James and Tagg, N Z Dent J. 1991; 87:80-3) and show strong anti-S. mutans activity. A disadvantage with the use of S. mutans effector strains is the cariogenic potential of these strains. S. salivarius is an alternative streptococcus species which avoids this disadvantage. In WO 01/27143 S. salivarius strains are identified which have utility in the treatment of dental caries caused at least in part by S. sobrinus. No activity was recorded against MS generally or S. mutans in particular. Similarly, in Balakrishnan (supra), S. salivarius K3 is identified as active against S. sobrinus when grown on trypticase soy broth yeast extract calcium carbonate agar medium, but had no effect on S. mutans. S. salivarius TOVE-R (Tanzer, J.M. et al.; Infect Immun., 1985, 48:44-50) is an antagonist strain and which brought about a reduction in dental caries. There have been no reports of BLIS production by this strain. The applicants have now identified BLIS-producing S. salivarius strains with a broad spectrum of activity against MS dental caries causing organisms including S. mutans. The present invention is broadly directed to these novel S. salivarius strains, and the use of anti-MS S. salivarius strains in the treatment of dental caries, or at least provides the public with a useful choice. SUMMARY OF THE INVENTION Accordingly, in one aspect, the present invention may broadly be said to consist in a biologically pure culture of a Streptococcus salivarius strain which is a Salivaricin A2 producer and which exhibits anti-MS activity, with the proviso that the strain is not S. salivarius K12(K12). What is sought is a non-virulent analog of the disease-causing S. mutans, or a so called effector strain. To serve as an effector strain in replacement therapy in bacterial infection, the microorganism must be non-virulent itself and able to compete successfully with the pathogenic microorganism either via competitive action and/or antibiotic action. S. mutans effector strains have been identified (Hillman et al., J Dent Res. 1987; 66:1092-4; James and Tagg, N Z Dent J. 1991; 87:80-3) and show strong anti-S. mutans activity. A disadvantage with the use of S. mutans effector strains is the cariogenic potential of these strains. S. salivarius is an alternative streptococcus species which avoids this disadvantage. In WO 01/27143 S. salivarius strains are identified which have utility in die treatment of dental caries caused at least in part by S. sobrinus. No activity was recorded against MS generally or S. mutans in particular. Similarly, in Balakzishnan (supra), S. salivarius K3 is identified as active against S. sobrinus when grown on trypticase soy broth yeast extract calcium carbonate agar medium, but had no effect on S, mutans. • S. salivarius TOVE-R (Tauzer, J.M. et al.; Infect Immun., 1985, 48:44-50) is an antagonist strain and which brought about a reduction in dental caries. There have been no reports of BLIS production by this strain. The applicants have now identified BLIS-producing S. salivarius strains with a broad spectrum of activity against MS dental caries causing organisms including S. mutans. The present invention is broadly directed to these novel S. salivarius strains, and the use of anti-MS S. salivarius strains in the treatment of dental caries, or at least provides the public with a useful choice. SUMMARY OF THE INVENTION Accordingly, in one aspect, the present invention may broadly be said to consist in a biologically pure culture of a Streptococcus salivarius strain Mia on deposit at Deutsche Sammlung von Mikroorganismen Und Zellikulturen GmbH, Mascheroder Weg 1 b, D-38124, Braunschweig, Germany, Accession No. DSM14685. In another aspect, the invention provides a biologically pure culture of a Streptococcus salivarius strain which is a Salivaricin A2 producer, exhibits anti-MS activity, and for carbohydrate metabolism is positive for at least one of L-arabinose, inulin, glycogen, xylitol, and ß-gentiobiose use, or ß-galactosidase production; and/or is negative for at least one of glycerol, α-methyl-D-mannoside use, or alkaline phosphoaase production. Preferably, the strain is positive for each of L-arabinose, inulin, glycogen, xylitol, and ß-gentiobiose use, or P-galactosidase production; and/or is negative for each of glycerol, α-methyl-D-mannoside use, or alkaline phosphatase production. The invention further provides a biologically pure culture of Streptococcus salivarius strain Mia on deposit at Deutsche Sammlung von Mikroorganismen Und Zellkulturen GmbH, Mascheroder Weg 1 b, D-38124, Braunschweig, Germany, Accession No. DSM 14685, or a culture having the identifying characteristics thereof. The invention also provides an extract obtainable from Salivaricin A2-producing strains of S. salivarius, which extract has anti-MS activity. In particular, the extract has anti-5. mutans activity. Conveniently, the extract is obtainable from S. salivarius strains Mia or K.12. In a further aspect, the present invention provides an antibacterial composition which includes an S. salivarius or extract as defined above. In a still further aspect, the present invention provides a therapeutic formulation comprising an S. salivarius or extract as defined above, together with a diluent, carrier and/or excipient. In one embodiment, the composition or formulation further comprises a secondary antibacterial agent. In one embodiment, the therapeutic formulations are in the form of foods or drinks, preferably in the form of a dairy product-based food or drink. Alternative forms are medicaments, lozenges and confectionaries. The invention further provides a method for at least inhibiting the growth of bacteria sensitive to