Control of Alicyclobacillus acidoterrestris in fruit juices by enterocin AS-48

Evaluation of antibacterial properties of nisin peptide expressed in carrots

Nisin, derived from Lactococcus lactis, is a well-known natural food preservative. In the present study, the gene of nisin was transformed to carrot by Agrobacterium tumefaciens strain LBA4404 harboring the recombinant binary vector pBI121 containing neomycin phosphotransferase II (nptII) gene, peptide signal KDEL, and Kozak sequence. The integration of nisin and nptII transgenes into the plant genome was confirmed by polymerase chain reaction (PCR) and dot blot analysis. The gene expression was also performed by RT-PCR and Enzyme-Linked Immunosorbent Assay. The level of nisin expressed in one gram of transgenic plant ranged from 0.05 to 0.08 μg/ml. The stability of nisin varied in orange and peach juices depending on the temperature on the 70th day. The leaf protein extracted from the transgenic plant showed a significant preservative effect of nisin in peach and orange juice. A complete inhibition activity against Staphylococcus aureus and Escherichia coli in orange juice was observed within 24 h. After 24 h, log 1 and log 2 were obtained in a peach juice containing Staphylococcus aureus and Escherichia coli, respectively. Results of HPLC indicated that Chlorogenic and Chicoric acid compounds were increased in transgenic plants, but this increase was not significant. The study of determining the genetic stability of transgenic plants in comparison with non-transgenic plants showed high genetic stability between non-transgenic plants and transgenic plants. This study confirmed the significant inhibitory effect of nisin protein on gram-positive and gram-negative bacteria.

Determination of the effect of the bacteriocin enterocin AS-48 on the microbial loads and bacterial diversity of blueberries

Fresh fruits have been involved in transmission of foodborne pathogens. In the present work, five different batches of blueberries were used. One aliquot from each batch was washed with sterile saline solution (SSS) and the other one with a solution of the circular bacteriocin enterocin AS-48 in SSS. Then, the surface microbiota of controls and bacteriocin-treated samples was recovered and used for microbiota analyses, both using viable counts and high-throughput amplicon sequencing. Total aerobic mesophilic loads ranged from 2.70 to 4.09 log CFU/g in most of the samples. Only two samples yielded detectable viable counts on selective media (Enterobacteriaceae, presumptive Salmonella and coliforms), with values ranging from 2.84 to 3.81 log CFU/g. The bacteriocin treatment reduced viable cell counts of total aerobic mesophiles to a range of 1.40-1.88 log CFU/g. No viable cells were detected on selective media. Amplicon sequencing indicated large batch-to-batch variations in the surface microbiota of blueberries and also an effect of the bacteriocin treatment on microbiota composition.

Advances in the preclinical characterization of the antimicrobial peptide AS-48

Antimicrobial resistance is a natural and inevitable phenomenon that constitutes a severe threat to global public health and economy. Innovative products, active against new targets and with no cross- or co-resistance with existing antibiotic classes, novel mechanisms of action, or multiple therapeutic targets are urgently required. For these reasons, antimicrobial peptides such as bacteriocins constitute a promising class of new antimicrobial drugs under investigation for clinical development. Here, we review the potential therapeutic use of AS-48, a head-to-tail cyclized cationic bacteriocin produced by Enterococcus faecalis. In the last few years, its potential against a wide range of human pathogens, including relevant bacterial pathogens and trypanosomatids, has been reported using in vitro tests and the mechanism of action has been investigated. AS-48 can create pores in the membrane of bacterial cells without the mediation of any specific receptor. However, this mechanism of action is different when susceptible parasites are studied and involves intracellular targets. Due to these novel mechanisms of action, AS-48 remains active against the antibiotic resistant strains tested. Remarkably, the effect of AS-48 against eukaryotic cell lines and in several animal models show little effect at the doses needed to inhibit susceptible species. The characteristics of this molecule such as low toxicity, microbicide activity, blood stability and activity, high stability at a wide range of temperatures or pH, resistance to proteases, and the receptor-independent effect make AS-48 unique to fight a broad range of microbial infections, including bacteria and some important parasites.

