Partial Characterization of Nine Bacteriocins Produced by Lactic Acid Bacteria Isolated from Cold-Smoked Salmon with Activity against Listeria monocytogenes

Nine LAB bacteriocin-producers, isolated from vacuum-packaged cold-smoked salmon (CSS), were phenotypically and genotypically identified as Lactobacillus curvatus, Lactobacillus delbrueckii, Lactobacillus fermentum, Enterococcus faecium, and Pediococcus acidilactici. Their bacteriocins were partially characterized. The antimicrobial spectrum was determined against Listeria monocytogenes, E. faecalis, E. faecium, and Staphylococcus aureus. The molecular size of bacteriocins ranged from 2.8 to 4.5 kDa. They were inactivated by treatment with proteolytic enzymes but not by lipolytic or glycolytic enzymes. Maximal activity against L. monocytogenes ranged between 800 and 10000 AU/mL at pH 6.5. Most of the bacteriocins maintained full activity in a pH range of 2.0 to 8.0 but were partially or completely inactivated at pH 10.0. After heating at 60°C and 100°C, only two bacteriocins from Lb. curvatus strains partially lost activity. All bacteriocins showed a narrow spectrum of activity and a high anti-listerial activity, which is characteristic of the class IIa bacteriocins. Isolated bacteriocin-producing LAB could be used successfully in the bio-preservation of CSS and development of new potential bio-preservatives for CSS active against L. monocytogenes.     

Class IIa bacteriocins from lactic acid bacteria: antibacterial activity and food preservation

In the last decade, a variety of ribosomally synthesized antimicrobial peptides, or bacteriocins, produced by lactic acid bacteria have been identified and characterized. As a result of these studies, insight has been gained into various fundamental aspects of biology and biochemistry such as bacteriocin processing and secretion, mechanisms of cell immunity, and structure-function relationships. In parallel, there has been a growing awareness that bacteriocins may be developed into useful antimicrobial food additives. Class IIa bacteriocins can be considered as the major subgroup of bacteriocins from lactic acid bacteria, not only because of their large number, but also because of their significant biological activities and potential applications. The present review provides an overview of the knowledge available for class IIa bacteriocins and discusses common features and recent findings concerning these substances. The activity and potential food applications of class IIa bacteriocins are a major focus of this review.     

Production, purification, and characterization of micrococcin GO5, a bacteriocin produced by Micrococcus sp. GO5 isolated from kimchi

Strain GO5, a bacteriocin-producing bacterium, was isolated from green onion kimchi and identified as Micrococcus sp. The bacteriocin, micrococcin GO5, displayed a broad spectrum of inhibitory activity against a variety of pathogenic and nonpathogenic microorganisms, as tested by the spot-on-lawn method; its activity spectrum was almost identical to that of nisin. Micrococcin GO5 was inactivated by trypsin (whereas nisin was not) and was completely stable at 100 degrees C for 30 min and in the pH range of 2.0 to 7.0. Micrococcin GO5 exhibited a typical mode of bactericidal activity against Micrococcus flavus ATCC 10240. It was purified to homogeneity through ammonium sulfate precipitation, ultrafiltration, and CM-Sepharose column chromatography. The molecular mass of micrococcin GO5 was estimated to be about 5.0 kDa by tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and in situ activity assay with the indicator organism. The amino acid sequence of micrococcin GO5 lacks lanthionine and beta-methyllanthionine and is rich in hydrophobic amino acids and glycine, providing the basis for the high heat stability of this bacteriocin. The N-terminal amino acid sequence of micrococcin GO5 is Lys-Lys-Ser-Phe-Cys-Gln-Lys, and no homology to bacteriocins reported previously was observed in the amino acid composition or N-terminal amino acid sequence. Based on the physicochemical properties, small molecular size, and inhibition of Listeria monocytogenes, micrococcin GO5 has been placed with the class II bacteriocins, but its broad spectrum of activity differs from that of other bacteriocins in this class.     

Bacteriocins and their Food Applications

Over the last 2 decades, a variety of bacteriocins, produced by bacteria that kill or inhibit the growth of other bacteria, have been identified and characterized biochemically and genetically. This review article focuses on the ecology of bacteriocins, determination of bacteriocin activity, biosynthesis of bacteriocins, and mode of action. Bacteriocin production and modeling are discussed in the article. Nisin is discussed in some detail in this article since it is currently the only purified bacteriocin approved for food use in the U.S. and has been successfully used for several decades as a food preservative in more than 50 countries. For activity spectra and food applications, the review article focuses primarily on class I and class IIa bacteriocins produced by lactic acid bacteria (LAB) given their development as food preservatives.     

