Diversity of enterococcal bacteriocins and their grouping in a new classification scheme

Enterococci are lactic acid bacteria of importance in food, public health and medical microbiology. Many strains produce bacteriocins, some of which have been well characterized. This review describes the structural and genetic characteristics of enterocins, the bacteriocins produced by enterococci. Some of these can be grouped with typical bacteriocins produced by lactic acid bacteria according to traditional classification, whereas others are atypical and structurally distinct from the general classes of bacteriocins. These atypical enterocins recently played an important role in and prompted reclassification of the class II bacteriocins into a new scheme. In this review, a more simplified classification scheme for enterocins based on amino acid sequence homologies is proposed. Enterocins are of interest for their diversity and potential for use as food biopreservatives. The emergence of multiple antibiotic-resistant enterococci among agents of nosocomial disease and the presence of virulence factors among food isolates requires a careful safety evaluation of isolates intended for potential biotechnical use. Nevertheless, enterococcal bacteriocins produced by heterologous hosts or added as cell-free preparations may still be attractive for application in food preservation.     

细菌素的合成与作用机制

细菌素是由细菌产生的抗菌蛋白,可以杀死与产生菌相近的细菌。很多乳酸菌产生不同多样性的细菌素,虽然这些细菌素都是由发酵或非发酵食品中发现的乳酸菌产生的,但是迄今只有乳酸链球菌素(Nisin)作为食品防腐剂被广泛应用。和抗生素不同的是,细菌素由核糖体合成,需经翻译后修饰活化并且通过特定转运系统输到胞外才能发挥其功能,它一般通过作用于靶细胞膜来抑制靶细胞的生长,同时本身合成细菌素的细胞对其产物具有免疫性。细菌素能安全有效地抑制病原体生长,在食品行业中具有广阔的应用前景。     

Expression of bacteriocin divercin AS7 in Escherichia coli and its functional analysis

Bacteriocins are small peptides with antimicrobial activity, that are produced by bacteria. Four classes of bacteriocins produced by lactic acid bacteria have been defined. Class IIa bacteriocins are promising candidates for industrial applications due to their high biological activity and their physicochemical properties. Divercin AS7 is a class IIa bacteriocin produced by Carnobacterium divergens AS7. It shows antibacterial activity against pathogens and food spoilage flora including Listeria spp. Little is known about the impact of class IIa bacteriocins upon eukaryotic cells. The safe use of bacteriocins as food biopreservatives requires the absence of cytotoxicity to human cells. To analyze the impact of divercin AS7 on human enterocytes, we expressed the recombinant divercin AS7 in the Escherichia coli BL21DE3pLys strain and conducted in vitro studies to evaluate the safety of recombinant divercin AS7. No cytotoxic effect on differentiated monolayer Caco-2 cells and no apoptotic appearance were observed when recombinant divercin AS7 was used at a concentration of 2 μg ml^?1. In our study, divercin AS7 also did not interfere with differentiated Caco-2 cells monolayer integrity. The obtained results suggest that divercin AS7 is a promising peptide for the food industry.     

Bacteriocins ofLactobacillus plantarum strains from fermented foods

Bacteriocin-producing strains may be used as protective cultures to improve the microbial safety of foods. The crude or purified form of these antimicrobial agents may also be applied directly as food preservative. This review gives survey of the different bacteriocins produced byLactobacillus plantarum isolated from fermented food products with particular emphasis on their genetic and biochemical properties. A number of bacteriocins are produced byL. plantarum. These include plantaricin B, plantaricin BN, plantaricin A, plantaricin C, plantaricin S and T, plantaricin, F, plantaricin C19 and SA6 and other unnamed bacteriocins. However, with the exception of plantaricin A, information on the genetic and biochemical characteristics ofL. plantarum bacteriocins is still scant.     