Prospects of antimicrobial peptides as an alternative to chemical preservatives for food safety

Antimicrobial peptides (AMPs) are a potential alternative to antimicrobial agents that have got considerable research interest owing to their significant role in the inhibition of bacterial pathogens. These AMPs can essentially inhibit the growth and multiplication of microbes through multiple mechanisms including disruption of cellular membranes, inhibition of cell wall biosynthesis, or affecting intracellular components and cell division. Moreover, AMPs are biocompatible and biodegradable therefore, they can be a good alternative to antimicrobial agents and chemical preservatives. A few of their features for example thermostability and high selectivity are quite appealing for their potential use in the food industry for food preservation to prevent the spoilage caused by microorganisms and foodborne pathogens. Despite these advantages, very few AMPs are being used at an industrial scale for food preservation as these peptides are quite vulnerable to external environmental factors which deter their practical applications and commercialization. The review aims to provide an outline of the mechanism of action of AMPs and their prospects as an alternative to chemical preservatives in the food industry. Further studies related to the structure-activity relationship of AMPs will help to expand the understanding of their mechanism of action and to determine specific conditions to increase their stability and applicability in food preservation.

Targeting the Impossible: A Review of New Strategies against Endospores

Endospore-forming bacteria are ubiquitous, and their endospores can be present in food, in domestic animals, and on contaminated surfaces. Many spore-forming bacteria have been used in biotechnological applications, while others are human pathogens responsible for a wide range of critical clinical infections. Due to their resistant properties, it is challenging to eliminate spores and avoid the reactivation of latent spores that may lead to active infections. Furthermore, endospores play an essential role in the survival, transmission, and pathogenesis of some harmful strains that put human and animal health at risk. Thus, different methods have been applied for their eradication. Nevertheless, natural products are still a significant source for discovering and developing new antibiotics. Moreover, targeting the spore for clinical pathogens such as Clostridioides difficile is essential to disease prevention and therapeutics. These strategies could directly aim at the structural components of the spore or their germination process. This work summarizes the current advances in upcoming strategies and the development of natural products against endospores. This review also intends to highlight future perspectives in research and applications.

Bovicin HC5 and nisin reduce cell viability and the thermal resistance of Alicyclobacillus acidoterrestris endospores in fruit juices

BACKGROUND

Alicyclobacillus acidoterrestris is an important thermoacidophilic spore-forming bacterium in fruit-juice deterioration, and alternative non-thermal methods have been investigated to control fruit juice spoilage. This work aimed to evaluate the capacity of bovicin HC5 and nisin to inhibit the growth of vegetative cells and reduce the thermal resistance of endospores of A. acidoterrestris inoculated (10⁷ CFU mL^-1 ) in different fruit juices. The number of viable cells was determined after 12 h incubation at 43 °C in the presence and absence of nisin or bovicin HC5 (10-100 AU mL^-1 ). The exposure time (min) required to kill 90% of the initial population (reduction of one log factor) at 90 ºC (D_90ºC ) was used to assess the thermal resistance of A. acidoterrestris endospores exposed (80 AU mL^-1 ) or non-exposed to the bacteriocins. Additionally, the effect of bovicin and nisin on the morphology and cell structure of A. acidoterrestris was evaluated by atomic force microscopy (AFM).

RESULTS

Bovicin HC5 and nisin were bactericidal against A. acidoterrestris inoculated in fruit juices and reduced the D_90°C values up to 30-fold. AFM topographical images revealed substantial structural changes in the cellular framework of vegetative cells upon treatment with bovicin HC5 or nisin.

CONCLUSIONS

These results emphasize the potential application of lantibiotics as additional hurdles in food processing to control thermoacidophilic spoilage bacteria in fruit juices. © 2022 Society of Chemical Industry.

Enterocins: Classification, Synthesis, Antibacterial Mechanisms and Food Applications

Enterococci, a type of lactic acid bacteria, are widely distributed in various environments and are part of the normal flora in the intestinal tract of humans and animals. Although enterococci have gradually evolved pathogenic strains causing nosocomial infections in recent years, the non-pathogenic strains have still been widely used as probiotics and feed additives. Enterococcus can produce enterocin, which are bacteriocins considered as ribosomal peptides that kill or inhibit the growth of other microorganisms. This paper reviews the classification, synthesis, antibacterial mechanisms and applications of enterocins, and discusses the prospects for future research.

Fruit Juice Spoilage by Alicyclobacillus: Detection and Control Methods—A Comprehensive Review