S. salivarius of the invention, the method comprising contacting the sensitive bacteria with In another aspect, the invention provides a biologically pure culture of a Streptococcus salivcuius strain Mia which is a Salivaricin A2 producer, exhibits anti-MS activity, and for carbohydrate metabolism is positive for at least one of L-arabinose, inulin, glycogen, xylitol, and ß-gentiobiose use, or ß-galactosidase production; and/or is negative for at least one of glycerol, a-methyl-D-mannoside use, or alkaline phosphoaase production. Preferably, the strain is positive for each of L-arabinose, inulin, glycogen, xylitol, and 13-gentiobiose use, or ß-galactosidase production; and/or is negative for each of glycerol, a-methyl-D-mannoside use, or alkaline phosphatase production. The invention also provides an extract obtainable from S. salivarius strain Mia, which extract has anti-MS activity. In particular, the extract has anti-5. mmans activity. In a further aspect, the present invention provides an antibacterial composition which includes an S. salivarius strain Mia as defined above. In a still further aspect, the present invention provides a therapeutic formulation comprising an S. salivarius strain Mia or extract as defined above, together with a diluent, carrier and/or excipient In one embodiment, the composition or formulation further comprises a secondary antibacterial agent. In one embodiment, the therapeutic formulations are in the form of foods or drinks, preferably in the form of a dairy product-based food or drink. Alternative forms are medicaments, lozenges and confectionaries. The invention further provides a method for at least inhibiting the growth of bacteria sensitive to 5. salivarius of the invention, the method comprising contacting the sensitive bacteria with an inhibitory effective amount of an S. salivarius, extract or composition or formulation of the invention. Preferably the sensitive bacteria are MS, and more preferably S. mutans. The invention provides in another aspect a method for at least inhibiting the growth of MS or S. mutans, the method comprising contacting the MS or S. mutans with an inhibitory effective amount of: (i) an S. salivarius extract composition or formulation of the invention; or (ii) S. salivarius K12 or an anti-MS or anti-S. mutans active extract therefrom, or a composition or formulation comprising K12 or an active extract therefrom. In a further aspect, the invention provides a method of prophylactic or therapeutic treatment of dental caries caused at least in part by S. mutans in an individual in need thereof, the method comprising administering to said individual: (i) an S salivarius, extract, composition or formulation of the invention; or (ii) S. salivarius K12 or an anti-S mutans active extract therefrom, or a composition or formulation comprising K.12 or an active extract therefrom, in an amount effective to at least inhibit growth of S. mutans in the oral cavity of the individual. In a further aspect, the invention provides a method of controlling the incidence and severity of dental caries comprising introducing into the oral cavity of an individual susceptible to dental caries, a dental caries controlling amount of an S. salivarius, extract, composition or formulation of the invention. In one embodiment the dental caries is caused by MS. In that instance, S. salivarius K12 or an anti-MS active extract, or composition or formulation containing same may also be used. Preferably, S. salivarius is administered as part of a food, drink or nutraceutical. The methods of the invention may include the preliminary step of pre-treating the individual to at least reduce the normal microflora already present. an inhibitoiy effective amount of an S. salivarius strain Mia, extract or composition or formulation of the invention. Preferably the sensitive bacteria are MS, and more preferably S. mutans. The invention provides in another aspect a method for at least inhibiting the growth of MS or S. mutans, the method comprising contacting the MS or S. mutans with an inhibitory effective amount of an S. salivarius strain Mia extract composition or formulation of the invention. In a further aspect, the invention provides a method of prophylactic or therapeutic treatment of dental caries caused at least in part by S. mutans in an individual in need thereof, the method comprising administering to said individual an S. salivarius strain Mia, extract, composition or formulation of the invention in an amount effective to at least inhibit growth of S. mutans in the oral cavity of the individual In a further aspect, the invention provides a method of controlling the incidence and severity of dental caries comprising introducing into the oral cavity of an individual susceptible to dental caries, a dental caries controlling amount of an S. salivarius strain Mia extract, composition or formulation of the invention. In one embodiment the dental caries is caused by MS. In that instance, S. salivarius K12 or an anti-MS active extract, or composition or formulation containing same may also be used. Preferably, S. salivarius is administered as part of a food, drink or nutraceutkal. The methods of the invention may include the preliminary step of pre-treating the individual to at least reduce the normal microflora already present. The invention also relates to the use of S. salivarius or extracts of the invention in the compositions and methods discussed above. In another aspect, the invention also relates to the use of S. salivarius strains (including K12) and active extracts in the methods discussed above for inhibiting, controlling, preventing or treating dental caries caused at least in