Some chemical and physical properties of nisin, a small-protein antibiotic produced by Lactococcus lactis

A Comprehensive Review of Emulsion-Based Nisin Delivery Systems for Food Safety

Foodborne diseases are one of the most serious problems the food sector has to confront, while questions have been raised concerning the effects of several antimicrobial additives on consumer health. Nisin is a peptide produced primarily by Lactococcus lactis with antimicrobial properties mostly against Gram-positive bacteria. It is generally recognized as safe (GRAS) for use in a wide range of food categories. However, its interaction with components of the food matrix, its susceptibility to proteolytic degradation, or the competitive presence of other components may limit its activity. To enhance its effectiveness against Gram-negative bacteria, its combination with essential oils or other antimicrobial components has been investigated. In addition, its encapsulation in several types of nano-delivery systems has been used to protect nisin from food matrix sequestering while regulating its release. In this review, we present how nisin is utilized, alone or in combination with other antimicrobial agents in a range of emulsion types, as well as the standard techniques for the physicochemical characterization of these systems.

Optimization of Culture Medium Ingredients and Culture Conditions for Bacteriocin Production in Lactococcus lactis NCU036019

Bacteriocin lactococcin036019 was identified and characterized from Lactococcus lactis NCU036019, which displayed significant antibacterial activity toward foodborne pathogenic bacteria Staphylococcus aureus under various conditions. However, the in situ low-level expression of lactococcin036019 severely limited its wide application in food industry. In this study, we optimized the medium ingredients and culture conditions of L. lactis NCU036019 for maximum production of lactococcin036019. The effects of different carbon sources, nitrogen sources, inorganic salts, growth factors, surfactants, and buffer salts on the production of bacteriocin were studied using antibacterial titer and diameter of inhibitory zone as evaluation indexes. Through single-factor experiments, Plackett-Burman (PB) experiment, steepest ascent experiment and response surface methodology, yeast extract, zinc sulfate, sodium acetate, mannitol, Tween-80, and dipotassium hydrogen phosphate were identified to display significant influence on the production of bacteriocin. By optimizing Man Rogosa and Sharpe (MRS) culture medium ingredients, the antibacterial activity of lactococcin036019 in the cell-free supernatant raised from 46.19 to 300.14 Au/mL, namely, 6.5 times increased. Furthermore, the culture conditions, such as inoculation amount, culture time, and culture temperature, were optimized, and this further increased the antibacterial activity to 409 Au/mL, namely, 8.8 times increased. This study investigated the effects of culture media and conditions on the production of lactococcin036019, and they were optimized for a maximum harvest of bacteriocin, and the significant increase of bacteriocin production in L. lactis NCU036019 facilitates the application of the antibacterial substance in future work.

Current challenges and development strategies of bacteriocins produced by lactic acid bacteria applied in the food industry

Given the great importance of natural biopreservatives in the modern food industry, lactic acid bacteria (LAB)-producing bacteriocins have gained considerable attention due to their antimicrobial activity against foodborne pathogens and spoilage bacteria. Although numerous LAB-producing bacteriocins have demonstrated efficiency in preserving food quality in various applications, only a limited number of these compounds have been commercially approved to date. The currently unclear gastrointestinal metabolism of bacteriocins may pose safety risks, as well as cytotoxicity and immunogenicity, which need to be seriously considered before their application. A more noteworthy concern lies in whether bacteriocins induce an imbalance in the gut microbiota, thereby leading to alterations in the abundance of health-associated microorganisms and their metabolites in the gastrointestinal tract. Accordingly, this review presents unique insights into the challenges arising from metabolic interactions between LAB-producing bacteriocins and the gastrointestinal tract. Besides, the application of bacteriocins in the food industry faces challenges arising from the low production yield, weak stability, and insufficient antimicrobial activity. The corresponding development strategies are proposed for conducting the systematic and comprehensive evaluation of the potential safety risks of bacteriocins and their metabolites. The strategies also focus on the rational design to increase the activity and stability, the fermentation control to enhance the production yield, and the hurdle and embedding technology to improve the application effects. It definitively discloses the perspective of bacteriocins to become natural, sustainable, safe, and eco-friendly biological preservatives for the advancement of the food industry.

Simulation-Guided Molecular Modeling of Nisin and Lipid II Assembly and Membrane Pore Formation

The lantibiotic pore-forming peptide nisin is a promising candidate in the fight against multidrug-resistant bacteria due to its unique structure, which allows it to disrupt bacteria in two distinct ways─Lipid II trafficking and transmembrane pore formation. However, exactly how nisin and Lipid II assemble into oligomeric pore structures in the bacterial membrane is not known. Spontaneous peptide assembly into pores is difficult to observe in even the very long-time scale molecular dynamics (MD) simulations. In this study, we adopted an MD-guided modeling approach to investigate the nisin-nisin and nisin-Lipid II associations in the membrane environment. Through extensive microsecond-time scale all-atom MD simulations, we established that nisin monomers dimerize by forming β-sheets in a POPE:POPG lipid bilayer and oligomerize further to form stable transmembrane channels. We determined that these nisin dimers use Lipid II as a dimer interface to incur enhanced stability. Our results provide a clearer understanding of the self-assembly of nisin monomers within the membrane and insights into the role of Lipid II in the structural integrity of oligomeric structures.

