The present invention relates to an antibacterial mixture containing 4-(3-ethoxy-4-hydroxy-phenyl)butan-2-one and chlorphenesin, and also to a cosmetic composition containing such a mixture.
4-(3-Ethoxy-4-hydroxyphenyl)butan-2-one (ketone compound) is a useful substance as a preserving agent for cosmetic compositions, for protecting the compositions against micro-bial contamination, as described in the patent application WO 2011/039445.

However, it is desirable to be able to incorporate said ketone compound in reduced con-centration in compositions, especially cosmetic or dermatological compositions, while at the same time maintaining good antimicrobial conservation performance. Combinations of the ketone compound with other compounds that have antimicrobial efficacy are thus sought for this purpose.

The inventors have discovered, unexpectedly, that the combination of 4-(3-ethoxy-4-hy-droxyphenyl)butan-2-one with chlorphenesin makes it possible to obtain an antimicrobial mixture with synergistic antimicrobial activity, in particular on moulds, especially on Asper-gillus niger. The results of Example 1 described below show the synergistic antimicrobial activity obtained with the minimum inhibitory concentration (MIC) measurements taken with several mixtures. The antimicrobial activity is considered as being synergistic when the an-timicrobial mixture makes it possible to obtain a percentage of strain growth of less than or equal to 25%, or even less than or equal to 20%.

More precisely, a subject of the invention is an antimicrobial mixture comprising, or consti-tuted by (or consisting of), 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one and chlorphenesin A subject of the invention is also a composition, especially a cosmetic or dermatological composition, comprising, in a physiologically acceptable medium, said mixture described previously.

A further subject of the invention is a process for the non-therapeutic cosmetic treatment of keratin materials, comprising the application to the keratin materials of a composition as described above. The process may be a cosmetic process for caring for or making up or cleansing keratin materials.

4-(3-Ethoxy-4-hydroxyphenyl)butan-2-one is a compound of formula:

Chlorphenesin corresponds to the compound 3-(4-chlorophenoxy)-1,2-propanediol (CAS No.: 104-29-0) of formula:

Advantageously, 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one and chlorphenesin

are present in said mixture in a content such that the 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one/chlorphenesin weight ratio ranges from 0.1 to 0.9, preferably from 0.1 to 0.7 and preferentially from 0.15 to 0.6.

The compound 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one may be present in the composi-tion according to the invention at an amount ranging from 0.01% to 5% by weight relative to the total weight of the composition, preferably ranging from 0.01% to 3% by weight, pref-erentially ranging from 0.01% to 2.5% by weight and more preferentially ranging from 0.01% to 2% by weight.

A subject of the invention is also a composition comprising, in a physiologically acceptable medium, the antimicrobial mixture described previously.

The term "physiologically acceptable medium" means a medium that is compatible with hu-man keratin materials such as the skin, the scalp, the hair and the nails. Said medium may comprise one or more additional ingredients other than the ketone compound and chlor-phenesin.

The composition may comprise at least one additional ingredient chosen from water, oils, polyols containing from 2 to 10 carbon atoms, gelling agents, surfactants, film-forming pol-ymers, dyestuffs, fragrances, fillers, UV-screening agents, plant extracts, cosmetic and der-matological active agents, and salts.

The composition according to the invention may comprise an aqueous phase.

The composition may comprise water, which may be present at an amount ranging from 5% to 90% by weight relative to the total weight of the composition, and preferably ranging from 35% to 75% by weight.

The composition may also comprise a polyol that is water-miscible at room temperature (25°C), especially chosen from polyols especially containing from 2 to 10 carbon atoms, preferably containing from 2 to 6 carbon atoms, such as glycerol, propylene glycol, 1 ,3-propanediol, butylene glycol, pentylene glycol, hexylene glycol, dipropylene glycol, diethy-lene glycol or diglycerol. Advantageously, the composition according to the invention com-prises 1 ,3-propanediol, especially in a content ranging from 0.1% to 20% by weight, prefer-ably ranging from 0.1% to 10% by weight and preferentially ranging from 0.5% to 5% by weight, relative to the total weight of the composition.

The compositions according to the invention may be in the form of oil-in-water (O/W) emul-sions, water-in-oil (W/O) emulsions or multiple emulsions (triple: W/O/W or O/W/O), oily solutions, oily gels, aqueous solutions, aqueous gels, solid compositions. These composi-tions are prepared according to the usual methods.

The compositions according to the invention may be more or less fluid and may have the appearance of a white or coloured cream, an ointment, a milk, a lotion, a serum, a paste or a foam. They may be optionally applied to the skin in aerosol form. They may also be in solid form, for example in the form of a stick or a compact powder.