part by S. mutans, and more usually by MS. Although the invention is broadly as described above, it will be appreciated by those persons skilled in the art that the invention is not limited thereto but also includes embodiments of which the following description gives examples. DETAILED DESCRIPTION OF THE INVENTION As noted above, the present invention is directed in a first aspect to Streptococcus salivarius strains which produce Salivaricin A2 and which exhibit anti-MS activity. When grown on TSBCaYE agar, the S. salivarius strains desirably exhibit activity against a broader spectrum of MS including S. mutans. Salivaricin A2 and an A2-producing S. salivarius strain (strain K12) are described for example in WO 01/27143 incorporated herein by reference. In one embodiment the invention is directed to S. salivarius strain Mia and S. salivarius strains having the identifying characteristics thereof. Strain Mia is distinct from strain K12 in its biochemical characteristics as determined using API 20 Strep kit (bioMerieux) and API 50 CH (bioMerieux) which allow study of the carbohydrate metabolism. The differences are summarised as follows: API 20 Strep kit MIA K12 P-galactosidase + Alkaline phosphatase - + API 50 CH The invention also relates to the use of S. salivarius strain Mia or extracts of the invention in the compositions and methods discussed above. In another aspect, the invention also relates to the use of S. salivarius strain Mia and active extracts in the methods discussed above for inhibiting, controlling, preventing or treating dental caries caused at least in part by S. mutans, and more usually by MS. Also disclosed is the use of S. salivarius K12 or an anti-MS or anti-S mutans active extract therefrom or a composition comprising same in the methods discussed above for inhibiting, controlling, preventing or treating dental caries caused at least in part by S. mutans, and more usually by MS. Although the invention is broadly as described above, it will be appreciated by those persons skilled in the art that the invention is not limited thereto but also includes embodiments of which the following description gives examples. DETAILED DESCRIPTION OF THE INVENTION As noted above, the present invention is directed in a first aspect to Streptococcus salivarius strain Mia which produces Salivaricin A2 and which exhibits anti-MS activity. When grown on TSBCaYE agar, the S. salivarius strain desirably exhibit activity against a broader spectrum of MS including S. mutans. Salivaricin A2 and an A2-producing S. salivarius strain (strain K12) are described for example in WO 01/27143 incorporated herein by reference. In one embodiment the invention is directed to S. salivarius strain Mia and S. salivarius strains having the identifying characteristics thereof Strain Mia is distinct from strain K12 in its biochemical characteristics as determined using API 20 Strep kit (bioMerieux) and API 50 CH (bioMerieux) which allow study of the carbohydrate metabolism. The differences are summarised as follows: API20 Strep kit MIA K12 ß-galactosidasc + Alkaline phosphatase - + API 50 CH Glycerol - + anaerobic L-arabinose + α-methyl-D-mannoside - + aerobic Inulin + Glycogen + Xylitol + {3-gentiobiose + Preferably, strains for use in the invention exhibit at least one, preferably at least three, more preferably at least six, and even more preferably all of the distinguishing biochemical characteristics of strain Mia. Mia also exhibits stronger anti-MS, and in particular stronger anti-S. mutans activity than K12. S. salivarius strain Mia is a BLIS-producing strain with activity against other bacteria, particularly streptococci, and more particularly MS, including S. mutans. S. salivarius strain Mia was deposited with Deutche Sammlung von Mikroorganismen Und Zellkulturen GmbH, Mascheroder Weg 1 b, D-38124, Braunschweig, Germany on 12 December 2001 and has been assigned Accession No. DSM 14685. As noted above MS are considered the primary causative agents in dental caries with S. mutans being of particular significance. While BLIS-producing strains of 5. salivarius active against streptococci have been reported previously, this is the first time that BLIS producing S. salivarius active against MS and S. mutans in particular, have been identified. The S salivarius strains of the invention exhibit broad spectrum antibacterial activity, particularly when grown on TSBCaYE agar media. The S. salivarius are therefore useful as antibacterial agents per se as well as therapeutically. In this context, "therapeutic" includes prophylactic treatment. Therapeutic uses include the treatment or prevention of microbial infections, especially streptococcal infections. The salivarius' of the invention are particularly suitable for use against MS and S. mutans. Conditions amenable to treatment with the strains or extracts of the invention include dental caries, sore throats, and bad breath. The invention also relates to extracts obtainable from salivaricin A2-producing strains of S. - salivarius and especially from strains of the invention. These active extracts may similarly be used in therapeutic formulations and methods. Extracts can be obtained using known art protocols, conveniently by cell culture and centrifugation. A "therapeutic formulation" is a formulation appropriate for administration of an S. salivarius strain or extract of the invention, to an individual in need of same, particularly a dental caries-susceptible individual. In general, therapeutic formulations of the invention are composed of an S. salivarius strain or extract of the invention and an acceptable carrier, diluent and/or excipient. An "acceptable carrier, diluent and/or