Lantibiotics, class I bacteriocins from the genus Bacillus

Antimicrobial peptides exhibit high levels of antimicrobial activity against a broad range of spoilage and pathogenic microorganisms. Compared with bacteriocins produced by lactic acid bacteria, antimicrobial peptides from the genus Bacillus have been relatively less recognized despite their broad antimicrobial spectra. These peptides can be classified into two different groups based on whether they are ribosomally (bacteriocins) or nonribosomally (polymyxins and iturins) synthesized. Because of their broad spectra and high activity, antimicrobial peptides from Bacillus spp. may have great potential for applications in the food, agricultural, and pharmaceutical industries to prevent or control spoilage and pathogenic microorganisms. In this review, we introduce ribosomally synthesized antimicrobial peptides, the lantibiotic bacteriocins produced by members of Bacillus. In addition, the biosynthesis, genetic organization, mode of action, and regulation of subtilin, a well-investigated lantibiotic from Bacillus subtilis, are discussed.     

Application of Bacteriocins in the Control of Foodborne Pathogenic and Spoilage Bacteria

Bacteriocins are antimicrobial peptides or proteins produced by strains of diverse bacterial species. The antimicrobial activity of this group of natural substances against foodborne pathogenic, as well as spoilage bacteria, has raised considerable interest for their application in food preservation. Application of bacteriocins may help reduce the use of chemical preservatives and/or the intensity of heat and other physical treatments, satisfying the demands of consumers for foods that are fresh tasting, ready to eat, and lightly preserved. In recent years, considerable effort has been made to develop food applications for many different bacteriocins and bacteriocinogenic strains. Depending on the raw materials, processing conditions, distribution, and consumption, the different types of foods offer a great variety of scenarios where food poisoning, pathogenic, or spoilage bacteria may proliferate. Therefore, the effectiveness of bacteriocins requires careful testing in the food systems for which they are intended to be applied against the selected target bacteria. This and other issues on application of bacteriocins in foods of dairy, meat, seafood, and vegetable origins are addressed in this review.     

Application of bacteriocins in the control of foodborne pathogenic and spoilage bacteria

Bacteriocins are antimicrobial peptides or proteins produced by strains of diverse bacterial species. The antimicrobial activity of this group of natural substances against foodborne pathogenic, as well as spoilage bacteria, has raised considerable interest for their application in food preservation. Application of bacteriocins may help reduce the use of chemical preservatives and/or the intensity of heat and other physical treatments, satisfying the demands of consumers for foods that are fresh tasting, ready to eat, and lightly preserved. In recent years, considerable effort has been made to develop food applications for many different bacteriocins and bacteriocinogenic strains. Depending on the raw materials, processing conditions, distribution, and consumption, the different types of foods offer a great variety of scenarios where food poisoning, pathogenic, or spoilage bacteria may proliferate. Therefore, the effectiveness of bacteriocins requires careful testing in the food systems for which they are intended to be applied against the selected target bacteria. This and other issues on application of bacteriocins in foods of dairy, meat, seafood, and vegetable origins are addressed in this review.     

Bacteriocins from lactic acid bacteria and their potential in the preservation of fruit products

Bacteriocins produced by lactic acid bacteria (LAB) are well-recognized for their potential as natural food preservatives. These antimicrobial peptides usually do not change the sensorial properties of food products and can be used in combination with traditional preservation methods to ensure microbial stability. In recent years, fruit products are increasingly being associated with food-borne pathogens and spoilage microorganisms, and bacteriocins are important candidates to preserve these products. Bacteriocins have been extensively studied to preserve foods of animal origin. However, little information is available for their use in vegetable products, especially in minimally processed ready-to-eat fruits. Although, many bacteriocins possess useful characteristics that can be used to preserve fruit products, to date, only nisin, enterocin AS-48, bovicin HC5, enterocin 416K1, pediocin and bificin C6165 have been tested for their activity against spoilage and pathogenic microorganisms in these products. Among these, only nisin and pediocin are approved to be commercially used as food additives, and their use in fruit products is still limited to certain countries. Considering the increasing demand for fresh-tasting fruit products and concern for public safety, the study of other bacteriocins with biochemical characteristics that make them candidates for the preservation of these products are of great interest. Efforts for their approval as food additives are also important. In this review, we discuss why the study of bacteriocins as an alternative method to preserve fruit products is important; we detail the biotechnological approaches for the use of bacteriocins in fruit products; and describe some bacteriocins that have been tested and have potential to be tested for the preservation of fruit products.     