Strategies for effective high pressure germination or inactivation of Bacillus spores involving nisin

The major challenge in employing high pressure (HP) at moderate temperature for sterilization is the remarkable resistance of bacterial spores. High isostatic pressure can initiate spore germination, enabling subsequent inactivation under mild conditions. However, not all spores could be triggered to germinate under pressure at temperatures ≤80°C so far. In this study, germination treatment combinations were evaluated for Bacillus spores involving moderate HP (150 MPa, 37°C, 5 min), very HP (vHP, 550 MPa, 60°C, 2.5 or 9 min), simple and complex nutrient germinants [L-valine, L-alanine, and tryptic soy broth (TSB)], nisin, and incubation at atmospheric pressure (37°C). The most effective combinations for Bacillus subtilis resulted in a reduction of culturable dormant spores by 8 log10 units. The combinations involved nisin, a nutrient germinant (L-valine or TSB), a first vHP treatment (550 MPa, 60°C, 2.5 min), incubation at atmospheric pressure (37°C, 6 h), and a second vHP treatment (550 MPa, 60°C, 2.5 min). Such treatment combination with L-valine reduced Bacillus amyloliquefaciens spores by only 2 log10 units. B. amyloliquefaciens, thus, proved to be substantially more HP-resistant compared to B. subtilis, validating previous studies. Despite combining different germination mechanisms, complete germination could not be achieved for either species. The natural bacteriocin nisin did seemingly not promote HP germination initiation under chosen HP conditions, contrary to previous literature. Nevertheless, nisin might be beneficial to inhibit the growth of HP-germinated or remaining ungerminated spores. Future germination experiments might consider that nisin could not be completely removed from spores by washing, thereby affecting plate count enumeration.

IMPORTANCE

Extremely resistant spore-forming bacteria are widely distributed in nature. They infiltrate the food chain and processing environments, posing risks of spoilage and food safety. Traditional heat-intensive inactivation methods often negatively affect the product quality. HP germination-inactivation offers a potential solution for better preserving sensitive ingredients while inactivating spores. However, the presence of ungerminated (superdormant) spores hampers the strategy's success and safety. Knowledge of strategies to overcome resistance to HP germination is vital to progress mild spore control technologies. Our study contributes to the evaluation and development of mild preservation processes by evaluating strategies to enhance the HP germination-inactivation efficacy. Mild preservation processes can fulfill the consumers' demand for safe and minimally processed food.

Determination of the combined effect of grape seed extract and cold atmospheric plasma on foodborne pathogens and their environmental stress knockout mutants

The study aimed to explore the antimicrobial efficacy of grape seed extract (GSE) and cold atmospheric plasma (CAP) individually or in combination against L. monocytogenes and E. coli wild type (WT) and their isogenic mutants in environmental stress genes. More specifically, we examined the effects of 1% (wt/vol) GSE, 4 min of CAP treatment, and their combined effect on L. monocytogenes 10403S WT and its isogenic mutants ΔsigB, ΔgadD1, ΔgadD2, ΔgadD3, as well as E. coli K12 and its isogenic mutants ΔrpoS, ΔoxyR, and ΔdnaK. In addition, the sequence of the combined treatments was tested. A synergistic effect was achieved for all L. monocytogenes strains when exposure to GSE was followed by CAP treatment. However, the same effect was observed against E. coli strains, only for the reversed treatment sequence. Additionally, L. monocytogenes ΔsigB was more sensitive to the individual GSE and the combined GSE/CAP treatment, whereas ΔgadD2 was more sensitive to CAP, as compared to the rest of the mutants under study. Individual GSE exposure was unable to inhibit E. coli strains, and individual CAP treatment resulted in higher inactivation of E. coli in comparison to L. monocytogenes with the strain ΔrpoS appearing the most sensitive among all studied strains. Our findings provide a step toward a better understanding of the mechanisms playing a role in the tolerance/sensitivity of our model Gram-positive and Gram-negative bacteria toward GSE, CAP, and their combination. Therefore, our results contribute to the development of more effective and targeted antimicrobial strategies for sustainable decontamination.IMPORTANCEAlternative approaches to conventional sterilization are gaining interest from the food industry, driven by (i) the consumer demand for minimally processed products and (ii) the need for sustainable, environmentally friendly processing interventions. However, as such alternative approaches are milder than conventional heat sterilization, bacterial pathogens might not be entirely killed by them, which means that they could survive and grow, causing food contamination and health hazards. In this manuscript, we performed a systematic study of the impact of antimicrobials derived from fruit industry waste (grape seed extract) and cold atmospheric plasma on the inactivation/killing as well as the damage of bacterial pathogens and their genetically modified counterparts, for genes linked to the response to environmental stress. Our work provides insights into genes that could be responsible for the bacterial capability to resist/survive those novel treatments, therefore, contributing to the development of more effective and targeted antimicrobial strategies for sustainable decontamination.

Microfluidic preparation and optimization of (Kollicoat ® IR-b-PCL) polymersome for co-delivery of Nisin-Curcumin in breast cancer application

This work aimed to develop amphiphilic nanocarriers such as polymersome based diblock copolymer of Kollicoat ® IR -block-poly(ε-caprolactone) (Kollicoat ® IR-b-PCL) for potential co-delivery of Nisin (Ni) and Curcumin (CUR) for treatment of breast cancer. To generate multi-layered nanocarriers of uniform size and morphology, microfluidics was used as a new technology. In order to characterise and optimize polymersome, design of experiments (Design-Expert) software with three levels full factorial design (3-FFD) method was used. Finally, the optimized polymersome was produced with a spherical morphology, small particle size (dH < 200 nm), uniform size distribution (PDI < 0.2), and high drug loading efficiency (Ni 78 % and CUR 93 %). Furthermore, the maximum release of Ni and CUR was found to be roughly 60 % and 80 % in PBS, respectively. Cytotoxicity assays showed a slight cytotoxicity of Ni and CUR -loaded polymersome (N- Ni /CUR) towards normal cells while demonstrating inhibitory activity against cancer cells compared to the free drugs. Also, the apoptosis assays and cellular uptake confirmed the obtained results from cytotoxic analysis. In general, this study demonstrated a microfluidic approach for preparation and optimization of polymersome for co-delivery of two drugs into cancer cells.