Fruit juices have an important place in humans’ healthy diet. They are considered to be shelf stable products due to their low pH that prevents the growth of most bacteria. However thermo-acidophilic endospore forming bacteria of the genus Alicyclobacillus have the potential to cause spoilage of commercially pasteurized fruit juices. The flat sour type spoilage, with absence of gas production but presence of chemical spoilage compounds (mostly guaiacol) and the ability of Alicyclobacillus spores to survive after pasteurization and germinate under favorable conditions make them a major concern for the fruit juice industry worldwide. Their special characteristics and presence in the fruit juice industry has resulted in the development of many isolation and identification methods based on cell detection (plating methods, ELISA, flow cytometry), nucleic acid analysis (PCR, RAPD-PCR, ERIC-PCR, DGGE-PCR, RT-PCR, RFLP-PCR, IMS-PCR, qPCR, and 16S rRNA sequencing) and measurement of their metabolites (HPLC, GC, GC-MS, GC-O, GC-SPME, Electronic nose, and FTIR). Early detection is a big challenge that can reduce economic loss in the industry while the development of control methods targeting the inactivation of Alicyclobacillus is of paramount importance as well. This review includes a discussion of the various chemical (oxidants, natural compounds of microbial, animal and plant origin), physical (thermal pasteurization), and non-thermal (High Hydrostatic Pressure, High Pressure Homogenization, ultrasound, microwaves, UV-C light, irradiation, ohmic heating and Pulse Electric Field) treatments to control Alicyclobacillus growth in order to ensure the quality and the extended shelf life of fruit juices.

Purification and Characterization of Plantaricin YKX and Assessment of Its Inhibitory Activity Against Alicyclobacillus spp

Consumers prefer natural over synthetic chemical preservatives on a food label. Therefore, it is crucial to ensure the safety and efficacy of such natural preservatives. The emergence of heat-resistant spore-forming Alicyclobacillus spp. has been associated with spoilage problems in the fruit juice industry. Herein, a bacteriocin-producing stain YKX was isolated from the traditional pickles in Hanzhong City, China, and it was identified as Lactobacillus plantarum by morphological, biochemical, physiological, and genotypic features. A stable bacteriocin, plantaricin YKX, was isolated, purified, and tested for its efficacy against Alicyclobacillus acidoterrestris. Plantaricin YKX is a 14-amino acid peptide (Lys-Tyr-Gly-Asn-Gly-Leu-Ser-Arg-Ile-Phe-Ser-Ala-Leu-Lys). Its minimal inhibitory concentrations (MICs) against the tested bacterial and fungal strains were ranged from 16 to 64 μg/mL. It is thermostable and active at pH 3-8. The flow cytometry data and microscopic observations suggested that plantaricin YKX can augment cell membrane permeability, induce potassium ion leakage and pore formation, and disrupt cell membranes. It also affects spore germination and guaiacol production of A. acidoterrestris, probably due to upregulation of the luxS gene linked to quorum sensing.

Control of the growth of Alicyclobacillus acidoterrestris in industrialized orange juice using rosemary essential oil and nisin

The use of rosemary essential oil (RO) and its combination with nisin (RO+N) in preventing the multiplication of Alicyclobacillus acidoterrestris in orange juice was evaluated. The minimum inhibitory and bactericidal concentrations (MIC and MBC) for RO were both 125 μg ml^-1 while RO+N displayed a synergistic effect. The use of RO and RO+N at concentrations of 1, 4 and 8× MIC in orange juice for 96 h was evaluated in terms of their sporicidal effectiveness. With regard to the action against A. acidoterrestris spores, RO at 8× MIC was sporostatic, whereas RO+N at 1× MIC was sporicidal. Morphological changes in the structure of the micro-organism after treatment were also observed by microscopy. Furthermore, flow cytometric analysis showed that most cells were damaged or killed after treatment. In general, the antioxidant activity after addition of RO+N decreased with time. The results demonstrate that using the combination of RO and nisin can prevent the A. acidoterrestris growth in orange juice.

Effects of ultraviolet-C light-emitting diodes at 275 nm on inactivation of Alicyclobacillusacidoterrestris vegetative cells and its spores as well as the quality attributes of orange juice

Alicyclobacillus acidoterrestris is a thermoacidophilic, spore-forming bacillus. A. acidoterrestris and its spores can survive in pasteurized juices and cause microbial spoilage. In this work, the effects of ultraviolet-C light-emitting diodes at 275 nm on the inactivation of A. acidoterrestris vegetative cells and its spores in commercial pasteurized orange juice were studied. Meanwhile, the effects of ultraviolet-C light-emitting diodes on the quality attributes of the orange juice were also investigated. The quantities of A. acidoterrestris vegetative cells and its spores inoculated in orange juice were reduced by 6.04 and 2.49 log₁₀ CFU/mL after ultraviolet-C light-emitting diode treatment at 220 mJ/cm², respectively. The Weibull and Weibull plus tail models were satisfactorily fitted to estimate the reductions of A. acidoterrestris vegetative cells and its spores in orange juice, respectively. Physicochemical properties (pH, titratable acidity, total soluble solids, and clarity) of orange juice did not change significantly after exposure to ultraviolet-C light-emitting diodes. However, the total phenolic content of orange juice decreased with increasing fluence. In addition, ultraviolet-C light-emitting diode treatment at a higher fluence led to a noticeable color difference. These results indicate that ultraviolet-C light-emitting diode treatment has a potential application in the juice processing industry.

