these and other aspects , features and advantages will become apparent to those of ordinary skill in the art from a reading of the following detailed description and the appended claims . for the avoidance of doubt , any feature of one aspect of the present invention may be utilized in any other aspect of the invention . the word “ comprising ” is intended to mean “ including ” but not necessarily “ consisting of ” or “ composed of .” in other words , the listed steps or options need not be exhaustive . it is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se . similarly , all percentages are weight / weight percentages unless otherwise indicated . except in the operating and comparative examples , or where otherwise explicitly indicated , all numbers in this description indicating amounts of material or conditions of reaction , physical properties of materials and / or use are to be understood as modified by the word “ about ”. unless specified otherwise , numerical ranges expressed in the format “ from x to y ” are understood to include x and y . when for a specific feature multiple preferred ranges are described in the format “ from x to y ”, it is understood that all ranges combining the different endpoints are also contemplated . the invention provides for a transparent / translucent liquid antimicrobial composition in microemulsion format capable of acting as a mouthwash for disinfecting the oral cavity . the composition is unique in that it is substantially free of low boiling alcohols like ethanol or ipa ( isopropyl alcohol ) while ensuring high microbial kill in short time frames . the composition may be used as such ( without dilution ) or may be diluted with water before rinsing or washing mouth . the composition comprises an antimicrobial active , a surfactant , an electrolyte and water . the microemulsion composition of the invention is preferably transparent . this format of the composition is especially preferred since the transparent form makes for an appealing visual impact on consumers . in a preferred aspect , the dispersed phase droplets in the microemulsion are in the size range of 6 to 125 nm , more preferably in the size range of 6 to 15 nm . the antimicrobial active is selected from the class comprising terpenes , essential oils , cationic oils , c6 to c10 fatty acids , fatty acid methyl esters , or organic per - acids having a solubility in water of less than 2000 ppm at 25 ° c . of the above classes , the more preferred ones are terpenes , essential oils , c6 to c10 fatty acids or organic per - acids , a further more preferred list includes terpenes , essential oils , or organic per - acids and most preferred actives are the class of terpenes or essential oils . the following are the preferred list of actives from each class . amyl salicylate , carvacrol , cymene , e . g . ρ - cymene , dihydroeugenol , eugenol , hexyl eugenol , hexyl salicylate , isoeugenol , methyl eugenol , methyl isoeugenol , methyl salicylate , tert butyl cresol , thymol , and vanillin . examples of non - aromatic essential oils of terpenoid compounds include cedrene , cineole , citral ( including geranial and neral ), citronellal , citronellol , eucalyptol ( also known as 1 , 8 cineole ) paradihydrolinalool , dihydromyrcenol ( dh myrcenol ), farnesol , geraniol , hexyl cinnamaldehyde , hydroxycitronallol , hydroxycitronellal , isocitral , limonene , preferably d - limonene , linalool , longifolene , menthol , nerol , nerolidiol , pinene , e . g . α - pinene , phellendrene , terpinene , e . g . α - terpinene and γ - terpinene , terpineol , e . g . γ - terpineol and terpin - 4 - ol , and tetrahydromyrcenol ( thm ). quaternary ammonium cationic vegetble oil and charged aminopolydimethylsilane of the chemical formula ( ch 3 ) 3 — si —[ si ( ch 3 ) 2 — o ]—[ si ( ch 3 )—(( ch 2 ) 3 — nh —( ch 2 ) 2 — nh 2 )— o ] 2 — si —( ch 3 ) 3 . have the general structure r — cooh where r is a hydrocarbon chain which may be branched or linear with carbon atom varying from 6 - 10 . have the general structure r — coor ′ where r and r ′ are hydrocarbon chains which may be branched or linear with carbon atoms such that the sum of the number of carbon atoms in r and r ′ is greater than or equal to 7 . examples of organic acids suitable for use in the composition of the invention are e - phthalimidoperoxyhexanoic acid , diperoxyketals , peroxydicarbonates peroxyesters , diacyl preoxides , benzoyl peroxide , ketone peroxides , dialkyl peroxides , hydroperoxides . more preferred antimicrobial actives are terpineol , thymol , eugenol , borneol , limonene , iso - borneol , eucalyptol , camphor or mixtures thereof . most preferred antimicrobial actives are terpineol , thymol , eugenol , borneol or limonene . an especially preferred composition comprises thymol and terpineol . an even further preferred composition comprises thymol , terpineol and eugenol . the antimicrobial active is present in 0 . 