Novel method to extract large amounts of bacteriocins from lactic acid bacteria.

Antimicrobial peptides, bacteriocins, produced by lactic acid bacteria were adsorbed on the cells of producing strains and other gram-positive bacteria. pH was a crucial factor in determining the degree of adsorption of these peptides onto cell surfaces. In general, between 93 and 100% of the bacteriocin molecules were adsorbed at pHs near 6.0, and the lowest (< or = 5%) adsorption took place at pH 1.5 to 2.0. On the basis of this property, a novel isolation method was developed for bacteriocins from four genera of lactic acid bacteria. By using this method we made preparations of pediocin AcH, nisin, sakacin A, and leuconocin Lcm1 that were potent and concentrated. This method produced a higher yield than isolation procedures, which rely on precipitation of the bacteriocins from the cell-free culture liquor. It is simple and can be used to produce large quantities of bacteriocins from lactic acid bacteria to be used as food biopreservatives.     

Novel method to extract large amounts of bacteriocins from lactic acid bacteria.

Antimicrobial peptides, bacteriocins, produced by lactic acid bacteria were adsorbed on the cells of producing strains and other gram-positive bacteria. pH was a crucial factor in determining the degree of adsorption of these peptides onto cell surfaces. In general, between 93 and 100% of the bacteriocin molecules were adsorbed at pHs near 6.0, and the lowest (< or = 5%) adsorption took place at pH 1.5 to 2.0. On the basis of this property, a novel isolation method was developed for bacteriocins from four genera of lactic acid bacteria. By using this method we made preparations of pediocin AcH, nisin, sakacin A, and leuconocin Lcm1 that were potent and concentrated. This method produced a higher yield than isolation procedures, which rely on precipitation of the bacteriocins from the cell-free culture liquor. It is simple and can be used to produce large quantities of bacteriocins from lactic acid bacteria to be used as food biopreservatives.     

Gassericin A: a circular bacteriocin produced by Lactic acid bacteria Lactobacillus gasseri

During the recent years extensive efforts have been made to find out bacteriocins from lactic acid bacteria (LAB) active against various food spoilage and pathogenic bacteria, and superior stabilities against heat treatments and pH variations. Bacteriocins isolated from LAB have been grouped into four classes. Circular bacteriocins which were earlier grouped among the four groups of bacteriocins, have recently been proposed to be classified into a different class, making it class V bacteriocins. Circular bacteriocins are special molecules, whose precursors must be post translationally modified to join the N to C termini with a head-to-tail peptide bond. Cyclization appears to make them less susceptible to proteolytic cleavage, high temperature and pH, and, therefore, provides enhanced stability as compared to linear bacteriocins. The advantages of circularization are also reflected by the fact that a significant number of macrocyclic natural products have found pharmaceutical applications. Circular bacteriocins were unknown two decades ago, and even to date, only a few circular bacteriocins from a diverse group of Gram positive organisms have been reported. The first example of a circular bacteriocin was enterocin AS-48, produced by Enterococcus faecalis AS-48. Gassereccin A, produced by Lactobacillus gasseri LA39, Reutericin 6 produced by Lactobacillus reuteri LA6 and Circularin A, produced by Clostridium beijerinickii ATCC 25,752, are further examples of this group of antimicrobial peptides. In the present scenario, Gassericin A can be an important tool in the food preservation owing to its properties of high pH and temperature tolerance and the fact that it is produced by LAB L. gasseri, whose many strains are proven probiotic.     