Altering Specificity and Enhancing Stability of the Antimicrobial Peptides Nisin and Rombocin through Dehydrated Amino Acid Residue Engineering

Nisin serves as the prototype within the lantibiotic group of antimicrobial peptides, exhibiting a broad-spectrum inhibition against Gram-positive bacteria, including important food-borne pathogens and clinically relevant antibiotic-resistant strains. The gene-encoded nature of nisin allows for gene-based bioengineering, enabling the generation of novel derivatives. It has been demonstrated that nisin mutants can be produced with improved functional properties. Here, we particularly focus on the uncommon amino acid residues dehydroalanine (Dha) and dehydrobutyrin (Dhb), whose functions are not yet fully elucidated. Prior to this study, we developed a new expression system that utilizes the nisin modification machinery NisBTC to advance expression, resulting in enhanced peptide dehydration efficiency. Through this approach, we discovered that the dehydrated amino acid Dhb at position 18 in the peptide rombocin, a short variant of nisin, displayed four times higher activity compared to the non-dehydrated peptide against the strain Lactococcus lactis. Furthermore, we observed that in the peptides nisin and rombocin, the dehydrated amino acid Dha at residue positon 18 exhibited superior activity compared to the dehydrated amino acid Dhb. Upon purifying the wild-type nisin and its variant nisinG18/Dha to homogeneity, the minimum inhibitory concentration (MIC) indicated that the variant exhibited activity similar to that of wild-type nisin in inhibiting the growth of Bacillus cereus but showed twice the MIC values against the other four tested Gram-positive strains. Further stability tests demonstrated that the dehydrated peptide exhibited properties similar to wild-type nisin under different temperatures but displayed higher resistance to proteolytic enzymes compared to wild-type nisin.

The modification of nisin with homocysteine thiolactone and its effect on antimicrobial activity

The aim of the present study is to make an important contribution to the literature by focusing on the preparation of the N-homocysteine conjugate of nisin and evaluating the effect of the N-homocysteinylation reaction on its antimicriobial activity. The modification process was monitored using both acetic acid urea polyacrylamide gel electrophoresis (AAU-PAGE) and tricine sodium dodecyl sulphate polyacrylamide gel electrophoresis (tricine SDS-PAGE). The antibacterial effectiveness of modified nisin was assessed against Staphylococcus aureus ATCC 6538, Enterococcus faecium ATCC 9097, Bacillus subtilis ATCC 6633, Lactococcus lactis ssp. cremoris AÜ, Listeria monocytogenes NCTC 5348, and Escherichia coli RSKK. Optimal conditions for achieving the highest N-homocysteinylation degree (6.30%) were determined as 6 mg/mL nisin, 150 mM homocysteine thiolactone, 150 rpm shaking rate, pH of 3.0, and a reaction time of 6 h. The modified nisin obtained did not have a significant inhibitory effect on the strains tested except E. faecium. E. faecium was inhibited by the modified nisin and its antibacterial activity was determined as approximately 10% of the antibacterial activity of unmodified nisin. On the other hand, hydrolysis of nisin by trypsin and thermolysin resulted in significant specific side chain modifications induced by the homocysteine-thiolactone reaction, especially at Lys12 and Lys22. The results provide valuable insights into the potential of N-homocysteinylation to improve the antibacterial properties of nisin and also suggest that the effects of specific modifications identified during the modification process should be investigated.

Nisin lantibiotic prevents NAFLD liver steatosis and mitochondrial oxidative stress following periodontal disease by abrogating oral, gut and liver dysbiosis

Oral microbiome dysbiosis mediates chronic periodontal disease, gut microbial dysbiosis, and mucosal barrier disfunction that leads to steatohepatitis via the enterohepatic circulation. Improving this dysbiosis towards health may improve liver disease. Treatment with antibiotics and probiotics have been used to modulate the microbial, immunological, and clinical landscape of periodontal disease with some success. The aim of the present investigation was to evaluate the potential for nisin, an antimicrobial peptide produced by Lactococcus lactis, to counteract the periodontitis-associated gut dysbiosis and to modulate the glycolipid-metabolism and inflammation in the liver. Periodontal pathogens, namely Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia and Fusobacterium nucleatum, were administrated topically onto the oral cavity to establish polymicrobial periodontal disease in mice. In the context of disease, nisin treatment significantly shifted the microbiome towards a new composition, commensurate with health while preventing the harmful inflammation in the small intestine concomitant with decreased villi structural integrity, and heightened hepatic exposure to bacteria and lipid and malondialdehyde accumulation in the liver. Validation with RNA Seq analyses, confirmed the significant infection-related alteration of several genes involved in mitochondrial dysregulation, oxidative phosphorylation, and metal/iron binding and their restitution following nisin treatment. In support of these in vivo findings indicating that periodontopathogens induce gastrointestinal and liver distant organ lesions, human autopsy specimens demonstrated a correlation between tooth loss and severity of liver disease. Nisin's ability to shift the gut and liver microbiome towards a new state commensurate with health while mitigating enteritis, represents a novel approach to treating NAFLD-steatohepatitis-associated periodontal disease.

Characterization of Lactococcus lactis 11/19-B1 Isolated from Kiwi Fruit as a Potential Probiotic and Paraprobiotic

Probiotics are live bacteria used as food additives that are beneficial to human health. Lactococcus lactis 11/19-B1 strain isolated from kiwi fruit stimulates innate immunity in silkworms. Intake of yogurt containing the living 11/19-B1 strain significantly decreases the level of low-density lipoproteins (LDLs) in high-LDL volunteers and improves atopic dermatitis in humans. In this study, the probiotic properties of the 11/19-B1 strain, such as sensitivity to antimicrobial compounds, biogenic amine production, some virulence genes for human health, antimicrobial activity, tolerance to gastric acid and bile acids, and ability to adhere to the intestinal mucosa, were evaluated. The 11/19-B1 strain did not show resistance to the tested antimicrobial compounds except cefoxitin and fosfomycin. In addition, no production of amines that can harm humans, the antimicrobial activity required for probiotics, and the absence of adhesion to Caco-2 cells suggest that it is unlikely to attach to the intestinal epithelium. The 11/19-B1 strain grew in 0.3% but not in 1% bile salt. In the presence of 2% skim milk, the survival rate of the 11/19-B1 strain under simulated gastrointestinal tract conditions was 67% even after 4 h. These results indicate that the 11/19-B1 strain may function as a probiotic or paraprobiotic to be utilized in the food industry.

