The antibacterial mechanism of Nisin against Gram-positive bacteria

As a natural antimicrobial peptide, Nisin’s core antimicrobial mechanism against Gram-positive bacteria is "targeted disruption of the cell membrane." It achieves bactericidal effects through multiple actions such as pore formation and metabolic interference, with no risk of drug resistance, making it an ideal natural preservative in food and pharmaceutical fields.

I. Core Antimicrobial Mechanism: Targeted Disruption of the Cell Membrane

1. Recognition and Binding to Targets

Lipid Ⅱ (a peptidoglycan precursor) present in the cell membrane of Gram-positive bacteria is Nisin’s specific binding target. The cyclic structures of Nisin, such as lanthionine and methyllanthionine, can form specific hydrogen bonds with the pyrophosphate group of lipid Ⅱ, enabling rapid anchoring to the cell membrane. This binding is highly specific, targeting only Gram-positive bacteria (Gram-negative bacteria’s outer membrane barrier prevents Nisin from accessing lipid Ⅱ).

2. Formation of Transmembrane Pores to Disrupt Osmotic Balance

After binding to lipid Ⅱ, the hydrophobic segments of Nisin insert into the hydrophobic region of the cell membrane. Six to eight Nisin molecules form transmembrane pores with lipid Ⅱ, with a diameter of approximately 2–3 nm. These pores allow the leakage of intracellular small molecules (e.g., potassium ions, amino acids, ATP) and massive influx of extracellular water. Ultimately, bacteria rupture and die due to osmotic imbalance—Nisin’s primary antimicrobial mechanism.

3. Interference with Cell Wall Synthesis

Lipid Ⅱ is a key precursor for bacterial cell wall peptidoglycan synthesis. Nisin’s binding to lipid Ⅱ blocks its transport to the cell wall and inhibits peptidoglycan cross-linking reactions. Impaired cell wall synthesis prevents bacteria from maintaining their morphology, making them more prone to rupture under osmotic pressure while weakening their resistance to the environment.

II. Auxiliary Antimicrobial Mechanisms: Metabolic Interference and Apoptosis-Like Response

1. Inhibition of Bacterial Metabolic Enzyme Activity

Nisin can penetrate the cell membrane into bacterial cells, inhibiting the activity of key metabolic enzymes such as ATPase and dehydrogenase. This reduces ATP production and blocks energy metabolic pathways. Insufficient energy supply prevents bacteria from synthesizing substances and dividing, leading to death.

2. Induction of Bacterial Apoptosis-Like Response

Some studies have found that Nisin can activate apoptosis-related genes in Gram-positive bacteria, promoting the production of reactive oxygen species (ROS). Accumulated ROS damages bacterial biomacromolecules such as DNA and proteins, triggering programmed cell death similar to apoptosis—particularly effective against bacteria in the logarithmic growth phase.

III. Key Factors Influencing Antimicrobial Efficacy

1. Nisin’s Own Characteristics

Purity: Nisin with a purity ≥90% exhibits 30%–50% higher antimicrobial activity than crude products; impurities interfere with binding to lipid Ⅱ.

Concentration: The effective antimicrobial concentration ranges from 0.1 to 10 μg/mL. Low concentrations only inhibit bacterial growth, while excessively high concentrations (>50 μg/mL) may reduce activity due to molecular aggregation.

2. Bacterial Characteristics

Strain Type: Highest efficacy against Staphylococcus, Streptococcus, and Bacillus spp.; remains effective against some drug-resistant strains (e.g., methicillin-resistant Staphylococcus aureus, MRSA).

Growth Phase: Bacteria in the logarithmic growth phase have higher cell membrane permeability, with antimicrobial efficacy 2–3 times that of stationary-phase bacteria. Spore-forming bacteria require higher Nisin concentrations (usually 10–100 times that of vegetative cells) to inhibit germination due to their dense cell wall structure.

3. Environmental and Application Conditions

pH Value: Stable activity in the pH range of 2–6; at pH >7, molecular conformation changes, reducing antimicrobial activity by over 50%. Suitable for acidic foods (e.g., yogurt, fruit juice, pickled products).

Temperature: Heat-resistant (retains 80% activity after autoclaving at 121℃), but prolonged high temperatures (>100℃) cause partial degradation. Stable at low temperatures (4℃), suitable for refrigerated food preservation.

Food Matrix: Proteins and fats bind to Nisin, reducing its free concentration. Appropriate dosage increases are required (e.g., 20%–30% higher addition in meat products than in fruit juice).

IV. Typical Applications and Research Evidence

1. Application Scenarios

Food Preservation: Added to dairy products, meat products, and canned foods to inhibit pathogenic bacteria such as Listeria and Staphylococcus aureus, extending shelf life by 2–4 times.

Pharmaceutical Field: Used for topical treatment of skin infections and oral inflammation, with adjuvant therapeutic effects on drug-resistant Gram-positive bacterial infections.

2. Research Data Support

In Vitro Experiments: 0.5 μg/mL Nisin achieves a 99% inhibition rate against Staphylococcus aureus; 1 μg/mL Nisin can completely kill logarithmic-phase Bacillus subtilis within 2 hours.

Animal Experiments: After intraperitoneal injection of Nisin (5 mg/kg) in mice infected with Listeria, the bacterial load in organs decreased by 60%–70%, and survival rate improved.

Clinical Studies: Nisin-containing oral rinse reduced oral Streptococcus counts by 80% within 7 days and alleviated gingivitis symptoms.

V. Research Trends and Core Advantages

1. Core Advantages

Natural and Safe: Produced by Lactococcus lactis fermentation, degradable by human digestive enzymes, non-residual, and non-toxic, complying with national food additive standard GB 2760.

No Drug Resistance: Its mechanism involves physical disruption of the cell membrane, making it difficult for bacteria to develop resistance through gene mutation—addressing the resistance issue of chemical preservatives.

Synergistic Enhancement: Compound formulations with EDTA, organic acids, or plant extracts enhance efficacy against Gram-positive bacteria and expand the antimicrobial spectrum (some combinations can inhibit Gram-negative bacteria).

2. Future Research Directions

Modification and Optimization: Genetic engineering to modify Nisin’s molecular structure, improving its stability in neutral and alkaline environments and expanding application scope.

Delivery Systems: Developing nano-carriers (e.g., liposomes, chitosan microspheres) to load Nisin, reducing the impact of food matrices on its activity and enhancing targeting.

Biofilm Research: Further exploring Nisin’s mechanism of disrupting bacterial biofilms to address biofilm-related infections.