Physicochemical properties and mode of action of a novel bacteriocin BM1122 with broad antibacterial spectrum produced by Lactobacillus crustorum MN047

Bacteriocins are defined as ribosomally synthesized antibacterial peptides/proteins that either kill or inhibit the growth of other bacteria. In the present study, the physicochemical properties, mode of action, and potential use in food preservation of a novel bacteriocin BM1122 from Lactobacillus crustorum MN047 were studied. It exhibited a broad inhibitory spectrum against selected Gram-positive and Gram-negative bacteria. Kinetic curves revealed efficient time-dependent bactericidal activity. Moreover, BM1122 possessed low hemolytic activity and good thermal stability between 60 and 120 °C. It was resistant to a wide range of pH (2 to 11) and proteinases. The scanning and transmission electron microscopy showed that BM1122 led to plasmolysis of Staphylococcus aureus and pore formation in Escherichia coli. Flow cytometric analysis demonstrated that BM1122 destroyed cell membrane integrity. Additionally, BM1122 could also inhibit biofilm formation and disturb the normal cell cycles of S. aureus and E. coli. Finally, BM1122 may enhance the inhibition of S. aureus and E. coli on beef meat stored at 4 °C for a duration of 10 days. These findings indicated that BM1122 had the potential for use as a natural preservative in the food industry. PRACTICAL APPLICATION: Fresh raw meats are highly perishable products. Bacteriocin BM1122 with a broad antibacterial spectrum can inhibit the growth of microorganisms in beef meat during refrigerated storage.

Ocins for Food Safety

The food industry produces highly perishable products. Food spoilage represents a severe problem for food manufacturers. Therefore, it is important to identify effective preservation solutions to prevent food spoilage. Ocins (e.g., bacteriocins, lactocins, and enterocins) are antibacterial proteins synthesized by bacteria that destroy or suppress the growth of related or unrelated bacterial strains. Ocins represent a promising strategy for food preservation, because of their antagonist effects toward food spoilage microorganisms, high potency, and low toxicity. Additionally, they can be bioengineered. The most common and commercially available ocins are nisin, plantaracin, sakacin P, and pediocin. Several ocins have been characterized and studied biochemically and genetically; however, their structure-function relationship, biosynthesis, and mechanism of action are not understood. This narrative review focuses primarily on ocins and their relevance to the food industry to help prevent food spoilage. In particular, the applications and limitations of ocins in the food industry are highlighted.

Co-expression of Nisin Z and Leucocin C as a Basis for Effective Protection Against Listeria monocytogenes in Pasteurized Milk

Nisin, an important bacteriocin from Lactococcus lactis subsp., is primarily active against various Gram-positive bacteria. Leucocin C, produced by Leuconostoc carnosum 4010, is a class IIa bacteriocin used to inhibit the growth of Listeria monocytogenes. Because two bacteriocins have different modes of action, the combined use of them could be a potential strategy for effective inhibition of foodborne pathogens. In this study, L. lactis N8-r-lecCI (N8 harboring lecCI gene) coexpressing nisin–leucocin C was constructed based on the food-grade carrier L. lactis N8. Production of both bacteriocins was stably maintained. Antimicrobial measurements showed that the recombinant strain is effectively against Listeria monocytogenes and Staphylococcus aureus and moderately against Salmonella enterica serovar Enteritidis and Escherichia coli because of its stronger antibacterial activity than the parental strain, this result first demonstrated that the co-expression of nisin and leucocin C results in highly efficient antimicrobial activity. The checkerboard assay showed that the antibacterial activity of L. lactis N8-r-lecCI supernatant was enhanced in the presence of low concentration of EDTA. Analysis of the scanning electron microscope image showed the biggest cellular morphology change in L. monocytogenes treated with a mixture of EDTA and L. lactis N8-r-lecCI supernatant. The practical effect was verified in pasteurized milk through time-kill assay. The L. lactis N8-r-lecCI strain expressing both nisin and leucocin C has a promising application prospect in pasteurized milk processing and preservation because of its strong antibacterial activity.