Bacteriocinogenic LAB Strains for Fermented Meat Preservation: Perspectives,Challenges, and Limitations

Over the last decades, much research has focused on lactic acid bacteria (LAB) bacteriocins because of their potential as biopreservatives and their action against the growth of spoilage microbes. Meat and fermented meat products are prone to microbial contamination, causing health risks, as well as economic losses in the meat industry. The use of bacteriocin-producing LAB starter or protective cultures is suitable for fermented meats. However, although bacteriocins can be produced during meat processing, their levels are usually much lower than those achieved during in vitro fermentations under optimal environmental conditions. Thus, the direct addition of a bacteriocin food additive would be desirable. Moreover, safety and technological characteristics of the bacteriocinogenic LAB must be considered before their widespread applications. This review describes the perspectives and challenges toward the complete disclosure of new bacteriocins as effective preservatives in the production of safe and “healthy” fermented meat products.     

环状细菌素研究进展

细菌素是一类由细菌核糖体合成的抗菌肽,是产生菌获得生存优势的重要手段。与大多数线性细菌素不同,环状细菌素具有N端和C端共价连接的特殊结构。这种环状结构赋予环状细菌素良好的耐热性、广泛的pH适应性和抗蛋白酶降解能力,在食品防腐和对治耐药性细菌领域表现出巨大的应用潜能。通过对已发现的环状细菌素结构分析发现,相对于一级结构,其三级结构的相似性更高,可以作为环状细菌素归类的依据。环状细菌素的生物合成机制尚不清楚,但其环化机制是最具价值的研究热点,可为其他一些肽类物质的合成提供支架,从而提高应用潜能。环状细菌素抑菌机制主要是在目标菌株的细胞膜上穿孔,使胞内物质外流,进而导致目标细菌死亡。其有类似于抗生素的抑菌活性和有别于抗生素的抑菌机制,为治疗日益严重的耐药性病原菌提供了可靠备选资源。本文综述了环状细菌素的构效关系、生物合成和抑菌机制方面的研究进展,希望能够对环状细菌素的深入研究和应用提供有价值的参考。     

益生菌产生的细菌素及其功能机制

细菌素是细菌核糖体合成的具有抑菌活性的小肽.细菌素的产生是益生菌重要的益生特性,它们天然无毒,不仅对食品腐败菌和人体致病菌有很好的抑菌活性,还具有有助益生菌定殖和调节肠道菌群等益生特性.本文综述了益生菌产生的细菌素的种类、条件性合成、益生功能及其作用机理等,以期为深入认识益生菌的益生功能及其作用方式,研究开发对人体有益...     

Antibacterial metabolites of lactic acid bacteria: their diversity and properties

The review is devoted to literature data on antimicrobial metabolites produced by lactic acid bacteria (LAB), which have long been used for the preparation of cultured dairy products. This paper summarizes data on low-molecular-weight antimicrobial substances, which are primary products or by-products of lactic fermentation. Individual sections are devoted to a variety of antifungal agents and bacteriocins produced by LAB; their potential use as food preservatives has been discussed. The characteristics and classification of bacteriocins are presented in a greater detail; their synthesis and mechanism of action are described using the example of nisin A, which belongs to class I lantibiotics synthesized by the bacterium Lactococcus lactis subsp. lactis. The mechanism of action of class II bacteriocins has been demonstrated with lacticin. Prospective directions for using LAB antimicrobial metabolites in industry and medicine are discussed in the Conclusion.     

Native and heterologous production of bacteriocins from gram-positive microorganisms

In nature, microorganisms can present several mechanisms for setting intercommunication and defense. One of these mechanisms is related to the production of bacteriocins, which are peptides with antimicrobial activity. Bacteriocins can be found in Gram-positive and Gram-negative bacteria. Nevertheless, bacteriocins produced by Gram-positive bacteria are of particular interest due to the industrial use of several strains that belong to this group, especially lactic acid bacteria (LAB), which have the status of generally recognized as safe (GRAS) microorganisms. In this work, we will review recent tendencies in the field of invention and state of art related to bacteriocin production by Gram-positive microorganism. Hundred-eight patents related to Gram-positive bacteriocin producers have been disclosed since 1965, from which 57% are related bacteriocins derived from Lactococcus, Lactobacillus, Streptococcus, and Pediococcus strains. Surprisingly, patents regarding heterologous bacteriocins production were mainly presented just in the last decade. Although the major application of bacteriocins is concerned to food industry to control spoilage and foodborne bacteria, during the last years bacteriocin applications have been displacing to the diagnosis and treatment of cancer, and plant disease resistance and growth promotion.     

