Systematic characterization of position one variants within the lantibiotic nisin

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.

Facile Halogenation of Antimicrobial Peptides As Demonstrated by Producing Bromotryptophan-Labeled Nisin Variants with Enhanced Antimicrobial Activity

Antimicrobial peptides (AMPs) have raised significant interest, forming a potential new class of antibiotics in the fight against multi-drug-resistant bacteria. Various AMPs are ribosomally synthesized and post-translationally modified peptides (RiPPs). One post-translational modification found in AMPs is the halogenation of Trp residues. This modification has, for example, been shown to be critical for the activity of the potent AMP NAI-107 from Actinoallomurus. Due to the importance of organohalogens, establishing methods for facile and selective halogen atom installation into AMPs is highly desirable. In this study, we introduce an expression system utilizing the food-grade strain Lactococcus lactis, facilitating the efficient incorporation of bromo-Trp (BrTrp) into (modified) peptides, exemplified by the lantibiotic nisin with a single Trp residue or analogue incorporated at position 1. This provides an alternative to the challenges posed by halogenase enzymes, such as poor substrate selectivity. Our method yields expression levels comparable to that of wild-type nisin, while BrTrp incorporation does not interfere with the post-translational modifications of nisin (dehydration and cyclization). One brominated nisin variant exhibits a 2-fold improvement in antimicrobial activity against two tested pathogens, including a WHO priority pathogen, while maintaining the same lipid II binding and bactericidal activity as wild-type nisin. The work presented here demonstrates the potential of this methodology for peptide halogenation, offering a new avenue for the development of diverse antimicrobial products labeled with BrTrp.

Proteases Involved in Leader Peptide Removal during RiPP Biosynthesis

Ribosomally synthesized and post-translationally modified peptides (RiPPs) have received much attention in recent years because of their promising bioactivities and the portability of their biosynthetic pathways. Heterologous expression studies of RiPP biosynthetic enzymes identified by genome mining often leave a leader peptide on the final product to prevent toxicity to the host and to allow the attachment of a genetically encoded affinity purification tag. Removal of the leader peptide to produce the mature natural product is then carried out in vitro with either a commercial protease or a protease that fulfills this task in the producing organism. This review covers the advances in characterizing these latter cognate proteases from bacterial RiPPs and their utility as sequence-dependent proteases. The strategies employed for leader peptide removal have been shown to be remarkably diverse. They include one-step removal by a single protease, two-step removal by two dedicated proteases, and endoproteinase activity followed by aminopeptidase activity by the same protease. Similarly, the localization of the proteolytic step varies from cytoplasmic cleavage to leader peptide removal during secretion to extracellular leader peptide removal. Finally, substrate recognition ranges from highly sequence specific with respect to the leader and/or modified core peptide to nonsequence specific mechanisms.

MAFB shapes human monocyte-derived macrophage response to SARS-CoV-2 and controls severe COVID-19 biomarker expression

Monocyte-derived macrophages, the major source of pathogenic macrophages in COVID-19, are oppositely instructed by macrophage CSF (M-CSF) or granulocyte macrophage CSF (GM-CSF), which promote the generation of antiinflammatory/immunosuppressive MAFB+ (M-MØ) or proinflammatory macrophages (GM-MØ), respectively. The transcriptional profile of prevailing macrophage subsets in severe COVID-19 led us to hypothesize that MAFB shapes the transcriptome of pulmonary macrophages driving severe COVID-19 pathogenesis. We have now assessed the role of MAFB in the response of monocyte-derived macrophages to SARS-CoV-2 through genetic and pharmacological approaches, and we demonstrate that MAFB regulated the expression of the genes that define pulmonary pathogenic macrophages in severe COVID-19. Indeed, SARS-CoV-2 potentiated the expression of MAFB and MAFB-regulated genes in M-MØ and GM-MØ, where MAFB upregulated the expression of profibrotic and neutrophil-attracting factors. Thus, MAFB determines the transcriptome and functions of the monocyte-derived macrophage subsets that underlie pulmonary pathogenesis in severe COVID-19 and controls the expression of potentially useful biomarkers for COVID-19 severity.