Evaluation of the efficacy of nisin-loaded chitosan nanoparticles against foodborne pathogens in orange juice

The current study aimed to fabricate nisin-loaded chitosan (N-CS) nanoparticles through ionic interactions between positive amino groups of chitosan and negatively charged tripolyphosphate ions in the presence of nisin and to evaluate their efficacy against foodborne pathogens in orange juice. The synthesized nanoparticles were sphere-shaped and homogenous with an average size of 64.34 ± 2.1 and 147.93 ± 2.9 for chitosan and N-CS nanoparticles, respectively. The encapsulation efficiency of nisin into nanoparticles was 67.32 ± 0.63%. Both chitosan and N-CS nanoparticles showed greater stability, as indicated by a higher zeta potential value of + 49.3 and + 33.4 mV, respectively. The in vitro antibacterial activities of chitosan and N-CS nanoparticles were investigated against the Gram-positive bacteria Staphylococcus aureus and Listeria monocytogenes and the Gram-negative bacteria Escherichia coli O157:H7 and Salmonella Typhimurium. N-CS nanoparticles showed higher activity compared with chitosan nanoparticles. The highest reduction of microorganisms was recorded for S. aureus of 3.82 log CFU/ml and L. monocytogenes of 3.61 log CFU/ml. The antimicrobial activity of N-CS nanoparticles in orange juice for 48 h revealed higher activity compared with the control against all the tested strains. The highest microbial reduction was recorded for N-CS nanoparticles against S. aureus with a 3.84 log CFU/ml reduction. L. monocytogenes and E. coli 0157:H7 were reduced by 3.54 and 3.44 log CFU/ml, respectively. The results showed high potential for the N-CS nanoparticles to be used as potent antibacterial agents in food and other related areas.

Plantaricyclin A, a Novel Circular Bacteriocin Produced by Lactobacillus plantarum NI326: Purification, Characterization, and Heterologous Production

Bacteriocins from lactic acid bacteria (LAB) are of increasing interest in recent years due to their potential as natural preservatives against food and beverage spoilage microorganisms. In a screening study for LAB, we isolated from olives a strain, Lactobacillus plantarum NI326, with activity against the beverage-spoilage bacterium Alicyclobacillus acidoterrestris Genome sequencing of NI326 enabled the identification of a gene cluster (designated plc) encoding a putative circular bacteriocin and proteins involved in its modification, transport, and immunity. This novel bacteriocin, named plantaricyclin A (PlcA), was grouped into the circular bacteriocin subgroup II due to its high degree of similarity with other gassericin A-like bacteriocins. Purification of PlcA from the supernatant of Lb. plantarum NI326 resulted in an active peptide with a molecular mass of 5,570 Da, corresponding to that predicted from the (processed) PlcA amino acid sequence. The plc gene cluster was cloned and expressed in Lactococcus lactis NZ9000, resulting in the production of an active 5,570-Da bacteriocin in the supernatant. PlcA is believed to be produced as a 91-amino-acid precursor with a 33-amino-acid leader peptide, which is predicted to be removed, followed by joining of the N and C termini via a covalent linkage to form the mature 58-amino-acid circular bacteriocin PlcA. We report the characterization of a circular bacteriocin produced by Lb. plantarum The inhibition displayed against A. acidoterrestris highlights its potential use as a preservative in food and beverages.IMPORTANCE In this work, we describe the purification and characterization of an antimicrobial peptide, termed plantaricyclin A (PlcA), produced by a Lactobacillus plantarum strain isolated from olives. This peptide has a circular structure, and all genes involved in its production, circularization, and secretion were identified. PlcA shows antimicrobial activity against different strains, including Alicyclobacillus acidoterrestris, a common spoilage bacterium, which causes substantial economic losses in the beverage industry every year. In this study, we describe a circular antimicrobial peptide, PlcA, for a Lactobacillus plantarum strain.

Continuous ohmic heating of commercially processed apple juice using five sequential electric fields results in rapid inactivation of Alicyclobacillus acidoterrestris spores

Spores of Alicyclobacillus acidoterrestris, a spoilage bacterium, cause problems for the apple juice industry because they are resistant to thermal treatment. Here, we examined the sporicidal effect of an ohmic heating (OH) system with five sequential electric fields and compared it with that of conventional heating. Apple juice product (50kg) inoculated with A. acidoterrestris spores were subjected to OH (electric field strength=26.7V/cm; frequency=25kHz) at 85-100°C for 30-90s. The effect of conventional heating was also examined under these conditions. OH treatment at 100°C for 30s resulted in total inactivation of the inoculum, with no recovery of viable cells (initial population=4.8-4.9logCFU/ml), whereas 3.6-4.9logCFU/ml of the spores survived conventional heating. OH did not alter the quality (°Brix, color, and pH) of commercial apple juice (p>0.05). These results suggest that the OH system is superior to conventional heating for rapid sterilization (30s) of apple juice to assure microbiological quality in the absence of chemical additives.