Antibacterial metabolites of lactic acid bacteria: Their diversity and properties

The review is devoted to literature data on antimicrobial metabolites produced by lactic acid bacteria (LAB), which have long been used for the preparation of cultured dairy products. This paper summarizes data on low-molecular-weight antimicrobial substances, which are primary products or by-products of lactic fermentation. Individual sections are devoted to a variety of antifungal agents and bacteriocins produced by LAB; their potential use as food preservatives has been discussed. The characteristics and classification of bacteriocins are presented in a greater detail; their synthesis and mechanism of action are described using the example of nisin A, which belongs to class I lantibiotics synthesized by the bacterium Lactococcus lactis subsp. lactis. The mechanism of action of class II bacteriocins has been demonstrated with lacticin. Prospective directions for using LAB antimicrobial metabolites in industry and medicine are discussed in the Conclusion.     

Inhibition of the growth of enteropathogenic bacilli by bacteriocins produced by micro-organisms from the sediment of wells

The bacterial flora of the sediment of 20 wells of water for human consumption in the rural area of the VII Region in Chile was examined. Fourteen strains of bacteria, from different wells, produced bacteriocins which inhibited the growth of Salmonella typhi, Salm. typhimurium, Shigella sonnei and enterotoxigenic Escherichia coli. About 50% of these strains contained plasmids of different molecular weight and a large number of these codified for bacteriocins. The results suggest what is required to implement an efficient, simple and economical biological system for the purification or control of the number of enteropathogenic bacilli of well water in the rural area.     

A New Structure-based Classification of Gram-positive Bacteriocins

Bacteriocins are ribosomally-synthesized peptides or proteins produced by a wide range of bacteria. The antimicrobial activity of this group of natural substances against foodborne pathogenic and spoilage bacteria has raised considerable interest for their application in food preservation. Classifying these bacteriocins in well defined classes according to their biochemical properties is a major step towards characterizing these anti-infective peptides and understanding their mode of action. Actually, the chosen criteria for bacteriocins’ classification lack consistency and coherence. So, various classification schemes of bacteriocins resulted various levels of contradiction and sorting inefficiencies leading to bacteriocins belonging to more than one class at the same time and to a general lack of classification of many bacteriocins. Establishing a coherent and adequate classification scheme for these bacteriocins is sought after by several researchers in the field. It is not straightforward to formulate an efficient classification scheme that encompasses all of the existing bacteriocins. In the light of the structural data, here we revisit the previously proposed contradictory classification and we define new structure-based sequence fingerprints that support a subdivision of the bacteriocins into 12 groups. The paper lays down a resourceful and consistent classification approach that resulted in classifying more than 70% of bacteriocins known to date and with potential to identify distinct classes for the remaining unclassified bacteriocins. Identified groups are characterized by the presence of highly conserved short amino acid motifs. Furthermore, unclassified bacteriocins are expected to form an identified group when there will be sufficient sequences.     

Interactive effects of pH and temperature on the bacteriocin stability by response surface analysis

The combined influence of pH and temperature on bacteriocins produced by three lactic acid bacteria, Pediococcus pentosaceus MMZ26, Enterococcus faecium MMZ17 and Lactococcus lactis MMZ25, isolated from Tunisian traditional dry fermented meat was studied using a second order orthogonal factorial design and response-surface methodology (RSM). This method allows estimating the interactive effects of pH and temperature on the stability of each bacteriocin. The high heat stability of the three bacteriocins was demonstrated, with optimum values at light acidic pH around 5.0, temperature below 90 degrees C and short incubation times. This study contributes to a better understanding of relation between bacteriocins production and stability in order to enhance their, in situ, application as a food and feed biopreservative in fermented and/or heated food products.