WO2001014043A1

WO2001014043A1 - Immobilisation of a biocide on activated carbon

Info

Publication number: WO2001014043A1
Application number: PCT/US2000/015147
Authority: WO
Inventors: James Coulson; Alan Grint
Original assignee: Calgon Carbon Corporation
Priority date: 1999-08-17
Filing date: 2000-06-01
Publication date: 2001-03-01
Also published as: AU5313900A

Abstract

A filter material comprising of an activated carbon with 0.1 to 20 % of its adsorbent sites coated with an antimicrobial composition containing antimicrobial materials selected from the groups consisting essentially of benzalkonium salts and isothiazolin-ones, preferably in a glycol solvent, preferably propan-1,2-diol, or similar solvents.

Description

TITLE

IMMOBILISATION OF A BIOCIDE ON ACTIVATED CARBON

FIELD OF THE INVENTION

The present invention relates to the development of filter media containing activated carbon or activated charcoal fibres, sheets, fabric or cloth material containing antimicrobial and polymer formations.

BACKGROUND OF THE INVENTION

Activated carbon and activated charcoal cloth have long been known to be useful for adsorbing offensive odours from heavily infected wounds. Activated carbon fabric and entangled masses of carbon fibres have also been shown to adsorb bacteria and to form the basis for preparing surgical dressings utilizing the capillary action of the fibres to take up various chemical substances intended to act therapeutically or aseptically, such as iodine (British Patent 386.067). However, Iodine is highly labile in such dressings when applied as an aqueous alcoholic solution, usually called an iodophor, and is known to be released and to discolor, irritate and injure the skin and wounds when used for treating biological tissues. Attempts have been made to eliminate this disadvantage of iodine in water soluble iodophors, for example by complexing it with polyvinylpyrrolidone (British Patent 2,031 ,441) and with various cross-linked

polysaccharides (U.S. Patent No. 4,010,259). Alternatively, iodine and other antimicrobial agents have been bound to activated charcoal cloth in attempts to reduce their leakage and it has

been shown that no more than 20% of the adsorptive sites on the activated charcoal can be beneficially saturated with the antimicrobial agent, leaving at least 80% of the adsorptive sites available to adsorb offensive odors and micro-organisms (European Patent Application 0053936). Known disadvantages of these applications are that the antimicrobial materials remain partially labile in aqueous conditions, are not effective when substantially dry, and their effective incorporation rates make them less acceptable in terms of cell tissue toxicity.

Accordingly, it is one object of the present invention to provide a surgical dressing containing activated carbon, activated charcoal cloth and the like along with an antimicrobial composition that has been applied to the activated surface so that it is an effective and rapidly acting antimicrobial agent while remaining adsorbent to foul odours, organic materials and microorganisms.

It is a further object of the present invention to provide antimicrobial activated carbon and charcoal cloth based compositions for surgical dressings which remain antimicrobial when substantially dry as well as when partially or wholly hydrated.

It is also an object of the present invention to provide antimicrobial activated carbon and charcoal cloth based compositions for surgical dressings which have antimicrobial properties for

extended times.

It is an even further object of the present invention to provide antimicrobial activated carbon and charcoal based compositions for absorbative devices including filters and surgical dressings which exhibit low cell tissue toxicity. SUMMARY OF THE INVENTION

In a first embodiment of the present invention, a composition is provided that consists essentially of an antimicrobial agent or combination of antimicrobial agents selected for their microbial killing effect and low cell tissue toxicity and an activated carbon.

