Bacteriocins: Recent Trends and Potential Applications

Bacteriocins: potentials and prospects in health and agrifood systems

Bacteriocins are highly diverse, abundant, and heterogeneous antimicrobial peptides that are ribosomally synthesized by bacteria and archaea. Since their discovery about a century ago, there has been a growing interest in bacteriocin research and applications. This is mainly due to their high antimicrobial properties, narrow or broad spectrum of activity, specificity, low cytotoxicity, and stability. Though initially used to improve food quality and safety, bacteriocins are now globally exploited for innovative applications in human, animal, and food systems as sustainable alternatives to antibiotics. Bacteriocins have the potential to beneficially modulate microbiota, providing viable microbiome-based solutions for the treatment, management, and non-invasive bio-diagnosis of infectious and non-infectious diseases. The use of bacteriocins holds great promise in the modulation of food microbiomes, antimicrobial food packaging, bio-sanitizers and antibiofilm, pre/post-harvest biocontrol, functional food, growth promotion, and sustainable aquaculture. This can undoubtedly improve food security, safety, and quality globally. This review highlights the current trends in bacteriocin research, especially the increasing research outputs and funding, which we believe may proportionate the soaring global interest in bacteriocins. The use of cutting-edge technologies, such as bioengineering, can further enhance the exploitation of bacteriocins for innovative applications in human, animal, and food systems.

Fermented foods and gastrointestinal health: underlying mechanisms

Although fermentation probably originally developed as a means of preserving food substrates, many fermented foods (FFs), and components therein, are thought to have a beneficial effect on various aspects of human health, and gastrointestinal health in particular. It is important that any such perceived benefits are underpinned by rigorous scientific research to understand the associated mechanisms of action. Here, we review in vitro, ex vivo and in vivo studies that have provided insights into the ways in which the specific food components, including FF microorganisms and a variety of bioactives, can contribute to health-promoting activities. More specifically, we draw on representative examples of FFs to discuss the mechanisms through which functional components are produced or enriched during fermentation (such as bioactive peptides and exopolysaccharides), potentially toxic or harmful compounds (such as phytic acid, mycotoxins and lactose) are removed from the food substrate, and how the introduction of fermentation-associated live or dead microorganisms, or components thereof, to the gut can convey health benefits. These studies, combined with a deeper understanding of the microbial composition of a wider variety of modern and traditional FFs, can facilitate the future optimization of FFs, and associated microorganisms, to retain and maximize beneficial effects in the gut.

Anti-Listerial Activity of Bacteriocin-like Inhibitory Substance Produced by Enterococcus lactis LBM BT2 Using Alternative Medium with Sugarcane Molasses

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, thus reaching final products by cross-contamination. With the growing demand for clean-label products, the search for natural antimicrobials as biopreservants, such as bacteriocins, has shown promising potential. In this context, this study aimed to evaluate the anti-listerial action of bacteriocins produced by Enterococcus lactis LBM BT2 in an alternative medium containing sugarcane molasses (SCM). Molecular analyses were carried out to characterize the strain, including the presence of bacteriocin-related genes. In the kinetic study on SCM medium E. lactis, LBM BT2 showed biomass and bacteriocin productions similar to those observed on a sucrose-based medium (control), highlighting the potential of the sugarcane molasses as a low-cost substrate. Stability tests revealed that the molecule remained active in wide ranges of pH (4-10) and temperature (60-100 °C). Furthermore, the proteolytic treatment reduced the biomolecule's antimicrobial activity, highlighting its proteinaceous nature. After primary purification by salting out and tangential flow filtration, the bacteriocin-like inhibitory substance (BLIS) showed bacteriostatic activity on suspended L. monocytogenes cells and against biofilm formation at a concentration of 0.625 mg/mL. These results demonstrate the potential of the produced BLIS as a biopreservative in the food industry.

Engineering of Salmonella Phages into Novel Antimicrobial Tailocins

Due to the extensive use of antibiotics, the increase of infections caused by antibiotic-resistant bacteria is now a global health concern. Phages have proven useful for treating bacterial infections and represent a promising alternative or complement to antibiotic treatment. Yet, other alternatives exist, such as bacteria-produced non-replicative protein complexes that can kill their targeted bacteria by puncturing their membrane (Tailocins). To expand the repertoire of Tailocins available, we suggest a new approach that transforms phages into Tailocins. Here, we genetically engineered the virulent Ackermannviridae phage S117, as well as temperate phages Fels-1, -2 and Gifsy-1 and -2, targeting the food pathogen Salmonella, by deleting the portal vertex or major capsid gene using CRISPR-Cas9. We report the production of Tailocin particles from engineered virulent and temperate phages able to kill their native host. Our work represents a steppingstone that taps into the huge diversity of phages and transforms them into versatile puncturing new antimicrobials.

Understanding the role of gut microfloral bifidobacterium in cancer and its potential therapeutic applications

Gut microbiota research has gained a tremendous amount of attention from the scientific community because of its contribution to gut homeostasis, human health, and various pathophysiological conditions. The early colonizer of the human gut, i.e., bifidobacteria, has emerged as an efficient probiotic in various diseased conditions, including cancer. This review explores the pros and cons of Bifidobacterium in various malignancies and various therapeutic strategies. We have illustrated the controversial role of bifidobacteria participating in various malignancies as well as described the current knowledge regarding its use in anticancer therapies. Ultimately, this article also addresses the need for further extensive research in elucidating the mechanism of how bifidobacteria is involved and is indirectly affecting the tumor microenvironment. Exhaustive and large-scale research is also required to solve the controversial questions regarding the involvement of bifidobacteria in cancer research.

Producing Tailocins from Phages Using Osmotic Shock and Benzalkonium Chloride

In the light of the worldwide antimicrobial resistance crisis, new substitutes to antibiotics are urgently needed. Tailocins or phage tail-like bacteriocin particles, produced by bacteria for environmental competition, are a potential antimicrobial alternative to antibiotic treatment. Yet, the availability of characterized Tailocins is limited. We explored the possibility to produce new Tailocins from phage particles, using osmotic shock or chemical treatment by the ammonium quaternary compound benzalkonium chloride on Ackermannviridae phage S117 and using Straboviridae phage T4 as control. We report that phage S117 was resistant to such treatment, while successful production of Tailocins by osmotic shock was achieved for phage T4. Finally, chemical treatment with benzalkonium chloride was inefficient on phage S117 but successfully inactivated phage T4 without production of Tailocins. Further studies are needed to implement such treatments of phages for producing Tailocins with killing activity.