Lipidated variants of the antimicrobial peptide nisin produced via incorporation of methionine analogs for click chemistry show improved bioactivity

The increase in antibiotic resistance calls for accelerated molecular engineering strategies to diversify natural products for drug discovery. The incorporation of non-canonical amino acids (ncAAs) is an elegant strategy for this purpose, offering a diverse pool of building blocks to introduce desired properties into antimicrobial lanthipeptides. We here report an expression system using Lactococcus lactis as a host for non-canonical amino acid incorporation with high efficiency and yield. We show that incorporating the more hydrophobic analog ethionine (instead of methionine) into nisin improves its bioactivity against several Gram-positive strains we tested. New-to-nature variants were further created by click chemistry. By azidohomoalanine (Aha) incorporation and subsequent click chemistry, we obtained lipidated variants at different positions in nisin or in truncated nisin variants. Some of them show improved bioactivity and specificity against several pathogenic bacterial strains. These results highlight the ability of this methodology for lanthipeptide multi-site lipidation, to create new-to-nature antimicrobial products with diverse features, and extend the toolbox for (lanthi)peptide drug improvement and discovery.

After a century of nisin research - where are we now?

It is almost a century since nisin was discovered in fermented milk cultures, coincidentally in the same year that penicillin was first described. Over the last 100 years this small, highly modified pentacyclic peptide has not only found success in the food industry as a preservative but has also served as the paradigm for our understanding of the genetic organization, expression, and regulation of genes involved in lantibiotic biosynthesis-one of the few cases of extensive post-translation modification in prokaryotes. Recent developments in understanding the complex biosynthesis of nisin have shed light on the cellular location of the modification and transport machinery and the co-ordinated series of spatio-temporal events required to produce active nisin and provide resistance and immunity. The continued unearthing of new natural variants from within human and animal gastrointestinal tracts has sparked interest in the potential application of nisin to influence the microbiome, given the growing recognition of the role the gastrointestinal microbiota plays in health and disease. Moreover, interdisciplinary approaches have taken advantage of biotechnological advancements to bioengineer nisin to produce novel variants and expand nisin functionality for applications in the biomedical field. This review will discuss the latest progress in these aspects of nisin research.

Engineered bacterial host for genetic encoding of physiologically stable protein nitration

Across scales, many biological phenomena, such as protein folding or bioadhesion and cohesion, rely on synergistic effects of different amino acid side chains at multiple positions in the protein sequence. These are often fine-tuned by post-translational modifications that introduce additional chemical properties. Several PTMs can now be genetically encoded and precisely installed at single and multiple sites by genetic code expansion. Protein nitration is a PTM of particular interest because it has been associated with several diseases. However, even when these nitro groups are directly incorporated into proteins, they are often physiologically reduced during or shortly after protein production. We have solved this problem by using an engineered Escherichia coli host strain. Six genes that are associated with nitroreductase activity were removed from the genome in a simple and robust manner. The result is a bacterial expression host that can stably produce proteins and peptides containing nitro groups, especially when these are amenable to modification. To demonstrate the applicability of this strain, we used this host for several applications. One of these was the multisite incorporation of a photocaged 3,4-dihydroxyphenylalanine derivative into Elastin-Like Polypeptides. For this non-canonical amino acid and several other photocaged ncAAs, the nitro group is critical for photocleavability. Accordingly, our approach also enhances the production of biomolecules containing photocaged tyrosine in the form of ortho-nitrobenzyl-tyrosine. We envision our engineered host as an efficient tool for the production of custom designed proteins, peptides or biomaterials for various applications ranging from research in cell biology to large-scale production in biotechnology.

