Porous high-dispersion Ag / Cu / Cu2O composite material for enhancing antibacterial property of microbial exopolysaccharide (EPS) and application of porous high-dispersion Ag / Cu / Cu2O composite material to food packaging

Abstract

The invention discloses a porous high-dispersion Ag / Cu / Cu2O composite material for enhancing the antibacterial property of microbial exopolysaccharide (EPS) and applying the composite material to food packaging, and belongs to the field of antibacterial materials. The invention aims to solve the technical problem that the application of lactobacillus exopolysaccharides in the fields of food preservation, anti-infection medical dressings and the like is limited. The porous high-dispersion Ag / Cu / Cu2O nano-composite is synthesized by taking PVP as a carbon source and a template agent, Cu (NO3) 2 as a Cu source and a small amount of AgNO3 as an Ag source, the method is simple, and raw materials are cheap. After EPS is connected with the Ag / Cu / Cu2O nano-composite, compared with EPS-Ag and EPS-Cu / Cu2O, the sterilization characteristic of the EPS-Ag / Cu / Cu2O nano-composite is greatly improved. The Ag / Cu / Cu2O nano-composite can greatly reduce the usage amount of noble metal Ag, and shows very excellent antibacterial characteristics, so that the Ag / Cu / Cu2O nano-composite has a wider practical application value.

Description

Technical Field

[0001] The present invention belongs to the field of antibacterial materials, and in particular relates to an EPS-Ag / Cu / Cu2O nanocomposite and a preparation method and application thereof. Background Art

[0002] Lactic acid bacteria exopolysaccharides (EPS) are natural polymers secreted by lactic acid bacteria during their growth and metabolism. Their molecular structure is complex and diverse, composed of different monosaccharides linked by glycosidic bonds to form linear or branched structures. These unique molecular structures, like precision instruments in the microscopic world, endow them with remarkable functional properties such as thickening, stabilization, emulsification, antioxidant properties, and immunomodulation. In the food industry, when incorporated into yogurt and fermented dairy products, EPS form a stable three-dimensional network in solution, acting like a fine molecular mesh that locks in moisture. This not only imparts a silky, thick texture but also effectively delays oil oxidation, extending shelf life. In the pharmaceutical industry, EPS act as a precise delivery vehicle, leveraging their excellent biocompatibility and biodegradability to deliver active ingredients precisely to diseased areas. Furthermore, EPS can stimulate the immune system by binding to receptors on the surface of immune cells, acting as an immunity booster. In cosmetics, its excellent moisturizing properties are due to the rich hydrophilic groups on the polysaccharide molecules, which can form a water-locking film on the skin surface to keep the skin hydrated; in the agricultural field, as a biofilm material, it can provide a physical barrier for plants, reduce water loss, and regulate soil microbial communities, providing strong support for plant growth and soil improvement.

[0003] Despite widespread applications, lactic acid bacteria exopolysaccharides lack antimicrobial properties, limiting their application in areas such as food preservation and anti-infective medical dressings. In terms of food preservation, they are unable to protect perishable foods from microbial attack, and in treating open wounds, they are difficult to prevent infection, significantly limiting their potential for widespread application. Summary of the Invention

[0004] The present invention aims to solve the technical problem of limited application of lactic acid bacteria exopolysaccharides in the fields of food preservation, anti-infection medical dressings, etc., and provides an EPS-Ag / Cu / Cu2O nanocomposite and its preparation method and application.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: The object of the present invention is to provide a method for preparing an EPS-Ag / Cu / Cu2O nanocomposite, which is characterized by comprising the following steps: Step 1: Dissolve Cu(NO3)2·3H2O and AgNO3 in deionized water, then add dropwise to the PVP solution, stir vigorously until uniform and stable, dry the water, grind until uniform, and carbonize under a nitrogen atmosphere to obtain Ag / Cu / Cu2O nanomaterials.

[0006] Step 2: Add the Ag / Cu / Cu2O nanomaterial into ultrapure water, stir thoroughly and ultrasonicate until uniform, then add the lactic acid bacteria exopolysaccharide (EPS) solution, stir thoroughly and ultrasonicate, and freeze-dry to obtain the EPS-Ag / Cu / Cu2O nanocomposite material.