Active Packaging for the Extended Shelf-Life of Meat: Perspectives from Consumption Habits, Market Requirements and Packaging Practices in China and New Zealand

Active packaging (AP) has been developed to improve the safety, quality and integrity of food, and minimise food waste, while its application in meat is scarce. This review aims to describe meat production and consumption culture in China and New Zealand to provide the context for packaging innovation requirements, focusing on the emerging opportunities for AP to be used for the improvement of the shelf-life of pre-rigor, aged, and frozen-thawed meat products. Sustainable polymers utilised in the manufacturing of AP, manufacturing techniques, the release mechanisms of actives, and legal and regulatory constraints are also discussed. Diverse market compositions and consumption cultures in China and New Zealand require different packaging solutions to extend the shelf-life of meat. AP containing antimicrobials, moisture regulating agents, and antioxidants may be used for pre-rigor, dry- and wet-aged products and in improving the quality and shelf-life of frozen-thawed meat. Further innovations using sustainably produced polymers for AP, along with incorporating active compounds of multiple functions for effectively improving meat quality and shelf-life are necessary. Challenges remain to resolve issues with scaling the technology to commercially relevant volumes as well as complying with the rigorous legal and regulatory constraints in various countries.

Lactic Acid Bacteria in Raw-Milk Cheeses: From Starter Cultures to Probiotic Functions

Traditional cheeses produced from raw milk exhibit a complex microbiota, characterized by a sequence of different microorganisms from milk coagulation and throughout maturation. Lactic acid bacteria (LAB) play an essential role in traditional cheese making, either as starter cultures that cause the rapid acidification of milk or as secondary microbiota that play an important role during cheese ripening. The enzymes produced by such dynamic LAB communities in raw milk are crucial, since they support proteolysis and lipolysis as chief drivers of flavor and texture of cheese. Recently, several LAB species have been characterized and used as probiotics that successfully promote human health. This review highlights the latest trends encompassing LAB acting in traditional raw milk cheeses (from cow, sheep, and goat milk), and their potential as probiotics and producers of bioactive compounds with health-promoting effects.

Postbiotics as potential new therapeutic agents for metabolic disorders management

The prevalence of obesity, diabetes, non-alcoholic fatty liver disease, and related metabolic disorders has been steadily increasing in the past few decades. Apart from the establishment of caloric restrictions in combination with improved physical activity, there are no effective pharmacological treatments for most metabolic disorders. Many scientific-studies have described various beneficial effects of probiotics in regulating metabolism but others questioned their effectiveness and safety. Postbiotics are defined as preparation of inanimate microorganisms, and/or their components, which determine their safety of use and confers a health benefit to the host. Additionally, unlike probiotics postbiotics do not require stringent production/storage conditions. Recently, many lines of evidence demonstrated that postbiotics may be beneficial in metabolic disorders management via several potential effects including anti-inflammatory, antibacterial, immunomodulatory, anti-carcinogenic, antioxidant, antihypertensive, anti-proliferative, and hypocholesterolaemia properties that enhance both the immune system and intestinal barrier functions by acting directly on specific tissues of the intestinal epithelium, but also on various organs or tissues. In view of the many reports that demonstrated the high biological activity and safety of postbiotics, we summarized in the present review the current findings reporting the beneficial effects of various probiotics derivatives for the management of metabolic disorders and related alterations.

Nisin Induces Cell-Cycle Arrest in Free-Living Amoebae Acanthamoeba castellanii

PURPOSE

Acanthamoeba spp. are free-living amoebas with worldwide distribution and play an important role as disease-causing agents in humans. Drug inability to completely eradicate these parasites along with their toxic effects suggest urgent need for new antimicrobials. Nisin is a natural antimicrobial peptide produced by Lactococcus lactis. Nisin is also the only bacteriocin approved for use in food preservation. In this work, we analyzed the effect of nisin on the growth of Acanthamoeba castellanii trophozoites.

METHODS

A total of 8 × 10⁴ trophozoites were exposed to increasing concentrations of nisin to determine its activity. Changes in cell membrane and cellular cycle of trophozoites were investigated by flow cytometry, and nisin cytotoxicity in mammalian cells was evaluated in L929 cells by MTT method.

RESULTS

After 24 h exposure to increasing nisin concentrations, an IC₅₀ of 4493.2 IU mL^-1 was obtained for A. castellanii trophozoites. However, after 72 h a recovery in amoebic growth was observed, and it was no longer possible to determine IC₅₀. Flow cytometry analysis showed that nisin has no effect on the membrane integrity. Treatment with nisin induced cell-cycle arrest during G1 and S phases in A. castellanii trophozoites, which recovered their growth after 72 h.

CONCLUSION

This is one of the first studies showing the effect of internationally approved nisin against A. castellanii trophozoites. Nisin caused cell-cycle arrest in trophozoites, momentarily interfering with the DNA replication process. The data highlight the amoebostatic activity of nisin, and suggest its use as an adjuvant for the treatment of infections caused by Acanthamoeba spp.

Combating biofilms of foodborne pathogens with bacteriocins by lactic acid bacteria in the food industry

Most foodborne pathogens have biofilm-forming capacity and prefer to grow in the form of biofilms. Presence of biofilms on food contact surfaces can lead to persistence of pathogens and the recurrent cross-contamination of food products, resulting in serious problems associated with food safety and economic losses. Resistance of biofilm cells to conventional sanitizers urges the development of natural alternatives to effectively inhibit biofilm formation and eradicate preformed biofilms. Lactic acid bacteria (LAB) produce bacteriocins which are ribosomally synthesized antimicrobial peptides, providing a great source of nature antimicrobials with the advantages of green and safe properties. Studies on biofilm control by newly identified bacteriocins are increasing, targeting primarily onListeria monocytogenes, Staphylococcus aureus, Salmonella, and Escherichia coli. This review systematically complies and assesses the antibiofilm property of LAB bacteriocins in controlling foodborne bacterial-biofilms on food contact surfaces. The bacteriocin-producing LAB genera/species, test method (inhibition and eradication), activity spectrum and surfaces are discussed, and the antibiofilm mechanisms are also argued. The findings indicate that bacteriocins can effectively inhibit biofilm formation in a dose-dependent manner, but are difficult to disrupt preformed biofilms. Synergistic combination with other antimicrobials, incorporation in nanoconjugates and implementation of bioengineering can help to strengthen their antibiofilm activity. This review provides an overview of the potential and application of LAB bacteriocins in combating bacterial biofilms in food processing environments, assisting in the development and widespread use of bacteriocin as a promising antibiofilm-agent in food industries.

What Do We Know about the Microbiome in Cystic Fibrosis? Is There a Role for Probiotics and Prebiotics?