The antimicrobial compositions suitable for use in the present invention includes a wide range of halogen containing compounds, phenolic compounds, quaternary ammonium compounds and nitrogen based heterocyclic compounds which are strongly antimicrobial. Examples of these antimicrobial compositions include the following:

Amino compounds including long chain N-alkyl derivatives of amino acids such as glycine, alanine and beta-amino butyric acid, particular examples being dodecyl beta- alanine, dodecyl beta-aminobutyric acid, dodecylamino-di (aminoethylamino) glycine and N-(3-dodecylamino) propylglycine;

Iodophores (meaning herein complexes of iodine with a carrier, such as a polymer, typically one increasing the solubility of iodine in water, providing a sustained release

of iodine and reducing the equilibrium concentrations of free iodine) which may be made from polymer carriers for example polyvinylpyrrolidone polyether glycols such as polyethylene glycols, poly vinyl alcohols, polyacrylates, polyamides, polyalkylenes and polysaccharides;

Quatemary ammonium compounds including compounds of the general formula RlR2R3R4x wherein one or two of the R groups are alkyl chains optionally substituted by an aryl group, or optionally interrupted by or a heteroatom such as oxygen, and the other R groups are the same or different and are C1-C4 alkyl groups and in particular methyl groups, which compounds include benzalkonium halides, aryl ring substituted benzalkonium halides and twin chain quaternary ammonium compounds such as dialkldimethyl ammonium compounds wherein the two non-methyl alkyl groups are selected from medium and long chain alkyl groups such as octyl groups and dodecyl groups, quaternary ammonium compounds in which an alkyl group R contains a heteroatom alkylpyridinium compounds such as cetylpyridinium chloride, and bridged cyclic amino compounds.

Methyl, halo and aryl substituted phenolic compounds such as 2-phenylphenol, l-benzyl-4 chlorphenol, 2-chlorphenol,l 2-cyclopentyl-4 chlorophenol, 4-t- amylphenol, 4-t- butylphenol, 4-chloro-2-pentylphenol, 6-chloro-2-pentylphenol, p-chloro-m-xylenol, 2,4,4'-trichloro-2'-hydroxydiphenol, thymol, chlorothymol, 3-methyl-4-chlorophenol,

2,6-dichloro-4-alkylphenols, 2,4-dichloro-m-xylenol, 2,4,5-trichlorophenoland2-benzyl- 4-chlorophenol; Chlorine compounds including alkali-metal and alkaline earth metal hypochlorites such as lithium hypochlorite, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and chlorinated trisodium phosphate, their various hydrates, chlorine- containing or chlorine-releasing agents such as chloro-hexidine, 1 , 3-dichloro-5, 5- dimethylhydantoin, and various chlorisocyanuric acid derivatives; and

Nitrogen-containing antibacterial agents including pyridine derivatives such as 4-pyridine carboxylic acid hydrazine, sodium 2-pyridenthiol-l oxide, bis-(2-pyridylthio) zinc 1 , 1 '- dioxide triazoles and imidazoles such as 2-(4-thiazolyl) benzimidazole, 1 ,2- benzisothiazoline-3-one, 2-bromo-2-nitro-l , 3-propanediol, 3-trifluoromethyl-4, 4'- dichlorocarbanilide, quinacrine hydrochloride, ciprofloxacin and nalidixic acid and its various derivaties.

A presently preferred antimicrobial composition has a composition that is low toxicity to cell tissues at its effective incorporation level and includes synergistic compositions consisting of ammonium dimethyl benzalkonium chloride (alkyl =40% C12, 50% C14, 10% C16), 5-chloro- 2-methyl-4-isothiazolin-3-one, and 2-methyl-4-isothiazolin-3-one, and 2-methyl-4-isothiazolin-3-

one as the active antimicrobials, with a surfactant in a non-volatile solvent. An example of effective antimicrobial composition is Bioprotect 33 (available from Microbac Limited, Consett

Business Park, Consett, DH8 68P) which contains substantially the same composition as the preferred composition. In a second embodiment, the present invention provides a composition consisting essentially of a polymer formulation in a volatile solvent capable of adhering to a surface, and in particular to activated carbon and activated charcoal cloth and the like together with an antimicrobial composition.

The liquid polymer compositions suitable for use in the present invention may include a wide range of film forming polymers, such as polymers which provide the following additional properties:

1) Stable in terms of drying temperature.

2) Stable in terms of the other biocidal components. 3) Liquid.