[0007] It is further defined that in step 1, 1.5 g Cu(NO3)2·3H2O) and 0.05 g AgNO3 are dissolved in 20 mL of deionized water.

[0008] It is further defined that in step 1, the PVP solution is obtained by completely dissolving 1.0 g of polyvinylpyrrolidone (PVP) in 30 mL of deionized water.

[0009] Further defined, in step 1, at 5℃min -1 The carbonized samples were heated to 600 °C at a heating rate of 100 °C and kept at that temperature for 1 h.

[0010] It is further defined that in step 2, 10 mg of Ag / Cu / Cu2O nanomaterials are added to 10 mL of ultrapure water, and then 10 mL of EPS solution with a concentration of 5 mg / mL is added.

[0011] Further defined, in step 2, EPS is prepared according to the following steps: Step 1: Inoculate 1% (v / v) of Leuconostoc mesenteroides DRP105 stored in a glycerol tube into 20 mL / 50 mL MRS medium for activation, culture at 30°C, 140 rpm on a shaker for 18 h, and subculture 2-3 times on MRS agar solid medium. Pick a single colony of strain DRP105 and transfer it to 20 mL / 50 mL MRS medium, culture at 30°C, 140 rpm for 18 h to obtain a seed solution (1×10 8 CFU / mL); Step 2: Inoculate the seed solution into MRS-S medium at a ratio of 2% and culture at 30°C and 140 rpm for 42 h; Step 3: The fermentation broth after fermentation and cultivation in step 2 was centrifuged at 4°C and 1000 rpm for 30 min to remove the bacteria, and then three volumes of pre-cooled 95% (v / v) ethanol were added to the supernatant, and the mixture was allowed to stand at 4°C overnight for alcohol precipitation. The mixture was centrifuged again to collect the polysaccharide precipitate and completely dissolved in 100 mL of double-distilled water. 100 mL of 10% (v / v) trichloroacetic acid solution was added and treated at 4°C for 4 h. The mixture was centrifuged for the third time to remove the protein precipitate in the polysaccharide solution, and three volumes of pre-cooled 95% (v / v) ethanol were added to the supernatant. The mixture was allowed to stand at 4°C overnight for alcohol precipitation. Finally, the liquid after alcohol precipitation was centrifuged and the polysaccharide precipitate was dissolved in double-distilled water. A dialysis bag with a molecular weight cutoff of 14 kDa was used, and the water was changed every 8 h. The mixture was dialyzed for two days to obtain a crude EPS solution. Step 4: Then elute with Sephadex G-100 gel column, use purified water as eluent, and the flow rate is 0.2 mL / min. Collect the eluent according to the peak time on the elution spectrum, freeze the collected eluent in refrigerators at -20°C and -80°C to a temperature close to that of the freeze dryer, and then perform vacuum freeze drying to obtain pure EPS dry product.

[0012] Another object of the present invention is to provide an EPS-Ag / Cu / Cu2O nanocomposite prepared by any of the above methods.

[0013] Application of the EPS-Ag / Cu / Cu2O nanocomposite in the preparation of food packaging.

[0014] Application of the EPS-Ag / Cu / Cu2O nanocomposite of the present invention in preparing anti-infection medical dressings.

[0015] The EPS-Ag / Cu / Cu2O nanocomposite of the present invention is used as an antibacterial agent.

[0016] This invention synthesizes porous, highly dispersed Ag / Cu / Cu2O nanocomposites using PVP as a carbon source and template, Cu(NO3)2 as a Cu source, and a small amount of AgNO3 as an Ag source. This method is simple and uses inexpensive raw materials. After linking EPS to the Ag / Cu / Cu2O nanocomposite, the EPS-Ag / Cu / Cu2O composite exhibits significantly enhanced bactericidal properties compared to EPS-Ag and EPS-Cu / Cu2O. This is attributed to the unique electronic and interfacial effects of the Ag / Cu / Cu2O composite. The molar ratio of Cu to Ag in the Ag / Cu / Cu2O composite is 20.7:1, and the mass ratio of Cu to Ag is 12.3:1. This means that the introduction of inexpensive Cu significantly reduces the amount of precious metal Ag used, while exhibiting excellent antibacterial properties. This composite has broad practical applications, such as in food packaging and anti-infective medical dressings.

