the compositions according to a first aspect of the invention comprise an antiseptic agent , preferably molecular iodine , ionic silver , chlorhexidine , or hydrochloric acid or an oxidizing agent such as sodium hypochlorite , chlorine dioxide , hydrogen peroxide or peroxy acid salts . the antiseptic agent is preferably included in the composition at a level of from 0 . 01 % to 10 % by weight , more preferably 0 . 1 % to 5 % by weight . iodine is preferably included in the composition at a level of from 0 . 01 % to 10 % by weight and more preferably from 0 . 1 % to 1 . 0 % by weight . preferably , the source of iodine is an iodide and the composition further comprises an oxidant and a buffer , the oxidant being held separately from the iodide until the point of use . the buffer is preferably capable of maintaining the ph of the composition at between 4 . 5 and 6 so that iodine is generated at a physiologically acceptable and efficacious rate . compositions comprising iodide and an oxidant held separately from the iodide are described further in ep1158859b . where iodide is present , the amount of oxidant in the composition is tailored to provide a stoichiometric match with iodide . preferably , the oxidant is iodate and is provided in a molar ratio of from 1 : 4 to 1 : 10 with iodide . in this way , the iodide present in the composition fully reacts with the oxidant . iodide and iodate are preferably present as sodium salts although other usual counter ions may be present . where the antiseptic agent is ionic silver , it is preferably included in the composition at a level of from 0 . 1 % to 10 % by weight and more preferably 0 . 5 % to 1 . 5 % by weight . the ph of the composition is generally below 8 and preferably between 4 and 8 , more preferably between 4 and 6 and most preferably between 4 . 5 and 5 . 5 . the desired ph may be achieved by incorporating buffering agents in the composition . examples of buffering agents which may be included are citric acid / di - sodium hydrogen phosphate , citric acid / sodium citrate , acetic acid / sodium acetate . the buffering agent may conveniently be present in an amount of about 1 % to 20 % by weight of the composition , preferably about 4 % to 6 % by weight and more preferably about 5 % by weight so as to provide an isotonic composition edta is preferably present as the di -, tri - or tetra - basic salts of edta . we have found that these salts are effective for eradicating microorganisms in the free floating or planktonic state and biofilm state alone or in the presence of an antiseptic agent . for example , we have found that edta at concentrations of 0 . 1 - 40 % weight by volume was effective in killing a range of microorganisms both in the planktonic and biofilm state . microorganisms that were effectively killed by edta included pseudomonas aeruginosa , serratia marcescens , vancomycin resistant enterococcus ( vre ) and methicillin resistant staphylococcus aureus ( mrsa ). edta is preferably present in the compositions of either aspect of the present invention at a level of 0 . 5 % to 10 % by weight of the composition , more preferably 1 % to 3 % by weight . the compositions of the present invention may be in the form of a water based gel which maintains a moist wound healing environment and promotes healing . a gel gives the advantage of flow into the wound to form an intimate contact with the wound bed and provide antimicrobial effects to the whole wound . preferably , the gel has a high enough viscosity that it does not flow out of wounds on areas of the body that are or become non - horizontal . preferably , the ph of the gel is buffered at around 5 . 5 as this does not alter the ph balance of the peri - wound tissue and , therefore , protects it . compositions containing iodine and edta were prepared by making a pair of aqueous gels ( see table 1 for gel a and table 2 for gel b ) which were intimately mixed at the point of use . each gel was made by preparing an aqueous solution containing all of the appropriate water - soluble parts according to the formulations below and then adding a slurry of a non - ionic cellulosic viscosifier ( hydroxyethylcellulose ) in propylene glycol . a commercially available cadexomer iodine ointment was present as a positive control as it contains 0 . 9 % iodine . intrasite is an amorphous hydrogel and was present as a negative control as it contains 0 % iodine . 9 ml of simulated wound fluid was added to a 17 ml volume cell well . a 1 ml culture of staphylococcus aureus was added to each well to give a final culture concentration of 10 6 cfu / ml . controls for this experiment involved adding 2 g of cadexomor iodine ointment ( positive control ) and nydrogel ( negative control ) separately to three cell wells each . 1 g of gels a and b , with different concentrations of edta , were then added to separate cell wells ( in triplicate ). the cell wells containing the culture and gels were then shaken at 600 rpm at 35 ° c . after time intervals of 4 , 24 , 48 , 72 and 96 hours , a 0 . 1 ml test sample was taken from each well and placed into 9 . 