Antibacterial Effects of Theaflavins against Staphylococcus aureus and Salmonella paratyphi B: Role of Environmental Factors and Food Matrices

This study aimed to investigate the effects of different environmental factors (temperature, pH, and NaCl) and food matrices (skimmed milk powder, lecithin, and sucrose) on the antibacterial activity of theaflavins (TFs) against Staphylococcus aureus (S. aureus) and Salmonella paratyphi B (S. paratyphi B). TFs showed a larger diameter of inhibition zone (DIZ, 12.58 ± 0.09 mm-16.36 ± 0.12 mm) value against S. aureus than that of S. paratyphi B (12.42 ± 0.43 mm-15.81 ± 0.24 mm) at the same concentration (2-10 mg/mL). When temperatures were 25-121 °C, the DIZ of TFs against both S. aureus and S. paratyphi B was not significantly different. As pH increased from 2 to 10, their DIZ values decreased significantly from 16.78 ± 0.23 mm to 13.43 ± 0.08 mm and 15.63 ± 0.42 mm to 12.18 ± 0.14 mm, respectively. Their DIZ values increased slightly as the NaCl concentration increased from 0.2 mol/L to 0.8 mol/L, while their DIZ values decreased significantly for skimmed milk powder concentrations in the range of 20-120 g/L. Regarding the concentrations of lecithin and sucrose were 2-12 g/L and 10-60 g/L, their DIZ values showed no significant change against S. paratyphi B, but an increased trend for S. aureus. Under the above different environmental factors and food matrices, TFs maintained excellent antibacterial activity against S. aureus and S. paratyphi B, providing a theoretical guidance for applying TFs as novel antibacterial additives in the food industry.

Food matrix design can influence the antimicrobial activity in the food systems: A narrative review

Antimicrobial agents are safe preservatives having the ability to protect foods from microbial spoilage and extend their shelf life. Many factors, including antimicrobials' chemical features, storage environments, delivery methods, and diffusion in foods, can affect their antimicrobial activities. The physical-chemical characteristics of the food itself play an important role in determining the efficacy of antimicrobial agents in foods; however the mechanisms behind it have not been fully explored. This review provides new insights and comprehensive knowledge regarding the impacts of the food matrix, including the food components and food (micro)structures, on the activities of antimicrobial agents. Studies of the last 10 years regarding the influences of the food structure on the effects of antimicrobial agents against the microorganisms' growth were summarized. The mechanisms underpinning the loss of the antimicrobial agents' activity in foods are proposed. Finally, some strategies/technologies to improve the protection of antimicrobial agents in specific food categories are discussed.

Synergistic antimicrobial effect of nisin-octanoic acid nanoemulsions against E. coli and S. aureus

Food safety is a major public health concern all over the world. Therefore, the prevention of food contamination is becoming extremely crucial. In this study, an antimicrobial nanoemulsion composed of water-soluble nisin and fat-soluble octanoic acid was successfully prepared. The results showed that the average particle size and the polymer dispersity index of the nisin-octanoic acid (NOA) nanoemulsion were around 52.21 nm and 0.253, respectively. The NOA nanoemulsion required less amounts of nisin and octanoic acid to achieve the effective antimicrobial effect against Escherichia coli and Staphylococcus aureus. In addition, the growth curves of E. coli and S. aureus were determined. The OD₆₀₀ of NOA nanoemulsion was significantly lower than free nisin after being incubated for 24 h (p < 0.001), indicating that the antimicrobial effect of NOA nanoemulsion was outstanding. Meanwhile, the synergistic antimicrobial property of NOA nanoemulsion against E. coli and S. aureus was significantly better than free nisin under nonacid conditions (p < 0.05). Overall, the results of this study may provide guidance for the further application of nisin in more forms.

Bioengineering of a Lactococcus lactis subsp. lactis strain enhances nisin production and bioactivity

Lactococcus lactis subsp. lactis is a food bacterium that has been utilized for decades in food fermentation and the development of high-value industrial goods. Among these, nisin, which is produced by several strains of L. lactis subsp. lactis, plays a crucial role as a food bio-preservative. The gene expression for nisin synthesis was evaluated using qPCR analysis. Additionally, a series of re-transformations of the strain introducing multiple copies of the nisA and nisRK genes related to nisin production were developed. The simultaneous expression of nisA and nisZ genes was used to potentiate the effective inhibition of foodborne pathogens. Furthermore, qPCR analysis indicated that the nisA and nisRK genes were expressed at low levels in wild-type L. lactis subsp. lactis. After several re-transformations of the strain with the nisA and nisRK genes, a high expression of these genes was obtained, contributing to improved nisin production. Also, co-expression of the nisA and nisZ genes resulted in extremely effective antibacterial action. Hence, this study would provide an approach to enhancing nisin production during industrial processes and antimicrobial activity.

Evidence of Self-Association and Conformational Change in Nisin Antimicrobial Polypeptide Solutions: A Combined Raman and Ultrasonic Relaxation Spectroscopic and Theoretical Study