05 to 10 %, more preferably 0 . 05 to 5 %, more preferably 0 . 1 to 5 % by weight of the microemulsion composition . the microemulsion composition of the invention comprises 0 . 05 to 10 %, preferably 0 . 05 to 8 %, more preferably 0 . 5 to 5 % surfactant by weight of the composition . the surfactant is of the cationic or anionic class , more preferably of the cationic class . when anionic surfactant is present it is preferably chosen from alkali or alkaline earth metal salts of alkyl sulphonic acid , fatty acid , or alkyl ether sulphate . when a cationic surfactant is present it is benzalkonium chloride , alkyl pyridinium chloride or quaternary ammonium gemini surfactants . without wishing to be bound by theory it is believed that the advantages of the invention accrue from the synergistic interaction between the anionic / cationic surfactant at the low concentrations used with the anti - microbial agent to provide the desired anti - microbial efficacy in the oral cavity while the low concentration of the surfactant interacting with the electrolye provides the desired microemulsion stability . the microemulsion composition of the invention is substantially free of low molecular weight alcohol viz . c1 to c3 alcohols e . g . ethanol or isopropyl alcohol . by the term substantially free of low molecular weight alcohols is meant that the alcohol is present in an amount which does not significantly affect the microbial kill . preferably c1 to c3 alcohols is present in less than 2 %, more preferably less than 1 % and most preferably absent from the composition of the invention . the composition of the invention preferably comprises 50 to 99 . 9 %, preferably 50 to 80 %, further more preferably 50 to 70 % water by weight of the composition . the composition of the invention includes an electrolyte at 0 . 01 to 50 % by weight of the composition . preferred electrolyte may be chosen from a chloride , sulphate , acetate , or carbonante of an alkali , alkaline earth or transition metal . of these , multivalent electrolyes are especially preferred . more useful electrolytes include chloride , sulphate or acetate of an alkaline earth metal . examples of electrolytes useful in including in the composition of the invention are calcium chloride , sodium chloride , magnesium chloride , zinc sulphate , aluminium chloride or zinc acetate . the more preferred electrolytes are calcium chloride , magnesium chloride , zinc sulphate or zinc acetate while the most preferred electrolytes are zinc sulphate or zinc acetate . electrolyte is preferably present in 0 . 01 to 30 %, more preferably 0 . 01 to 10 %, further more preferably 0 . 05 to 5 % by weight of the composition . without wishing to be bound by theory it is believed that another advantage for inclusion of the electrolyte in the microemulsion composition of the invention in addition to meeting all of the objects of the invention is to ensure that low molecular weight alcohols are substantially absent from the composition . the microemulsion composition of the invention is to be used for disinfecting the oral mucosa either by using the composition as - is i . e with no dilution or after diluting the composition with water . the preferred weight ratio of composition to water for the dilution step is in the range of 1 : 1 to 1 : 200 , more preferably 1 : 5 to 1 : 50 and optimally 1 : 15 to 1 : 30 and ideally about 1 : 20 . by the term transparent or translucent composition is meant that the composition has a turbidity value of 0 to 200 ntu . the composition of the invention preferably has a ph ranging from 3 to 8 , more preferably from 3 . 5 to 8 at 25 ° c . according to another aspect of the invention there is provided a method of disinfecting the oral mucosa comprising the step of rinsing the mouth / oral mucosa with the composition of the invention . the composition of the invention is preferably diluted with water in a ratio in the range of 1 : 1 to 1 : 200 before the rinsing step . the predetermined time for rinsing the mouth / oral mucosa with the composition may be up to two minutes , preferably up to one minute and more preferably up to 30 seconds . according to another aspect of the invention there is provided use of a composition of the invention for disinfecting oral mucosa . the use is preferably non - therapeutic . the invention will now be illustrated with the help of the following non - limiting examples . efficacy of various mouthwash compositions against s . mutans in a one minute