[0017] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the accompanying drawings are provided for reference and illustration only and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the XRD pattern of Cu / Cu2O; Figure 2 is the XRD pattern of Ag; Figure 3 is the XRD pattern of Ag / Cu / Cu2O prepared by the method of Example 1; Figure 4 is the SEM image of Cu / Cu2O; Figure 5 is the SEM image of Ag; Figure 6 is a SEM image of Ag / Cu / Cu2O prepared by the method of Example 1; Figure 7 This is the effect of the Ag / Cu / Cu2O composite coating prepared by the method of Example 1 on the appearance quality of Mei Zao cherry (CK: control group, PE: plastic wrap group, TM: composite coating group). DETAILED DESCRIPTION

[0019] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art further understand the present invention and are not intended to limit the present invention in any way. It should be noted that those skilled in the art may make various modifications and improvements without departing from the scope of the present invention. These modifications and improvements are all within the scope of protection of the present invention.

[0020] Example 1 Step 1: Preparation of Ag / Cu / Cu2O nanocomposites At room temperature (25°C), 1.0 g of polyvinylpyrrolidone (PVP) was dissolved in 30 mL of deionized water and completely dissolved under magnetic stirring. 1.5 g of copper nitrate trihydrate (Cu(NO3)2·3H2O) and 0.05 g of silver nitrate (AgNO3) were dissolved in 20 mL of deionized water to obtain a mixed metal ion solution. This mixed solution was added dropwise to the PVP solution and stirred vigorously for 6 h to form a uniform and stable PVP-Ag solution. + -Cu 2+ The precursor solution was dried in an oven at 100°C for 24 hours to obtain a gel-like PVP-Ag + -Cu 2+For solid precursor, grind the dry product in a mortar to a uniform powder.

[0021] Finally, the powder was placed in a tube furnace and heated at 5 °C min -1 The material was heated to 600°C at a constant temperature and held for 1 hour for carbonization, ultimately producing a porous, highly dispersed carbon-supported Ag / Cu / Cu2O nanocomposite. Separate carbon-supported Ag nanoparticles and Cu / Cu2O nanoparticles were also obtained using the same method, except that the added metal raw materials were AgNO3 and Cu(NO3)2·3H2O.

[0022] Step 2: Fermentation of the strain to produce EPS solution Leuconostoc mesenteroides DRP105 stored in glycerol tubes was inoculated into 20 mL / 50 mL MRS medium at 1% (v / v) for activation and cultured on a shaker at 30°C and 140 rpm for 18 h. The strain was then subcultured 2-3 times on MRS agar solid medium. A single colony of strain DRP105 was picked and transferred to 20 mL / 50 mL MRS medium and cultured at 30°C and 140 rpm for 18 h to obtain a seed solution (1×10 8 CFU / mL).

[0023] The seed liquid was inoculated into MRS-S medium (120 g sucrose, 10 g beef extract, 10 g peptone, 5 g yeast extract powder, 0.1 g anhydrous sodium sulfite, 0.2 g magnesium sulfate, 0.05 g manganese sulfate, 2 g ammonium citrate, 2 g dipotassium hydrogen phosphate, 5 g anhydrous sodium acetate, 1 L distilled water; pH 5.5, autoclaved at 108°C for 20 min) at a ratio of 2% and cultured at 30°C and 140 rpm for 42 h.

[0024] The fermentation broth was centrifuged at 1000 rpm for 30 minutes at 4°C to remove bacterial cells. Three volumes of pre-chilled 95% (v / v) ethanol were then added to the supernatant, and the mixture was allowed to settle overnight at 4°C. The polysaccharide precipitate was collected by centrifugation again (8000 rpm for 30 minutes) and completely dissolved in 100 mL of double-distilled water. 100 mL of 10% (v / v) trichloroacetic acid solution was added and the mixture was incubated at 4°C for 4 hours. A third centrifugation (8000 rpm for 30 minutes) was performed to remove protein precipitates from the polysaccharide solution. Three volumes of pre-chilled 95% (v / v) ethanol were then added to the supernatant, and the mixture was allowed to settle overnight at 4°C. Finally, the precipitated solution was centrifuged, and the polysaccharide precipitate was dissolved in an appropriate amount of double-distilled water. The solution was dialyzed for two days using a 14 kDa dialysis tubing, with the water changed every 8 hours, to obtain a crude EPS solution.