Cystic fibrosis (CF) is a life-shortening genetic disorder that affects the cystic fibrosis transmembrane conductance regulator (CFTR) protein. In the gastrointestinal (GI) tract, CFTR dysfunction results in low intestinal pH, thick and inspissated mucus, a lack of endogenous pancreatic enzymes, and reduced motility. These mechanisms, combined with antibiotic therapies, drive GI inflammation and significant alteration of the GI microbiota (dysbiosis). Dysbiosis and inflammation are key factors in systemic inflammation and GI complications including malignancy. The following review examines the potential for probiotic and prebiotic therapies to provide clinical benefits through modulation of the microbiome. Evidence from randomised control trials suggest probiotics are likely to improve GI inflammation and reduce the incidence of CF pulmonary exacerbations. However, the highly variable, low-quality data is a barrier to the implementation of probiotics into routine CF care. Epidemiological studies and clinical trials support the potential of dietary fibre and prebiotic supplements to beneficially modulate the microbiome in gastrointestinal conditions. To date, limited evidence is available on their safety and efficacy in CF. Variable responses to probiotics and prebiotics highlight the need for personalised approaches that consider an individual’s underlying microbiota, diet, and existing medications against the backdrop of the complex nutritional needs in CF.

Cold Shock Proteins Promote Nisin Tolerance in Listeria monocytogenes Through Modulation of Cell Envelope Modification Responses

Listeria monocytogenes continues to be a food safety challenge owing to its stress tolerance and virulence traits. Several listeriosis outbreaks have been linked to the consumption of contaminated ready-to-eat food products. Numerous interventions, including nisin application, are presently employed to mitigate against L. monocytogenes risk in food products. In response, L. monocytogenes deploys several defense mechanisms, reducing nisin efficacy, that are not yet fully understood. Cold shock proteins (Csps) are small, highly conserved nucleic acid-binding proteins involved in several gene regulatory processes to mediate various stress responses in bacteria. L. monocytogenes possesses three csp gene paralogs; cspA, cspB, and cspD. Using a panel of single, double, and triple csp gene deletion mutants, the role of Csps in L. monocytogenes nisin tolerance was examined, demonstrating their importance in nisin stress responses of this bacterium. Without csp genes, a L. monocytogenes ΔcspABD mutant displayed severely compromised growth under nisin stress. Characterizing single (ΔcspA, ΔcspB, and ΔcspD) and double (ΔcspBD, ΔcspAD, and ΔcspAB) csp gene deletion mutants revealed a hierarchy (cspD > cspB > cspA) of importance in csp gene contributions toward the L. monocytogenes nisin tolerance phenotype. Individual eliminations of either cspA or cspB improved the nisin stress tolerance phenotype, suggesting that their expression has a curbing effect on the expression of nisin resistance functions through CspD. Gene expression analysis revealed that Csp deficiency altered the expression of DltA, MprF, and penicillin-binding protein-encoding genes. Furthermore, the ΔcspABD mutation induced an overall more electronegative cell surface, enhancing sensitivity to nisin and other cationic antimicrobials as well as the quaternary ammonium compound disinfectant benzalkonium chloride. These observations demonstrate that the molecular functions of Csps regulate systems important for enabling the constitution and maintenance of an optimal composed cell envelope that protects against cell-envelope-targeting stressors, including nisin. Overall, our data show an important contribution of Csps for L. monocytogenes stress protection in food environments where antimicrobial peptides are used. Such knowledge can be harnessed in the development of better L. monocytogenes control strategies. Furthermore, the potential that Csps have in inducing cross-protection must be considered when combining hurdle techniques or using them in a series.

Metagenomic analysis of microflora structure and functional capacity in probiotic Tibetan kefir grains

Tibetan kefir grains (TKGs) are distinctive and complex mixtures with protein-lipid-polysaccharide matrices and multiple microorganism species. The objective of this study was to evaluate the microflora composition, probiotic species and functional genes within TKGs. Metagenomic analysis was used to evaluate communities of three TKGs, revealing the presence of 715 species, with Lactobacillus kefiranofaciens as the most dominant species. The relative abundances of acetic acid bacteria and yeast significantly differed among the three TKGs (acetic acid bacteria: p < 0.01; yeast: p < 0.05), and the dominant yeast species also varied across three TKGs. Lactobacillus helveticus was the most abundant listed probiotic species, and its abundance did not significantly differ across three TKGs. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that ko01501 was the most abundant pathway that related to human disease. There are 16 different KOs (KEGG Orthology) in the ko01501 pathway were annotated in TKGs, which helps to resist β-lactam. This study provided a new insight into the microbial community structures and the presence of probiotic species within TKGs and provides a foundation for further targeted studies.

Isolation and partial characterization of a novel bacteriocin from Pseudomonas azotoformans with antimicrobial activity against Pasterella multocida

In this study, a bacteriocin PA996 isolated from Pseudomonas azotoformans (P. azotoformans) was purified to homogeneity by ammonium sulphate precipitation and SP-Sepharose column chromatography. P. azotoformans began to grow at 6 h, reached exponential phase at 12-18 h. Bacteriocin PA996 was produced at 18 h and reached a maximum level of 2400 AU/mL. The molecular mass of purified bacteriocin PA996 was estimated by SDS-PAGE and its molecular mass was approximately 50 kDa. By screening in vitro, the bacteriocin PA996 showed an antimicrobial activity against Pasteurella multocida (P. multocida). The bacteriocin PA996 showed antibacterial activity in the range of pH2-10 and it was heat labile. The inhibitory activities were diminished after treatment with proteinase K, trypsin and papain, respectively, while catalase treatment was ineffective. The minimal inhibitory concentration (MIC) and bactericidal kinetics curves showed that the bacteriocin PA996 had a good inhibitory ability against P. multocida. Our data indicate that bacteriocin PA996 could inhibit the growth of P. maltocida and it may have the potential to apply as an alternative therapeutic drug.

Characterization of the antimicrobial activity produced by Bacillus sp. isolated from wetland sediment

Bacteria of the genus Bacillus sp. present the potential for inhibiting various pathogens, making them a promising starting point in the search for new antimicrobial substances. In this study, bacteria were isolated from sediment samples from humid areas of a Natural Conservation Unit in the state of Rio Grande do Sul, Brazil. The isolate Bacillus sp. sed 1.4 was selected for production of antimicrobial activity, and was characterized by MALDI-TOF and 16S rDNA sequencing. Phylogenetic analysis showed that Bacillus sed 1.4 was closely related to Bacillus altitudinis and Bacillus pumilus. The cell-free supernatant was partially purified using ammonium sulfate precipitation, gel filtration chromatography (Sephadex G-200) and an ultrafiltration membrane. Partial purification resulted in specific activity of 769.23 AU/mg, with a molecular mass of approximately 148 kDa. This antimicrobial substance showed stability at 100°C for 5 min, and was inactivated by proteolytic enzymes. An antimicrobial effect against Listeria species was observed. Considering the importance of the Listeria genus in the area of food safety, this antimicrobial activity should be further explored, specifically in the field of dairy products and with a focus on food biopreservation studies.