4) Non- toxic.

5) Compatibility with other biocidal components and solvents.

The liquid polymer composition is preferably dissolved in a volatile solvent, preferably a mixture of propan-2-ol and butyl acetate, or similar solvents.

A presently preferred liquid polymer composition is of low toxicity to cell tissues at its effective incorporation level, such as in Bioprotect 33. Bioprotect 33 contains a liquid polymer composition consisting of polydimethylslloxane in a volatile solvent, a drying agent and a scavenger. The polymer composition can prevent the active antimicrobial composition from

leaching from a surface thus reducing the potential toxicity of the formulation further and reducing the potential deactivation of the formulation further and reducing the potential deactivation of formulation thus extending its period of effectiveness and allowing the formulation to be active in the substantially dry state as well as in any hydrated state.

In a third aspect the present invention, surfaces are coated or partially coated with the composition of the present invention. Such surfaces may include activated carbon or charcoal based materials in powder, granule, fibre, sheet, fabric or cloth form. In this case, such surfaces are preferable only partially coated, for example from about 1.0% to 6.0% , with the compositions of the present invention so that sufficient adsorbent sites in the activated carbon or charcoal based materials remain available for the adsorption of foul odors, organic materials and micro-organisms.

The activated carbon or charcoal based materials partially coated with the low cell tissue toxicity antimicrobial and liquid polymer compositions of the present invention can be used, for example, to manufacture absorbative devices including filters and surgical dressings with enhanced

properties.

To assess whether available biocides and biocidal cleaners are effective in controlling bacteria after dryer on Activated Charcoal Cloth, a number of commercial obtainable biocides and biocidal cleaners have been impregnated onto activated charcoal cloth and tested against

staphyloccus aureus. The bacterial suspension of the test organism at approximately 10⁶ colonies/ml was applied by immersion to 20mts x 20 mm square of Activated Charcoal Cloth that had been previously soaked for 8-10 seconds in the biocide sample and dried to 105 °c to constant weight. The total surface of one side of the charcoal cloth squares was swabbed and bacterial loadings were measured using standard microbiological techniques.

The results of these trials are shown in Table 1.

The results outlined in Table 1 show their ineffectiveness in the control of bacteria. This ineffectiveness is due to the absence of a film forming liquid polymer material that would have allowed the active biocides to remain on the activated charcoal cloth after drying.

Such surgical filters and dressings can be useful in adsorbing offensive odours, organic materials and micro-organisms due to the activated carbon or charcoal content, can rapidly kill micro-organisms when partially or wholly hydrated or when the materials are effectively dry and can remain antimicrobial for prolonged periods of time while exhibiting reduced cell tissue toxicity due to the low levels of incorporation of the effective antimicrobial formulation held in conjunction with the liquid polymer film on a number of the adsorbent sites on the activated carbon or charcoal composition.

The compositions and articles of the present invention have antimicrobial effectiveness against wide ranges of bacteria, yeasts, molds, algae and other fungi and viruses. Other advantages of the present invention will become apparent from a perusal of the following description of presently preferred embodiments.

PRESENTLY PREFERRED EMBODIMENTS

To demonstrate the effectiveness of the presently preferred embodiment of the invention, tests were conducted using prior art compositions and the invention. In this test, the antimicrobial

effectiveness of activated charcoal cloth impregnated with silver (prior art) and with silver plus Bioprotect 33. 20mmx20mm squares of activated charcoal cloth were immersed in Bioprotect 33 for 8 seconds and dried to constant weight.

Table 2 shows the basic properties for the activated charcoal cloth (FM5K/250 MED) and Biocide, Bioprotect 33 treatment and activated charcoal cloth (Sample No. 65822).

The data shows that the addition of the biocide has very little impact on the basic properties of

the activated charcoal cloth.

The small change in the Ethyl acetate uptake % w/w shows that the addition of the biocide has

virtually no effect on the material's adsorption properties. In comparison 20 mm x 20 mm squares of activated charcoal cloth prepared by impregnation with silver were supplied by Charcoal Cloth International. Samples of the silver impregnated cloth were also immersed in Bioprotect 33 for 8 seconds and dried to constant weight.