excipient" means a vehicle for delivery of a S. salivarius strain or extract of the invention, to the individual, in which the vehicle is compatible with bacterial cell viability, or activity of the extract. Acceptable carriers suitable for use in the administration of viable S. salivarius strains of the invention and extracts are well known to those skilled in the art. Suitable carriers are generally inert and can be either solid or liquid. In one embodiment, the carrier is a pharmaceutically acceptable carrier. Pharmaceutically acceptable carriers suitable for use with the S. salivarius strains herein include, but are not limited to, water, buffered saline solutions (e.g., phosphate-buffered saline), pharmaceutically acceptable culture media (e.g. BACa, TSBCaYE agar), or other solutions which maintain the viability of the bacterium. Additionally, such pharmaceutically acceptable carriers may be aqueous or non-aqueous solutions, suspensions, and emulsions. A variety of pharmaceutically acceptable carriers suitable for oral administration of viable or lyophilized bacteria are well known in the art (see, for example, Remington's Pharmaceutical Sciences, 18th ed., Gennaro, ed., 1990, Mack Publishing Co., Easton, Pa., incorporated herein by reference; and the pharmaceutical composition LACTINEX™, a commercially available formulation for oral administration of viable lactobacilli). Suitable solid carriers known in the art include, for example, magnesium carbonate; magnesium stearate; celluloses; talc; sugars such as fructose, sucrose, mannitol, lactose; starches; flours; and skim milk, and similar edible powders, but are not limited thereto. Carriers for administration of extracts are similarly well known. Typical diluents, by way of example, are: starches; lactose; mannitol; kaolin; calcium phosphate or sulphate; inorganic salts such as sodium chloride; and powdered sugars or celluloses. The compositions may also include excipients such as tableting aids; resins; fillers; binders; lubricants; solvents; glidants; disintegrants; preservatives; buffers; flavourings; colourings; sweeteners; and fragrances as appropriate. A preferred excipient for tablet flowability and compactability is ProSoIv™ (Penwest, NY, USA). A preferred sweetener is isomalt. Typical binders include starch; gelatin; sugars such as lactose, fructose, and glucose; and the like. Natural and synthetic gums are also convenient, including acacia; alginates; methylcellulose; polyvinylpyrrolidine tragacanth; and the like. Polyethylene glycol; ethyl cellulose; and waxes can also serve as binders. A currently preferred binder is Emdex™ (Penwest, NY, USA). Lubricants to prevent sticking to the die during formation include slippery solids such as talc, silica, magnesium and calcium stearate, polyethylene glycol, stearic acid and hydrogenated vegetable oils. Disintegrators are substances which swell when wetted to break up the lozenge and release the S. salivarius or extract. The disintegrators include starches; clays; celluloses; algins and gums; more particularly corn and potato starches; methylcellulose; agar; bentonite; wood cellulose; cation exchange resins; alginic acid; guar gum; citrus pulp; carboxymethylcellulose; powdered sponge; and sodium lauryl sulfate. The S. salivarius strains or extracts of the invention can be formulated in any of a variety of compositions suitable for oral administration. For example, the S. salivarius strains can be formulated for administration as a lyophil or cell paste prepared from a S. salivarius culture, or can be directly administered to the oral cavity. The strain or extract can also be administered in the form of a mouthwash, mouth rinse, toothpaste, mouthspray, gargle, capsule, lozenge, syrup, floss, chewing gum, or chewable tablet but the forms are not limited thereto. Therapeutic formulations may include food, confectionary or drink. In one embodiment, the foodstuff or drink is a dairy product-based food or drink including by way of example, yoghurt, cheese, milk, milk power, milk biscuits, and flavoured milks. In the case of confectionary, the formulation can be a chewing gum such as described in WO 00/05972. One preferred formulation employs freeze dried S. salivarius of the invention in milk powder formulations in a manner similar to that previously reported for the preparation of Bifidus Milk Powder (Nagawa et al. (1988); J. Dairy Sci. 71:1777-1782). One orally administrable formulation of S. salivarius is a blend of freeze dried S. salivarius strains with skim milk powder or the like which has been flavoured to enhance palatability. Presently preferred orally administrable formulation of S. salivarius, or extracts of the invention are lozenges, chewable tablets, or capsules. Lozenges are particularly preferred. A suckable lozenge according to the invention comprises an S. salivarius strain or extract of the invention, isomalt and emdex. The lozenge may be prepared by direct compression, wet granulation, or dry granulation. The lozenges may be coated according to well known pharmaceutical practice. The therapeutic formulation can additionally contain nutrients to maintain the viability of the bacterium in the formulation. As noted above, the formulation can also contain flavouring agents, colouring agents, fragrances, or other compounds which increase the palatability of the composition and/or enhance patient compliance without compromising the effectiveness of the formulation. Methods for preparation of formulations for oral administration are well known in the art (see, for example, Remington's Pharmaceutical Sciences, 18th ed., supra, incorporated herein by reference). For general antimicrobial