The polypeptide Nisin is characterized by antibacterial properties, making it a compound with many applications, mainly in the food industry. As a result, a deeper understanding of its behaviour, especially after its dissolution in water, is of the utmost importance. This could be possible through the study of aqueous solutions of Nisin by combining vibrational and acoustic spectroscopic techniques. The velocity and attenuation of ultrasonic waves propagating in aqueous solutions of the polypeptide Nisin were measured as a function of concentration and temperature. The computational investigation of the molecular docking between Nisin monomeric units revealed the formation of dimeric units. The main chemical changes occurring in Nisin structure in the aqueous environment were tracked using Raman spectroscopy, and special spectral markers were used to establish the underlying structural mechanism. Spectral changes evidenced the presence of the dimerization reaction between Nisin monomeric species. The UV/Vis absorption spectra were dominated by the presence of π → π* transitions in the peptide bonds attributed to secondary structural elements such as α-helix, β-sheets and random coils. The analysis of the acoustic spectra revealed that the processes primarily responsible for the observed chemical relaxations are probably the conformational change between possible conformers of Nisin and its self-aggregation mechanism, namely, the dimerization reaction. The activation enthalpy and the enthalpy difference between the two isomeric forms were estimated to be equal to ΔH₁* = 0.354 ± 0.028 kcal/mol and ΔH₁⁰ = 3.008 ± 0.367 kcal/mol, respectively. The corresponding thermodynamic parameters of the self-aggregation mechanism were found to be ΔH₂* = 0.261 ± 0.004 kcal/mol and ΔH₂⁰ = 3.340 ± 0.364 kcal/mol. The effect of frequency on the excess sound absorption of Nisin solutions enabled us to estimate the rate constants of the self-aggregation mechanism and evaluate the isentropic and isothermal volume changes associated with the relaxation processes occurring in this system. The results are discussed in relation to theoretical and experimental findings.

Bacteriocin: A natural approach for food safety and food security

The call to cater for the hungry is a worldwide problem in the 21st century. Food security is the utmost prime factor for the increasing demand for food. Awareness of human health when using chemical preservatives in food has increased, resulting in the use of alternative strategies for preserving food and enhancing its shelf-life. New preservatives along with novel preservation methods have been instigated, due to the intensified demand for extended shelf-life, along with prevention of food spoilage of dairy products. Bacteriocins are the group of ribosomally synthesized antimicrobial peptides; they possess a wide range of biological activities, having predominant antibacterial activity. The bacteriocins produced by the lactic acid bacteria (LAB) are considered to be of utmost importance, due to their association with the fermentation of food. In recent times among various groups of bacteriocins, leaderless and circular bacteriocins are gaining importance, due to their extensive application in industries. These groups of bacteriocins have been least studied as they possess peculiar structural and biosynthetic mechanisms. They chemically possess N-to-C terminal covalent bonds having a predominant peptide background. The stability of the bacteriocins is exhibited by the circular structure. Up till now, very few studies have been performed on the molecular mechanisms. The structural genes associated with the bacteriocins can be combined with the activity of various proteins which are association with secretion and maturation. Thus the stability of the bacteriocins can be used effectively in the preservation of food for a longer period of time. Bacteriocins are thermostable, pH-tolerant, and proteolytically active in nature, which make their usage convenient to the food industry. Several research studies are underway in the domain of biopreservation which can be implemented in food safety and food security.

Nisin Variants Generated by Protein Engineering and Their Properties

Nisin, a typical lantibiotic, has robust antimicrobial activity combined with limited cytotoxicity, and the development of resistance to it is slow. These properties make nisin a promising antimicrobial agent to control pathogenic microorganisms in dairy foods. However, its low solubility, poor stability and short half-life at neutral pH limit its application within the dairy industry. Protein engineering technology has revealed the potential of modifying nisin to improve its properties, and many valuable variants have emerged. This review summarizes progress in the generation of nisin variants for the dairy industry and for other purposes. These nisin variants with additional modification have improved properties and can even expand the inhibition spectrum range of nisin. Nisin, as the most thoroughly studied lantibiotic, and its variants can also guide the modification of other lantibiotics.

Synergistic antimicrobial interactions of nisin A with biopolymers and solubilising agents for oral drug delivery

In order to develop bacteriocins, like the lantibiotic nisin A, into effective alternatives to existing antibiotics, their biophysical and physicochemical properties must first be assessed, from solubility, to susceptibility and absorption. It has been well established that formulation strategies at early drug development stages can be crucial for successful outcomes during preclinical and clinical phases of development, particularly for molecules with challenging physicochemical properties. This work elucidates the physicochemical challenges of nisin A in terms of its susceptibility to digestive enzymes like pepsin, pancreatin and proteinase K and its poor solubility at physiological pHs. Low solution concentrations, below the minimum inhibitory concentration against Staphylococcus aureus, were obtained in phosphate buffered saline (PBS, pH 7.4) and in fasted state simulated intestinal fluid (FaSSIF, pH 6.5), while higher solubilities at more acidic pH's such as in a KCl/HCl buffer (pH 2) and in fasted state simulated gastric fluid (FaSSGF, pH 1.6) are observed. Tween® 80 (0.01% v/v) significantly increased the solution concentration of nisin A in PBS (pH 7.4, 24 hr). Pancreatin doubled nisin A's solution concentration at pH 7.4 (PBS) but reduced its' inhibitory activity to ∼ 20%, and pepsin almost completely degraded nisin (after 24 hr), but retained activity at biologically relevant exposure times (∼ 15 min). Harnessing synergism between nisin A and either glycol chitosan or ε-poly lysine, combined with the solubilizing effect of Tween®, increased the antimicrobial activity of nisin A six fold in an in vitro oral administration model.

Ring-opening reactions for the solid-phase synthesis of nisin lipopeptide analogues

Strategy for the solid-phase synthesis of nisin lipopeptide analogues using orthogonally protected lanthionines synthesised by ring-opening chemistry, and on-resin formation of dehydroalanine and dehydrobutyrine residues.

Bromelain and Nisin: The Natural Antimicrobials with High Potential in Biomedicine

Infectious diseases along with various cancer types are among the most significant public health problems and the leading cause of death worldwide. The situation has become even more complex with the rapid development of multidrug-resistant microorganisms. New drugs are urgently needed to curb the increasing spread of diseases in humans and livestock. Promising candidates are natural antimicrobial peptides produced by bacteria, and therapeutic enzymes, extracted from medicinal plants. This review highlights the structure and properties of plant origin bromelain and antimicrobial peptide nisin, along with their mechanism of action, the immobilization strategies, and recent applications in the field of biomedicine. Future perspectives towards the commercialization of new biomedical products, including these important bioactive compounds, have been highlighted.