[0025] Step 3: Prepare pure EPS dry sample (1) Pretreatment of gel column Soak the Sephadex G-100 powdered particles in an excess of purified water for 12 hours to allow the particles to fully swell. Stir gently to remove impurities and particles floating on the surface, and replace with purified water for later use. After installing the gel column vertically, use a glass rod to drain the treated gel solution. Alternate between standing and filling until the gel height exceeds about 1 / 2 of the column length, and keep the purified water 1-2 cm away from the gel surface. Ensure that the system is airtight and leak-proof, let the gel column settle overnight, and keep the liquid level stable. Before loading, adjust the UV detector so that the absorbance value A at 220 nm remains stable.

[0026] (2) Purification of polysaccharides After the baseline stabilizes, begin loading the sample at a volume of 1-2 mL using purified water as the eluent at a flow rate of 0.2 mL / min. Collect the eluent according to the peak time on the elution spectrum and freeze it in refrigerators at -20°C and -80°C, respectively, to a temperature close to that of the freeze dryer. Then, perform vacuum freeze drying to obtain pure EPS dry product.

[0027] Step 4: Preparation of EPS-Ag / Cu / Cu2O, EPS-Ag, and EPS-Cu / Cu2O samples 10 mg of Ag / Cu / Cu2O was dissolved in 10 mL of ultrapure water, stirred thoroughly for 1 hour, and sonicated for 1 hour. Then, 10 mL of a 5 mg / mL EPS solution (prepared from the pure EPS dry product) was added. Stir thoroughly for 12 hours, sonicated for 2 hours, and freeze-dried to produce the EPS-Ag / Cu / Cu2O composite. The EPS-Ag and EPS-Cu / Cu2O samples were prepared using the same method as above, except that pure carbon-supported Ag nanoparticles and Cu / Cu2O nanoparticles were used as the substrates.

[0028] Antibacterial performance analysis Cultured indicator bacteria (Staphylococcus aureus ATCC 6538, Micrococcus luteus ATCC 4698, Bacillus subtilis KLM HLJU, and Escherichia coli ATCC 68004) were inoculated into pre-solidified LB medium to prepare indicator plates. 6-mm-diameter wells were punched into the plates using an Oxford cup. 200 μL of sample (EPS, EPS-Ag, EPS-Cu / Cu2O, and EPS-Ag / Cu / Cu2O) was added to the wells (EPS concentration was 5 mg / mL). The plates were incubated at 30°C for 24 hours. The size of the inhibition zone was measured using a vernier caliper to assess the antibacterial properties of the composite materials.

[0029] 6. Minimum inhibitory concentration test The minimum inhibitory concentration (MIC) of the composite material against different indicator bacteria was determined by the two-fold dilution method. The specific steps were as follows: 10 μL of the composite material diluted 2 times was added to 90 μL of indicator bacteria suspension (10 6 CFU / mL) in a 96-well plate. The 96-well plate was sealed with a plate cover to prevent contamination from environmental bacteria and incubated at 30°C for 16 hours. A sterile culture solution without indicator bacteria was used as a negative control, and a bacterial suspension with Nisin added was used as a positive control. The OD value of the samples in the 96-well plate was measured using a microplate reader. 600 nm The MIC was defined as the minimum concentration of the composite material that inhibited the growth of the indicator bacteria.

[0030] The present invention uses X-ray diffraction (XRD) to systematically characterize the crystal structure of the sample. Figure 1 As shown in (Cu / Cu2O), characteristic diffraction peaks corresponding to the (111), (200) and (220) crystal planes of metallic Cu (JCPDS No. 04#0836) were observed at 2θ = 43.297°, 50.433° and 74.130°, respectively. Meanwhile, characteristic peaks of the (110), (111), (200), (220) and (311) crystal planes of Cu2O (JCPDS No. 78#2076) were detected at 29.582°, 36.441°, 42.328°, 61.406° and 77.414°, confirming the coexistence of Cu and Cu2O. Figure 2(Ag) shows clear diffraction peaks of Ag (JCPDS No. 87-0597) (111), (200), (220) and (311) crystal planes at 2θ = 38.114°, 44.298°, 64.441° and 77.395°, indicating that metallic silver nanoparticles were successfully prepared. It is worth noting that the ternary composite material ( Figure 3 The XRD pattern of Ag / Cu / Cu2O) includes the characteristic peaks of Cu (43.297°, 50.433°, 74.130°), Cu2O (36.441°, 61.406°, 77.414°) and Ag (38.114°, 64.441°), indicating that the Ag / Cu / Cu2O composite was successfully synthesized.