Listeria monocytogenes biofilm inhibition on food contact surfaces by application of postbiotics from Lactobacillus curvatus B.67 and Lactobacillus plantarum M.2

Owing to their preservative and antimicrobial effects, postbiotics (metabolic byproducts of probiotics) are promising natural components for the food industry. Therefore, the present study aimed to investigate the efficacy of postbiotics collected from isolated Lactobacillus curvatus B.67 and Lactobacillus plantarum M.2 against Listeria monocytogenes pathogens in planktonic cells, motility, and biofilm states. The analysis of the metabolite composition of the postbiotics revealed various organic acids, along with a few well-known bacteriocin-encoding genes with potential antimicrobial effects. Postbiotics maintained their residual antimicrobial activity over the pH range 1-6 but lost all activity at neutral pH (pH 7). Full antimicrobial activity (100%) was observed during heat treatment, even under the autoclaving condition.Minimum inhibitory concentration (MICs) of L. curvatus B.67 and L. plantarum M.2 against L. monocytogenes were 80 and 70 mg/mL, respectively. However, four sub-MICs of the postbiotics (1/2, 1/4, 1/8, and 1/16 MIC) were tested for inhibition efficacy against L. monocytogenes during different experiment in this study. Swimming motility, biofilm formation, and expression levels of target genes related to biofilm formation, virulence, and quorum-sensing were significantly inhibited with increasing postbiotics concentration. Postbiotics from L. plantarum M.2 exhibited a higher inhibitory effect than the postbiotics from L. curvatus B.67. Nonetheless, both these postbiotics from Lactobacillus spp. could be used as effective bio-interventions for controlling L. monocytogenes biofilm in the food industry.

New Insight into Bacterial Interaction with the Matrix of Plant-Based Fermented Foods

Microorganisms have been harnessed to process raw plants into fermented foods. The adaptation to a variety of plant environments has resulted in a nearly inseparable association between the bacterial species and the plant with a characteristic chemical profile. Lactic acid bacteria, which are known for their ability to adapt to nutrient-rich niches, have altered their genomes to dominate specific habitats through gene loss or gain. Molecular biology approaches provide a deep insight into the evolutionary process in many bacteria and their adaptation to colonize the plant matrix. Knowledge of the adaptive characteristics of microorganisms facilitates an efficient use thereof in fermentation to achieve desired final product properties. With their ability to acidify the environment and degrade plant compounds enzymatically, bacteria can modify the textural and organoleptic properties of the product and increase the bioavailability of plant matrix components. This article describes selected microorganisms and their competitive survival and adaptation in fermented fruit and vegetable environments. Beneficial changes in the plant matrix caused by microbial activity and their beneficial potential for human health are discussed as well.

Microbial biopreservatives for controlling the spoilage of beef and lamb meat: their application and effects on meat quality

Biopreservation is a recognized natural method for controlling the growth of undesirable bacteria on fresh meat. It offers the potential to inhibit spoilage bacteria and extend meat shelf-life, but this aspect has been much less studied compared to using the approach to target pathogenic bacteria. This review provides comprehensive information on the application of biopreservatives of microbial origin, mainly bacteriocins and protective cultures, in relation to bacterial spoilage of beef and lamb meat. The sensory effect of these biopreservatives, an aspect that often receives less attention in microbiological studies, is also reviewed. Microbial biopreservatives were found to be able to retard the growth of the major meat spoilage bacteria, Brochothrix thermosphacta, Pseudomonas spp., and Enterobacteriaceae. Their addition did not have any discernible negative impact on the sensory properties of meat, whether assessed by human sensory panels or instrumental and chemical analyses. Although results are promising, the concept of biopreservation for controlling spoilage bacteria on fresh meat is still in its infancy. Studies in this area are still lacking, especially for lamb. Biopreservatives need more testing under conditions representative of commercial meat production, along with studies of any possible sensory effects, in order to validate their potential for large-scale industrial applications.

Characterization, modes of action, and application of a novel broad-spectrum bacteriocin BM1300 produced by Lactobacillus crustorum MN047

Bacteriocins are ribosomally synthesized peptides with antibacterial activity against food-borne pathogenic bacteria that cause spoilage, possessing important potential for use as a natural preservative in the food industry. The novel bacteriocin BM1300 produced by Lactobacillus crustorum MN047 was identified after purification in this study. It displayed broad-spectrum antibacterial activity against some selected Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration (MIC) values of BM1300 against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 were 13.4 μg/mL and 6.7 μg/mL, respectively. Moreover, BM1300 showed excellent thermal (between 60 and 120 °C), pH (2-11), and chemical (Tween-40, Tween-80, Triton X-100, and EDTA) stabilities. Time-kill curves revealed that BM1300 exhibited bactericidal activity against S. aureus and E. coli. The scanning and transmission electron microscopy indicated that BM1300 acted by disrupting the cell membrane integrity and increasing cell membrane permeabilization of indicator bacteria. The disruption of cell membrane integrity caused by BM1300 was further demonstrated by the uptake of propidium iodide (PI) and the release of intracellular lactate dehydrogenase (LDH) and nucleic acid and proteins. Moreover, BM1300 affected cell cycle distribution to exert antibacterial activity collaboratively. Meanwhile, BM1300 inhibited the growth of S. aureus and E. coli of beef meat and improved the microbiological quality of beef meat. These findings place BM1300 as a potential biopreservative in the food industry.

The Analysis of Field Strains Isolated From Food, Animal and Clinical Sources Uncovers Natural Mutations in Listeria monocytogenes Nisin Resistance Genes

Nisin is a commonly used bacteriocin for controlling spoilage and pathogenic bacteria in food products. Strains possessing high natural nisin resistance that reduce or increase the potency of this bacteriocin against Listeria monocytogenes have been described. Our study sought to gather more insights into nisin resistance mechanisms in natural L. monocytogenes populations by examining a collection of 356 field strains that were isolated from different foods, food production environments, animals and human infections. A growth curve analysis-based approach was used to access nisin inhibition levels and assign the L. monocytogenes strains into three nisin response phenotypic categories; resistant (66%), intermediate (26%), and sensitive (8%). Using this categorization isolation source, serotype, genetic lineage, clonal complex (CC) and strain-dependent natural variation in nisin phenotypic resistance among L. monocytogenes field strains was revealed. Whole genome sequence analysis and comparison of high nisin resistant and sensitive strains led to the identification of new naturally occurring mutations in nisin response genes associated with increased nisin resistance and sensitivity in this bacterium. Increased nisin resistance was detected in strains harboring RsbU_G77S and PBPB3_V240F amino acid substitution mutations, which also showed increased detergent stress resistance as well as increased virulence in a zebra fish infection model. On the other hand, increased natural nisin sensitivity was detected among strains with mutations in sigB, vir, and dlt operons that also showed increased lysozyme sensitivity and lower virulence. Overall, our study identified naturally selected mutations involving pbpB3 (lm0441) as well as sigB, vir, and dlt operon genes that are associated with intrinsic nisin resistance in L. monocytogenes field strains recovered from various food and human associated sources. Finally, we show that combining growth parameter-based phenotypic analysis and genome sequencing is an effective approach that can be useful for the identification of novel nisin response associated genetic variants among L. monocytogenes field strains.