The specimens of cloth were tested for their ability to kill Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli and

Streptococcus faecalis.

Bacterial suspensions of the test organisms at approximately 10⁶ colonies/ml were prepared from laboratory stock cultures. Square pieces (20mm x 20mm) of each of the test specimens of cloth were placed into each of the bacterial suspensions (4ml) and agitated for 15 minutes at 20 °c.

All bacterial counts were performed using sterile phosphate buffer pH 7.5 as diluent and standard pour plate techniques using nutrient agar.

The results of these tests are shown in Tables 3 , 4 to 5.

Table 3

Activated Charcoal Cloth with Biocide, Bioprotect 33

Table 4

Activated Charcoal Cloth with Silver

Table 5

Charcoal Cloth with Silver and Biocide, Bioprotect 33

It will be seen that charcoal cloth impregnated with the biocide, Bioprotect 33, improves its antimicrobial performance compared to that impregnated with silver for all of the microorganisms tested. (Table 3 vs. Table 4).

The combination of biocide, Bioprotect 33, and silver on the charcoal cloth showed an improved antimicrobial performance against some of the bacterial species tested. (Table 3 vs. Table 5)

To assess the relative killing power of the biocide, Bioprotect 33 and impregnated silver on activated charcoal cloth, a test was carried out to assess the remaining bacteria after the respective cloths had been treated with standard bacterial solutions.

1. Test Samples Three samples were tested.

Sample 1 Charcoal Cloth No. 65873 FM5K/250 MED with biocide.

Bioprotect 33

Sample 2 Charcoal Cloth No. 65873 FM5K/250 MED without biocide. Sample 3 Charcoal Cloth with Silver.

The biocide Bioprotect 33 was applied to the Charcoal Cloth by immersion for 8 seconds followed by draining and drying to constant weight at 105°c.

2. Methodology

a. Biocide Used Bioprotect 33 (using dilution 1 : 10) b. Impregnation of Biocide

Small squares of Charcoal Cloth (20 mm x 20 mm) were immersed in biocide (1 : 10 dilution with water)(20 ml) for 8 seconds, drained and dried to constant weight at 105 °c.

c. Bacterial Strain

Staphylococcus aureus, NCTC 10788, 7.4 x 10⁶ colonies/ml.

d. Method

Charcoal Cloth square were placed in the bacterial suspension (4 ml) and agitated for 15 minutes to allow good contact.

The Charcoal Cloth squares were allowed to drain for 2 hours and were then immersed in sterile deionized water (20 ml) for 10 seconds to remove any extraneous non-adsorbed bacteria and allowed to drain for 5 minutes.

The total surfaces of one side of the Charcoal Cloth squares were swabbed and bacterial loadings were measured using standard microbiological techniques.

3. Results The results of the tests on the swab samples are shown in Table 6.

Table 6

Note: TNC = Too numerous to count ( > 10³ colonies/cm²)

4. Conclusions From the results obtained it can be concluded that the biocide Bioprotect 33 has produced an effective kill of the bacteria (S. aureus) on the Charcoal Cloth compared to the untreated Charcoal Cloth where the bacteria have survived.

Present Results

The above table demonstrates that Bioprotect 33 acts as an effective biocide, killing bacteria, while the silver impregnate acts at best as a bacteriostat limiting the growth of bacterial colonies. A sample of charcoal cloth impregnated with the biocide, Bioprotect 33, was stored at 20 ^oc for 9 months, inoculated with S. aureus and assessed as in the above experiment.

The results of this test are shown in Table 7.

