Natural approach of using nisin and its nanoform as food bio-preservatives against methicillin resistant Staphylococcus aureus and E.coli O157:H7 in yoghurt.

BACKGROUND: Natural antimicrobial agents such as nisin were used to control the growth of foodborne pathogens in dairy products. The current study aimed to examine the inhibitory effect of pure nisin and nisin nanoparticles (nisin NPs) against methicillin resistant Staphylococcus aureus (MRSA) and E.coli O157:H7 during the manufacturing and storage of yoghurt. Nisin NPs were prepared using new, natural, and safe nano-precipitation method by acetic acid. The prepared NPs were characterized using zeta-sizer and transmission electron microscopy (TEM). In addition, the cytotoxicity of nisin NPs on vero cells was assessed using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The minimum inhibitory concentrations (MICs) of nisin and its nanoparticles were determined using agar well-diffusion method. Further, fresh buffalo's milk was inoculated with MRSA or E.coli O157:H7 (1 × 106 CFU/ml) with the addition of either nisin or nisin NPs, and then the inoculated milk was used for yoghurt making. The organoleptic properties, pH and bacterial load of the obtained yoghurt were evaluated during storage in comparison to control group. RESULTS: The obtained results showed a strong antibacterial activity of nisin NPs (0.125 mg/mL) against MRSA and E.coli O157:H7 in comparison with control and pure nisin groups. Notably, complete eradication of MRSA and E.coli O157:H7 was observed in yoghurt formulated with nisin NPs after 24 h and 5th day of storage, respectively. The shelf life of yoghurt inoculated with nisin nanoparticles was extended than those manufactured without addition of such nanoparticles. CONCLUSIONS: Overall, the present study indicated that the addition of nisin NPs during processing of yoghurt could be a useful tool for food preservation against MRSA and E.coli O157:H7 in dairy industry.

Assessing the synergistic potential of bacteriophage endolysins and antimicrobial peptides for eradicating bacterial biofilms.

Phage-encoded endolysins have emerged as a potential substitute to conventional antibiotics due to their exceptional benefits including host specificity, rapid host killing, least risk of resistance. In addition to their antibacterial potency and biofilm eradication properties, endolysins are reported to exhibit synergism with other antimicrobial agents. In this study, the synergistic potency of endolysins was dissected with antimicrobial peptides to enhance their therapeutic effectiveness. Recombinantly expressed and purified bacteriophage endolysin [T7 endolysin (T7L); and T4 endolysin (T4L)] proteins have been used to evaluate the broad-spectrum antibacterial efficacy using different bacterial strains. Antibacterial/biofilm eradication studies were performed in combination with different antimicrobial peptides (AMPs) such as colistin, nisin, and polymyxin B (PMB) to assess the endolysin's antimicrobial efficacy and their synergy with AMPs. In combination with T7L, polymyxin B and colistin effectively eradicated the biofilm of Pseudomonas aeruginosa and exhibited a synergistic effect. Further, a combination of T4L and nisin displayed a synergistic effect against Staphylococcus aureus biofilms. In summary, the obtained results endorse the theme of combinational therapy consisting of endolysins and AMPs as an effective remedy against the drug-resistant bacterial biofilms that are a serious concern in healthcare settings.

Sensitivity of Salmonella Typhimurium to nisin in vitro and in orange juice under refrigeration.

The influence of environmental factors on Salmonella sensitivity to nisin in vitro and in refrigerated orange juice were investigated. Nisin activity was observed in the different conditions, but the highest efficiency was achieved at lower pH (4.0) and with higher bacteriocin concentration (174 µM). Moreover, the bactericidal action was directly proportional to the incubation period. When tested in orange juice, nisin caused a reduction of up to 4.05 logarithm cycles in the Salmonella population. So, environmental factors such as low pH and low temperature favored the sensitization of Salmonella cells to the bactericidal action of nisin. Therefore, this may represent an alternative to control Salmonella in refrigerated foods.

Comparison of fidaxomicin, thuricin CD, vancomycin and nisin highlights the narrow spectrum nature of thuricin CD.