use, formulations may also be produced for other methods of administration including topically administrable formulations but not limited thereto. K12 and active extracts thereof discussed above may similarly be prepared as above, including in the compositions and formulations discussed. The formulations and compositions of the invention may further comprise one or more secondary antibacterial agents. These secondary agents may, for example, be antibiotics, or other antibacterial agent or antibacterial producing microorganisms. Useful antibacterials include nisin, and other BLIS for example. Preferably, the secondary antibacterial agent is a BLIS or BLIS producing microorganism. The BLIS may be one or more of salivaricin A, A1, A2 and B. Other antibacterial microorganisms include known S. salivarius such as K12 and K30. S. salivarius strains of the invention are primarily found on the tongue surface. Combinations with S. salivarius that grow in dental plaque such as TOVE-R (supra) would be useful. The formulation and compositions of the invention may additionally comprise other anti-cariogenic agents, for example, xylitol, fluoride, Manuka honey, and tannins. In the treatment of dental caries, S. salivarius strains or extracts of the invention can be administered to any dental caries-susceptible individual, usually an individual in which S. mutans or MS colonises the oral cavity such that the dental caries is caused at least in part by S. mutans and more commonly by MS. The term "individual" as used herein includes humans, horses, dogs, cats, pigs, sheep, cattle, goats but is not limited thereto. Preferably, the individual is a human. The S. salivarius strains can be administered to the individual at any age, e.g. childhood, adolescence, or adulthood. The S. salivarius of the invention or K12 can be orally administered in a variety of ways. For example, in the form of compositions or formulations discussed above, or as suspensions, sustained release formulas (e.g. an oral implant containing the S. salivarius strain) or lyophil powders. The S. salivarius strains can also be administered by direct application of a lyophil, culture, or cell paste to the teeth or tongue of the individual. Any mode of administration is suitable as long as the therapeutic formulation is applied to the oral cavity. In one embodiment, the S. salivarius or extracts are administered by applying directly to the teeth of the individual, e.g. by brushing and/or flossing. In general, the amount of S. salivarius administered to the individual will be an amount effective for replacement of dental caries-causing MS strains, or at least S. mutans in the oral cavity of the host. "An amount effective for replacement of dental caries-causing MS strains or at least S. mutans in the oral cavity of the host" means an amount effective for oral cavity colonisation by the S. salivarius strain, and significant reduction of the resident dental caries-causing S. mutans or MS strains (e.g. by competition between the bacteria for nutrients and/or by the production of BLIS by the S. salivarius strain). The term "unit dose" when used in reference to a therapeutic formulation of die present invention refers to physically discrete units suitable as unitary dosage for the individual, each unit containing a predetermined quantity of active material (viable S. salivarius or active extract thereof) calculated to produce the desired therapeutic effect in association with the required diluent, carrier, or excipient. Specific dosages can vary widely according to various individual variables including size, weight, age, disease severity (e.g. the tenacity and/or number of dental caries-causing resident MS) and responsiveness to therapy (e.g. the susceptibility of the individual's oral cavity to colonisation). Methods for determining the appropriate route of administration and dosage may be determined by the consumer as they deem appropriate, or on a case-by-case basis by an attending dentist or other clinician. Such determinations are routine to one of ordinary skill in the art (see for example, Remington's Pharmaceutical Sciences, 8th ed., Gennaro, ed., Mack Publishing Company, Easton, Pa., 1990). In general, the number of S. salivarius administered to the individual will range from about 102 to 1015 bacteria, preferably from about 103 to 1014 bacteria, more preferably from about 105 to 1012 bacteria, normally about 109 to 1010 colony forming units (CFU) per dose. One lozenge formulation employs 3.8 x 109 CFU/ml. Multiple doses of the S. salivarius strain can be administered to achieve oral cavity colonisation and replacement of the resident, dental caries-causing MS strains, particularly S. mutans, of the individual. The S. salivarius strain or extract may need to be administered to the patient once only or repeatedly. Repeat treatments may be once a month, once a week, once a day, twice a day, or as may otherwise be required. Conveniently, the administration may be effected as part of the patient's routine dental care, e.g. as a component of a lozenge, gum, toothpaste, floss, or mouthwash. To facilitate colonisation, in one embodiment the treatment method of the invention includes a preliminary step of pre-treating the individual to at least reduce the normal microflora present in the oral cavity, including dental caries causing organisms. This pre-treatment comprises the step of administering an antimicrobial agent such as chlorhexidine, lactoperoxidase, green tea, or pineapple juice (freeze dried), but not limited thereto, or may follow a prescribed course of antibiotics such as penicillin, erythromycin, or amoxycillin administered to said individual. S. salivarius