Characterization of bacteriocin N15 produced by Enterococcus faecium N15 and cloning of the related genes

Enterococcus faecium N15 was isolated from nuka (Japanese rice-bran paste), which is utilized as starter in the fermenting of vegetables, and was found to produce a bacteriocin that exhibited a broad spectrum of activity, including activity against Listeria monocytogenes and Bacillus circulans JCM2504. The bacteriocin was sensitive to proteases (alpha-chymotrypsin, proteinase K, trypsin, and pepsin) and alpha-amylase, but it was resistant to lipase. The bacteriocin was resistant to heat treatment at 100 degrees C for 2 h, but its activity was completely lost after autoclaving at 121 degrees C for 15 min. It was active over a wide pH range from 2.0 to 10.0. The bacteriocin showed bactericidal activity against Lactobacillus sake JCM1157 at a concentration of 40 AU/ml. Its molecular weight was estimated by SDS-PAGE to be about 3-5 kDa. PCR primers were designed based on the conserved amino acid sequences of class IIa bacteriocins. A 3-kb DNA fragment was amplified and three open reading frames (ORFs) were found. The first encodes a probable immunity protein of 103 amino acid residues and shows complete homology with the putative immunity protein of E. faecium DPC1146. The second and third ORFs respectively encode a probable transposase gene and an inducing factor. The upstream region of the immunity gene, in which the bacteriocin structural gene is located, was amplified. A homology search revealed that the bacteriocin produced by E. faecium N15 exhibits complete identity to enterocin A, a bacteriocin produced by E. faecium DPC1146. PCR using the primers designed in this study is a rapid and sufficient method of screening for bacteriocin-producing strains.     

Lactobacillus acidophilus: Characterization of the Species and Application in Food Production

L. acidophilus is a homofermentative, microaerophilic, short chain gram positive microorganism with rod morphology having its bacteriocins belonging to class II a. Several bacteriocins of L. acidophilus have been isolated and characterized. These are structurally similar, but their molecular weight varies as well as their spectrum of antimicrobial activity. They exhibit important technical properties, i.e., thermostability and retaining of activity at a wide pH range along with strong inhibitory actions against food spoilage and pathogenic bacteria make them an important class of biopreservatives. L. acidophilus can be added as an adjunct in many food fermentation processes contributing to unique taste, flavor, and texture. It also preserves the products by producing lactic acid and bacteriocins. A lot of new information regarding the bacteriocins of L. acidophilus has emerged during the last few years. In this review, an attempt has been made to summarize and discuss all the available information regarding the sources of bacteriocins production, their characteristics, and their antimicrobial action along with their application.     

传统干酪中一株产IIa类细菌素乳酸菌的分离与鉴定

从内蒙古传统干酪中分离到一株产抑菌活性物质的乳酸菌M-2，其对单核细胞增生李斯特氏菌、金黄色葡萄球菌等食品中常见致病菌和腐败菌都有抑制作用。排除有机酸、H202等的干扰后，仍有抑菌活性：进一步硫酸铵沉淀、透析及浓缩处理后，其抑菌活性显著增强；用蛋白酶K处理后，其抑菌活性消失，因此确定该抑菌活性物质为蛋白类物质，进而确定乳酸菌M-2为细菌素产生菌。通过生理生化实验和16SrRNA基因序列分析对该菌株进行了鉴定。PCR扩增得到1675bp的16SrRNA序列，并将其通过BLAST软件在NCBI网站中进行同源性比，同时，通过Bioedit7．0和Treedrawing软件绘制系统发育树。结果显示，M-2的16SrRNA序列和数据库中的屎肠球菌SF菌株的序列的同源性为99．87％。在细菌系统发育分类学上，M-2菌株归属屎肠球菌（Enterococcus faecium）。这与生理生化实验初步鉴定结果一致。根据细菌素的分类原则，将该细菌素归类为IIa类细菌素。     

Charakterisierung einiger Bacteriocine im Hinblick auf mögliche Anwendungen im Lebensmittelbereich. 1. Mitt. Stammauswahl