Postbiotics produced by lactic acid bacteria: The next frontier in food safety

There are many critical challenges in the use of primary and secondary cultures and their biological compounds in food commodities. An alternative is the application of postbiotics from the starter and protective lactic acid bacteria (LAB). The concept of postbiotics is relatively new and there is still not a recognized definition for this term. The word "postbiotics" is currently used to refer to bioactive compounds, which did not fit to the traditional definitions of probiotics, prebiotics, and paraprobiotics. Therefore, the postbiotics may be presently defined as bioactive soluble factors (products or metabolic byproducts), produced by some food-grade microorganisms during the growth and fermentation in complex microbiological culture (in this case named cell-free supernatant), food, or gut, which exert some benefits to the food or the consumer. Many LAB are considered probiotic and their postbiotic compounds present similar or additional health benefits to the consumer; however, this review aimed to address the most recent applications of the postbiotics with food safety purposes. The potential applications of postbiotics in food biopreservation, food packaging, and biofilm control were reviewed. The current uses of postbiotics in the reduction and biodegradation of some food safety-related chemical contaminants (e.g., biogenic amines) were considered. We also discussed the safety aspects, the obstacles, and future perspectives of using postbiotics in the food industry. This work will open up new insights for food applications of postbiotics prepared from LAB.

Fermentation Characteristics of Lactococcus lactis subsp. lactis Isolated From Naturally Fermented Dairy Products and Screening of Potential Starter Isolates

It is well known that consumers are keen to try fermented milk products with different flavors and starter cultures are important in determining the resulting fermented dairy products. Here, we present the phenome of 227 Lactococcus lactis subsp. lactis isolates from traditionally fermented dairy products and the selection of potential starter strains. Large-scale phenotyping revealed significant technological diversity in fermentation characteristics amongst the isolates including variation in fermentation time, viscosity, water holding capacity (WHC) and free amino nitrogen (FAN) production. The 16 isolates with the best fermentation characteristics were compared, in a sensory evaluation, with the commercial starter Chr. Hansen R-704 as excellent fermentation characteristics to identify potential starter isolates and find the isolate which can product good flavors. From these, and from solid phase micro extraction (SPME) - gas chromatography (GC)-mass spectrometry (MS) analysis, we identified IMAU11823 and IMAU11919 as producing 3-methyl butanal and 3-methyl-2-butanone which contribute to the malt aroma. This study expands the characterization of L. lactis subsp. lactis phenotypic dataset and technological diversity and identified isolates with potential culture starter in the fermentation industry.

Characterization of Pediococcus acidilactici PFC69 and Lactococcus lactis PFC77 Bacteriocins and Their Antimicrobial Activities in Tarhana Fermentation

Tarhana is a traditional cereal product fermented by lactic acid bacteria (LAB) and yeast strains that has gained special interest recently as an infant nutrition. Tarhana contains wheat flour, yogurt, and various vegetables that might create a microbiological toxicological risk, especially for Bacillus cereus and Staphylococcus aureus. In this study, characterization of the metabolites responsible for antibacterial activity of Pediococcus acidilactici PFC69 and Lactococcus lactis PFC77 strains obtained from tarhana was performed, and antibacterial effects were detected against B. cereus ATCC 11778 and S. aureus ATCC 29213 during the fermentation. A total of 12,800 AU/mL antibacterial activity was observed for the supernatants of the PFC69 and PFC77 strains that were found to be stable at high temperature and in low pH conditions and sensitive to proteases, suggesting the antimicrobial metabolite is a bacteriocin. These bacteriocins were further purified and their molecular sizes were determined as 4.5 and 3.5 kDa, respectively. Importantly, inoculation of PFC69 and PFC77 to tarhana dough significantly decreased B. cereus ATCC 11778 and S. aureus ATCC 29213 amounts from the fifth day of fermentation compared to the control dough samples. P. acidilactici PFC69 and L. lactis PFC77 strains were concluded as bioprotective cultures for tarhana and these strains were offered for other cereal-based fermentations.

Antibiotics and their alternatives in Artificial Breeding in livestock

Antibiotics are mandatory components of semen extenders for the control of bacterial contamination and growth. The increasing rate of worldwide resistance to conventional antibiotics in semen preservation media requires the development of new antimicrobial alternatives. This review provides an update on this topic and also highlights the improvement of hygiene in Artificial Insemination centers in order to prevent the development of bacterial resistance. Ideas are shared on future diagnostic tools for bacterial contamination in Artificial Breeding. Finally, new methods to remove or reduce bacteria in semen will be discussed.

Biotechnology for bacteriocin synthesis using photostimulation

This article presents results of a study of the effect of blue color on the bacteriocin activity. It was revealed that photostimulation of Lactobacillus Lactis with light in the blue spectrum (435-470 nm) with a light flux intensity of 1800 mcd for 50-60 minutes positively affects the bacteriocin activity (increases by 60.1%), while titer of the Lactobacillus lactis is 2 times higher. It was found that it was in the first 18 hours that the irradiated samples had a greater difference in terms of activity and titers than unirradiated samples. Oxidative stress affects the culture’s viability, both in samples treated with blue light and in the untreated cultures. However, impact intensity on the treated cultures is weaker. These outcomes indicate the possibility of using blue light for stimulating bacteriocin biosynthesis in order to use it as a food additive for prolongation of shelf life of food products.

Investigation of genomic characteristics and carbohydrates' metabolic activity of Lactococcus lactis subsp. lactis during ripening of a Swiss-type cheese

Genetic diversity and metabolic properties of Lactococcus lactis subsp. lactis were explored using phylogenetic, pan-genomic and metatranscriptomic analysis. The genomes, used in the current study, were available and downloaded from the GenBank which were primarily related with microorganisms isolated from dairy products and secondarily from other foodstuffs. To study the genetic diversity of the microorganism, various bioinformatics tools were employed such as average nucleotide identity, digital DNA-DNA hybridization, phylogenetic analysis, clusters of orthologous groups analysis, KEGG orthology analysis and pan-genomic analysis. The results showed that Lc. lactis subsp. lactis strains cannot be sufficiently separated into phylogenetic lineages based on the 16S rRNA gene sequences and core genome-based phylogenetic analysis was more appropriate. Pan-genomic analysis of the strains indicated that the core, accessory and unique genome comprised of 1036, 3146 and 1296 genes, respectively. Considering the results of pan-genomic and KEGG orthology analyses, the metabolic network of Lc. lactis subsp. lactis was rebuild regarding its carbohydrates' metabolic capabilities. Based on the metatranscriptomic data during the ripening of the Swiss-type Maasdam cheese at 20 °C and 5 °C, it was shown that the microorganism performed mixed acid fermentation producing lactate, formate, acetate, ethanol and 2,3-butanediol. Mixed acid fermentation was more pronounced at higher ripening temperatures. At lower ripening temperatures, the genes involved in mixed acid fermentation were repressed while lactate production remained unaffected resembling to a homolactic fermentation. Comparative genomics and metatranscriptomic analysis are powerful tools to gain knowledge on the genomic diversity of the lactic acid bacteria used as starter cultures as well as on the metabolic activities occurring in fermented dairy products.