[0031] Scanning electron microscopy (SEM) showed that all three samples had a honeycomb-like porous structure ( Figure 4-6 This three-dimensional honeycomb structure is composed of interconnected carbon walls, forming uniform microporous channels with micrometer-scale diameters. SEM images clearly show a large number of nanoparticles uniformly distributed within the carbon matrix, with no apparent agglomeration. This hierarchical structure, combining a microporous carbon framework with highly dispersed active nanoparticles, provides an extremely high specific surface area and abundant active sites, which are crucial for enhancing antibacterial performance by improving interfacial interactions.

[0032] Table 1 shows the inhibitory effects of different materials on indicator bacteria. While EPS itself had no inhibitory effect on indicator bacteria, the other three composite materials all exhibited significant antibacterial activity against these bacteria. The EPS-Ag / Cu / Cu2O composite exhibited the strongest antibacterial activity, followed by the EPS-Ag and EPS-Cu / Cu2O composites. This indicates that the addition of Cu and Ag imbues EPS with antibacterial properties, with Ag exhibiting a stronger antibacterial capacity than Cu. Combining EPS with Cu and Ag further enhanced the material's antibacterial capacity. The inhibition zone diameters of EPS-Ag / Cu / Cu2O composite material against S. aureus, M. luteus, B. subtilis and E. coli were 14.89±0.32 mm, 14.93±0.58 mm, 14.55±0.51 mm, 14.03±0.66 mm, 10.83±0.34 mm and 10.77±0.23 mm, respectively, which were significantly higher than those of EPS-Ag and EPS-Cu / Cu2O, indicating that the introduction of Ag / Cu / Cu2O enhanced the antibacterial properties of EPS.

[0033] Table 1 Inhibitory effects of different materials on indicator bacteria

[0034] The MIC of EPS-Ag / Cu / Cu2O composite materials against indicator bacteria are shown in Table 2. EPS-Ag / Cu / Cu2O composite materials can effectively inhibit S. aureus, M. luteus, B. subtilis and E. coli , and the MICs were 4.93 μg / mL, 4.03 μg / mL, 3.74 μg / mL and 2.82 μg / mL, respectively.

[0035] Table 2 MIC of EPS-Ag / Cu / Cu2O composite materials against indicator bacteria

[0036] 1.1Analysis of the preservation performance of EPS-Ag / Cu / Cu2O composite coating on early cherry 1.2 Appearance quality of Meizao cherry To further explore the potential application of composite materials in fruit preservation, the effects of three treatments, namely the control group (CK), the plastic wrap group (PE), and the composite film group (TM), on the appearance quality of Mei Zao cherries were observed during a 15-day storage period to evaluate the preservation effect of the composite materials. Figure 7 As shown, the control group's Meizao cherries, unprotected and exposed to natural environmental factors, saw rapid growth and proliferation of mold and bacteria on the fruit's surface, leading to slight decay, noticeable browning, and softening on the 9th day. The high humidity created by the PE film wrapping in the Meizao cherries in the plastic wrap group likely accelerated yeast growth, inducing anaerobic metabolism and ethanol accumulation in the cherries, accelerating decomposition and spoilage. This resulted in earlier decay in the Meizao cherries in the plastic wrap group than in the control group, with skin decay appearing on the 6th day. No obvious skin decay was observed in the composite coating group on the 12th and 15th days. This is attributed to the significant inhibition of surface spoilage bacteria by the EPS-Ag / Cu / Cu2O composite coating. Furthermore, the microporous structure of the composite coating effectively stabilized the O2 / CO2 ratio, slowing respiratory transitions and reducing ethanol release. These results confirm the excellent preservation effect of the composite coating on Meizao cherries. Subsequent experiments will further explore the preservation mechanism of the composite coating.