Characterization of some bacteriocins with regard to possible applications in food industry. Part 1. Selection of strains. The ability to produce bacteriocins is common in all genera of lactic acid bacteria. Thirty-four out of 223 strains of lactic acid bacteria from the culture collection of the University Potsdam produced bacteriocins active against one or more indicator strains. Seventeen Gram-positive and Gram-negative strains, frequent occur as spoilage bacteria in food industry, were chosen as indicator strains, and 11 of them were inhibited by one or several bacteriocin producers. Most of the bacteriocin producers belong to the genera Enterococcus or Lactobacillus. Bacteriocins derived from Enterococcus faecium and Pediococcus acidilactici exhibited the widest inhibitory spectrum. The properties of Enterococcus faecium 10.051 and Enterococcus faecium 10.211 bacteriocins were further investigated to evaluate their potential use as natural food preservatives. The bacteriocin produced by Enterococcus faecium 10.211 exhibited a very wide inhibitory spectrum against food-spoiling strains. It was heat stable (100 °C for 60 min) and stable in a wide range of pH (1.2–10.0). The bacteriocin produced by Enterococcus faecium 10.051 showed a smaller inhibitory spectrum, and it was less stable against temperature and pH as the bacteriocin from strain 10.211. Both bacteriocins were inactivated by proteinase K. pronase E, and α-chymotrypsin. Bacteriocin from strain 10.211 will be the object of further investigations for application of bacteriocins in food industry.     

Potential of lactic acid bacteria isolated from specific natural niches in food production and preservation

Autochthonous strains of lactic acid bacteria (LAB) have been isolated from traditionally homemade cheeses collected from specific ecological localities across Serbia and Montenegro. Genetic and biochemical analysis of this LAB revealed that they produce bacteriocins, proteinases and exopolysaccharides. LAB produces a variety of antimicrobial substances with potential importance for food fermentation and preservation. Apart from the metabolic end products, some strains also secrete antimicrobial substances known as bacteriocins. Among the natural isolates of LAB from homemade cheeses, bacteriocin producers were found in both lactococci and lactobacilli. Lactococcus lactis subsp. lactis BGMN1-5 was found to produce three narrow spectrum class II heat-stable bacteriocins. In addition to bacteriocin production, BGMN1-5 synthesized a cell envelope-associated proteinase (CEP) and shows an aggregation phenotype. Another isolate, L. lactis subsp. lactis BGSM1-19 produces low molecular mass (7 kDa) bacteriocin SM19 that showed antimicrobial activity against Staphylococcus aureus, Micrococcus flavus and partially against Salmonella paratyphi. Production of bacteriocin reaches a plateau after 8 h of BGSM1-19 growth. Bacteriocin SM19 retained activity within the wide pH range from 1 to 12 and after the treatment at 100 degrees C for 15 min. Among collection of lactobacilli, the isolate Lactobacillus paracasei subsp. paracasei BGSJ2-8 produces heat-stable bacteriocin SJ (approx. 5 kDa) polypeptide. It retained activity after treatment for 1 h at 100 degrees C, and in the pH range from 2 to 11. In addition to isolates from cheeses, bacteriocin-producing human oral lactobacilli were detected. Most of them showed antimicrobial activity against streptococci, staphylococci and micrococci, but not against Candida. Isolate BGHO1 that showed the highest antimicrobial activity was determined as L. paracasei. Interestingly, Lactobacillus helveticus BGRA43, which was isolated from the human intestine showed strong activity against Clostridium sporogenes, but it was not possible to detect any bacteriocin production in this isolate by using standard procedures. Further analysis of antimicrobial activity revealed that BGRA43 has a relatively broad spectrum. Lactobacilli resistant to nisin were also detected among natural isolates. They produce bacteriocins, which have no activity against nisin producing lactococci.     

Bacteriocins of lactic acid bacteria: Their potentials as food biopreservative

Abstract

Numerous strains of lactic acid bacteria used in the fermentation of foods are known to produce bacteriocins. In general, bacteriocins are a group of proteinaceous antimicrobial substances that inhibit the growth of closely related bacteria. However, some bacteriocins produced by lactic acid bacteria (LAB) exhibit a relatively broad antimicrobial spectrum and are active against several food‐spoilage and health‐threatening microorganisms. Many investigators have reported on the use of bacteriocins as food preservative to extend the shelflife of various foods. This review decribes the research that has been conducted on bacteriocinogenic lactic acid bacteria— isolated from a wide variety of foods and in some instances of animal origin—and the characteristics of bacteriocins. Special emphasis is placed on their potentials for use as food preservative and on their physicochemical nature, antibacterial spectrum, and genetic behavior.     