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

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

Application of bacteriocin RC20975 in apple juice

Alicyclobacillus acidoterrestris is one of the most spoilage-causing bacteria in fruit juices. In this paper, controlling A. acidoterrestris in apple juice by bacteriocin RC20975 was described. Twenty-one strains of A. acidoterrestris were used to investigate the activity spectrum of bacteriocin RC20975 in apple juice with the result that 16 strains were sensitive . The ratio of activity in apple juice to the activity in laboratory medium was 42%. The reduction of antimicrobial activity in apple juice might be due to problems related to its interaction with food components. Adsorption of bacteriocin RC20975 to A. acidoterrestris cells varied according to the strains and the testing conditions (pH and temperatures). In an acid environment (pH 3 and pH 5), the adsorption was higher than that of the neutral environment. Dynamic model of killing bacteria was built under the condition of different temperatures with the addition of bacteriocin. Electron microscopy examination of vegetative cells revealed substantial cell damage and bacterial lysis after bacteriocin treatment. Although the endospores could not be killed, the addition of bacteriocin RC20975 contributed to the reduction of the thermal resistance of A. acidoterrestris spores in apple juice. In sum, bacteriocin RC20975 was proved to have a good effect on killing A. acidoterrestris in apple juice.

Isolation and Structural Elucidation of Brevibacillin, an Antimicrobial Lipopeptide from Brevibacillus laterosporus That Combats Drug-Resistant Gram-Positive Bacteria

A new environmental bacterial strain exhibited strong antimicrobial characteristics against methicillin-resistant Staphylococcus aureus, vancomycin-resistant strains of Enterococcus faecalis and Lactobacillus plantarum, and other Gram-positive bacteria. The producer strain, designated OSY-I1, was determined to be Brevibacillus laterosporusvia morphological, biochemical, and genetic analyses. The antimicrobial agent was extracted from cells of OSY-I1 with isopropanol, purified by high-performance liquid chromatography, and structurally analyzed using mass spectrometry (MS) and nuclear magnetic resonance (NMR). The MS and NMR results, taken together, uncovered a linear lipopeptide consisting of 13 amino acids and an N-terminal C6 fatty acid (FA) chain, 2-hydroxy-3-methylpentanoic acid. The lipopeptide (FA-Dhb-Leu-Orn-Ile-Ile-Val-Lys-Val-Val-Lys-Tyr-Leu-valinol, where Dhb is α,β-didehydrobutyric acid and valinol is 2-amino-3-methyl-1-butanol) has a molecular mass of 1,583.0794 Da and contains three modified amino acid residues: α,β-didehydrobutyric acid, ornithine, and valinol. The compound, designated brevibacillin, was determined to be a member of a cationic lipopeptide antibiotic family. In addition to its potency against drug-resistant bacteria, brevibacillin also exhibited low MICs (1 to 8 μg/ml) against selected foodborne pathogenic and spoilage bacteria, such as Listeria monocytogenes,Bacillus cereus, and Alicyclobacillus acidoterrestris Purified brevibacillin showed no sign of degradation when it was held at 80 °C for 60 min, and it retained at least 50% of its antimicrobial activity when it was held for 22 h under acidic or alkaline conditions. On the basis of these findings, brevibacillin is a potent antimicrobial lipopeptide which is potentially useful to combat drug-resistant bacterial pathogens and foodborne pathogenic and spoilage bacteria.

Bacteriocins: Novel Solutions to Age Old Spore-Related Problems?

Bacteriocins are ribosomally synthesized antimicrobial peptides produced by bacteria, which have the ability to kill or inhibit other bacteria. Many bacteriocins are produced by food grade lactic acid bacteria (LAB). Indeed, the prototypic bacteriocin, nisin, is produced by Lactococcus lactis, and is licensed in over 50 countries. With consumers becoming more concerned about the levels of chemical preservatives present in food, bacteriocins offer an alternative, more natural approach, while ensuring both food safety and product shelf life. Bacteriocins also show additive/synergistic effects when used in combination with other treatments, such as heating, high pressure, organic compounds, and as part of food packaging. These features are particularly attractive from the perspective of controlling sporeforming bacteria. Bacterial spores are common contaminants of food products, and their outgrowth may cause food spoilage or food-borne illness. They are of particular concern to the food industry due to their thermal and chemical resistance in their dormant state. However, when spores germinate they lose the majority of their resistance traits, making them susceptible to a variety of food processing treatments. Bacteriocins represent one potential treatment as they may inhibit spores in the post-germination/outgrowth phase of the spore cycle. Spore eradication and control in food is critical, as they are able to spoil and in certain cases compromise the safety of food by producing dangerous toxins. Thus, understanding the mechanisms by which bacteriocins exert their sporostatic/sporicidal activity against bacterial spores will ultimately facilitate their optimal use in food. This review will focus on the use of bacteriocins alone, or in combination with other innovative processing methods to control spores in food, the current knowledge and gaps therein with regard to bacteriocin-spore interactions and discuss future research approaches to enable spores to be more effectively targeted by bacteriocins in food settings.