Vancomycin and metronidazole are commonly used treatments for Clostridioides difficile infection (CDI). However, these antibiotics have been associated with high levels of relapse in patients. Fidaxomicin is a new treatment for CDI that is described as a narrow spectrum antibiotic that is minimally active on the commensal bacteria of the gut microbiome. The aim of this study was to compare the effect of fidaxomicin on the human gut microbiome with a number of narrow (thuricin CD) and broad spectrum (vancomycin and nisin) antimicrobials. The spectrum of activity of each antimicrobial was tested against 47 bacterial strains by well-diffusion assay. Minimum inhibitory concentrations (MICs) were calculated against a select number of these strains. Further, a pooled fecal slurry of 6 donors was prepared and incubated for 24 h with 100 µM of each antimicrobial in a mini-fermentation system together with a no-treatment control. Fidaxomicin, vancomycin, and nisin were active against most gram positive bacteria tested in vitro, although fidaxomicin and vancomycin produced larger zones of inhibition compared to nisin. In contrast, the antimicrobial activity of thuricin CD was specific to C. difficile and some Bacillus spp. The MICs showed similar results. Thuricin CD exhibited low MICs (<3.1 µg/mL) for C. difficile and Bacillus firmus, whereas fidaxomicin, vancomycin, and nisin demonstrated lower MICs for all other strains tested when compared to thuricin CD. The narrow spectrum of thuricin CD was also observed in the gut model system. We conclude that the spectrum of activity of fidaxomicin is comparable to that of the broad-spectrum antibiotic vancomycin in vitro and the broad spectrum bacteriocin nisin in a complex community.

In Bacterial Membranes Lipid II Changes the Stability of Pores Formed by the Antimicrobial Peptide Nisin.

Resistance to available antibiotics poses a growing challenge to modern medicine, as this often disallows infections to be controlled. This problem can only be alleviated by the development of new drugs. Nisin, a natural lantibiotic with broad antimicrobial activity, has shown promise as a potential candidate for combating antibiotic-resistant bacteria. However, nisin is poorly soluble and barely stable at physiological pH, which despite attempts to address these issues through mutant design has restricted its use as an antibacterial drug. Therefore, gaining a deeper understanding of the antimicrobial effectiveness, which relies in part on its ability to form pores, is crucial for finding innovative ways to manage infections caused by resistant bacteria. Using large-scale molecular dynamics simulations, we find that the bacterial membrane-specific lipid II increases the stability of pores formed by nisin and that the interplay of nisin and lipid II reduces the overall integrity of bacterial membranes by changing the local thickness and viscosity.

Milk-derived antimicrobial peptides incorporated whey protein film as active coating to improve microbial stability of refrigerated soft cheese.

Nisin is the first FDA-approved antimicrobial peptide and shows significant antimicrobial activity against Gram-positive bacteria, but only a weakly inhibitory effect on Gram-negative bacteria. The aim of this study was to prepare whey protein-based edible films with the incorporation of milk-derived antimicrobial peptides (αs2-casein151-181 and αs2-casein182-207) and compare their mechanical properties and potential application in cheese packaging with films containing nisin. These two antimicrobial peptides showed similar activity against B. subtilis and much higher activity against E. coli than bacteriocin nisin, representing that these milk-derived peptides had great potential to be applied as food preservatives. Antimicrobial peptides in whey protein films caused an increase in film opaqueness and water vapor barrier properties but decreased the tensile strength and elongation at break. Compared to other films, the whey protein film containing αs2-casein151-181 had good stability in salt or acidic solution, as evidenced by the results from scanning electron microscope and Fourier transform infrared spectroscopy. Whey protein film incorporated with αs2-casein151-181 could inhibit the growth of yeasts and molds, and control the growth of psychrotrophic bacteria present originally in the soft cheese at refrigerated temperature. It also exhibited significant inhibitory activity against the development of mixed culture (E. coli and B. subtilis) in the cheese due to superficial contamination during storage. Antimicrobial peptides immobilized in whey protein films showed a higher effectiveness than their direct application in solution. In addition, films containing αs2-casein151-181 could act as a hurdle inhibiting the development of postprocessing contamination on the cheese surface during the 28 days of storage. The films in this study exhibited the characteristics desired for active packaging materials.