A potential probiotic Chromobacterium aquaticum with bacteriocin-like activity enhances the expression of indicator genes associated with nutrient metabolism, growth performance and innate immunity against pathogen infections in zebrafish (Danio rerio)

The use of probiotics as alternatives to antibiotics for disease control is a relatively eco-friendly approach in aquaculture; hence, studies isolating and assessing the benefit of potential probiotics to fish farming are common. The zebrafish is an excellent model system for validating beneficial functions of potential probiotics before their practical application in aquaculture. Here, a potentially probiotic Chromobacterium aquaticum was isolated from lake water samples and characterized by biochemical analysis and 16S rDNA sequencing. The probiotic produced extracellular enzymes (protease and xylanase) and a bacteriocin-like substance, which exhibited tolerance to extreme pH and high-temperature conditions and broad-spectrum bactericidal activity against diverse pathogens, including aquatic, foodborne, clinical and plant pathogens. The effects of C. aquaticum on zebrafish nutrient metabolism, growth performance and innate immunity were evaluated by measuring the expression of indicator genes after C. aquaticum feeding for 8 weeks. Fish administered the probiotic exhibited significantly increased hepatic mRNA expression of carbohydrate metabolism-related genes, including glucokinase (GK), hexokinase (HK), glucose-6-phosphatase (G6Pase), and pyruvate kinase (PK-L), and growth-related genes, including the growth hormone receptor (GHR) and insulin-like growth factor-1 (IGF-1). Innate immune-related genes (IL-1β, IL-6, TNF-α, IL-10, IL-21, NF-κb, lysozyme and complement C3b) were induced in fish with probiotic supplementation. Probiotic-treated fish exhibited a higher survival rate than control fish after challenge with Aeromonas hydrophila and Streptococcus iniae. Together, these data suggest that C. aquaticum, as a probiotic feed supplement, could enhance nutrient metabolism and growth performance and could modulate innate immunity against A. hydrophila and S. iniae in zebrafish.

Probiotics and prebiotics in intestinal health and disease: from biology to the clinic

Probiotics and prebiotics are microbiota-management tools for improving host health. They target gastrointestinal effects via the gut, although direct application to other sites such as the oral cavity, vaginal tract and skin is being explored. Here, we describe gut-derived effects in humans. In the past decade, research on the gut microbiome has rapidly accumulated and has been accompanied by increased interest in probiotics and prebiotics as a means to modulate the gut microbiota. Given the importance of these approaches for public health, it is timely to reiterate factual and supporting information on their clinical application and use. In this Review, we discuss scientific evidence on probiotics and prebiotics, including mechanistic insights into health effects. Strains of Lactobacillus, Bifidobacterium and Saccharomyces have a long history of safe and effective use as probiotics, but Roseburia spp., Akkermansia spp., Propionibacterium spp. and Faecalibacterium spp. show promise for the future. For prebiotics, glucans and fructans are well proven, and evidence is building on the prebiotic effects of other substances (for example, oligomers of mannose, glucose, xylose, pectin, starches, human milk and polyphenols).

Study of the effectiveness of staphylococcins in biopreservation of Minas fresh (Frescal) cheese with a reduced sodium content

Reducing salt content in foods such as cheeses, while limiting the growth of spoilage microorganisms and foodborne pathogens, is a difficult challenge. One method that may prove useful is use of staphylococcins, which are bacteriocins produced by staphylococci. Therefore, staphylococcin antimicrobial activity against six strains of S. aureus isolated from cheese was tested aiming at their industrial application in biopreservation of Minas fresh (Frescal) cheese with reduced sodium content. Three staphylococcins were selected for these tests: Pep 5, aureocin A53 and lysostaphin. All three staphylococcins proved to be bacteriolytic against all six strains of S. aureus. The antimicrobial activity of the partially purified staphylococcins was subsequently investigated against strains S. aureus Q1 and QJ3 in cheese matrices (6.0 log CFU/g) with different NaCl contents (control, a 25% reduction, and a 50% reduction), kept under refrigeration at 4 °C, for 21 days. Both strains were shown to be of concern for food industry as they carry the SEA, SEB and SEH enterotoxin genes, and are resistant to β-lactam drugs and moderate biofilm formers when grown in TSB. When used singly, Pep5, aureocin A53 and lysostaphin reduced approximately 95%, 99% and 99.99% of the viable cell counts, respectively, irrespective of the sodium content of the cheese matrix. The combined action of aureocin A53 and Pep5 resulted in an additional and significant reduction (p < 0.05) of ~1.0 log CFU/g when compared with the reduction caused by the use of either one singly. The combined action of lysostaphin and aureocin A53 or lysostaphin and Pep5 resulted in a reduction similar to or slightly smaller (p > 0.05) than that observed when lysostaphin was employed singly. Lysostaphin also proved to reduce the number of the staphylococcal viable cells to a level (~ 2.0 log CFU/g) at which enterotoxin production should not reach a sufficient quantity to cause food poisoning. Therefore, lysostaphin may have a practical application in the food industry to control staphylococcal contamination of Minas fresh cheese with a sodium content reduced up to 50%, providing consumers with more safe options to reduce their intake of sodium.

Lactobacillus delbrueckii subsp. bulgaricus F17 and Leuconostoc lactis H52 supernatants delay the decay of strawberry fruits: a microbiome perspective

Lactobacillus delbrueckii subsp. bulgaricus F17 and Leuconostoc lactis H52 as the potential biopreservative, which delayed the decay and changed the structure of microbial community of the ‘Benihoppe’ strawberry fruits.