Dual-functional antibacterial and osteogenic nisin-based layer-by-layer coatings

Implanted biomaterials can be regarded in a cornerstone in the domain of bone surgery. Their surfaces are expected to fulfil two particular requirements: preventing the settlement and the development of bacteria, and stimulating bone cells in view to foster osseointegration. Therefore, a modern approach consists in the design of dual functional coatings with both antibacterial and osteogenic features. To this end, we developed ultrathin Layer-by-Layer (LbL) coatings composed of biocompatible polyelectrolytes, namely chondroitin sulfate A (CSA) and poly-l-lysine (PLL). The coatings were crosslinked with genipin (GnP), a natural and biocompatible crosslinking agent, to increase their resistance against environmental changes, and to confer them adequate mechanical properties with regards to bone cell behaviors. Antibacterial activity was obtained with nisin Z, an antimicrobial peptide (AMP), which is active against gram-positive bacteria. The coatings had a significant bactericidal impact upon Staphylococcus aureus, with fully maintained bone cell adhesion, proliferation and osteogenic differentiation.

Pre-formulation and delivery strategies for the development of bacteriocins as next generation antibiotics

Bacteriocins, a class of antimicrobial peptide produced by bacteria, may offer a potential alternative to traditional antibiotics, an important step towards mitigating the ever-increasing antimicrobial resistance crisis. They are active against a range of clinically relevant Gram-positive and Gram-negative bacteria. Bacteriocins have been discussed in the literature for over a century. Although they are used as preservatives in food, no medicine based on their antimicrobial activity exists on the market today. In order to formulate them into clinical antibiotics, pre-formulation studies on their biophysical and physicochemical properties that will influence their activity in vivo and their stability during manufacture must be elucidated. Thermal, pH and enzymatic stability of bacteriocins are commonly studied and regularly reported in the literature. Solubility, permeability and aggregation properties on the other hand are less frequently reported for many bacteriocins, which may contribute to their poor clinical progression. Promising cytotoxicity studies report that bacteriocins exhibit few cytotoxic effects on a variety of mammalian cell lines, at active concentrations. This review highlights the lack of quantitative data and in many cases even qualitative data, on bacteriocins' solubility, stability, aggregation, permeability and cytotoxicity. The formulation strategies that have been explored to date, proposed routes of administration, trends in in vitro/in vivo behaviour and efforts in clinical development are discussed. The future promise of bacteriocins as a new generation of antibiotics may require tailored local delivery strategies to fulfil their potential as a force to combat antimicrobial-resistant bacterial infections.

Influence of Gallic Acid and Thai Culinary Essential Oils on Antibacterial Activity of Nisin against Streptococcus mutans

Streptococcus mutans is a well-known oral pathogen commonly associated with a normal dental problem and life-threatening infection. A bacteriocin nisin and the plant-derived compounds including gallic acid (GA) and Thai culinary essential oils (EOs) have been reported to have activity against oral pathogens. However, their synergistic interaction against S. mutans has not been explored. The purposes of this study were primarily to investigate anti-S. mutans properties and the antibiofilm formation of nisin, GA, and five EOs by using the broth microdilution method. Besides, the morphological change, killing rate, and antibacterial synergism were determined by scanning electron microscopy (SEM), time-kill assay, and checkerboard method, respectively. The results demonstrated that kaffir lime leaf (KLL) oil, lemongrass (LG) oil, and GA showed a potent anti-S. mutans activity and inhibited biofilm formation with the possible mechanism targeted on the cell membrane. Additionally, KLL oil revealed anti-S. mutans synergism with GA, LG oil, and chlorhexidine with the fractional inhibitory concentration (FIC) indexes ≤ 0.5. Interestingly, GA displayed a high potential to enhance anti-S. mutans activity of nisin by lowering the minimum inhibitory concentrations (MICs) to at least 8-fold in a bacteriostatic manner. These results suggest that GA and KLL oil may be potentially used as an adjunctive therapy along with nisin and chlorhexidine to control S. mutans infection.

Elaboration and characterization of curcumin-loaded soy soluble polysaccharide (SSPS)-based nanocarriers mediated by antimicrobial peptide nisin

Curcumin was recently attracted great interest owing to its multiple bioactivities; however, the use of curcumin was hindered by its poor solubility and stability. In this study, curcumin-nisin-soy soluble polysaccharide nanoparticles (Cur-Nisin-SSPS-NPs, size = 118.76 nm) have been successfully elaborated to improve the application of curcumin. The formation of Cur-Nisin-SSPS-NPs was mediated by amphiphilic and positively charged nisin: SSPS encapsulated nisin, which was mainly driven by electrostatic attraction. And nisin-SSPS complex encapsulated curcumin mainly through hydrophobic interactions between nisin and curcumin. The encapsulation efficiency of curcumin (91.66%) in this novel nanocarriers was significantly higher than that in nanoparticles prepared by a single SSPS (31.82%) or nisin (41.69%), most likely because more hydrophobic regions of nisin were exposed after interacting with SSPS through electrostatic interaction. Consequently, this facile and green nanocarriers improved the solubility/dispersibility and stability of curcumin and nisin, as well as endowed SSPS-based nanoparticles with antioxidant and antimicrobial activities.

Isolation, Characterization and Structure Elucidation of a Novel Lantibiotic From Paenibacillus sp

We have isolated and characterized a novel antibacterial peptide, CMB001, following an extensive screening effort of bacterial species isolated from diverse environmental sources. The bacterium that produces CMB001 is characterized as a Gram (+) bacillus sharing approximately 98.9% 16S rRNA sequence homology with its closest match, Paenibacillus kyungheensis. The molecule has been purified to homogeneity from its cell-free supernatant by a three-step preparative chromatography process. Based on its primary structure, CMB001 shares 81% identity with subtilin and 62% with nisin. CMB001 is active mainly against Gram-positive bacteria and Mycobacteriaceae but it is also active against certain Gram-negative bacteria, including multi-drug resistant Acinetobacter baumannii. It retains full antibacterial activity at neutral pH and displays a low propensity to select for resistance among targeted bacteria. Based on NMR and mass spectrometry, CMB001 forms a unique 3D-structure comprising of a compact backbone with one α-helix and two pseudo-α-helical regions. Screening the structure against the Protein Data Bank (PDB) revealed a partial match with nisin-lipid II (1WCO), but none of the lantibiotics with known structures showed significant structural similarity. Due to its unique structure, resistance profile, relatively broad spectrum and stability under physiological conditions, CMB001 is a promising drug candidate for evaluation in animal models of bacterial infection.