Comparative antimicrobial activity of enterocin L50, pediocin PA-1, nisin A and lactocin S against spoilage and foodborne pathogenic bacteria

The present work compares, under the same stated experimental conditions, the antimicrobial activity of crude and purified enterocin L50, pediocin PA-1, nisin A and lactocin S, produced by lactic acid bacteria (LAB) isolated from Spanish dry-fermented sausages. The bacteriocins were purified to homogeneity by ammonium sulphate precipitation, gel filtration (for lactocin S), and cation-exchange, hydrophobic-interaction, and reverse-phase-chromatography; high yields of pure bacteriocins were obtained. Minimal inhibitory concentration (MIC) of pure enterocin L50, pediocin PA-1, nisin A and lactocin S was determined against a broad spectrum of Gram-positive bacteria, including spoilage and foodborne pathogenic bacteria. The purified bacteriocins showed a broad antimicrobial spectrum similar to that exerted by crude bacteriocins. Enterocin L50 and pediocin PA-1 were very active againstListeria monocytogenes, which was quite resistant to nisin A and lactocin S. Enterocin L50 also displayed antimicrobial activity againstStaphylococcus aureus,Clostridium perfringensandClostridium botulinum. However, these pathogens were weakly inhibited, or not at all, by the other pure bacteriocins.     

Isolation of Bacillus circulans and Paenibacillus polymyxa strains inhibitory to Campylobacter jejuni and characterization of associated bacteriocins

We evaluated anti-Campylobacter activity among 365 Bacillus and Paenibacillus isolates from poultry production environments. One novel antagonistic Bacillus circulans and three Paenibacillus polymyxa strains were identified and further studied. Cell-free ammonium sulfate precipitate (crude antimicrobial preparation) was obtained from each candidate culture. Zones of Campylobacter growth inhibition surrounding 10 microl of this crude antimicrobial preparation were quantified using a spot test. Campylobacter growth resumed when the preparation was preincubated with selected protease enzymes, demonstrating peptide characteristics consistent with a bacteriocin. These peptides were further purified using combinations of molecular mass resolution and ion exchange chromatography. Molecular masses of the peptides were estimated at approximately 3,500 Da by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Isoelectric focusing was used to determine the pI values of the peptides. Amino acid sequences of the bacteriocins and more precise molecular masses were obtained by matrix-assisted laser desorption and ionization-time of flight (MALDI-TOF) analysis. The bacteriocin from P. polymyxa NRRL B-30507 had a pI of 4.8, that from P. polymyxa NRRL B-30509 had a pI of 7.2, that from P. polymyxa NRRL B-30508 had a pI of 4.8, and that from B. circulans NRRL B-30644 had a pI of 7.8. The amino acid sequences were consistent with those of class IIa bacteriocins. These antagonists and the corresponding bacteriocins may be useful in the control of Campylobacter infection in poultry.     

Development of Wide-Spectrum Hybrid Bacteriocins for Food Biopreservation

The food industry demands new procedures and methods to produce minimally processed, ready to eat food with intact nutritional, taste, and flavor properties. The biopreservation and the use of both bacteriocins produced by lactic acid bacteria (LAB) and bacteriocinogenic strains as an alternative to substitute chemical antimicrobial for food preservation became increasingly important in the last two decades. When the new proposed natural preservatives techniques are applied, probiotics food can be obtained and, simultaneously, foodborne pathogens and spoilage contaminants can diminish. However, bacteriocins produced by LAB have a narrow antibacterial spectrum and are inactive against Gram-negative bacteria like Salmonella and the emergent enterohemorrhagic Escherichia coli. Knowing the mechanism of action and the structural features of microcins synthesized by Gram-negative bacteria and with potent antimicrobial activity against the mentioned microorganism, the proposal is to obtain hybrid peptides (microcin–bacteriocin) with broad antimicrobial spectrum. This review explains how the inability of bacteriocins to cross the outer membrane of Gram-negative bacteria unable them to act on the bacteria. It will also be discussed how a hybrid bacteriocin can be obtained.     