The composition according to the invention may especially be in the form of:

- a makeup product, especially for making up the skin of the face, the body, or the lips or the eyelashes;

- an aftershave gel or lotion; a shaving product;

- a deodorant (stick, roll-on or aerosol);

- a hair-removing cream;

- a body hygiene composition such as a shower gel or a shampoo;

- a pharmaceutical composition;

- a solid composition such as a soap or a cleansing bar;

- an aerosol composition also comprising a pressurized propellant;

- a hairsetting lotion, a hair-styling cream or gel, a dye composition, a permanent-waving composition, a lotion or a gel for combating hair loss, or a hair conditioner;

- a composition for caring for or cleansing the skin.

A subject of the invention is also a process for preparing a composition, especially a cosmetic or dermatological composition, comprising a step of mixing 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one, chlorphenesin and one or more additional ingredients, especially cosmetic or dermatological ingredients, such as those described previously.

The invention is illustrated in greater detail in the example that follows. The amounts of the ingredients are expressed as weight percentages.

Example 1 : determination of the synergistic antimicrobial activity in MIC on the mi-crobial strain Aspergillus niger

The demonstration of a synergistic antimicrobial activity effect with a mixture of 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one (referred to as substance A) and of chlorphenesin (referred to as substance B) is performed by calculating the synergy index (or FIC index) according to the following formula

with:

- MICa with B: minimum concentration of product A in the combination A + B which makes it possible to obtain an inhibitory effect.

- MICb with A: minimum concentration of product B in the combination A + B which makes it possible to obtain the inhibitory effect.

- MICa: minimum inhibitory concentration of product A alone.

- MICb: minimum inhibitory concentration of product B alone.

This formula was described for the first time in the article by F.C. Kull, P.C. Eisman, H.D. Sylwestrowka, and R.L. Mayer, Applied Microbiology 9:538-541 , 1961.

For each compound tested alone, the MIC is considered as the first concentration which makes it possible to obtain a microbial growth percentage of less than or equal to 25%.

As regards the combinations tested, MICa with b and MICb with a are the respective con-centrations of A and of B in the combinations which make it possible to obtain a microbial growth percentage of less than or equal to 25%.

Interpretation of the FIC Index:

When the FIC index value is less than or equal to 1 , it is considered that the combination of test compounds has a synergistic effect.

The results obtained are summarized in the following tables.

The microbial strain Aspergillus niger ATCC 6275, and a double-concentration Sabouraud broth liquid culture medium supplemented with polyoxyethylenated (20 OE) sorbitan mono-palmitate (Tween 40 from Croda) and Phytagel© BioReagent were used (i.e. a mixture of 5 g of Phytagel + 0.6 g Tween 40 + 60 g of Sabouraud broth).

A 96-well microplate at an incubation temperature of 32.5°C is used.

The incubation time of the microplate is from 24 to 48 hours aerobically.

Test

For each compound:

A = 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one compound

B = chlorphenesin compound

A 10% (weight/volume) stock solution was prepared by mixing 1 g of compound in 9 ml of aqueous 1 %o agar solution. Successive dilutions were made with the 1 %o agar solution.

• Test of compounds A and B alone

the microplate wells. 100 μL of Sabouraud liquid nutrient broth inoculated with the strain Aspergillus niger and 50 μL of aqueous 1%o agar solution are also added thereto.

• Test of compounds A and B as a mixture

50 μL of each of the daughter solutions obtained containing compound A and 50 μL of each of the daughter solutions obtained containing compound B are added to the microplate wells. 100 μL of Sabouraud liquid nutrient broth inoculated at double concentration with the strain Aspergillus niger are also added thereto.

Microbial growth control

A positive microbial growth control was also prepared. The positive microbial growth control corresponds to a mixture of 100 μL of aqueous 1%o agar solution with 100 μL of Sabouraud liquid nutrient broth inoculated at double concentration with the strain Aspergillus niger in the absence of compounds A and B.

Absorbance control of compounds A and B alone

An absorbance control was performed in parallel on compounds A and B alone. This control corresponds to 100 μL of double concentration sterile Sabouraud liquid nutrient broth + 100 μL of double concentration compound A or B.

In the three cases (absorbance control, growth control and test), the final volume present in each of the microplate wells is 200 μL.

In the two cases (test and control), the inoculum represents the concentration of the strain Aspergillus niger present in the final volume of the wells (200 μL) and is between 2 and 6x105 cfu/ml of Aspergillus niger.

The minimum inhibitory concentration (MIC) of each compound A and B alone and in com- bination was determined in a known manner by means of optical density measurements at a wavelength of 620 nm.

The following results were obtained:

The results obtained show synergistic inhibitory activity for the mixtures

i) 0.0625% of A and 0.25% of B, i.e. ratio A/B = 0.25

ii) 0.125% of A and 0.25% of B, i.e. ratio A/B = 0.5

Example 2: determination of the antimicrobial activity of the antimicrobial mixture

The antimicrobial efficacy of the 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one + chlor-phenesin antimicrobial mixture (respective weight ratio of 0.16) was evaluated by the Challenge Test method.