Comparison of controlling capabilities of lactobionic acid, nisin, and K-Sorbate against dairy-borne Staphylococcus aureus, Escherichia coli, and mold in soft cheese.

Background: The utilization of chemical preservatives holds the promise of effectively controlling microbial growth in soft cheese. Aim: The first trial aimed to compare the effectiveness of lactobionic acid (LBA) and K-Sorbate in controlling the proliferation of Staphylococcus aureus, Escherichia coli, and mold in white soft cheese. The subsequent part of the study explored the inhibitory effects of K-Sorbate, nisin, and LBA on mold populations in cheese whey. Methods: Two sets of soft cheese were produced. One set was contaminated with S. aureus, while the other was with E. coli, each at concentrations of 1 log CFU/ml and 1 log CFU/100 ml. Different concentrations of LBA were incorporated into these sets of cheese. Similar cheese samples were treated with K-Sorbate. For the subsequent part of the study, it was manufactured and divided into groups that inoculated with LBA with different concentrations, K-Sorbate, and nisin. Results: With higher S. aureus inoculation, by day 18, the positive control exhibited growth exceeding 5 log CFU/g. In contrast, the LBA treatment dropped below limit of detection (LOD) and K-Sorbate yielded 4.8 log CFU/g. While with lower S. aureus inoculation, the positive control reached log CFU/g, while LBA treatment fell below LOD by day 14, and K-Sorbate reached 2.9 log CFU/g. For E. coli inoculation, with higher concentrations, by day 18, the positive control exceeded 5 log CFU/g. Conversely, LBA treatment greatly decreased and K-Sorbate treatment measured 5.1 log CFU/g. With lower E. coli concentrations, the positive control surpassed 3 log CFU/g, yet LBA treatment dropped below LOD by day 3. Mold counts indicated some inhibition with the K-Sorbate treatment, while control groups showed growth. LBA treatments exhibit noticeable growth inhibition. About the other part of the study, the outcomes demonstrated that while growth of mold occurred in the control group, inhibitory effects were apparent in the treatment groups, and significant distinctions existed between K-Sorbate, nisin, LBA treatments, and the control group. Conclusion: Our findings suggest that LBA has the potential to effectively control the growth of E. coli, S. aureus, and mold in soft cheese. Moreover, LBA displays greater preservative efficacy compared to K-Sorbate and nisin.

Bacterial nanocellulose loaded with bromelain and nisin as a promising bioactive material for wound debridement.

The bacterial nanocellulose (BnC) membranes were produced extracellularly by a novel aerobic acetic acid bacterium Komagataeibacter melomenusus. The BnC was modified in situ by adding carboxymethyl cellulose (CMC) into the culture media, obtaining a BnC-CMC product with denser fibril arrangement, improved rehydration ratio and elasticity in comparison to BnC. The proteolytic enzyme bromelain (Br) and antimicrobial peptide nisin (N) were immobilized to BnC matrix by ex situ covalent binding and/or adsorption. The optimal Br immobilization conditions towards the maximized specific proteolytic activity were investigated by response surface methodology as factor variables. At optimal conditions, i.e., 8.8 mg/mL CMC and 10 mg/mL Br, hyperactivation of the enzyme was achieved, leading to the specific proteolytic activity of 2.3 U/mg and immobilization efficiency of 39.1 %. The antimicrobial activity was observed against Gram-positive bacteria (S. epidermidis, S. aureus and E. faecalis) for membranes with immobilized N and was superior when in situ modified BnC membranes were used. N immobilized on the BnC or BnC-CMC membranes was cytocompatible and did not cause changes in normal human dermal fibroblast cell morphology. BnC membranes perform as an efficient carrier for Br or N immobilization, holding promise in wound debridement and providing antimicrobial action against Gram-positive bacteria, respectively.

Nisin variants: What makes them different and unique?

