The activity of Nisin

Nisin's activity is influenced by molecular structure integrity, environmental conditions (pH, temperature, ionic strength), application matrix, and microbial characteristics. Its stability and antimicrobial activity can be enhanced through structural modification, formulation optimization, or synergistic combination. Currently, significant progress has been made in activity optimization research in fields such as food preservation and clinical antimicrobial therapy.

I. Key Factors Influencing Nisin's Activity

1. Molecular Structure Integrity (Core Premise)

Nisin's activity depends on the intact cross-linked structure of its 5 lanthionine rings and the functional regions of the N/C termini:

Disruption of the ring structure (e.g., thioether bond cleavage due to chemical degradation or enzymatic hydrolysis) directly leads to loss of antimicrobial activity.

The first 3 N-terminal rings are responsible for binding lipid Ⅱ, while the C-terminal rings and flexible tail participate in transmembrane pore formation. Deletion of either region causes a significant decrease in activity (e.g., removing 9 C-terminal residues reduces activity by 100-fold).

2. Regulatory Role of Environmental Conditions

pH Value: Stable activity in acidic environments (pH 2~6); at pH＞7, molecular conformation changes, amino protonation weakens, binding capacity to bacterial targets decreases, and activity is lost by 50%~80%.

Temperature: Minimal impact on activity under conventional heating (＜80℃); 60%~70% of activity is retained after 15 minutes of autoclaving at 121℃. However, prolonged high temperatures (＞100℃) cause ring structure depolymerization, significantly reducing activity.

Ionic Strength: High concentrations of metal ions (e.g., Ca²⁺, Mg²⁺＞10 mmol/L) bind to Nisin molecules, interfering with their interaction with bacterial cell membranes and slightly reducing activity; low concentrations (＜5 mmol/L) have no obvious effect.

3. Interference Effect of Application Matrix

Matrices with high protein and fat content (e.g., dairy products, meat products) adsorb Nisin, reducing its free concentration and leading to a 20%~40% decrease in antimicrobial activity.

Polysaccharides (e.g., starch, pectin) encapsulate Nisin, hindering its diffusion to the bacterial surface. Higher concentrations are required to offset matrix interference.

4. Influence of Microbial Characteristics

Bacterial Species: Highest activity against Gram-positive bacteria (minimum inhibitory concentration, MIC 0.01~10 μg/mL); due to the outer membrane barrier, MIC against Gram-negative bacteria exceeds 100 μg/mL when used alone.

Bacterial State: Bacteria in the logarithmic growth phase are more sensitive to Nisin; spore forms require higher concentrations (usually 10~100 times that of vegetative cells) to inhibit germination.

II. Main Research Directions for Nisin Activity Optimization

1. Structural Modification and Transformation

Site-Directed Mutagenesis: Genetic engineering replaces key amino acids in Nisin (e.g., substituting histidine at position 27 with asparagine to obtain Nisin Z), improving water solubility and antimicrobial activity. Nisin Z’s activity against some strains is 30%~50% higher than that of the wild type.

Chemical Modification: Covalent modification of Nisin with fatty acids or polysaccharides enhances hydrophobicity and cell membrane penetration, expanding the antimicrobial spectrum against Gram-negative bacteria.

2. Formulation Optimization to Improve Stability

Microencapsulation: Embedding Nisin with natural materials such as sodium alginate and chitosan isolates it from oxygen, moisture, and matrix interference. Activity retention rate increases by 40%~60% in neutral or high-humidity environments, and the duration of action is extended.

Composite Membrane Formulations: Loading Nisin into edible films (e.g., gelatin, polylactic acid films) for food packaging enables controlled release of Nisin, maintaining sustained antimicrobial activity while avoiding direct adsorption with food matrices.

3. Synergistic Combination to Enhance Activity

Combination with Chemical Preservatives: Synergistic use with sorbic acid, citric acid, etc., reduces intracellular pH of bacteria and disrupts cell membrane integrity, enhancing antimicrobial activity by 2~4 times and reducing Nisin dosage.

Combination with Physical Technologies: Synergistic treatment with pulsed electric fields or ultraviolet light disrupts the outer membrane of Gram-negative bacteria, facilitating Nisin’s access to targets, expanding the antimicrobial spectrum, and reducing physical treatment intensity.

Combination with Biological Agents: Synergistic use with probiotics (e.g., lactic acid bacteria) or plant extracts (e.g., tea polyphenols) enhances antimicrobial effects through nutrient competition and resistance inhibition, suitable for natural food preservation.

III. Activity Research Progress in Different Fields

1. Food Preservation Field

Liquid Foods: Adding Nisin (50~100 μg/mL) to fruit juices and beverages inhibits the growth of thermophilic bacteria (e.g., Bacillus spp.) and extends shelf life by 2~3 times. When combined with EDTA, the inhibition rate against E. coli in fruit juices exceeds 99%.

Solid Foods: Using Nisin microcapsules (addition amount 0.1%~0.2%) in meat products and pastries effectively inhibits Staphylococcus aureus and Listeria monocytogenes, extending room-temperature shelf life by 5~7 days.

2. Clinical and Pharmaceutical Fields

Antimicrobial Dressings: Loading Nisin into medical sponges and gauze for wound infection treatment achieves an inhibition rate of over 95% against methicillin-resistant Staphylococcus aureus (MRSA), reducing antibiotic use and the risk of drug resistance.

Oral Care: Toothpaste and mouthwash containing Nisin inhibit oral Streptococcus and Porphyromonas gingivalis, reducing the incidence of dental caries and periodontitis without irritating oral mucosa.

IV. Research Trends and Challenges

1. Future Research Directions

Development of efficient modification technologies: Precise modification of Nisin structure through gene editing and enzymatic modification to further improve activity and broad-spectrum effectiveness.

Design of intelligent formulations: Development of responsive formulations (e.g., pH-responsive, temperature-responsive) for targeted release of Nisin in the target environment, improving utilization efficiency.

Expansion of clinical applications: Exploring Nisin’s application in treating multidrug-resistant bacterial infections and regulating intestinal flora, and developing new antimicrobial drugs.

2. Existing Challenges

Limited inhibitory effect against Gram-negative bacteria; further optimization of combination schemes or modification technologies is needed.

High cost of large-scale industrial production of high-purity Nisin restricts its widespread application.

Long-term safety data are still insufficient, especially the applicability in special populations (e.g., pregnant women, infants) requires in-depth research.