Screening for anti-listerial bacteriocin-producing lactic acid bacteria from "Gueddid" a traditionally Tunisian fermented meat

Forty eight lactic acid bacteria strains isolated from “Gueddid”, a traditionally Tunisian fermented meat, were screened for bacteriocin production. Four strains named MMZ 04, 09, 13, and 17 showed antimicrobial activity and were identified as Enterococcus faecium by molecular methods based on the 16S-23S rDNA ISR, PCR-RFLP analysis of the 16S-23S rDNA ISR and species-specific primers. The four antimicrobial compounds were heat stable (121 °C for 15 min), active over a wide pH range (3–9) and the antimicrobial activity was lost after treatment with trypsin, -chymotrypsin and proteinase K but not by lysozyme and lipase. The mode of action of enterocin MMZ17 was identified as bactericidal. The MMZ17 bacteriocin was partially purified by ammonium sulphate precipitation and C₁₈ Sep-Pack chromatography. The apparent molecular size of enterocin MMZ17 as indicated by activity detection after SDS-PAGE was lower than 6.5 KDa. According to these assays, enterocin MMZ17 can be classified as a small, heat-stable Listeria-active peptide, presumably belonging to class IIa bacteriocins.     

Nisin-curvaticin 13 combinations for avoiding the regrowth of bacteriocin resistant cells of Listeria monocytogenes ATCC 15313

Nisin (25-100 IU/ml) and curvaticin 13 (160 AU/ml), a bacteriocin produced by Lactobacillus curvatus SB13, were shown to have a bactericidal effect against Listeria monocytogenes ATCC 15313 in TSB-YE broth (pH 6.5), but it was only transitory. Regrowth was not due to the loss of bacteriocin activity. Cells surviving nisin or curvaticin 13 were more resistant to the respective bacteriocin than the parental strain. Survivors to curvaticin 13 were resistant to the class IIa bacteriocins (camocin CP5, pediocin AcH) but remained sensitive to nisin. The frequencies of spontaneous nisin resistants decreased with increasing bacteriocin concentration and the presence of salts (NaCl, K2HPO4). The behaviour of nisin (1000 IU/ml) or curvaticin 13 (640 AU/ml) resistant variants (Nis1000, Curv645) was investigated in the presence of nisin (100 IU/ml) or curvaticin 13 (320 AU/ml) at 22 and 37 degrees C, and compared with that of the parental strain. The effectiveness of nisin was the same at both temperatures, whereas curvaticin 13 displayed a faster bactericidal action at 37 degrees C. Nis1000 cells were less sensitive to curvaticin 13 than the parental strain, whereas Curv640 cells were more sensitive to nisin than the parental strain. Simultaneous or sequential additions of nisin (50 IU/ml) and curvaticin 13 (160 AU/ml) were performed at 22 degrees C in broth inoculated with the parental strain. All combinations induced a greater inhibitory effect than the use of a single bacteriocin. Simultaneous addition of bacteriocins at t0 led to the absence of viable cells in the broth after 48 h.     

Enterococcus faecium P21: a strain occurring naturally in dry-fermented sausages producing the class II bacteriocins enterocin A and enterocin B

Enterococcus faecium P21 isolated from a Spanish dry-fermented sausage shows a narrow antimicrobial activity against closely related lactic acid bacteria and strong antimicrobial activity against spoilage and foodborne Gram-positive pathogenic bacteria such as Listeria monocytogenes, Staphylococcus aureus, Clostridium perfringens and Clostridium botulinum. The antimicrobial activity is produced during growth in MRS broth at 32°C; it is heat resistant (20 min at 80–100°C) and abolished by protease treatment, and withstands exposure to pH 2–11, freeze-thawing, lyophilization and long term storage at −20°C. Purification of the antimicrobial activity by ammonium sulphate precipitation, gel filtration, and cation-exchange, hydrophobic interaction and reverse-phase chromatographies showed that the broad antimicrobial spectrum exerted by E. faecium P21 was indeed due to two peptide bacteriocins. Studies on theirN -terminal amino acid sequences and PCR and DNA analyses revealed that these bacteriocins are identical to the class II bacteriocins enterocin A and enterocin B. The genetic organization of the enterocin A (EntA) operon in E. faecium P21 shows that the bacteriocin structural gene (entA), the immunity gene (entiA) and the induction peptide gene (entF) are clustered and colinearly arranged. Strikingly, this organization was structurally different to that reported for the EntA-producer E. faecium CTC492.     