Nisin A is a lantibiotic bacteriocin typically produced by strains of Lactococcus lactis. This bacteriocin has been approved as a natural food preservative since the late 1980 s and shows antimicrobial activity against a range of food-borne spoilage and pathogenic microorganisms. The therapeutic potential of nisin A has also been explored increasingly both in human and veterinary medicine. Nisin has been shown to be effective in treating bovine mastitis, dental caries, cancer, and skin infections. Recently, it was demonstrated that nisin has an affinity for the same receptor used by SARS-CoV-2 to enter human cells and was proposed as a blocker of the viral infection. Several nisin variants produced by distinct bacterial strains or modified by bioengineering have been described since the discovery of nisin A. These variants present modifications in the peptide structure, biosynthesis, mode of action, and spectrum of activity. Given the importance of nisin for industrial and therapeutic applications, the objective of this study was to describe the characteristics of the nisin variants, highlighting the main differences between these molecules and their potential applications. This review will be useful to researchers interested in studying the specifics of nisin A and its variants.

Preparation of modified chitosan-based nano-TiO2-nisin composite packaging film and preservation mechanism applied to chilled pork.

Here, we developed a nano-TiO2-nisin-modified chitosan composite packaging film and investigated its properties and antibacterial activity, as well as its effect on chilled pork preservation time. The results indicated that the preservation time of chilled pork coated with a nano-TiO2-nisin-modified chitosan film (including 0.7 g/L nano-TiO2, irradiated with ultraviolet light for 40 min, and dried for 6 h) followed by modified atmosphere packaging (50% CO2 + 50% N2) increased from 7 to 20 days at 4 °C. Both nano-TiO2 and nisin enhanced the mechanical strength of the chitosan film, and nisin promoted nano-TiO2 dispersion and compatibility in chitosan. Treatment with 0.4 g/L nano-TiO2 for 60 min considerably inhibited spoilage bacteria, particularly Acinetobacter johnnii XBB1 (A. johnnii XBB1). As nano-TiO2 concentration and photocatalytic time increased, K+, Ca2+, and Mg2+ leakage in A. johnnii XBB1 increased but Na+/K+-ATPase and Ca2+/Mg2+-ATPase activities decreased. In A. johnnii XBB1, TiO2 significantly downregulated the expression of putrefaction-related genes such as cysM and inhibited cell self-regulation and membrane wall system repair. Therefore, our nano-TiO2-nisin-modified chitosan film could extend the shelf life without the addition of any chemical preservatives, demonstrating great potential for application in food preservation.

Suppression of planktonic and biofilm of Escherichia coli by the synergistic lantibiotics-polymyxins combinations.

Escherichia coli are generally resistant to the lantibiotic's action (nisin and warnerin), but we have shown increased sensitivity of E. coli to lantibiotics in the presence of subinhibitory concentrations of polymyxins. Synergistic lantibiotic-polymyxin combinations were found for polymyxins B and M. The killing of cells at the planktonic and biofilm levels was observed for two collection and four clinical multidrug-resistant E. coli strains after treatment with lantibiotic-polymyxin B combinations. Thus, 24-h treatment of E. coli mature biofilms with warnerin-polymyxin B or nisin-polymyxin B leads to five to tenfold decrease in the number of viable cells, depending on the strain. AFM revealed that the warnerin and polymyxin B combination caused the loss of the structural integrity of biofilm and the destruction of cells within the biofilm. It has been shown that pretreatment of cells with polymyxin B leads to an increase of Ca2+ and Mg2+ ions in the culture medium, as detected by atomic absorption spectroscopy. The subsequent exposure to warnerin caused cell death with the loss of K+ ions and cell destruction with DNA and protein release. Thus, polymyxins display synergy with lantibiotics against planktonic and biofilm cells of E. coli, and can be used to overcome the resistance of Gram-negative bacteria to lantibiotics.

Potential diagnostic and drug target markers in glioblastoma.