Efficacy of nisin derivatives with improved biochemical characteristics, alone and in combination with endolysin PlyP100 to control Listeria monocytogenes in laboratory-scale Queso Fresco

Nisin is an antimicrobial peptide that is commonly used as a food preservative and capable of inhibiting the pathogen Listeria monocytogenes. However, nisin is ineffective in controlling L. monocytogenes in Queso Fresco (QF). To address the challenge, in this work, we used synthetic biology strategies to create a series of nisin A derivatives by substituting residues 27, 30, 31 and 32 with positively charged amino acids (H, K and R). Our results showed that nisin derivatives exhibited reduced antilisterial activity in vitro compared to nisin A; however, they were all more stable under QF-like experimental conditions (pH 7 + 22% milk fat), notably H27/31K. Compared to nisin A, the derivatives H31K and V32K exhibited slight antilisterial improvement in QF and H27/31K was able to reduce the initial population of L. monocytogenes by up to 1.5 Log CFU/g. L. monocytogenes isolates exhibited similar susceptibility to nisin A or H27/31K after 7 or 14 days of nisin exposure in QF. Notably, when combined with endolysin PlyP100, the application of H27/31K resulted in non-enumerable levels of L. monocytogenes after 14 days of cold storage. Our results highlight the potential of bioengineered nisin derivatives for stabilized and enhanced control of L. monocytogenes in QF.

Nevertheless, She Resisted - Role of the Environment on Listeria monocytogenes Sensitivity to Nisin Treatment in a Laboratory Cheese Model

The growth of Listeria monocytogenes on refrigerated, ready-to-eat food products is a major health and economic concern. The natural antimicrobial nisin targets the bacterial cell wall and can be used to inhibit L. monocytogenes growth on cheese. Cell wall composition and structure, and therefore the efficacy of cell wall acting control strategies, can be severely affected by environmental and stress conditions. The goal of this study was to determine the effect of a range of pH and temperatures on the efficacy of nisin against several strains of L. monocytogenes in a lab-scale, cheese model. Cheese was made with or without the addition of nisin at different pH and then inoculated with L. monocytogenes; L. monocytogenes numbers were quantified after 1, 7, and 14 days of incubation at 6, 14, or 22°C. While our data show that nisin treatment is able to reduce L. monocytogenes numbers, at least initially, growth of this pathogen can occur even in the presence of nisin, especially when cheese is stored at higher temperatures. Several environmental factors were found to affect nisin efficacy against L. monocytogenes. For example, nisin is more effective when cheese is stored at lower temperatures. Nisin is also more effective when cheese is made at higher pH (6 and 6.5), compared to cheese made at pH 5.5, and this effect is at least partially due to the activity of cell envelope modification genes dltA and mprF. Serotype was also found to affect nisin efficacy against L. monocytogenes; serotype 4b strains showed lower susceptibility to nisin treatment compared to serotype 1/2 strains. Overall, our results highlight the importance of considering environmental conditions specific to a food matrix when developing and applying nisin-based intervention strategies against L. monocytogenes.

Effect of the addition of microcapsules with avocado peel extract and nisin on the quality of ground beef

This study evaluated the incorporation of microcapsules containing nisin and avocado peel extract on the shelf life of ground beef. Ten treatments were studied and divided into two groups: one packaged under vacuum and the other in permeable packaging. Each group contained: (a) control, (b) extract, (c) nisin, (d) empty microcapsules (only wall microcapsule system), and (e) microcapsules with extract and nisin. The samples containing the microcapsules presented lower bacterial growth and less oxidation. On day 10, the vacuum-packaged samples with microencapsulated preservative presented a reduction in the oxidation of proteins of approximately 45%, of 30% in the growth of mesophiles, and of 38% in the growth of coliforms, as well as a reduction in the changes in the pH and ɑ W that occur during storage, compared with the permeable control. The combination of microcapsules with vacuum packaging reduced the physicochemical and microbiological changes that occur in the controls.

Invited review: Advances in nisin use for preservation of dairy products

Dairy product safety is a global public health issue that demands new approaches and technologies to control foodborne pathogenic microorganisms. Natural antimicrobial agents such as nisin can be added to control the growth of pathogens of concern in dairy foods, namely Listeria monocytogenes and Staphylococcus aureus. However, several factors affect the antimicrobial efficacy of nisin when directly added into the food matrix such as lack of stability at neutral pH, interaction with fat globules, casein, and divalent cations. To overcome these limitations, new and advanced strategies are discussed including nisin encapsulation technology, addition to active packaging, bioengineering, and combination with other antimicrobials. This review highlights advanced technologies with potential to expand and improve the use of nisin as a dairy preservative.