Table 7

Activated Chardcoal Cloth with Biocide, Bioprotect 33

Count, cpm, Log Count, cpm, after Log Log initial contact with cloth reduction suspension (stored 9 months)

S. aureus 2.0 x 10⁶ 6.30 5.0 x 10⁴ 4.70 1.60

It will be seen from Table 7 that storage for 9 months of activated charcoal cloth impregnated with the biocide, Bioprotect 33, produces a similar log reduction to that with the freshly prepared impregnated charcoal cloth (Table 3). This demonstrates that the antimicrobial properties are retained for an extended time.

It is anticipated that bacteria that have become resistant to antibodies and are implicated in infection outbreaks in hospitals will have similar effects to their analogous non-resistant bacterial species. To confirm this, methacilin resistant S. aureus (MRSA) was utilised in place of S. aureus in the above experiment, with silver used as the control biocide.

The results of these tests are shown in Tables 8 and 9. Table 8

Activated Charcoal Cloth with Biocide, Bioprotect 33

a e

Activated Charcoal Cloth with Biocide, Bioprotect 33

It will be seen from Tables 8 and 9 that impregnation of the charcoal cloth with the biocide. Bioprotect 33, produces an improved log reduction on MRSA over its effect on S. aureus (Table 3) and an increased kill compared to the silver treated charcoal cloth.

The contact time of 15 minutes between the charcoal cloths impregnated with the biocide,

Bioprotect 33, and the bacterial suspensions in the above tests is relatively short showing that

the antimicrobial effect is rapid. In a further test, the rapidity of the antimicrobial effectiveness of activated charcoal cloth impregnated with Bioprotect 33 was assessed by conducting the same test procedure as that used above except that the test specimens of charcoal cloth were placed into the S. aureus bacterial suspension and agitated for only 30 seconds.

The results of this test are shown in Table 10.

Table 9 Activated Charcoal Cloth with Biocide, Bioprotect 33

It will be seen from Table 10 that the log reduction in 30 seconds is comparable to the log reduction achieved in 15 minutes contact between the activated charcoal cloths impregnated with

Bioprotect 33 (Table 3). Thus, the activated charcoal cloth impregnated with Bioprotect 33 is very rapid in its antibacterial action. A further test was conducted by taking the used activated charcoal cloths impregnated with Bioprotect 33 from the above 30 second inoculation with S. aureus experiment and drying it at 105 °c to constant weight. The 30 second inoculation test above with S. aureus was then repeated utilizing the used and dried charcoal cloth.

Table 11 Activated Charcoal Cloth with Biocide, Bioprotect 33

It will be seen from Table 11 that the log reduction from the used and re-dried carbon cloth is comparable to the log reduction achieved originally in the same 30 second inoculation period (Table 10). Thus, the activated charcoal cloth impregnated with Bioprotect 33, remains antimicrobial and absorbent to microorganisms and is likely, therefore, to also remain adsorbent

to foul odours and organic materials.

To assess the potential reactivity, in vitro, of leachable substances from activated charcoal cloth impregnated with the biocide, Bioprotect 33, a cytotoxicity assessment was carried out. The test sample (0.3g) was heated in extractant (6ml) at 31 °c for 24 hours and the filtered extractant was applied to cells (Mouse L929) growing on the surface of the tissue culture plates. After 48 hours incubation at 37 °c in a humidified atmosphere of 5 % CO₂ in air, the cultures were fixed with two 5 minute applications of methanol and were stained with 10% Glemsa stain in pH 6.8 buffer for 20 minutes, washed with distilled water and allowed to air dry.

Cultures were examined macroscopically for absence of staining due to sloughing of dead cells and microscopically using an inverted microscope at 100 x magnification for evidence of cell death cell unaccompanied by sloughing.

The results of this test are shown in Table 12.

Table 12

Activated Charcoal Cloth with Biocide, Bioprotect 33

test material showed no cytotoxicity and is not anticipated to be harmful to mammalian cells.