Microbial Ecology of Fermented Vegetables and Non-Alcoholic Drinks and Current Knowledge on Their Impact on Human Health

Fermented foods are currently experiencing a re-discovery, largely driven by numerous health benefits claims. While fermented dairy, beer, and wine (and other alcoholic fermented beverages) have been the subject of intensive research, other plant-based fermented foods that are in some case widely consumed (kimchi/sauerkraut, pickles, kombucha) have received less scientific attention. In this chapter, the current knowledge on the microbiology and potential health benefits of such plant-based fermented foods are presented. Kimchi is the most studied, characterized by primarily acidic fermentation by lactic acid bacteria. Anti-obesity and anti-hypertension properties have been reported for kimchi and other pickled vegetables. Kombucha is the most popular non-alcoholic fermented drink. Kombucha's microbiology is remarkable as it involves all fermenters described in known fermented foods: lactic acid bacteria, acetic acid bacteria, fungi, and yeasts. While kombucha is often hyped as a "super-food," only antioxidant and antimicrobial properties toward foodborne pathogens are well established; and it is unknown if these properties incur beneficial impact, even in vitro or in animal models. The mode of action that has been studied and demonstrated the most is the probiotic one. However, it can be expected that fermentation metabolites may be prebiotic, or influence host health directly. To conclude, plant-based fermented foods and drinks are usually safe products; few negative reports can be found, but more research, especially human dietary intervention studies, are warranted to substantiate any health claim.

Stability of Bacteriocin-Like Inhibitory Substance (BLIS) Produced by Pediococcus acidilactici kp10 at Different Extreme Conditions

Nowadays, bacteriocin industry has substantially grown replacing the role of chemical preservatives in enhancing shelf-life and safety of food. The progress in bacteriocin study has been supported by the emerging of consumer demand on the applications of natural food preservatives. Since food is a complex ecosystem, the characteristics of bacteriocin determine the effectiveness of their incorporation into the food products. Among four commercial media (M17 broth, MRS broth, tryptic soy broth, and nutrient broth) tested, the highest growth of Pediococcus acidilactici kp10 and bacteriocin-like-inhibitory substance (BLIS) production were obtained in the cultivation with M17. BLIS production was found to be a growth associated process where the production was increased concomitantly with the growth of producing strain, P. acidilactici kp10. The antimicrobial property of BLIS against three indicator microorganisms (Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus) remained stable upon heating at 100°C but not detectable at 121°C. The BLIS activity was also observed to be stable and active at a wide pH range (pH 2 to pH 7). The BLIS activity remained constant at -20°C and -80°C for 1 month of storage. However, the activity dropped after 3 and 6 months of storage at 4°C, -20°C, and -80°C with more than 80% reduction. The ability of bacteriocin from P. acidilactici kp10 to inhibit food-borne pathogens while remaining stable and active at extreme pH and temperature is of potential interest for future applications in food preservatives.

Genome Analysis of Lactobacillus plantarum LL441 and Genetic Characterisation of the Locus for the Lantibiotic Plantaricin C

Bacteriocins are ribosomally synthesized peptides produced by bacteria with antimicrobial activity. The bacteriocins produced by lactic acid bacteria (LAB) may inhibit food-borne pathogens and spoilage organisms, and therefore have potential as natural preservatives. Lactobacillus plantarum LL441 produces a lantibiotic bacteriocin known as plantaricin C, a pore-forming antimicrobial peptide containing modified amino acids that inhibits cell wall synthesis by forming a complex with the peptidoglycan precursor lipid II. The present work describes the genome sequencing of L. plantarum LL441 and the characterisation of the plantaricin C locus. The draft genome sequence of L. plantarum LL441 consisted of 170 contigs and had a total 3,124,603 bp; the GC content was 44.52%. The plantaricin C locus was found in an 18 kbp-long contig, and consisted of six genes organized in an operon-like arrangement. This locus included the bacteriocin structural gene (plnC), followed by a gene encoding a LanM-like protein thought to be involved in the maturation of plantaricin C, and four downstream genes encoding ABC-type transporter components, probably belonging to its putative immunity and export machinery. plnC encodes a precursor of the bacteriocin, i.e., a 58-amino acid peptide containing a 31-amino acid double-glycine leader peptide and a 27-amino acid core peptide. In silico analysis and hybridisation experiments placed the plantaricin C locus to be located on pLL441-1, a large plasmid of L. plantarum LL441. Joining up the gaps between the contigs by conventional PCR, sequencing of the amplicons, and sequence assemblage, allowed the complete 55.3 kbp pLL441-1 molecule to be established. A portion of pLL441-1 larger than 34 kbp, which included the plantaricin C region, was identified in a plasmid-derived contig from the L. plantarum Nizo 3893 genome. Further, the plantaricin C coding locus (about 8.7 kbp) was shown to share 91% nucleotide identity with a portion of the plasmids pPECL-6 from Pediococcus claussenii ATCC BAA-344 and pL11995-4 from Lactobacillus paracollinoides TMW 1.1995. Knowledge of the sequence of the plantaricin C coding region will help in studying its molecular components and allow their involvement in bacteriocin synthesis to be investigated, facilitating the use of the bacteriocin or its genetic elements in new biotechnological applications.

Characterization, yield optimization, scale up and biopreservative potential of fermencin SA715, a novel bacteriocin from Lactobacillus fermentum GA715 of goat milk origin

BACKGROUND

Emergence of antibiotic resistance and growing consumer trend towards foods containing biopreservatives stimulated the search for alternative antimicrobials. This research is aimed at characterizing, investigating the mechanism of action, scale up optimization and evaluating the biopreservative potential of a bacteriocin from Lactobacillus fermentum.

RESULTS

Fermencin SA715 is a novel, broad-spectrum, non-pore-forming and cell wall-associated bacteriocin isolated from L. fermentum GA715 of goat milk origin. A combination of hydrophobic interaction chromatography, solid-phase extraction and reversed-phase HPLC was necessary for purification of the bacteriocin to homogeneity. It has a molecular weight of 1792.537 Da as revealed by MALDI-TOF mass spectrometry. Fermencin SA715 is potent at micromolar concentration, possesses high thermal and pH stability and inactivated by proteolytic enzymes thereby revealing its proteinaceous nature. Biomass accumulation and production of fermencin SA715 was optimum in a newly synthesized growth medium. Fermencin SA715 did not occur in the absence of manganese(II) sulphate. Tween 80, ascorbic acid, sodium citrate and magnesium sulphate enhanced the production of fermencin SA715. Sucrose is the preferred carbon source for growth and bacteriocin production. Sodium chloride concentration higher than 1% suppressed growth and production of fermencin SA715. Optimum bacteriocin production occurred at 37 °C and pH 6-7. Scale up of fermencin SA715 production involved batch fermentation in a bioreactor at a constant pH of 6.5 which resulted in enhanced production. Fermencin SA715 doubled the shelf life and improved the microbiological safety of fresh banana. Bacteriocin application followed by refrigeration tripled the shell life of banana.

CONCLUSIONS

This study reveals the huge potential of fermencin SA715 as a future biopreservative for bananas and reveals other interesting characteristics which can be exploited in the preservation of other foods. Furthermore insights on the factors influencing the production of fermencin SA715 have been revealed and optimized condition for its production has been established facilitating future commercial production.