Glioblastoma multiforme (GBM) IDH-wildtype is the most prevalent brain malignancy in adults. However, molecular mechanisms, which leads to GBM have not been completely elucidated. Granulocyte colony-stimulating factor (GCSF), Granulocyte colony-stimulating factor receptor GCSFR, and Signal transducers and activators of transcription 3 (STAT3) have been involved in the occurrence and development of various cancers, but their role in GBM is little known. Herein, we have investigated the gene and protein expression of GCSF, GCSFR, and STAT3 in 21 tissue biopsy samples and also in tumor associated normal tissue (TANT) samples derived from glioblastoma patients, which revealed significantly differential expression of these genes. To validate our findings, we performed a comprehensive integrated analysis of transcriptomic and proteomic profiling of respective genes by retrieving GBM RNA-sequence data from Genome Atlas Databases. GO and KEGG analysis revealed enrichment in disease-related pathways, such as JAK/STAT pathway activation, which were associated with GBM progression. We further performed computational docking analysis of potential drug candidate Nisin against GCSF, and the results were validated in vitro through cytotoxic activity assay using a human glioblastoma cell line SF-767 in a dose-dependent manner. Our comprehensive analysis reveals that GCSF augments glioma progression, and its blockade with anticancer bacteriocin peptide Nisin can potentially inhibit the growth and metastasis of GBM.

Facile fabrication of microfibrillated cellulose-based aerogels incorporated with nisin/ß-cyclodextrin microcapsule for channel catfish preservation.

In this study, a hydrophobic and antibacterial pad was prepared to preserve Channel Catfish (Ictalurus punctatus). The pad composite the microfibrillated cellulose and ß-cyclodextrin/nisin microcapsules. The hydrophobic pad ensures a dry surface in contact with the fish, reducing microbial contamination. The pad has a low density and high porosity, making it lightweight and suitable for packaging applications, while also providing a large surface area for antibacterial activity. Results demonstrated that this antibacterial pad exhibits an ultralow density of 9.0 mg/cm3 and an ultrahigh porosity of 99.10%. It can extend the shelf life of Channel Catfish fillets to 9 days at 4 °C, with a total volatile base nitrogen below 20 mg/100 g. The study proposes a novel solution for preserving aquatic products by combining antibacterial substances with the natural base material aerogel. This approach also extends the utilization of aerogel and nisin in food packaging.

Bacteriostasis of nisin against planktonic and biofilm bacteria: Its mechanism and application.

Food safety incidents caused by bacterial contamination have always been one of the public safety issues of social concern. Planktonic cells, viable but non-culturable (VBNC) cells, and biofilm cells of bacteria can coexist in food or food processing, posing more serious challenges to public health and safety by increasing bacterial survival and difficulty in detection. As a non-toxic, no side effect, and highly effective bacteriostatic substance, nisin has received wide attention from researchers. In this review, we summarized the species and biosynthesis of nisin, the effects of nisin alone or in combination with other treatments on planktonic and biofilm cells, and its applications in the fields of food, feed, and medicine by consulting numerous studies. Meanwhile, the mechanism of nisin on planktonic and biofilm cells was proposed based on existing researches. Nisin not only has antibacterial activity against most G+ bacteria but also exhibits a bacteriostatic effect on G- bacteria when combined with other antibacterial treatments. In addition to planktonic cells, nisin also has significant effects on bacterial cells in biofilms by changing the thickness, density, and composition of biofilms. Based on the three action processes of nisin on biofilms, we summarized the changes of bacteria in biofilms, including the causes of bacterial death and the formation of the VBNC state. We consider that research on the relationship between nisin and VBNC state should be strengthened.

Effect of Fermented Milk Supplemented with Nisin or Plantaricin Q7 on Inflammatory Factors and Gut Microbiota in Mice.