To assess the effectiveness of the presently preferred embodiment of the invention in air filters, the antimicrobial effectiveness of activated charcoal cloth impregnated with Bioprotect 33 was compared with that of identical untreated activated charcoal cloth. 150mm x 150 mm squares of activated charcoal cloth were immersed in Bioprotect 33 for 8 seconds and dried to constant

weight. The test cloths and identical untreated cloths were mounted into air filter frames and air was drawn through them from suitable identical fans. The charcoal cloths were then assessed for their microbial load by swabbing the activated charcoal cloth's total filtration surface and measuring the total viable count (TVC) using standard microbiological techniques.

Table 13 shows the biocidal effect of these filters on an air flow of 500 liters/minute through the filter for 20 days. Table 13

It will be seen from Table 13 that, at a relatively high air flow through the activated charcoal cloth filters, the filter treated with Bioprotect 33 significantly reduced the microbial load on the filter compared with the untreated filter.

Table 14 shows the biocidal effect of these filters on an air flow of 50 liters/minutes through the

filter for 5 days.

Table 14

If will be seen from Table 14 that at a relatively low air flow through the activated charcoal cloth filters, the filter treated with Bioprotect 33 significantly reduced the microbial load on the filter compared with the untreated filter.

Claims

What is claimed is:

1. An enhanced filter material comprising of an activated carbon adsorbed on from about 0.1 to 20% of the surface sites of said activated carbon an antimicrobial composition containing antimicrobial materials selected from the groups consisting essentially benzalkonium salts (quats) and isothiazolin-ones, preferably in a glycol solvent, preferably propan-1 , 2-diol, or similar solvents.

2. An enhanced filter material as set forth in Claim 1 wherein 1 % to 6% of said surface cites have adsorbed thereon said antimicrobial compositions.

3. An enhanced filter material as set forth in Claim 1 wherein said antimicrobial composition is ammonium 5-chloro-2-methyl-4-isothiazolin-3-one plus 2-methyl-4- isothiazolin-3-one.

4. An enhanced filter material as set forth in Claim 1 , 2 or 3 wherein said antimicrobial composition is in a glycol solvent.

5. An enhanced filter material as set forth in Claim 1 , 2 or 3 wherein said antimicrobial includes from about 0.1 % to 10.0% of liquid polymer selected from the group consisting essentially polydimethylsiloxane and other film forming liquid polymers, in a volatile

solvent.

6. An enhanced filter material as set forth in Claim 5 wherein said solvent is a mixture of propan-2-ol and butyl acetate.

7. An enhanced filter material as set forth in Claims 1 , 2 or 3 wherein said activated carbon is selected from the group of activated charcoal cloth, fibrous carbons and granular and powder carbons.

8. An enhanced filter material as set forth in Claim 1 , 2, 3 or 5 wherein said antimicrobial materials is selected from the group consisting of ammonium dimethyl banzalkonium chloride (aklyl=40% C12, 50% C14 and 10% C16) and 5-chloro-2-methyl-4- isothiazolin-3-one plus 2-methyl-4 isothiazolin-3-one in synergistic combination or in a

glycol solvent.

9. An enhanced microbial material as set forth in Claim 1 , 2 or 3 wherein said antimicrobial

includes from about 0.1 %-10.0% of liquid polymer selected from the group consisting essentially of polydimethylsiloxane and other film forming liquid polymers in a volatile

solvent.

10. An enhanced filter as set forth in Claim 8 wherein said volatile solvent is a mix of propan-2-ol and butyl acetate, or similar solvents.

11. A microbial material as set forth in Claim 1 , 2 or 3 wherein the activated carbon is an activated charcoal cloth, an activated fibrous carbons, granular and powder carbons.

12. A microbial material set forth in Claim 1 , 2 or 3 used in chemical dressing to kill bacteria, molds, yeasts and viruses.

13. A microbial material set forth in Claim 1 , 2 or 3 used a filter media to kill bacteria, molds, yeast and viruses.

14. The enhanced clinical dressing as set forth in Claim 11 having a negative impact on invitro studies.

15. The enhanced clinical dressings as set forth in Claim 11 having long term storage properties.

16. The enhanced clinical dressing as set forth in Claim 11 having the ability to kill MRSA and similar antibiotic resistant strains.