9 ml mrd ( maximum recovery diluent ) containing 1 % sodium thiosulphate . a 1 ml sample was then transferred to tryptone soy agar plates and incubated for 48 hours . bacterial counts were then recorded . these results show that by adding as little as 0 . 5 % edta ( calculated as the di - sodium salt ) to iodine , the efficacy of iodine , at 0 . 3 %, is enhanced when compared to the control of 0 . 3 % iodine with no edta . clearly , from the results , edta enhances the effects of iodine within 24 hours to the same efficacy of 0 . 9 % iodine ( positive control ). seven antibiotic resistant microorganisms were used to evaluate the efficacy of edta in killing bacteria and yeasts grown on agar . for this experiment , filter paper discs were soaked in edta at concentrations ranging from 0 . 1 - 40 %. edta was made up by dissolving it in an appropriate amount of sterile double distilled water . the filters were then added onto muller hinton agar which had been inoculated with a microorganism under study for 24 hours at 35 ° c . all microorganisms were tested twice . the results in fig2 show that the “ zones of inhibition ” generally ranged from about 20 to 43 mm ( including disc 13 mm ). zones were higher with increasing levels of edta indicating that edta alone is an effective antiseptic agent . poloxamer f127 hydrogels ( univar , basildon , essex , uk ) are di - block co - polymers of polyoxyethylene and polyoxypropylene that demonstrate thermo - reversible gelation properties . at temperatures below 15 ° c ., poloxamer is liquid and fully miscible with water but changes to a firm gel at temperatures in excess of 15 ° c . poloxamer encourages bacteria to exhibit a more clinically relevant biofilm phenotype . in the use of poloxamer hydrogels for the assessment of biofilm susceptibility towards biocide treatments . gilbert p ., jones , m . v ., allison , d . g ., heys , s ., maira , t ., wood , p . journal of applied microbiology ( 1998 ; 85 : 985 - 990 ), gilbert , et al ., determined that p . aeruginosa cells grown on poloxamer hydrogel ( biofilm form ) express outer membrane proteins between 78 and 87 kda , which are not evident in cells grown on standard nutrient agar (‘ planktonic ’). consequently , poloxamer gel cultures mimic many of the properties of biofilm - grown p . aeruginosa ( gilbert et al ., 1998 ). this indicates that there is a phenotypic difference between p . aeruginosa cells grown on poloxamer hydrogel and nutrient agar , with only poloxamer grown cells resembling biofilm cells . it was found from wirtanen &# 39 ; s study ( performance evaluation of disinfectant formulations using poloxamer - hydrogel biofilm - constructs . wirtanen , g ., salo , s ., allison , d . g ., mattila - sandholm , t ., gilbert , p . journal of applied microbiology ( 1998 ; 85 : 965 - 971 )) that bacteria which are grown in poloxamer have biofilm properties and associated enhanced biocide resistance . gilbert and colleagues suggested that bacteria grown in poloxamer hydrogels could be exposed to biocides to provide a reproducible method for testing the antimicrobial efficacy of biocides against biofilm bacteria ( gilbert , et al ., 1998 ). seven antibiotic resistant microorganisms were used to evaluate the efficacy of edta in killing bacteria and yeasts grown on poloxamer gel ( biofilm state ). for this experiment , filter paper discs were soaked in edta at concentrations ranging from 0 . 1 - 40 %. in this present study , poloxamer f127 , a di - block copolymer of polyoxyethylene and polyoxypropylene , was used as a medium on which bacteria could be grown as a biofilm phenotype and express the characteristics more appropriate to the ‘ real world ’. the filters were then added onto muller hinton agar which had been inoculated with the microorganism under study for 24 hours at 35 ° c . all plates were done in duplicate . the results in fig3 show that the zones of inhibition were slightly smaller in the presence of poloxamer indicating that bacteria / yeasts growing as biofilms are physically more resistant to edta when compared to their planktonic couterparts . c kruzei and ps aeruginosa were the exception with larger zones with poloxamer . zones of inhibition were evident on all organisms tested at 40 % edta . at 10 % edta and 5 % edta there were no zones with serratia marcescens . at 0 . 1 % edta no zones of inhibition were evident with any organism studied indicating that edta is not effective at this level . minimum inhibitory concentrations ( mic &# 39 ; s ) and minimum bactericidal concentrations ( mbc &# 39 ; s ) with tetra , tri and di basic salts of edta a microtitre plate and optical density readings and visual inspection were performed to obtain the mic &# 39 ; s for a variety of microorganisms ( see table 4 ). concentrations of edta included in this study were 40 mg / ml ph 10 . 00 as tetra - na , 40 mg / ml as tri - na ph 6 . 84 , 40 mg / ml as di - na ph 5 . 