Lactic-acid-bacteria-derived bacteriocins are used as food biological preservatives widely. Little information is available on the impact of bacteriocin intake with food on gut microbiota in vivo. In this study, the effects of fermented milk supplemented with nisin (FM-nisin) or plantaricin Q7 (FM-Q7) from Lactiplantibacillus plantarum Q7 on inflammatory factors and the gut microbiota of mice were investigated. The results showed that FM-nisin or FM-Q7 up-regulated IFN-γ and down-regulated IL-17 and IL-12 in serum significantly. FM-nisin down-regulated TNF-α and IL-10 while FM-Q7 up-regulated them. The results of 16S rRNA gene sequence analysis suggested that the gut microbiome in mice was changed by FM-nisin or FM-Q7. The Firmicutes/Bacteroides ratio was reduced significantly in both groups. It was observed that the volume of Akkermansia_Muciniphila was significantly reduced whereas those of Lachnospiraceae and Ruminococcaceae were increased. The total number of short-chain fatty acids (SCFAs) in the mouse feces of the FM-nisin group and FM-Q7 group was increased. The content of acetic acid was increased while the butyric acid content was decreased significantly. These findings indicated that FM-nisin or FM-Q7 could stimulate the inflammation response and alter gut microbiota and metabolic components in mice. Further in-depth study is needed to determine the impact of FM-nisin or FM-Q7 on the host's health.

Preparation and characterization of nisin-loaded chitosan nanoparticles functionalized with DNase I for the removal of Listeria monocytogenes biofilms.

Listeria monocytogenes biofilms represent a continuous source of contamination, leading to serious food safety concerns and economic losses. This study aims to develop novel nisin-loaded chitosan nanoparticles (CSNPs) functionalized with DNase I and evaluate its antibiofilm activity against L. monocytogenes on food contact surfaces. Nisin-loaded CSNPs (CS-N) were first prepared by ionic cross-linking, and DNase I was covalently grafted on the surface (DNase-CS-N). The NPs were subsequently characterized by Zetasizer Nano, transmission electron microscopy, Fourier transform infrared (FT-IR), and X-ray diffraction (XRD). The antibiofilm activity of NPs was evaluated against L. monocytogenes on polyurethane (PU). The DNase-CS-N was fabricated and characterized with quality attributes (particle size-427.0 ± 15.1 nm, polydispersity [PDI]-0.114 ± 0.034, zeta potential-+52.5 ± 0.2 mV, encapsulation efficiency-46.5% ± 3.6%, DNase conjugate rate-70.4% ± 0.2). FT-IR and XRD verified the loading of nisin and binding of DNase I with chitosan. The DNase-CS-N caused a 3 log colony-forming unit (CFU)/cm2 reduction of L. monocytogenes biofilm cells, significantly higher than those in CSNPs (1.4 log), CS-N (1.8 log), and CS-N in combination with DNase I (2.2 log) treatment groups. In conclusion, nisin-loaded CSNPs functionalized with DNase I were successfully prepared and characterized with smooth surface and nearly spherical shape, high surface positive charge, and good stability, which is effective to eradicate L. monocytogenes biofilm cells on food contact surfaces, exhibiting great potential as antibiofilm agents in food industry. PRACTICAL APPLICATION: Listeria monocytogenes biofilms are a common safety hazard in food processing. In this study, novel nanoparticles were successfully constructed and are expected to be a promising antibiofilm agent in the food industry.

Engineering hybrid lantibiotics yields the highly stable and bacteriocidal peptide cerocin V.

Antimicrobial peptides (AMPs) show promise as alternatives to traditional antibiotics for treating drug-resistant infections. Their adaptability and diverse sequence possibilities allow for rational design by modulating physicochemical determinants to achieve desired biological properties, transforming them into peptides for potential new therapies. Nisin, one of the best-studied AMPs, is believed to have potential to be used as a therapeutic, particularly against antibiotic-resistant bacteria. However, its instability in physiological conditions limits its use in clinical applications and pharmaceutical development. Exploration of new natural variants of nisin has uncovered diverse properties using different domains. Shuffling peptide modules can fine-tune the chemical properties of these molecules, potentially enhancing stability while maintaining or improving antimicrobial activity. In this study, hybrid AMPs were created by combining domains from three unique nisin variants, i.e. nisin A, cesin and rombocin, leading to the identification of a promising variant, named cerocin A, which harbours only 25 amino acids compared to the typical 31-35 amino acid length of nisin. Cerocin A demonstrates potent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), approaching that of nisin itself. Cerocin A's mode of action involves a dual mechanism through the combination of two domains, consisting of a small ring/domain (6 amino acids) from the C-terminal end of rombocin attached to the preceding peptide of cesin, changing it from a bacteriostatic to a bactericidal peptide. Further mutation studies identified a new variant, cerocin V, with significantly improved resistance against trypsin degradation, while maintaining high potency. Importantly, cerocin V showed no undesired toxic effects on human red blood cells and remained stable in human plasma. In conclusion, we demonstrate that peptide construction using domain engineering is an effective strategy for manipulating both biological and physicochemical aspects, leading to the creation of novel bioactive molecules with desired properties. These constructs are appealing candidates for further optimization and development as novel antibiotics.