of the invention or S. salivarius K12 is then administered to the depopulated environment to repopulate same. A currently preferred treatment protocol for dental caries comprises pre-treatment by brushing teeth with chlorhexidine gel for 2 to 5 days, preferably 3 days. A lozenge is administered 1-4 hours, preferably 2 hours after the gel. This is followed by administration of a further 2-5, preferably 3 lozenges through the day at intervals of 1 -4 hours, preferably every 2 hours. This protocol is followed for 2-4 days to facilitate colonisation. For maintenance purposes 1, 2, or 3 lozenges, usually 1 to 2 lozenges are taken each day following ordinary tooth brushing. The regime is continued for as long as required. Successful colonisation of the individual's oral cavity by the S. salivarius strain can be established by culturing the bacteria of the individual's oral cavity, and identifying the S. salivarius strain by, for example, BLIS production or other methods well known in the art for bacterial strain identification. The methods and uses of the invention may further comprise the use of one or more secondary antibacterial agents, and/or anticariogenic agents as discussed above. Where the term comprise, comprises, comprised or comprising are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. Various aspects of the invention will now be illustrated in a non-limiting way by reference to the following experimental section. EXPERIMENTAL Identification Strain Mia was isolated from the oral cavity of a healthy adult human subject. It grows on Mitis salivarius agar at 37°C, 5% CO2 with morphology typical of S. salivarius as follows: Colony shape and size: round, 1 -2 mm in diameter Margin (edge): entire (smooth) Elevation: convex Colour: blue Texture: mucoid On Blood agar [Columbia Agar Base (GIBCO) with 5% human blood] at 37°C, 5% CO2 it is not haemolytic, and exhibits the following morphology: Colony shape and size: round , Margin (edge): entire (smooth) Elevation: convex Colour: white Texture: mucoid When cultivated on either Blood agar or on Trypticase soy broth (BBL) + Davis agar 1.5% supplemented with 0.1% calcium carbonate the bacterial growth appears relatively more firmly adherent to the agar surface than is typical of most S. salivarius. The API 20 Strep Identification code for the strain is 5050451, which corresponds to Streptococcus salivarius (98.4% identity). 16s rRNA Sequence Analysis with reference to the GENEBANK database established the strain to be Streptococcus salivarius (99.9% homology). Biochemical Characterization Biochemical characterization of S. salivarius MIA was conducted using the API 20 Strep kit (bioMerieux) and API 50 CH (bioMerieux) which allows the study of the carbohydrate metabolism. The API 20 Strep results are as follows: Acetone production positive Hydrolysis negative ß-glucosidase positive Pyrrolidonyl arylamidase negative α-galactosidase negative ß-gluuronidase negative ß-galactosidase positive alkaline phosphatase negative Leucine arylamidase positive Arginine dihyrolase negative Ribose negative L-arabinose negative Mannitol negative Sorbitol negative Lactose positive Trehalose positive Inulin negative Raffinose positive Starch weak positive Glycogen negative ß-haemolytic negative The API 50 CH results are as follows: Glycerol negative Erythritol negative D-Arabinose negative L-Arabinose positive (anaerobic only) Ribose negative D-Xylose negative Adonitol negative B Methyl-xyloside negative Galactose positive D-Glucose positive D-Fructose positive D-Mannose positive L-Sorbose negative Rhamnose negative Dulcitol negative Inositol negative Mannitol negative Sorbitol negative α Methyl-D-mannoside negative α Methyl-D-glucoside positive (anaerobic only) N-Acetyl glucosamine positive Amygdaline positive Arbutin positive Esculin positive Salicin positive Cellobiose positive Maltose positive Lactose positive Melibiose positive (aerobic only) Saccharose positive Trehalose positive Inulin positive (anaerobic only) Melezitose negative D-Raffinose positive Amidon positive Glycogen positive (anaerobic only) Xylitol positive (aerobic only) ß Gentiobiose positive D-Turanose negative D-Lyxose negative D-Tagatose positive (anaerobic only) D-Fucose negative L-Fucose negative D-Arabitol negative L-Arabitol negative Gluconate negative 2 ceto-gluconate negative 5 ceto-gluconate negative S. salivarius MIA is urease positive when grown on Christcnens urea agar. Inhibitory Activity Deferred Antagonism test for BLIS Activity When tested for bacteriocin-like inhibitory substance (BLIS) production on the Blood agar- based medium, Columbia agar Base (GIBCO) + 0.1% CaCO3 +5% human blood (BACa) according to the deferred antagonism test of Tagg and Bannister the P-type designation of strain Mia is 677. P-type of S. salivarius MIA Producer typing (P-type) describes the antimicrobial activity of bacteria against a set of standard indicators. The procedure was first described by Tagg and Bannister (J. Med. Microbiol. 