50 . into each microtitre plate , 100 μl of inoculum and edta was added . the plate was then incubated for 24 hours at 35 ° c . ± 3 ° c . following incubation all microtitre plates were inspected visually for growth . in general , all mic &# 39 ; s recorded were equivalent for all the salts of edta studied . this suggests that the ph of the solutions is equivalent . therefore , the activity of edta is not affected by the salt form added to the microtitre plate . these results show that low concentrations of edta are very effective on bacteria . the effect of edta on the antimicrobial efficacy of silver containing wound dressings the antimicrobial dressings used in this study were acticoat ™ ( smith and nephew ) and aquacel ® ag hydrofiber ® ( convatec ). acticoat is a nanocrystalline silver antimicrobial barrier dressing which consists of a rayon / polyester non - woven inner core laminated between two layers of silver - coated high density polyethylene mesh ( hdpe ). the layers are held together with ultrasound welds . aquacel ® ag is comprised of sodium carboxymethylcellulose hydrofiber ® and ionic silver . the silver cations in aquacel ® ag are associated with the individual highly absorbent anionic carboxymethylcellulose fibres of the hydrofiber ® dressing . aquacel ® hydrofiber ® dressing ( without silver ) was also used as a control . all dressings ( aquacel ® hydrofiber ® dressing [ control — without silver ], aquacel ® ag and acticoat ™ ( nanocrystalline dressing ) were hydrated with 20 mg / ml of tetra - na edta . all tests were performed against ps aeruginosa and tested on mueller hinton agar ( mha ) and poloxamer gel ( incorporating mueller hinton broth ( mhb ). this involved inoculating either a mh agar plate or poloxamer gel plate with a specific isolate and then adding an appropriate hydrated ( to saturation point ) wound dressing ( 360 i ( mrd ) for aquacel ® and aquacel ® ag and 150 i ( sterile distilled water — as per manufacturers instructions ) for acticoat ™). the plates were then incubated at 35 ° c . ± 3 ° c for 24 hours after which the zone of clearance ( no growth ) around the dressing was measured . zones of inhibition were measured horizontally and vertically ( inclusive of the dressing sample ) and a mean value was calculated from the duplicate set of results . the mean dressing size was then subtracted from the mean zone of inhibition to determine the corrected zone of inhibition ( czoi ). a czoi test allows for any inherent variability in the shape and size of zones created by the silver dressings which may change in dimension following hydration . table 5 shows the size of corrected zone of inhibition ( czoi ) in mm on mh agar and poloxamer gel . when edta was added to aquacel ®, no zones of inhibition were observed on mha ( non - biofilm state ). however , zoi &# 39 ; s were observed around aquacel ® ag on mha ( non - biofilm bacteria ) when edta or ( maximal recovery diluent ) mrd was added indicating the antimicrobial activity of silver . larger zoi &# 39 ; s were observed around acticoat ™ following the addition of edta when compared to hydration with water . in the presence of poloxamer gel an increase in the czoi was observed following hydration of aquacel ® ag with mrd when compared to edta indicating an additive effect with the use of edta . overall the results showed that edta enhances the effects of ionic silver on bacteria grown in the biofilm state ( poloxamer gel ). overall these results suggest that by using an edta dressing it is effective against both planktonic and biofilm microorganisms . table 6 shows the size of corrected zone of inhibition in mm on mh agar and poloxamer gel . minimum inhibitory concentrations ( mic ) for a two component gel comprising iodine and a two component gel as detailed in example 1 containing edta ( dina edta , trina edta and tetrana edta ) this experiment shows the effect of ph on the activity of a range of edta forms . for this experiment a two component gel as detailed in example 1 was made without the hec component ( gel ). this experiment was therefore performed using only liquid compositions ( see table 7 for tcg solution ( a ) and table 8 for tcg solution ( b )) in order for mic &# 39 ; s to be calculated . the ph of the tcg / edta solutions was approx 5 . 5 . the organisms tested included : staphylococcus aureus , pseudomonas aeruginosa , escherichia coli ( repeated twice ) and c albicans . mic &# 39 ; s were reduced considerably in the presence of edta ( di , tri and tetra na ). it can be seen that the mics , expressed as iodine concentration , are lower in the presence of di , tri and tetra sodium edta . the antimicrobial benefit of having edta present is achieved at concentrations of 0 . 31 mg / ml . despite different forms of edta being known to provide differential antimicrobial efficacy , at a constant ph ( 5 . 5 in this case ) all edta forms were equally effective in significantly reducing the mic &# 39 ; s for all three organisms compared to the iodine generating solution without edta .
an antiseptic composition suitable for use on skin and wounds comprising a source of an antimicrobial agent and an agent which disrupts biofilms . more , particularly the invention relates to a composition capable of providing effective antimicrobial activity while at the same time avoiding wound and skin irritation and retardation of wound healing .