Potential Applications of the Cyclic Peptide Enterocin AS-48 in the Preservation of Vegetable Foods and Beverages

Bacteriocins are antimicrobial peptides produced by bacteria. Among them, the enterococcal bacteriocin (enterocin) AS-48 stands for its peculiar characteristics and broad-spectrum antimicrobial activity. AS-48 belongs to the class of circular bacteriocins and has been studied in depth in several aspects: peptide structure, genetic determinants, and mode of action. Recently, a wealth of knowledge has accumulated on the antibacterial activity of this bacteriocin against foodborne pathogenic and spoilage bacteria in food systems, especially in vegetable foods and drinks. This work provides a general overview on the results from tests carried out with AS-48 in different vegetable food categories (such as fruit juices, ciders, sport and energy drinks, fresh fruits and vegetables, pre-cooked ready to eat foods, canned vegetables, and bakery products). Depending on the food substrate, the bacteriocin has been tested alone or as part of hurdle technology, in combination with physico-chemical treatments (such as mild heat treatments or high-intensity pulsed electric fields) and other antimicrobial substances (such as essential oils, phenolic compounds, and chemical preservatives). Since the work carried out on bacteriocins in preservation of vegetable foods and drinks is much more limited compared to meat and dairy products, the results reported for AS-48 may open new possibilities in the field of bacteriocin applications.

Bioprocess development for the production of sonorensin by Bacillus sonorensis MT93 and its application as a food preservative

Media composition and environmental conditions were optimized using statistical tools, Plackett Burman design and response surface methodology, to maximize the yield of a bacteriocin, named as sonorensin, from a new marine isolate Bacillus sonorensis MT93 showing broad spectrum of antimicrobial activity. Under optimized conditions, MT93 produced 15-fold higher yield of sonorensin compared to that under initial fermentation conditions. As oxygen supply is a critical parameter controlling growth and product formation in aerobic bioprocesses and used as a parameter for bioprocess scale up, the effects of oxygen transfer, in terms of volumetric oxygen transfer coefficient (kLa), on production of sonorensin was investigated using optimized medium composition in a bioreactor. Studies on effectiveness of sonorensin against Staphylococcus aureus and Listeria monocytogenes in fruit juice and as a preservative in pasteurized milk demonstrated its potential as a biopreservative in fruit products and shelf life extender of the pasteurized milk.

The Cyclic Antibacterial Peptide Enterocin AS-48: Isolation, Mode of Action, and Possible Food Applications

Enterocin AS-48 is a circular bacteriocin produced by Enterococcus. It contains a 70 amino acid-residue chain circularized by a head-to-tail peptide bond. The conformation of enterocin AS-48 is arranged into five alpha-helices with a compact globular structure. Enterocin AS-48 has a wide inhibitory spectrum on Gram-positive bacteria. Sensitivity of Gram-negative bacteria increases in combination with outer-membrane permeabilizing treatments. Eukaryotic cells are bacteriocin-resistant. This cationic peptide inserts into bacterial membranes and causes membrane permeabilization, leading ultimately to cell death. Microarray analysis revealed sets of up-regulated and down-regulated genes in Bacillus cereus cells treated with sublethal bacteriocin concentration. Enterocin AS-48 can be purified in two steps or prepared as lyophilized powder from cultures in whey-based substrates. The potential applications of enterocin AS-48 as a food biopreservative have been corroborated against foodborne pathogens and/or toxigenic bacteria (Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Escherichia coli, Salmonella enterica) and spoilage bacteria (Alicyclobacillus acidoterrestris, Bacillus spp., Paenibacillus spp., Geobacillus stearothermophilus, Brochothrix thermosphacta, Staphylococcus carnosus, Lactobacillus sakei and other spoilage lactic acid bacteria). The efficacy of enterocin AS-48 in food systems increases greatly in combination with chemical preservatives, essential oils, phenolic compounds, and physico-chemical treatments such as sublethal heat, high-intensity pulsed-electric fields or high hydrostatic pressure.