1979; 12: 397-411). For P-typing S. salivarius MIA was grown as a diametric streak culture on a Blood agar + 0.1% calcium carbonate plate or Trypticase soy-yeast extract-calcium carbonate agar (Trypticase soy broth, 30; yeast extract, 20 g; calcium carbonate, 2.5 g; agar, 15 g; distilled water, 1000 ml), incubated at 37°C, 5% CO2 for 18 h. The growth was then removed and the surface of the plate sterilised with chloroform. Nine indicator strains were then cross-inoculated. After incubation at 37°C, 5% CO2 for 18 h inhibition of growth was recorded. The inhibition patterns were recorded in a code form by considering the nine indicators as three triplets (eg, I1, I2, I3, I4, I5, I6; I7, I8, I9). Positive reactions against each indicator were given a score of 4, 2 or 1 depending on whether the indicator was, respectively, the first, second or third member of the triplet. No inhibition was recorded as zero. The total score of each triplet thus specified uniquely the reactions against the three indicators. The complete P-type code is written as a sequence of three numbers, consecutively defining the reactions within the three triplets. S. salivarius MIA has a 677 P-type on Blood agar + calcium carbonate, and a 777 P-type on Trypticase soy-yeast extract-calcium carbonate agar. This corresponds to inhibition of all 9 bacteria in the panel of 9 indicator strains except for indicator 3. This pattern is typical of that given by salivaricin A- producing S. salivarius such as strain 20P3 (Ross et al Appl. Envir. Microbiol. 1993; 59;2014). However, when tested on trypticase soy broth (BBL) +Davis Agar (1.5%) + 0.25% calcium carbonate + yeast extract (2%) [TSBCaYE] the P-type is 777 (i.e. all 9 indicators are inhibited). Associated with this increased activity against indicator 3 there is also additional activity against a variety of other bacteria when tested as indicators (Table 1). Table 1: Antimicrobial activity of strain Mia on BACa and TSCaYE media (Table Removed) Deferred Antagonism Test of Anti-S. mutatis Activity The anti-S. mutans spectrum of inhibitory activity of salivaricin A2 producer strains was established by use of a deferred antagonism test, essentially as described by Tagg and Bannister [J. Med. Microbiol. 1979;12:397] . In brief, a 1-cm wide diametric streak culture of each producer strain was inoculated onto TSBCa and BACa media either with or without yeast extract (YE) supplementation. Following incubation in an anaerobic atmosphere for 24 hours at 37°C the macroscopic cell growth was removed with a glass slide and residual cells on the agar surface were killed by exposure to chloroform vapours for 30 minutes. The agar surface was then aired for 30 minutes and the indicator strained inoculated from 18 hour Todd Hewitt Broth (THB) cultures across the line of the original streak culture with use of cotton swabs. After incubation for 18 hours in 5% (v/v) CO2 at 37°C the extent of inhibition of each indicator strain was recorded. TSBCaYE medium (per 500 ml) Trypticase soy broth (BBL) 15 g Davis Agar 7.5 g Yeast Extract (Difco) 10 g CaCO3 1.25 g BACaYE medium (per 500 ml) Columbia Blood Agar base (Difco) 22 g CaCO3 0.5 g Yeast Extract (Difco) 10 The results are shown in Table 2. (Table Removed) Production of inhibitory activity in saliva fluid by strain Mia Saliva fluid was prepared as follows: Stimulated saliva was collected, heated at 60°C for 0.5 hr then centrifuged at 12000 x g for 10 min. The supernatant was supplemented with 0.5% maltose, 0.5% CaCO3 and 0.25 µg/ml cysteine (final concentrations). The supplemented supernatant was used as a basal fluid medium for growth of strain Mia at 37°C. The inoculum was from an 18 h TSBYECa culture at a ratio of 100µl per 2 ml supernatant. Different aliquots were supplemented as indicated. After 24 h incubation in an anaerobic atmosphere samples of the saliva cultures were tested for inhibitory activity against the indicators OMZ175, Mutll, and I1 either neat or following 10x concentration by rotary evaporation. The 10x concentrated supernatant from the culture grown in saliva supplemented with Maltose, Cysteine and CaCO3 had inhibitory activity against S. matans strain OMZ175 as shown in the table below. S. salivarins Mia therefore produces anti-S. mutans activity when grown in saliva. Assay of inhibitory activity Inhibitory activity was determined by end-point titration using a surface spot method in which 20 µL drops of two-fold serial dilutions of the test preparation in saline were spotted onto the surface of Blood Agar medium. When the drops had dried into the agar, the surface of the medium was sterilized by exposure to chloroform vapour for 30 minutes, aired and then inoculated by swabbing evenly from an 18 hour THB culture of indicator strain. Following incubation, the titre of inhibitory activity in Arbitrary Units (AU) per mL was taken to be the reciprocal of the highest dilution to show definite inhibitory activity. The results are shown in Table 3. Table 3: Production of inhibitory activity in saliva fluid by strain Mia (Table Removed) In vivo activity of S. salivarius MIA against MS. One subject brushed their teeth with 2% chlorhexidinc gel for 2 minutes on the first day and then sucked a tablet containing 3.8 x 109 colony forming units of S. salivarius MIA, two hours after the chlorhexidine treatment and then a further three tablets at two hourly intervals. On the second day the subject repeated the same procedure as for day one. The subject for the remaining 25 days of the trial sucked one tablet after brushing their teeth with a commercial toothpaste, in the morning and at night. Control subjects cleaned their teeth once a day for three days with 2% chlorhexidine gel and for the remaining time brushed their teeth with a commercial toothpaste. Saliva samples were collected from all subjects prior to starting the trial and at intervals throughout the trial to determine number of MS (colony forming units (cfu) per ml of saliva). The saliva sample was diluted in sterile saline and spiral plated onto Mutans selective agar, and the plates incubated under anaerobic conditions at 37°C for 2 days. The number of S. salivarius MIA in the saliva sample was also determined for the subject taking the tablets. The diluted saliva sample is spiral plated onto Mitis-salivarius agar and the plates are incubated at 37°C, 5% CO2 for 18-24 