Protocol

The method of the challenge test consists of an artificial contamination of the sample with microbial strains from collection (bacteria, yeasts and moulds) and of an evaluation of the number of revivable microorganisms seven days after inoculation.

In order to demonstrate the effect of the antimicrobial mixture, the antimicrobial activity of a cosmetic formulation containing 0.05% of 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one and 0.3% of chlorphenesin was compared with the same formula alone (control), after inocula-tion with about 106 cfu (colony-forming units)/gram of cosmetic formulation.

Cosmetic formulation

A facial care oil-in-water emulsion having the following composition was prepared (con-tents in weight percentages):

Sorbitan tristearate (Span 65 V from Croda) 0.9% Glyceryl mono/distearate (36/64)/potassium stearate mixture

(Tegin Pellets from Goldschmidt) 3%

Polyethylene glycol stearate (40 ethylene oxide units) 2%

4-(3-Ethoxy-4-hydroxyphenyl)butan-2-one 0.05%

Chlorphenesin 0.3%

Propane-1,3-diol 3 % Mixture of mineral oil, microcrystalline wax and paraffin

(Vaseline Blanche Codex 236 from Aiglon) 4%

Liquid fraction of shea butter (Shea Olein from Olvea) 1%

Cyclopentadimethylsiloxane 5%

Cetyl alcohol 4% Apricot kernel oil 0.3%

Hydrogenated polyisobutene (Parleam from NOF Corporation) 7.2%

Myristyl myristate 2%

Stearic acid 1 .2%

Caffeine 0.1% Citric acid 0.2%

Glycerol 3%

Sodium hydroxide 0.05%

Water qs 100%

Control formulation A: Formulation similar to the preceding one containing 0.05% of 4-(3- ethoxy-4-hydroxyphenyl)butan-2-one and without chlorphenesin (0.3% compensated with water)

Control formulation B: Similar formulation containing 0.3% of chlorphenesin and without 4- (3-ethoxy-4-hydroxyphenyl)butan-2-one (0.05% compensated with water)

Microorganism cultures

5 pure cultures of microorganisms were used.

ATCC = American Type Culture Collection

The strains of gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), gram-positive bacterium (Enterococcus faecalis), yeast (Candida albicans), and mould (As-pergillus niger) are inoculated into the subculturing medium, respectively the day before inoculation for the bacteria and the yeast, and 5 days before inoculation for the mould.

On the day of inoculation:

- a suspension in tryptone salt diluent is prepared, respectively, for the bacteria and the yeast, so as to obtain by spectrophotometer a suspension with an optical density of between 35% and 45% of transmitted light at 544 nm;

- for the mould, the spores are collected by washing the agar with 6 to 7 ml of harvesting solution and the suspension is recovered in a sterile tube or flask.

After homogenizing the microbial suspension, 0.2 ml of inoculum is introduced into each pill bottle (the suspensions are used pure: between 1 x108 and 3x108 cfu per ml) and the mi- crobial suspension in the 20 g of product (= cosmetic formulation) is homogenized thor- oughly using a spatula.

The content of microorganisms present in the product corresponds after homogenization to a concentration of 106 microorganisms per gram of product, i.e. inoculation to 1% of an inoculum containing 108 microorganisms per ml.

After 7 days of contact time between the microorganisms and the product at 22°C ± 2°C and in the dark, ten-fold dilutions are performed and the number of revivable microorgan- isms remaining in the product is counted.

Results

<200 CFU: sensitivity threshold of the method

CLAIMS

1. Antimicrobial mixture comprising 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one and chlor-phenesin.

2. Antimicrobial mixture according to the preceding claim, characterized in that it comprises 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one and chlorphenesin in amounts such that the 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one/chlorphenesin weight ratio ranges from 0.1 to 0.9, preferably ranges from 0.1 to 0.7, and preferentially ranges from 0.15 to 0.6.

3. Antimicrobial mixture according to either of Claims 1 and 2, characterized in that it has antimicrobial activity on moulds, in particular on Aspergillus niger.

4. Composition comprising, in a physiologically acceptable medium, an antimicrobial mixture according to one of Claims 1 to 3.

5. Composition according to the preceding claim, characterized in that it comprises at least one additional ingredient chosen from water, oils, polyols containing from 2 to 10 carbon atoms, gelling agents, surfactants, film-forming polymers, dyestuffs, fragrances, fillers, UV-screening agents, plant extracts, cosmetic and dermatological active agents, and salts.

6. Composition according to either of Claims 4 and 5, characterized in that the 4-(3-ethoxy-4-hydroxyphenyl)butan-2-one is present in a content ranging from 0.01% to 5% by weight relative to the total weight of the composition, preferably ranging from 0.01% to 3% by weight, and preferentially ranging from 0.01% to 2.5% by weight.