contact test in suspension streptococcus mutans ( s . mutans ) is a gram - positive , facultatively anaerobic bacterium commonly found in the human oral cavity . s . mutans is the leading cause of dental caries ( tooth decay ) worldwide and is considered to be the most cariogenic of all of the oral streptococci . s . mutans , sticks to the surface of teeth and subsists on a diverse group of carbohydrates . while metabolising sugar and other energy sources , the microbe produces acid that causes cavities in teeth the compositions listed in table - 1 were used to test the efficacy as a antibacterial mouth wash composition against s . mutans in a one minute contact test in suspension , using the following procedure . sub culture s . mutans was taken in a bhi broth at 37 grams per liter ( gpl ) and it was allowed to grow in co 2 incubator ( 15 % co 2 ) at 37 ° c . for 15 hours . the s . mutans culture was adjusted to a optical density to 0 . 3 (˜ 10 8 cfu / ml ) at 620 nm . 9 ml of the desired composition was taken and added to 1 ml of culture and mixed . after a one minute contact time with the culture , they were neutralized in d / e broth and after serial dilution they were plated in bhi agar ( 52 gpl ). the plates were incubated in co 2 incubator . the residual colonies were counted after 48 hours incubation . the efficacy was compared against a control sample . the amount of log reduction of the bacteria was measured and the data is summarized in table - 1 . the data in table - 1 indicates that the antibacterial efficacy of the composition of the invention ( example - 2 ) is comparable with a commercially available composition which has high levels of alcohol ( example - 1 ). further the data also indicates that neither the mixture of antibacterial actives in water ( example - 3 ), nor the surfactant ( example - 4 ) nor the electrolyte ( example - 5 ) in themselves are not efficacious in providing the antibacterial efficacy . efficacy of various mouthwash compositions against s . mutans in a thirty second contact test in suspension the compositions listed in table - 2 were used to test the efficacy as a antibacterial mouth wash composition against s . mutans in a thirty second contact test in suspension , using the same procedure as used for examples 1 to 5 except that the time of contact was 30 seconds instead of one minute . the data is summarized in table - 2 . sub culture s . mutans in bhi broth ( 37 gpl ) was allowed to grow in co 2 incubator ( 15 % co 2 ) at 37 ° c . for 15 hours . the culture was processed and the optical density was adjusted to 0 . 3 (˜ 10 8 cfu / ml ) in bhi broth at 620 nm . glucose ( 2 %) was added to the processed culture and it was dispensed on a 6 well plate and allowed to grow in a co 2 incubator . the media was replaced every 24 hours to make a 3 days old biofilm . the media was removed and about 2 ml of the various compositions of table - 3 were added to the biofilm . after one minute contact time , the compositions were removed and 2 ml of neutralizer was added immediately . the biofilm cells were removed with a cell scraper . the biofilm cells were mixed and serial diluted in d / e neutralizer and plated at 1 ml of the sample in bhi agar . the plates were incubated in co 2 incubator for 48 hrs and the colonies were counted . the efficacy of the mouthwash compositions in terms of log reduction are summarized in table - 3 . the present invention thereby provides for a mouthwash composition which is highly effective and yet substantially free of alcohol . the composition is also highly appealing since it has a transparent appearance .
the invention relates to a transparent / translucent liquid antimicrobial mouthwash composition that is substantially free of low molecular weight alcohol . it is a problem to include antimicrobial actives of natural origin which are generally substantially water insoluble materials in an aqueous composition that is transparent or translucent . one way of including such oils in water while ensuring transparency is to formulate them in a microemulsion composition . however microemulsion compositions generally require high amounts of surfactants and solvents especially low molecular weight alcohol . it is thus a challenge to formulate a mouthwash composition that is on the one hand effective in killing microbes while on the other hand has a transparent / translucent appearance while being substantially free of low molecular weight alcohol . the present inventors have solved this problem and have come up with a microemulsion mouthwash composition which meets all of the above objectives while being especially effective in killing s . mutans , a bacteria responsible for diseases in oral cavity .