Survey of molds, yeast and Alicyclobacillus spp. from a concentrated apple juice productive process

Bacteria and molds may spoil and/or contaminate apple juice either by direct microbial action or indirectly by the uptake of metabolites as off-flavours and toxins. Some of these microorganisms and/or metabolites may remain in the food even after extensive procedures. This study aim to identify the presence of molds (including heat resistant species) and Alicyclobacillus spp., during concentrated apple juice processing. Molds were isolated at different steps and then identified by their macroscopic and microscopic characteristics after cultivation on standard media at 5, 25 and 37 °C, during 7 days. Among the 19 isolated found, 63% were identified as Penicillium with 50% belonging to the P. expansum specie. With regards to heat resistant molds, the species Neosartorya fischeri, Byssochlamys fulva and also the genus Eupenicillium sp., Talaromyces sp. and Eurotium sp. were isolated. The thermoacidophilic spore-forming bacteria were identified as A. acidoterrestris by a further investigation based on 16S rRNA sequence similarity. The large contamination found indicates the need for methods to eliminate or prevent the presence of these microorganisms in the processing plants in order to avoid both spoilage of apple juice and toxin production.

Control of Alicyclobacillus acidoterrestris in fruit juices by a newly discovered bacteriocin

Alicyclobacillus acidoterrestris is one of the most spoilage-causing bacteria in fruit juices. Control of A. acidoterrestris in fruit juices by bificin C6165 (Pei et al. in J Appl Microbiol 114(5):1273-1284, 2013), a bacteriocin produced by Bifidobacterium animalis subsp. animalis CICC 6165, was described in this study. Activity spectrum of bificin C6165 was investigated and sixteen strains of A. acidoterrestris were sensitive to bificin C6165 in diluted Apple Juices. In the commercial fruit juices, vegetative cells of A. acidoterrestris were inactivated by bificin C6165 at 40 μg/ml. The inhibitory effect of bificin C6165 was better at lower pH (pH 3.5) and at a higher temperature of 45 °C. Furthermore, electron microscopy examination of the vegetative cells treated with bacteriocin revealed substantial cell damage and bacterial lysis. The result suggested that primary mode of action of bificin C6165 was most probably due to pore formation. Although no significantly activity of bificin C6165 was observed against the endospores of A. acidoterrestris in commercial apple juice, the addition of bacteriocin contributed to the reduction of the thermal resistance of A. acidoterrestris spores. Additionally, encapsulation of bificin C6165 with Ca-alginate gel was investigated. Encapsulation of bificin C6165 provided a promising method to control A. acidoterrestris in food juice industry.

Purification and characterization of anti-Alicyclobacillus bacteriocin produced by Lactobacillus rhamnosus

Lactobacillus rhamnosus CICC 20975 produces a 6,502-Da bacteriocin, named bacteriocin RC 20975, active against Alicyclobacillus acidoterrestris, Lactobacillus acidophilus, Lactobacillus brevis, Bacillus subtilis, and Listeria innocua. This bacteriocin is not quite heat stable but is effective after refrigerated storage and freeze-thaw cycles. Bacteriocin RC 20975 was added at a concentration of 256 AU/ml to the endospores of A. acidoterrestris DSM 3922; no viable cells were detected after 24 h. The primary mode of action of bacteriocin RC 20975 seems to be the formation of pores, as indicated by K⁺ efflux from metabolically active cells of A. acidoterrestris. However, efflux of larger cytoplasmic content was not observed within the first 30 min after bacteriocin RC 20975 treatment. In addition, adsorption of bacteriocin RC 20975 to target cells at different temperatures and pH levels and in the presence of surfactants was studied. Finally, the effect that different media, media components, and addition of vitamins to the media had on bacteriocin RC 20975 production was also studied.

Characterization of bacteriocin bificin C6165: a novel bacteriocin

AIMS

To purify and primarily characterize an anti-Alicyclobacillus bacteriocin produced by Bifidobacterium animalis subsp. animalis CICC 6165, suggested to be named bificin C6165.

METHODS AND RESULTS

During purification of the bificin C6165, optimal recovery was achieved with ammonium sulfate precipitation followed by two chromatographic steps. Mass spectrometry analyses revealed a distinctive peak corresponding to a molecular mass of 3395·1 Da. This bacteriocin was heat stable, effective after refrigerated storage and freeze-thaw cycles. The primary mode of action of bificin C6165 is most probably due to pore formation, as indicated by the efflux of K(+) from metabolically active cells of Alicyclobacillus acidoterrestris. In the presence of 10 mmol l(-1) gadolinium, bificin C6165 did not affect cells of Alicyclobacillus acidoterrestris. This suggests that the mode of action of bificin C6165 relies on a net negatively charged cell surface.

CONCLUSIONS

Bificin C6165 is indeed a novel bacteriocin and it exhibited remarkable potency for Alicyclobacillus control.

SIGNIFICANCE AND IMPACT OF THE STUDY

Application of bacteriocins in preservation of fruit juices has seldom been studied. Bificin C6165 may be an alternative method to control juice spoilage by this Alicyclobacillus acidoterrestris and meet increasing consumer demand for nature and artificial chemical additive-free food products.