What Is Bacteriocin?

Bacteriocins are a class of polypeptides or precursor polypeptides with antibacterial activity produced by ribosomal synthesis mechanisms during the metabolism of certain bacteria. It shows a narrow inhibitory spectrum on the same kind of related strains. It perforates on target cells, inhibits peptidoglycan synthesis, interacts with ribosomes or tRNA to inhibit protein synthesis, and directly degrades target cell DNA, thus exerting antibacterial effect. ^[1]

Bacteriocin is a type of bactericidal protein or polypeptide encoded by bacteria or archaea genes and synthesized by ribosomes. Bacteriocin-producing bacteria have immunity to bacteriocins secreted by themselves. Bacteriocins are a class of antibacterial substances that exist in the natural environment in which bacteria live. Early research suggested that bacteriocins only work on bacteria of the same or close relationship. However, in recent years, more and more research results show that One bacteriocin may also have a killing effect on many other bacteria.

In 1925, A. Grecia reported for the first time that E. coli V strain produced a substance that had a bactericidal effect on the E. coli strain , which was called

1.A kind produced by bacteria

1. Bacteriocin is named after the producing bacteria: for example, the bacteriocin produced by E. coli is called E. coli,

The synthesis of bacteriocin is strictly regulated. Research results show that bacteriocin generally begins to be synthesized and secreted in the middle of the logarithmic growth phase of bacteria, and increases with the increase in the number of bacteria until it reaches the early stage of the growth plateau. The highest peak of secretion. The synthesis of bacteriocin occurs under certain conditions. The mechanisms that cause bacteriocin synthesis and secretion are:

Group effect mechanism, which is a mechanism of regulation and regulation of most bacteriocins. In this mechanism, bacteriocin-producing bacteria regulate the production of bacteriocin by secreting an extracellular pheromone. When the number of bacteria is small, the content of this pheromone is very low, which is not enough to start the secretion of bacteriocin. However, as the number of bacteria continues to increase, the concentration of extracellular pheromones also increases accordingly. When the number of bacteria reaches a certain level, When the value is reached, the concentration of extracellular pheromone also reaches a threshold. At this time, the bacteriocin-producing bacteria will start the biosynthesis and secretion of bacteriocin.

Environmental induction mechanism, which is a mechanism that initiates bacteriocin secretion under special circumstances. There are many environmental factors that cause bacteriocin secretion, including hypoxia, stress, catabolism suppression and the addition of antibiotics, bacteriocin and other bacteria.

SOS stress mechanism, the secretion mechanism mainly exists in the secretion of bacteriocins of E. coli. It is characterized by the protective effect that the producing bacteria can obtain after sacrificing bacteriocins at the expense of some sibs, that is, to obtain more. Nutrients and living space. After bacteriocin synthesis, it must be finally released into the surrounding environment to achieve the role of bacterial flora regulation. The main pathways for bacteriocin release from bacterial cells are: ABC transport pathway, SEC transport pathway, cytolytic pathway (only seen in the secretion of E. coli and E. coli-like bacteriocin from Gram-negative bacteria), and other bacteriocin secretion. Dedicated approach. ^[2]

Bacteriocin is a powerful weapon used by bacteria to regulate the structure of the flora. As a competitive weapon in bacterial life, bacteriocin can not only help bacteriocin-producing bacteria invade an originally stable microbial flora, but also be a defensive weapon for bacteriocin-producing bacteria, preventing the stable flora established by itself from being affected by others. Bacteria infestation. The research results show that under the condition of inadequate inoculation, bacteriocin-producing bacteria are usually difficult to invade and grow in an orderly sensitive flora such as liquid culture. This is because a small amount of bacteriocin cannot kill sensitive bacteria after high dilution. Death, but the cost of fitness for bacteriocin synthesis puts bacteriocin-producing bacteria at a significant competitive disadvantage. On the contrary, if a small amount of sensitive bacteria is introduced into the bacteriocin-producing flora in liquid culture, it is impossible to survive the sensitive bacteria because of the presence of bacteriocin. However, in a structured environment such as solid culture, because of the inconsistencies in the nutrients contained in different spatial structures, bacteriocin-producing bacteria can occupy relatively weak places in nutrition competition, while sensitive bacteria can live in nutrient competition. More intense areas, so that the two are in harmony. In more complex natural habitats (such as the intestines of animals), the impact of bacteriocin secretion on the entire bacterial community is mainly determined by the price paid by bacteriocin-producing bacteria to secrete bacteriocin. In theory, bacteria A dynamic balance can be reached between the vegetative producing bacteria, the sensitive bacteria and the surrounding commensal flora. Intestinal bacteria that secrete bacteriocin are more conducive to its successful colonization in the intestine. The use of probiotics made by bacteria that secrete bacteriocin to maintain or restore the stability of the intestinal flora of animals has also been increasingly used. The results of a large number of laboratory pure culture studies also show that the secretion of bacteriocins generally occurs after the bacteria proliferate to a certain number, that is, the secretion begins in the late logarithmic growth and continues to the plateau stage. During this period, the number of bacteria in the environment increased rapidly, and living space and nutrients began to become insufficient. Bacteriocin-producing bacteria would start the secretion of bacteriocin under the mediation of different mechanisms such as group effects, in an attempt to kill the bacteria through the secretion of bacteriocin. Eliminate sensitive strains in the same living environment, so as to obtain more nutrients and living space to maintain their own survival. In addition, nutrients can be obtained by lysing bacteriocin to lyse sensitive bacteria. ^[2]

