The antibacterial mechanism of Nisin

Nisin exerts antimicrobial effects through a dual mechanism of "targeted binding to lipid Ⅱ + disrupting bacterial cell membranes," primarily acting on Gram-positive bacteria. It causes irreversible damage to bacterial cell wall synthesis and membrane integrity, ultimately leading to bacterial death with no significant risk of drug resistance.

Step 1: Targeted Recognition and Binding to Lipid Ⅱ (Core Target)

Lipid Ⅱ is a key precursor for bacterial cell wall peptidoglycan synthesis, widely present on the cell membrane of Gram-positive bacteria, and serves as the core target for Nisin’s antimicrobial action.

The first 3 lanthionine rings (Rings a, b, c) at the N-terminus of Nisin form a specific binding pocket, which precisely binds to the pyrophosphate group of lipid Ⅱ through hydrogen bonds and hydrophobic interactions, forming a stable Nisin-lipid Ⅱ complex.

This binding is highly specific: it does not interact with host cell components or the outer membrane structure of Gram-negative bacteria, resulting in no toxic side effects on human cells and strong targeted antimicrobial activity.

Binding directly blocks the transport of lipid Ⅱ to cell wall synthesis sites, inhibits peptidoglycan cross-linking reactions, and disrupts bacterial cell wall synthesis, preventing the maintenance of morphological integrity.

Step 2: Disrupting Bacterial Cell Membrane Integrity (Lethal Damage)

After binding to lipid Ⅱ, Nisin damages the bacterial cell membrane through two pathways, causing the leakage of intracellular substances:

Formation of Transmembrane Pores

Nisin-lipid Ⅱ complexes aggregate on the bacterial cell membrane, and multiple complexes interact to form transmembrane pores with a diameter of approximately 2–3 nm. These pores disrupt the membrane’s ion gradient and osmotic balance, leading to the rapid leakage of key intracellular substances such as K⁺ and ATP, while a large amount of extracellular water influxes. Ultimately, the bacteria swell and rupture.

Interfering with Membrane Structural Stability

The C-terminal region of Nisin (Rings d, e, and flexible tail) can insert into the phospholipid bilayer of the cell membrane, disrupting the ordered arrangement of lipid molecules, reducing membrane fluidity and stability. This further exacerbates membrane damage and accelerates bacterial death.

Antimicrobial Spectrum and Synergistic Characteristics

Main Targets

Gram-positive bacteria, including pathogenic bacteria and food spoilage bacteria such as Staphylococcus aureus, Listeria monocytogenes, Streptococcus spp., and Clostridium spp. It also inhibits the germination of bacterial spores.

Effect on Gram-Negative Bacteria

Weak activity when used alone, as the outer membrane barrier of Gram-negative bacteria blocks Nisin’s binding to lipid Ⅱ. Combined use with chelating agents such as EDTA can disrupt the outer membrane, expanding the antimicrobial spectrum.

Synergistic Enhancement

Combination with organic acids, probiotics, or plant extracts enhances antimicrobial efficacy through mechanisms such as reducing intracellular pH of bacteria and competing for nutrients. This allows for a reduction in Nisin dosage.

Core Reasons for No Significant Drug Resistance

Highly Conserved Target

Lipid Ⅱ is an essential substance for bacterial cell wall synthesis, with a highly conserved structure among Gram-positive bacteria. Bacteria rarely mutate to alter the structure of lipid Ⅱ to evade Nisin binding.

Irreversible Mechanism of Action

Nisin’s damage to the cell membrane is physical and irreversible, unlike antibiotics that act through enzyme inhibition or metabolic interference. Bacteria are unlikely to develop resistant mutations against this mechanism.

Naturally Occurring Antimicrobial Peptide

Nisin is a natural metabolite of Lactococcus lactis. No widely resistant strains have emerged through long-term natural selection, and reports of drug resistance in clinical and food applications are extremely rare.