hours. The number of S. salivarius colonies are then counted. To determine the percentage of colonization with S. salivarius MIA the following protocol is used. Fresh THB cultures of Micrococcus luteus and S. mutans OMZ175 arc spread separately on the top of a Blood agar/calcium plates. S. salivarius colonies are then picked into both plates. The plates are incubated at 37°C, 5% CO2 for 18-24 hours. S. salivarius MIA colonies produce zones of inhibition around the stab cultures on both plates. Percentage colonization is determined as the number of positive colonies divided by the total number of colonies picked. Brushing teeth with a 2% chlorhexidine gel resulted in a 1.7-2.4 log reduction in MS counts in both the control (Table 4) and the colonizing subject (Table 5). The MS cell' counts in the control subjects increased to pre-treatment levels, in the control subjects, between one to six days after brushing with the gel. The test subject was 100% colonized after the pre-treatment with the gel and remained highly colonized for the remaining trial period (Table 5). Numbers of MS were still 1.7 log lower than pre-treatment levels at 27 days. This shows that colonization with S. salivarius MIA is capable of preventing the re-establishment of high levels of MS. Table 4. The effect of 2% chlorhexidine gel on the levels of MS in the control subjects (Table Removed) Table 5. Effect of colonization with S. salivarins MIA on MS (Table Removed) Preparation of anti-MS active extract One hundred ml of molten Trypticase Soy agar containing 2% yeast extract and 0.25% calcium carbonate was poured into a 1 L schott bottle. One ml of an overnight culture of S. salivarius MIA, grown in Todd Hewitt broth at 37°C, in 5% CO2 in air, was added to the bottle. The culture was incubated anaerobically at 37°C for 18-24 hours. One hundred ml of Trypticase Soy broth containing 2% yeast extract and 0.25% calcium carbonate was added to the bottle, which had been preincubated under anaerobic conditions. The culture was then incubated for a further 24 hours anaerobically at 37°C. The broth was centrifuged to remove the bacterial cells and then ammonium sulphate was added to 50% (w/v) and incubated at 4°C for 18 hours. The sample was then centrifuged and the pellet resuspended in 1 ml of milli-Q water. Anti-MS activity of the sample was then tested using a well diffusion assay in Blood agar plates. Fifty µl of the sample is added to each well and air-dried. The plates were then chloroform treated. An overnight culture of the indicator strain was spread over the top of the plate and incubated at 37°C, 5% CO2 in air, for 18-24 hours. Zones of inhibition (distance from edge of the well to edge of inhibition of cell growth) were recorded against all the indicator strains (Table 6). Table 6. Well diffusion assay of S. salivarius MIA extract (Table Removed) DOSAGE FORM EXAMPLE Lozenge Ingredients Per 945 mg lozenge S. salivarius 3.8 x 109 CFU (freeze dried) Isomalt 600mg Emdex™ 150mg ProSolv HD™ 50mg Magnesium stearate 15mg Flavour 10mg The ingredients are blended and tablets produced using dry compression. INDUSTRIAL APPLICATION The results above demonstrate the antibacterial effect of S. salivarius strains, particularly strain Mia against a broad spectrum of microorganisms, particularly streptococci. These strains are the first BLIS producing S. salivarius to be identified which have activity against MS, and more particularly S. /nutans. The strains and related active extracts herein therefore have application in methods of therapeutically treating individuals against the harmful effects of streptococcus infection, especially in the oral cavity. These methods include treatment of dental caries in which MS or S. mutans are the primary causative agent. The S. salivarivs extracts and compositions of the invention also have application in the treatment of bad breath and sore throats. It will be appreciated that the above description is provided by way of example only and that variations in both the materials and techniques used which are known to those persons skilled in the art are contemplated. We Claim: 1. A biologically pure culture of a Streptococcus salivarius strain Mia, useful for controlling the incidence and severity of dental caries caused by Streptococcus mutans, said strain on deposit at Deutsche Sammlung von Mikroorganismen Und Zellkulturen GmbH, Mascheroder Weg 1 b, D-38124, Braunschweig, Germany, Accession No DSM14685. 2. An antibacterial composition or therapeutic formulation comprising S. salivarius strain Mia as claimed in claim 1, together with a diluent, carrier and/or excipient and other optional ingredients. 3. A composition or formulation as claimed in claim 2, which comprises one or more secondary antibacterial agents. 4. A composition or formulation as claimed in claim 3 wherein the secondary antibacterial agent is selected from nisin, bacteriocin-like inhibiting substances (BLIS) and BLIS producing microorganisms. 5. A composition or formulation as claimed in claim 4 wherein the BLIS is one or more BLIS selected from salivaricin A, A1, A2 and B. 6. A composition or formulation as claimed in claim 4 wherein the BLIS producing microorganism is K12 and/or K30. 7. A composition or formulation as claimed in any one of claims 2 to 6 which comprises one or more anti-cariogenic agents. 8. A composition or formulation as claimed in claim 7 wherein the secondary anti-cariogenic agent is selected from xylitol, fluoride, Manuka honey and tannin. 9. A composition of formulation as claimed in any one of claims 2 to 8 which is an orally administerable composition or formulation.

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