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.

Combination antimicrobial therapy: in vitro synergistic effect of anti-staphylococcal drug oxacillin with antimicrobial peptide nisin against Staphylococcus epidermidis clinical isolates and Staphylococcus aureus biofilms.

The ability of Staphylococcus epidermidis and S. aureus to form strong biofilm on plastic devices makes them the major pathogens associated with device-related infections (DRIs). Biofilm-embedded bacteria are more resistant to antibiotics, making biofilm infections very difficult to effectively treat. Here, we evaluate the in vitro activities of anti-staphylococcal drug oxacillin and antimicrobial peptide nisin, alone and in combination, against methicillin-resistant S. epidermidis (MRSE) clinical isolates and the methicillin-resistant S. aureus ATCC 43,300. The minimum inhibitory concentrations (MIC) and minimum biofilm eradication concentrations (MBEC) of oxacillin and nisin were determined using the microbroth dilution method. The anti-biofilm activities of oxacillin and nisin, alone or in combination, were evaluated. In addition, the effects of antimicrobial agents on the expression of icaA gene were examined by quantitative real-time PCR. MIC values for oxacillin and nisin ranged 4-8 µg/mL and 64-128 µg/mL, respectively. Oxacillin and nisin reduced biofilm biomass in all bacteria in a dose-dependent manner and this inhibitory effect was enhanced with combinatorial treatment. MBEC ranges for oxacillin and nisin were 2048-8192 µg/mL and 2048-4096 µg/mL, respectively. The addition of nisin significantly decreased the oxacillin MBECs from 8- to 32-fold in all bacteria. At the 1× MIC and 1/2× MIC, both oxacillin and nisin decreased significantly the expression of icaA gene in comparison with untreated control. When two antimicrobial agents were combined at 1/2× MIC concentration, the expression of icaA were significantly lower than when were used alone. Nisin/conventional oxacillin combination showed considerable anti-biofilm effects, including inhibition of biofilm formation, eradication of mature biofilm, and down-regulation of biofilm-related genes, proposing its applications for treating or preventing staphylococcal biofilm-associated infections, including device-related infections.

Activity of Gut-Derived Nisin-like Lantibiotics against Human Gut Pathogens and Commensals.

Recent advances in sequencing techniques unveiled the vast potential of ribosomally synthesized and post-translationally modified peptides (RiPPs) encoded in microbiomes. Class I lantibiotics such as nisin A, widely used as a food preservative, have been investigated for their efficacy in killing pathogens. However, the impact of nisin and nisin-like class I lantibiotics on commensal bacteria residing in the human gut remains unclear. Here, we report six gut-derived class I lantibiotics that are close homologues of nisin, four of which are novel. We applied an improved lantibiotic expression platform to produce and purify these lantibiotics for antimicrobial assays. We determined their minimal inhibitory concentration (MIC) against both Gram-positive human pathogens and gut commensals and profiled the lantibiotic resistance genes in these pathogens and commensals. Structure-activity relationship (SAR) studies with analogs revealed key regions and residues that impact their antimicrobial properties. Our characterization and SAR studies of nisin-like lantibiotics against both pathogens and human gut commensals could shed light on the future development of lantibiotic-based therapeutics and food preservatives.