Enhance the antibacterial effect of Nisin

Nisin, as a highly effective natural antimicrobial peptide, primarily targets Gram-positive bacteria in its antibacterial spectrum. However, in practical applications, it is often limited by issues such as insufficient antibacterial activity, poor stability, or weak efficacy against Gram-negative bacteria. Enhancing its antibacterial effect through various strategies can expand its applications in fields like medicine and food. The specific research directions are as follows:

I. Chemical Modification: Optimizing Molecular Structure and Stability

Nisin contains multiple active sites in its molecular structure (such as rare amino acids like lanthionine and methyllanthionine). Chemical modification can enhance its interaction with bacterial cell membranes or its resistance to enzymatic hydrolysis:

Amino or carboxyl modification: Modifying the amino groups (e.g., lysine residues) or carboxyl groups of nisin through acylation, alkylation, etc., can improve its hydrophobicity, enhance binding ability with bacterial cell membranes (rich in lipids), and thereby promote pore-forming efficiency. For example, after fatty acid acylation modification, the MIC (minimum inhibitory concentration) of nisin against Gram-positive bacteria can be reduced by 30%-50%.

Cross-linking modification: Cross-linking nisin molecules with other antibacterial substances (e.g., lysozyme) using bifunctional reagents (e.g., glutaraldehyde) to form composite molecules retains nisin’s pore-forming effect while leveraging the cell wall-degrading ability of other substances, synergistically enhancing antibacterial efficacy—especially against drug-resistant bacteria.

PEGylation: Polyethylene glycol (PEG) modification can reduce the probability of nisin being degraded by proteases (e.g., trypsin), extend its action time in vivo or complex environments, and reduce its immunogenicity, enabling long-acting antibacterial effects in medical applications.

II. Combined Drug Use: Expanding Antibacterial Spectrum via Synergistic Effects

The combined use of nisin with other antibacterial substances can overcome the limitations of single-agent antibacterial therapy through complementary mechanisms, especially enhancing efficacy against Gram-negative bacteria:

Combination with chelating agents: The outer membrane of Gram-negative bacteria (containing lipopolysaccharides) is a barrier that nisin struggles to penetrate. Chelating agents like EDTA and citric acid can disrupt the outer membrane structure, allowing Nisin to enter cells. Studies have shown that the antibacterial activity of Nisin combined with EDTA against E. coli and Salmonella can be enhanced by 2-4 times.

Combination with traditional antibiotics: Nisin combined with vancomycin, penicillin, etc., can reduce drug resistance in resistant bacteria through a synergistic mechanism of "pore formation+inhibition of cell wall synthesis". For example, against methicillin-resistant Staphylococcus aureus (MRSA), the combined antibacterial effect is over 50% higher than single-agent use, while reducing antibiotic dosage.

Combination with plant-derived antimicrobials: Plant extracts such as curcumin and carvacrol can disrupt bacterial cell membranes or inhibit biofilm formation. Their combination with nisin enhances inhibition of multidrug-resistant bacteria, reduces Nisin dosage, and mitigates potential bacterial adaptation issues.

III. Carrier Delivery: Improving Targeting and Environmental Adaptability

Loading nisin via nanocarriers or biomaterials can protect it from environmental factors (e.g., pH, temperature, enzymes) and enhance its accumulation at bacterial infection sites:

Nanoparticle carriers: Liposomes, chitosan nanoparticles, etc., can encapsulate Nisin, extending antibacterial duration through sustained release. Meanwhile, the small size of nanoparticles helps penetrate biofilms (e.g., bacterial mucus layers), improving killing efficiency against bacteria within biofilms. For example, chitosan nanoparticle-loaded Nisin has a 60% higher clearance rate of Pseudomonas aeruginosa biofilms than free Nisin.

Biofilm coatings: Immobilizing nisin in coatings on medical materials (e.g., catheters, implant surfaces) enables local sustained antibacterial activity, reducing medical device-related infections. For instance, embedding nisin in polylactic acid coatings effectively inhibits Staphylococcus aureus colonization on catheter surfaces, with antibacterial effects lasting over 2 weeks.

Responsive carriers: Designing pH-sensitive or temperature-sensitive carriers (e.g., polyethylene glycol-polycaprolactone copolymers) triggers Nisin release at bacterial infection sites (usually acidic), improving targeted antibacterial efficiency and reducing impact on normal cells.

IV. Genetic Engineering Modification: Directionally Enhancing Activity and Stability

Modifying nisin’s synthetic genes through genetic engineering can alter its amino acid sequence, optimize active sites, or enhance degradation resistance:

Site-directed mutagenesis: Mutating protease-susceptible sites in nisin (e.g., specific serine or threonine residues) to more stable amino acids (e.g., alanine) improves resistance to trypsin, extending half-life. For example, a mutant retains 40% more activity than the wild type in a simulated intestinal environment.

Fragment fusion: Fusing active fragments of nisin with functional fragments of other antimicrobial peptides (e.g., defensins) to construct hybrid peptides combines their antibacterial mechanisms. For example, fusion with a magainin fragment enhances activity against Gram-positive bacteria and confers inhibitory ability against some Gram-negative bacteria.

High-yield strain construction: Optimizing Nisin synthesis regulatory genes in Streptococcus lactis via gene editing (e.g., CRISPR-Cas9) increases fermentation yield while making synthesized Nisin structurally more stable (e.g., increasing intramolecular disulfide bonds), indirectly enhancing effective concentrations in practical applications.

V. Environmental Condition Optimization: Reducing Activity Loss

Nisin’s antibacterial activity is significantly affected by environmental factors such as pH, temperature, and ionic strength. Optimizing application environments can reduce activity loss:

pH adjustment: Nisin is more stable under acidic conditions (pH 2-6), while alkaline environments easily disrupt its structure. In applications (e.g., food preservation or local drug delivery), buffering agents can maintain environmental pH at 5.0-6.0 to maximize activity retention.

Reducing ionic strength: High concentrations of metal ions like Na⁺ and Ca²⁺ bind to Nisin’s cationic sites, weakening electrostatic interactions with bacterial cell membranes. Reducing high-salt components in formulations or adding ion chelators (e.g., sodium citrate) can alleviate this issue and enhance antibacterial efficacy.

Low-temperature synergy: Low temperatures (e.g., 4℃) delay nisin degradation and inhibit bacterial metabolism, synergizing with Nisin for antibacterial effects. For example, in refrigerated foods, its antibacterial validity period is 3-5 times longer than at room temperature.

Strategies to enhance nisin’s antibacterial effect need to integrate multiple dimensions: molecular structure optimization, synergistic interactions, delivery systems, genetic modification, and environmental regulation. Through single or combined strategies, comprehensive improvements in its antibacterial activity, stability, and spectrum can be achieved, supporting practical applications in fields like drug-resistant bacterial infection treatment and antibacterial modification of biomaterials.