Influencing factors of bacterial resistance to Nisin production

Nisin is a polypeptide with antibacterial activity produced by certain Streptococcus lactis, and it is widely used as a biological preservative in the food industry.

The influencing factors of bacterial resistance to Nisin mainly include the following aspects:

I. Characteristics of Bacteria Itself

Cell Wall Structure and Composition: The cell wall of Gram-positive bacteria is relatively thick and mainly composed of peptidoglycan. Nisin can exert its antibacterial effect by acting on the peptidoglycan layer. Gram-negative bacteria, due to the presence of the outer membrane of the cell wall, have a natural barrier effect against Nisin and are relatively more likely to develop resistance. In addition, the degree of cross-linking of peptidoglycan in the cell wall and the content of teichoic acid also affect the binding between Nisin and the bacterial cell wall, thereby influencing the sensitivity of bacteria to Nisin.

Cell Membrane Composition: The saturation of fatty acids, chain length, and the composition of phospholipids in the bacterial cell membrane can affect the fluidity and permeability of the cell membrane. When the fluidity of the cell membrane decreases or the permeability changes, Nisin is difficult to insert into the cell membrane to exert its effect, enabling bacteria to develop resistance. For example, some bacteria can reduce the fluidity of the cell membrane by increasing the content of saturated fatty acids in the cell membrane, and thus reduce their sensitivity to Nisin.

Resistance Genes: Certain bacteria may carry genes related to Nisin resistance. These genes can encode some proteins that can modify the target, promote the efflux of Nisin, or degrade proteins. For example, the ABC transporter protein genes in some bacteria can pump Nisin that has entered the cell out of the cell, reducing the concentration of Nisin inside the cell and thus developing resistance.

II. Environmental Factors

Temperature: Temperature has an important impact on the growth and metabolism of bacteria and also affects the sensitivity of bacteria to Nisin. Generally, at lower temperatures, bacteria grow slowly, the fluidity of the cell membrane decreases, and Nisin is difficult to insert into the cell membrane, so the resistance of bacteria to Nisin may increase. At higher temperatures, the fluidity of the bacterial cell membrane increases, and Nisin is more likely to exert its effect. However, excessively high temperatures may also cause bacteria to have a heat stress response, thereby changing the physiological state of the cells and affecting their sensitivity to Nisin.

pH Value: The environmental pH value can affect the stability and activity of Nisin, and also affect the charge and permeability of the bacterial cell membrane. In an acidic environment, the activity of Nisin is usually higher, while in an alkaline environment, Nisin may be denatured or degraded, and its activity decreases. In addition, different bacteria have different growth states and cell membrane characteristics at different pH values. For example, the cell membrane permeability of some bacteria increases under acidic conditions, making them more susceptible to the action of Nisin, while they may develop resistance under alkaline conditions.

Nutrient Components: Nutrient components such as carbon sources, nitrogen sources, and minerals in the culture medium can affect the growth and metabolism of bacteria, and thus influence their resistance to Nisin. Abundant nutrients are generally beneficial to the growth of bacteria, making them more sensitive to Nisin. When nutrients are lacking, bacteria may enter a stress state and enhance their resistance to Nisin by changing their physiological characteristics. For example, when certain amino acids are lacking in the culture medium, bacteria may adjust the synthesis of the cell wall and cell membrane, thereby reducing their sensitivity to Nisin.

III. Factors Related to Nisin

Concentration: Long-term exposure to sub-lethal concentrations of Nisin is an important factor inducing bacterial resistance. When the concentration of Nisin is low, it cannot completely inhibit the growth of bacteria, and some bacteria may gradually adapt to the Nisin environment through gene mutation or gene expression regulation, thus developing resistance. In an environment with a high concentration of Nisin, bacteria are more likely to be killed, and the probability of developing resistance is relatively low.

Action Time: The action time is also one of the factors affecting the development of bacterial resistance. As the action time of Nisin is prolonged, bacteria have more time to adapt to and cope with the pressure of Nisin, increasing the possibility of developing resistance. For example, short-term exposure to Nisin may only cause temporary damage to bacteria, while long-term exposure may lead to genetic changes in bacteria and the development of stable resistance.

In practical applications, these factors need to be comprehensively considered, and reasonable measures should be taken to prevent or reduce the resistance of bacteria to Nisin, such as reasonably controlling the usage concentration and action time of Nisin, optimizing environmental conditions, and combining with other preservation technologies, so as to fully exert its antibacterial effect and extend the shelf life of food.