The liposome carrier system of Nisin

As a natural antibacterial peptide, Nisin features strong water solubility but poor lipid solubility, with stability susceptible to environmental factors (e.g., gastric acid, enzymatic hydrolysis). Liposome carrier systems significantly improve its properties and optimize bacteriostatic effects by embedding Nisin in phospholipid bilayers, with specific mechanisms and application values as follows:

I. Construction and Characteristics of Liposome Carrier Systems

1. Carrier Design Principles

Liposomes form closed bilayer structures via self-assembly of phospholipids (e.g., lecithin) and cholesterol, embedding water-soluble Nisin in the internal aqueous phase while the bilayer lipid membrane protects it from environmental damage. Adjusting phospholipid types, cholesterol ratios, and preparation processes (e.g., thin-film dispersion, reverse evaporation) controls liposome particle size (typically 100–500nm), charge (positive/negative charge modification), and encapsulation efficiency (up to 60%–80%). For example, neutral liposomes prepared from egg yolk lecithin and cholesterol (molar ratio 3:1) show high Nisin encapsulation and good stability.

2. Key Advantages

Sustained-Release Properties: When liposomes contact microbial cell membranes, the phospholipid bilayer fuses with the bacterial membrane, gradually releasing Nisin to extend the action time. Studies show liposome-encapsulated Nisin releases only 1/3 of free Nisin within 48 hours, but its bacteriostatic duration exceeds 72 hours.

Enhanced Environmental Tolerance: Free Nisin loses activity easily under acidic conditions (pH 2.0) or in pepsin environments (half-life <1 hour), while liposome embedding extends the half-life to 4–6 hours, making it more suitable for oral formulations or acidic food preservation.

Improved Targeting: Modifying the liposome surface (e.g., grafting polysaccharides, antibodies) enables specific binding to receptors on bacterial cell membranes (e.g., peptidoglycan layers of Gram-positive bacteria), increasing local drug concentration. For instance, mannose-modified liposomes adsorb Staphylococcus aureus 2–3 times more efficiently than unmodified ones.

II. Mechanisms of Enhanced Bacteriostatic Effects

1. Synergistic Enhancement of Action Modes

Free Nisin inhibits bacteria by disrupting membrane permeability and blocking cell wall synthesis, while liposome carriers synergize via two pathways:

Membrane Fusion Damage: Liposome phospholipids interact with bacterial membrane lipids to exacerbate membrane disorder, while released Nisin inserts into the membrane to form transmembrane pores, accelerating content leakage.

Enzymatic Protection: The liposome barrier prevents proteases (e.g., trypsin) from contacting Nisin, maintaining its molecular integrity and activity in complex biological systems (e.g., intestine, food matrices). Experiments show the minimum inhibitory concentration (MIC) of liposome-encapsulated Nisin against Bacillus cereus is 50% lower than free Nisin.

2. Expansion of Broad-Spectrum Bacteriostasis

Free Nisin has limited effect on Gram-negative bacteria (due to outer membrane lipopolysaccharide barriers), while liposome carriers overcome this via:

Charge Neutralization: Cationic liposomes (e.g., dioleoyl phosphatidylcholine) bind to negative charges on the outer membrane of Gram-negative bacteria, disrupting barrier function and allowing Nisin to enter the periplasmic space. Studies show the bacteriostatic zone diameter of cationic liposome-encapsulated Nisin against E. coli is 1.5 times larger than free Nisin.

Nanoscale Penetration: Small-sized liposomes (<200nm) enter cells through bacterial outer membrane pores (e.g., porins), directly releasing Nisin to act on the inner membrane and 弥补 (compensate for) free Nisin’s penetration defects.

III. Typical Application Scenarios and Cases

1. Food Preservation

Dairy Products: Adding liposome-encapsulated Nisin to yogurt extends shelf life from 14 to 21 days and avoids inhibition of lactic acid bacteria fermentation (free Nisin ≥200 IU/mL inhibits fermentation, while liposome groups tolerate 500 IU/mL).

Meat Preservation: Spraying liposome Nisin on fresh beef surfaces inhibits spoilage bacteria like Bacillus stearothermophilus, reducing total bacterial count by 2 log CFU/g after 10 days of storage at 4℃ compared to controls.

2. Medical Antibacterial Applications

Local Infection Treatment: Liposome Nisin gel for skin wound infections targets Staphylococcus aureus biofilms, disrupting their structure and enabling sustained drug release. Animal experiments show this gel heals mouse burn infection models 30% faster than free Nisin.

Oral Antibacterials: Enteric-coated liposome Nisin resists gastric acid damage, inhibits pathogens like Clostridium difficile in the intestine, and avoids broad-spectrum killing of gut microbiota by conventional antibiotics.

3. Agricultural and Industrial Preservation

Fruit & Vegetable Preservation: Soaking strawberries in liposome Nisin solution inhibits Botrytis cinerea, extending shelf life by 5 days at room temperature without affecting color or sugar content.

Cosmetic Preservation: Adding liposome Nisin to moisturizing lotions effectively inhibits contaminating bacteria like Pseudomonas aeruginosa, preventing activity decline from interactions between free Nisin and surfactants.

IV. Existing Challenges and Optimization Directions

1. Scale Production Difficulties

Liposome preparation costs are high (e.g., high-purity phospholipid raw materials), and encapsulation efficiency fluctuates during scale-up. Optimization includes: developing low-cost plant-derived phospholipids (e.g., soybean lecithin), simplifying processes via high-pressure homogenization, and optimizing formula parameters using response surface methodology.

2. Stability and Storage Issues

Liposomes may aggregate or leak during long-term storage, ameliorated by:

Freeze-Drying Protection: Adding cryoprotectants like trehalose and mannitol maintains liposome structure integrity after lyophilization.

PEG Modification: Grafting polyethylene glycol (PEG) onto liposomes reduces aggregation via steric hindrance and extends in vivo circulation time (e.g., for medical applications).

3. Enhancement of Targeting Efficiency

Current targeting modifications rely on complex chemical conjugation; future bioinspired strategies may include:

Bacterial Membrane Bionics: Extracting pathogenic bacterial membrane components to modify liposomes, enhancing targeting via homologous recognition (e.g., streptococcal membrane protein-modified liposomes show 4-fold higher affinity for similar bacteria (similar bacteria)).

Intelligent Responsive Release: Introducing pH/temperature-sensitive phospholipids to enable rapid Nisin release in mildly acidic or high-temperature environments at infection sites, increasing local concentration.

Nisin’s liposome carrier system breaks through the stability and targeting bottlenecks of natural peptides via nano-encapsulation and intelligent delivery, fully unleashing its bacteriostatic activity in complex environments. With carrier technology iteration, this system is poised to achieve the leap from "passive preservation" to "precise antibacterial" in food, medicine, agriculture, etc., providing new technical pathways for addressing bacterial drug resistance.