Nisin/polyanion layer-by-layer films exhibiting different mechanisms in antimicrobial efficacy

Nisin/polyanion Layer-by-Layer (LbL) films are reported to exhibit different mechanisms in antimicrobial efficacy depending on the type of polyanion. LbL films consisting of nisin as the polycationic component were prepared using two different polyanionic constituents: poly acrylic acid (PAA) and dextran sulfate (DX). Due to the weaker interaction strength of carboxylate groups with nisin compared to sulfate/nisin, a larger molecular weight of PAA was needed to achieve LbL assembly. PAA-100K/nisin and DX-15K/nisin multilayer films exhibited significantly different properties. PAA–nisin films grew faster compared to DX–nisin films and showed, for 60 bilayer films, an average bilayer thickness of 21.6 nm compared to that of 6.1 nm in DX–nisin films. The total amount of nisin was found to be 17.1 ± 2.2 μg cm⁻² in (PAA–nisin)₆₀ and 6.8 ± 0.4 μg cm⁻² in (DX–nisin)₆₀ films. The stability of the films was investigated at three different pH values of 6.0, 7.4 and 9.5. (PAA–nisin)₆₀ films exhibited the release of nisin into the solution which resulted in the disintegration of the film over several hours. A burst release was observed in the first hour followed by a slower release and disintegration over 24 hours with a complete release at pH 9.5. The bacterial growth inhibition test against Staphylococcus epidermidis confirmed the antimicrobial activity of nisin released from PAA–nisin films. PAA was found to stabilize nisin and the film-released nisin retained its antimicrobial activity in the neutral and alkaline pH values. Unlike PAA–nisin films, (DX–nisin)₆₀ films were stable at the physiological conditions up to 14 days with no release of nisin. DX–nisin films were found to inhibit the attachment of Staphylococcus epidermidis and prevent biofilm formation. These results clearly demonstrate the effect of different polyanions on nisin LbL films to achieve different mechanisms in antimicrobial efficacy and show the potential of PAA–nisin multilayer films as promising local delivery systems for treatment of burns and wounds, while DX–nisin multilayer films can be employed as stable coatings against bacterial attachment and biofilm formation.

Polyanion–nisin multilayer films exhibit antimicrobial activity by controlled release of nisin or as stable biofilm inhibiting coatings depending on polyanion.

Antioxidants versus Food Antioxidant Additives and Food Preservatives

Natural and processed foods are fragile and can become unpalatable and/or rotten. The processed food industry uses preservatives to enable distribution, even to different continents, and to extend the useful life of their products. Preservatives impede oxidation, a mandatory step in rotting, either by aerobic or anaerobic mechanisms. From a functional point of view, these compounds are antioxidants, and, therefore, a kind of contradiction exists when a preservative is considered “bad” for human health while also thinking that antioxidants provide benefits. The basis of antioxidant action, the doses required for preservation, and the overall antioxidant action are revisited in this work. Finally, the bad and the good of food additives/preservatives are presented, taking into account the main mediator of antioxidant beneficial actions, namely the innate mechanisms of detoxification. Foods that strengthen such innate mechanisms are also presented.

Kinetics of interaction between antimicrobial peptide nisin and Langmuir monolayers of DPPC and DPPG molecules

We have studied the kinetics of the interaction between antimicrobial peptide nisin and Langmuir monolayers of phospholipids DPPC and DPPG at the air-water interface using the surface manometry technique. The charge on the nisin and the lipid molecules is controlled by varying the pH of the subphase, and the interactions between them are studied by measuring the surface pressure of the lipid monolayer as a function of time after injecting the nisin in the subphase. A model based on the diffusion of particles under the influence of a constant force is developed to obtain an analytical expression for surface pressure as a function of time. The expression was found to fit well with the experimental data. The average hydrodynamic radius and the translational diffusion constant of the nisin molecules are calculated from the fit parameters for the different subphase pH solutions.

Interaction of the antibiotic peptide nisin with anionic membranes in different phase-states: a vibrational study

Interactions between the antibiotic peptide nisin and multilamellar vesicles of phosphoglycerol lipids in different phase-states were studied using vibrational spectroscopy. The infrared amide I' band of nisin, both in solution and in the membrane-bound state, was analyzed in the temperature range comprised between 20 and 60 °C in order to study its conformational behavior. Nisin presented mainly unordered and β-turns conformations. Their relative populations varied according to the environment and as the temperature increased: β turns were more favored in the membrane-bound state than in solution, but at higher temperatures the disordered conformation was dominant in both states. Spectral changes of specific infrared bands belonging to the hydrocarbon and polar moieties of lipids were also analyzed to evaluate the perturbation of the lipid membrane order. Nisin interactions with the membrane polar region induced a high restriction to water incorporation, promoting a small increase in the temperature of the lipid phase transition. Raman spectra of nisin/phosphoglycerol systems at ambient temperature were also analyzed. They revealed that the peptide incorporation to a membrane in the fluid phase caused drastic structural modifications in the hydrophobic region of the bilayer. Although nisin may be able to disrupt the hydrophobic portion of the bilayer in the gel phase, the most of the peptide molecule remained at the membrane surface interacting with the polar headgroups. This work provides evidence of a differential effect of nisin on anionic membranes, depending on the phase-state of the lipid.

Sequence-based analysis and prediction of lantibiotics: A machine learning approach

Lantibiotics, an important group of ribosomally synthesized peptides, represent an important arsenal of novel promising antimicrobials showing high potency in fighting against the prevalence of antibiotic resistance among microbial pathogens. However, due to the lack of high throughput strategies for the isolation and identification of these compounds, our information regarding their structure and especially sequence-based properties is far from complete. Therefore, in the present study, a comprehensive sequence-based analysis of these peptides was performed with the help of machine learning approach together with a feature selection technique. Meanwhile, an attempt to develop an accurate computational model for prediction of lantibiotics was made via constructing two datasets of 280 and 190 lantibiotic and non-lantibiotic antimicrobial peptide sequences, respectively. Based on the conducted approach and as a result of our search for a subset of relevant features of lantibiotics, particular types of sequenced-based features were observed to be preferred in lantibiotics, the knowledge-based implementation of which can be used as strategies for lantibiotic bioengineering purposes. Moreover, a SMO-based classifier was developed for the prediction of lantibiotics with the accuracy and specificity values of 88.5% and 94%, respectively which shows the great potential of the developed algorithm for the prediction of lantibiotcs. Conclusively, the accurate predictor algorithm as well as the identified sequence-based distinctiveness properties of lantibiotics can give valuable information in both the fields of lantibiotic discovery and bioengineering.