Lactobacillus salivarius: Bacteriocin and probiotic activity

Lactic acid bacteria (LAB) antimicrobial peptides typically exhibit antibacterial activity against food-borne pathogens, as well as spoilage bacteria. Therefore, they have attracted the greatest attention as tools for food biopreservation. In some countries LAB are already extensively used as probiotics in food processing and preservation. LAB derived bacteriocins have been utilized as oral, topical antibiotics or disinfectants. Lactobacillus salivarius is a promising probiotic candidate commonly isolated from human, porcine, and avian gastrointestinal tracts (GIT), many of which are producers of unmodified bacteriocins of sub-classes IIa, IIb and IId. It is a well-characterized bacteriocin producer and probiotic organism. Bacteriocins may facilitate the introduction of a producer into an established niche, directly inhibit the invasion of competing strains or pathogens, or modulate the composition of the microbiota and influence the host immune system. This review gives an up-to-date overview of all L. salivarius strains, isolated from different origins, known as bacteriocin producing and/or potential probiotic.     

Paenibacillus polymyxa purified bacteriocin to control Campylobacter jejuni in chickens

Campylobacter spp. cause numerous foodborne diseases. Poultry is thought to be a significant source of this zoonosis. Although many interventions designed to control this agent have been researched, none have succeeded. We evaluated a bacteriocin-based treatment to reduce Campylobacter jejuni colonization in poultry. A previously described purified bacteriocin (class IIa; molecular mass, 3,864 Da), secreted by Paenibacillus polymyxa NRRL-B-30509, was microencapsulated in polyvinylpyrrolidone, and 0.25 g of the purified bacteriocin was incorporated into 1 kg of chicken feed. One-day-old chickens were orally challenged and colonized with one of four isolates of C. jejuni, then reared in isolation facilities. Birds were provided ad libitum access to standard broiler starter feed and water for 7 days until 3 days before sampling, when only the treated groups of birds were provided the bacteriocin-emended feed described. In each of the eight (four by two replicates) trials, significant reductions in colonization by C. jejuni were observed (P < or = 0.05). As an example of this highly consistent data, in the first trial, 10 untreated 10-day-old chickens were colonized at a mean log 7.2 + 0.3 CFU/g of feces, whereas none of the 10 bacteriocin-treated 10-day-old chickens were colonized with detectable numbers of C. jejuni. Bacteriocin treatment dramatically reduced both intestinal levels and frequency of chicken colonization by C. jejuni. Feeding bacteriocins before poultry slaughter appears to provide control of C. jejuni to effectively reduce human exposure. This advance is directed toward on-farm control of pathogens, as opposed to the currently used chemical disinfection of contaminated carcasses.     

Optimization and Partial Purification of Bacteriocins from Enterococcus spp. Indigenous to Pakistan

This study was conducted to optimize bacteriocin producing enterococcal strains isolated from indigenous fermented dairy products of Pakistan. Isolates IJ-06, IJ-21, and IJ-31 were identified as Enterococcus faecium and IJ-11 was identified as Enterococcus faecalis. All of these enterococcal isolates were catalase, gelatinase negative, and non-hemolytic on sterile sheep blood. Bacteriocin production trials confirmed E. faecium IJ-06, IJ- 21, and IJ- 31 as the potential producer of bacteriocin showing antimicrobial activity in cell-free supernatant (CFS). E. faecalis IJ-11 displayed activity after partial purification. Optimization of culture conditions for the production of bacteriocin by the selected strains showed that maximum production was achieved at 35–37°C with 1% inoculum after 16 h of incubation and at pH 7–8. The molecular mass of the partially purified enterocins falls in the range of 4.5–4.7 kDa. These enterocins were close to class IIa of bacteriocins and were highly active against Listeria monocytogenes, Bacillus subtilis, Bacillus cereus and other closely related strains.     

Effect of ecological factors on the inhibitory spectrum and activity of bacteriocins

The effect of food components and ecological factors on the activities of nisin, sakacin P and curvacin A was evaluated. Lactobacillus curvatus, Listeria innocua, Salmonella and Escherichia coli including E. coli O157:H7 were used as target organisms. Lecithin, casein, and divalent cations were antagonists of the bacteriocins at 0.1%, 0.1% and 10 mmol l(-1), respectively. A decrease in pH as well as the presence of EDTA, propyl-parabene or NaCl at concentrations of 0-1 mmol y(-1), 0-0.16 g l(-1), and 0-6% (w/w), respectively, increased the activity of all bacteriocins. These compounds as well as a pH < 5.5 rendered the Gram-negative target organisms sensitive against bacteriocins. Of practical importance is the respective effect of NaCl at concentrations > 5% which are achieved in fermentation and ripening processes, e.g. in production of fermented sausages. A characteristic response was observed for each of the bacteriocins. It is suggested that bacteriocins of lactic acid bacteria are effective against a wide range of microorganisms including E. coli O157:H7 if applied in combination with other preservative principles prevailing in foods.