Swapping the roles of bacteriocins and bacteriophages in food biotechnology

To move towards a safer and more sustainable food production chain, natural antimicrobials have been traditionally applied to enhance safety. This is well exemplified by the use of bacteriocins, antimicrobial peptides synthesized by bacteria, as food biopreservatives. However, as knowledge on bacteriocin biology develops, novel functions beyond food preservation emerge and a shift towards health applications is positioning bacteriocins as anti-infectives and modulators of gut microbiota. On the other hand, bacteriophages, viruses infecting bacteria, have been long regarded as a threat for dairy fermentations. However, they may also become allies when specific phages infecting pathogenic or spoilage bacteria are intentionally used. This review summarizes the `dark side' and rather unexplored roles of bacteriocins and phages that, certainly, have much to learn from each other.

Synthesis, antimicrobial activity and conformational analysis of the class IIa bacteriocin pediocin PA-1 and analogs thereof

The antimicrobial peptide pediocin PA-1 is a class IIa bacteriocin that inhibits several clinically relevant pathogens including Listeria spp. Here we report the synthesis and characterization of whole pediocin PA-1 and novel analogs thereof using a combination of solid- and solution-phase strategies to overcome difficulties due to instability and undesired reactions. Pediocin PA-1 thus synthesized was a potent inhibitor of Listeria monocytogenes (MIC = 6.8 nM), similar to the bacteriocin produced naturally by Pediococcus acidilactici. Of particular interest is that linear analogs lacking both of the disulfide bridges characterizing pediocin PA-1 were as potent. One linear analog was also a strong inhibitor of Clostridium perfringens, another important food-borne pathogen. These results are discussed in light of conformational information derived from circular dichroism, solution NMR spectroscopy and structure-activity relationship studies.

Recent Progress in the Chemical Synthesis of Class II and S-Glycosylated Bacteriocins

A wide variety of antimicrobial peptides produced by lactic acid bacteria (LAB) have been identified and studied in the last decades. Known as bacteriocins, these ribosomally synthesized peptides inhibit the growth of a wide range of bacterial species through numerous mechanisms and show a great variety of spectrum of activity. With their great potential as antimicrobial additives and alternatives to traditional antibiotics in food preservation and handling, animal production and in veterinary and medical medicine, the demand for bacteriocins is rapidly increasing. Bacteriocins are most often produced by fermentation but, in several cases, the low isolated yields and difficulties associated with their purification seriously limit their use on a large scale. Chemical synthesis has been proposed for their production and recent advances in peptide synthesis methodologies have allowed the preparation of several bacteriocins. Moreover, the significant cost reduction for peptide synthesis reagents and building blocks has made chemical synthesis of bacteriocins more attractive and competitive. From a protein engineering point of view, the chemical approach offers many advantages such as the possibility to rapidly perform amino acid substitution, use unnatural or modified residues, and make backbone and side chain modifications to improve potency, modify the activity spectrum or increase the stability of the targeted bacteriocin. This review summarized synthetic approaches that have been developed and used in recent years to allow the preparation of class IIa bacteriocins and S-linked glycopeptides from LAB. Synthetic strategies such as the use of pseudoprolines, backbone protecting groups, microwave irradiations, selective disulfide bridge formation and chemical ligations to prepare class II and S-glycosylsated bacteriocins are discussed.

Pentocin MQ1: A Novel, Broad-Spectrum, Pore-Forming Bacteriocin From Lactobacillus pentosus CS2 With Quorum Sensing Regulatory Mechanism and Biopreservative Potential

Micrococcus luteus, Listeria monocytogenes, and Bacillus cereus are major food-borne pathogenic and spoilage bacteria. Emergence of antibiotic resistance and consumer demand for foods containing less of chemical preservatives led to a search for natural antimicrobials. A study aimed at characterizing, investigating the mechanism of action and regulation of biosynthesis and evaluating the biopreservative potential of pentocin from Lactobacillus pentosus CS2 was conducted. Pentocin MQ1 is a novel bacteriocin isolated from L. pentosus CS2 of coconut shake origin. The purification strategy involved adsorption-desorption of bacteriocin followed by RP-HPLC. It has a molecular weight of 2110.672 Da as determined by MALDI-TOF mass spectrometry and a molar extinction value of 298.82 M⁻¹ cm⁻¹. Pentocin MQ1 is not plasmid-borne and its biosynthesis is regulated by a quorum sensing mechanism. It has a broad spectrum of antibacterial activity, exhibited high chemical, thermal and pH stability but proved sensitive to proteolytic enzymes. It is potent against M. luteus, B. cereus, and L. monocytogenes at micromolar concentrations. It is quick-acting and exhibited a bactericidal mode of action against its targets. Target killing was mediated by pore formation. We report for the first time membrane permeabilization as a mechanism of action of the pentocin from the study against Gram-positive bacteria. Pentocin MQ1 is a cell wall-associated bacteriocin. Application of pentocin MQ1 improved the microbiological quality and extended the shelf life of fresh banana. This is the first report on the biopreservation of banana using bacteriocin. These findings place pentocin MQ1 as a potential biopreservative for further evaluation in food and medical applications.

Bacteriocin biosynthesis contributes to the anti-inflammatory capacities of probiotic Lactobacillus plantarum

Plantaricin EF (PlnEF) is a class IIb bacteriocin produced by Lactobacillus plantarum. We compared L. plantarum NCIMB8826 and LM0419, a plnEFI deletion mutant of that strain lacking plnEF and the gene for the cognate immunity protein plnI, in a 2,4,6-trinitrobenzenesulfonic acid (TNBS) induced mouse model of acute inflammatory bowel disease. Mice fed either L. plantarum NCIMB8826 or LM0419 were not protected against TNBS according to either disease activity or histology (Ameho) scores. Mice consuming NCIMB8826 exhibited intermediate (non-significant) levels of colonic tumour necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) that ranged between the TNBS-treated animals and healthy controls. By comparison, TNF-α and IL-6 quantities were elevated in mice given L. plantarum LM0419 and equivalent to mice given TNBS alone. Both strains survived digestive tract transit in equal numbers and did not result in global changes to the bacterial composition in the intestine according to 16S rRNA gene sequencing either prior to or after TNBS administration. Examination of intestinal taxa showed that mice consuming wild-type L. plantarum, but not LM0419 contained lower proportions of Mucispirillum (Deferribacteres phylum) in the faeces prior to TNBS administration and Parabacteroides (Bacteroidetes phylum) in the caecum after disease induction. Parabacteroides also positively correlated with disease activity and histology scores. These findings suggest a role for PlnEFI production by L. plantarum in benefiting digestive tract health.