Bacteriocin is usually produced by Gram-positive bacteria and can inhibit other closely related Gram-positive bacteria. It has no inhibitory effect on most Gram-negative bacteria and fungi. Bacteriocin can inhibit many Gram-positive bacteria, such as

Since a bacteriocin does not inhibit every bacterium,

1. Application of bacteriocin in food preservation

Bacteriocin can effectively inhibit or kill spoilage or pathogenic bacteria in food. At the same time, it is a natural protein substance and is very safe for the human body. Studies have suggested that it will be degraded by proteases in the stomach and intestines, because digestive enzymes can quickly inactivate bacteriocins, so it cannot play a bacteriostatic effect in the gastrointestinal tract. Many regulatory agencies advocate using fence technology to solve such problems, such as combining several physical and chemical methods to control the growth of harmful microorganisms. The combination of Pediocin and low doses of radiation showed a strong inhibitory activity against the growth of S. tumefaciens. Nisin is the first bacteriocin approved for use in foods. Nisin has been recognized as a safe food preservative in more than 45 countries.

2. Application of bacteriocin in medicine

As the problem of resistance caused by antibiotics is getting more and more serious, people are constantly looking for drugs that can replace antibiotics against antibiotic-resistant bacteria. Among them, bacteriocin is considered to have great potential. Compared with the broad-spectrum antibacterial properties of antibiotics, bacteriocins have a narrower bacteriostatic spectrum, have certain specificity and targeting, and are not prone to drug resistance. At the same time, there are many types of bacteriocins, and normal bacteriocins can be found for certain pathogens. For example, Cerein 7 has a strong inhibitory effect on vancomycin-resistant Streptococcus avian and Streptococcus equi. At present, bacteriocins for bacterial infections are generally treated with bacteriocin-producing strains for bacterial intervention. Until now, no pure bacteriocin has been used directly as a drug in clinical practice, and it has only remained in the laboratory stage.

3. Application of bacteriocin in feed

Just as humans are facing the danger of antibiotic-resistant strains, the abuse of antibiotic additives in the animal husbandry industry has caused quite serious consequences. Such as MRSA (Methicillin-Resistant Staphylococcus aureus) ST398 caused a series of serious infections in European farms. Experts believe that MRSA ST398 appears because people add antibiotics to the feed to increase the resistance of the bacteria to the drug. Studies have shown that bacteriocin-producing strains have a certain effect on the intestinal flora of animals. When a strain of microcin 24 produced at a concentration close to 106 cells / mL was added to the chicken's drinking water, Salmonella typhimurium was no longer detected in 3 weeks. In the production of animal husbandry, with the emergence of bacteriocin and the deepening of research, it has become possible to replace antibiotics with bacteriocin to ensure the health of livestock and poultry, the safety of livestock products, and the safety of the breeding ecological environment.

4. Application of bacteriocin in Hurdle technology

Fence technology is a combination of different preservation methods to inhibit the growth of microorganisms. Bacteriocin is often used in conjunction with other treatments and can be used as a fence to improve food safety. The combined use of two bacteriocins can extend the shelf life of foods. For example, the combined use of Nisin and PendincinPA-1 / ACH can prevent dairy products, meat and fish food from spoiling. Some researchers have succeeded in using Nisin with lysozyme or Nisin and some milk instead of using two bacteriocins to inhibit food spoilage bacteria. Studies on the bacteriostatic effect of bacteriocin in combination with other chemical preservatives in milk, cheese, and fruit juice have shown that bacteriocins of Lactobacillus brevis and Bacillus mycobacterium show promising results in all processed foods. Bacteriocin-producing bacteria and lactic acid bacteria cultures can use fence technology to reduce foodborne illness. Understanding how each individual fence works can more effectively combine the various treatments together. For example, the application of pulsed electric field (PEF), which can increase the permeability of cell membranes, has been used in conjunction with Nisin, which also acts on cell membranes. ^[3]