[0037] The above describes the specific embodiments of the present invention. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing EPS-Ag / Cu / Cu2O nanocomposite, characterized in that: The following steps are involved: Step 1: Dissolve Cu(NO3)2·3H2O and AgNO3 in deionized water, then add dropwise to the PVP solution, stir vigorously until uniform and stable, dry the water, grind until uniform, and carbonize under a nitrogen atmosphere to obtain Ag / Cu / Cu2O nanomaterials.

2. Step 2: Add Ag / Cu / Cu2O nanomaterials into ultrapure water, stir thoroughly and ultrasonicate until uniform, then add lactic acid bacteria extracellular polysaccharide (EPS) solution, stir thoroughly and ultrasonicate, and freeze-dry to obtain EPS-Ag / Cu / Cu2O nanocomposite materials.

3. The method according to claim 1, characterized in that Dissolve 1.5 g Cu(NO3)2·3H2O) and 0.05 g AgNO3 in 20 mL deionized water.

4. The PVP solution was prepared by completely dissolving 1.0 g of polyvinylpyrrolidone (PVP) in 30 mL of deionized water.

5. The method according to claim 1, characterized in that: 5℃min -1 The carbonized samples were heated to 600 °C at a heating rate of 100 °C and kept for 1 h.

6. The method according to claim 1, characterized in that 10 mg of Ag / Cu / Cu2O nanomaterials were added to 10 mL of ultrapure water, and then 10 mL of 5 mg / mL EPS solution was added.

7. The method according to claim 1, characterized in that EPS is prepared according to the following steps: Step 1: Leuconostoc mesenteroides DRP105 stored in glycerol tubes was inoculated into MRS medium at 1% (v / v) for activation, cultured at 30°C, 140 rpm for 18 h, and subcultured on MRS agar solid medium for 2-3 times. A single colony of strain DRP105 was picked and transferred to MRS medium, cultured at 30°C, 140 rpm for 18 h, and a seed solution (1×10 8 CFU / mL); Step 2: Inoculate the seed solution into MRS-S medium at a ratio of 2% and culture at 30°C and 140 rpm for 42 h; Step 3: The fermentation broth after fermentation and cultivation in step 2 was centrifuged at 4°C and 1000 rpm for 30 min to remove the bacteria, and then three volumes of pre-cooled 95% (v / v) ethanol were added to the supernatant, and the mixture was allowed to stand at 4°C overnight for alcohol precipitation. The mixture was centrifuged again to collect the polysaccharide precipitate and completely dissolved in 100 mL of double-distilled water. 100 mL of 10% (v / v) trichloroacetic acid solution was added and treated at 4°C for 4 h. The mixture was centrifuged for the third time to remove the protein precipitate in the polysaccharide solution. Three volumes of pre-cooled 95% (v / v) ethanol were added to the supernatant and the mixture was allowed to stand at 4°C overnight for alcohol precipitation. Finally, the liquid after alcohol precipitation was centrifuged and the polysaccharide precipitate was dissolved in double-distilled water. A dialysis bag with a molecular weight cutoff of 14 kDa was used, and the water was changed every 8 h. The mixture was dialyzed for two days to obtain a crude EPS solution. Step 4: Then elute with Sephadex G-100 gel column, use purified water as eluent, and the flow rate is 0.2 mL / min. Collect the eluent according to the peak time on the elution spectrum, freeze the collected eluent in refrigerators at -20°C and -80°C to a temperature close to that of the freeze dryer, and then perform vacuum freeze drying to obtain pure EPS dry product.

8. An EPS-Ag / Cu / Cu2O nanocomposite prepared according to any one of claims 1 to 6.

9. Use of the EPS-Ag / Cu / Cu2O nanocomposite prepared according to any one of claims 1 to 6 in preparing food packaging.

10. Use of the EPS-Ag / Cu / Cu2O nanocomposite prepared according to any one of claims 1 to 6 in the preparation of anti-infective medical dressings.

11. An EPS-Ag / Cu / Cu2O nanocomposite prepared according to any one of claims 1 to 6 for use as an antibacterial agent.

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