Nisin Mutant Prevention Concentration and the Role of Subinhibitory Concentrations on Resistance Development by Diabetic Foot Staphylococci

The most prevalent microorganism in diabetic foot infections (DFI) is Staphylococcus aureus, an important multidrug-resistant pathogen. The antimicrobial peptide nisin is a promising compound for DFI treatment, being effective against S. aureus. However, to avoid the selection of resistant mutants, correct drug therapeutic doses must be established, being also important to understand if nisin subinhibitory concentrations (subMIC) can potentiate resistant genes transfer between clinical isolates or mutations in genes associated with nisin resistance. The mutant selection window (MSW) of nisin was determined for 23 DFI S. aureus isolates; a protocol aiming to prompt vanA horizontal transfer between enterococci to clinical S. aureus was performed; and nisin subMIC effect on resistance evolution was assessed through whole-genome sequencing (WGS) applied to isolates subjected to a MEGA-plate assay. MSW ranged from 5–360 μg/mL for two isolates, from 5–540 μg/mL for three isolates, and from 5–720 μg/mL for one isolate. In the presence of nisin subMIC values, no transconjugants were obtained, indicating that nisin does not seem to promote vanA transfer. Finally, WGS analysis showed that incubation in the presence of nisin subMIC did not promote the occurrence of significant mutations in genes related to nisin resistance, supporting nisin application to DFI treatment.

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.

Recombinant production of the lantibiotic nisin using Corynebacterium glutamicum in a two-step process

BACKGROUND

The bacteriocin nisin is naturally produced by Lactococcus lactis as an inactive prepeptide that is modified posttranslationally resulting in five (methyl-)lanthionine rings characteristic for class Ia bacteriocins. Export and proteolytic cleavage of the leader peptide results in release of active nisin. By targeting the universal peptidoglycan precursor lipid II, nisin has a broad target spectrum including important human pathogens such as Listeria monocytogenes and methicillin-resistant Staphylococcus aureus strains. Industrial nisin production is currently performed using natural producer strains resulting in rather low product purity and limiting its application to preservation of dairy food products.

RESULTS

We established heterologous nisin production using the biotechnological workhorse organism Corynebacterium glutamicum in a two-step process. We demonstrate successful biosynthesis and export of fully modified prenisin and its activation to mature nisin by a purified, soluble variant of the nisin protease NisP (sNisP) produced in Escherichia coli. Active nisin was detected by a L. lactis sensor strain with strictly nisin-dependent expression of the fluorescent protein mCherry. Following activation by sNisP, supernatants of the recombinant C. glutamicum producer strain cultivated in standard batch fermentations contained at least 1.25 mg/l active nisin.

CONCLUSIONS

We demonstrate successful implementation of a two-step process for recombinant production of active nisin with C. glutamicum. This extends the spectrum of bioactive compounds that may be produced using C. glutamicum to a bacteriocin harboring complex posttranslational modifications. Our results provide a basis for further studies to optimize product yields, transfer production to sustainable substrates and purification of pharmaceutical grade nisin.

A Bioengineered Nisin Derivative To Control Streptococcus uberis Biofilms

Antimicrobial peptides are evolving as novel therapeutic options against the increasing problem of multidrug-resistant microorganisms, and nisin is one such avenue. However, some bacteria possess a specific nisin resistance system (NSR), which cleaves the peptide reducing its bactericidal efficacy. NSR-based resistance was identified in strains of Streptococcus uberis, a ubiquitous pathogen that causes mastitis in dairy cattle. Previous studies have demonstrated that a nisin A derivative termed nisin PV, featuring S29P and I30V, exhibits enhanced resistance to proteolytic cleavage by NSR. Our objective was to investigate the ability of this nisin derivative to eradicate and inhibit biofilms of S. uberis DPC 5344 and S. uberis ATCC 700407 (nsr⁺) using crystal violet (biomass), 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) (viability) assays, and confocal microscopy (viability and architecture). When preestablished biofilms were assessed, both peptides reduced biofilm biomass by over 60% compared to that of the untreated controls. However, a 42% higher reduction in viability was observed following treatment with nisin PV compared to that of nisin A. Accordingly, confocal microscopy analysis revealed significantly more dead cells on the biofilm upper surface and a reduced thickness following treatment with nisin PV. When biofilm inhibition was assessed, nisin PV inhibited biofilm formation and decreased viability up to 56% and 85% more than nisin A, respectively. Confocal microscopy analysis revealed a lack of biofilm for S. uberis ATCC 700407 and only dead cells for S. uberis DPC 5344. These results suggest that nisin PV is a promising alternative to effectively reduce the biofilm formation of S. uberis strains carrying NSR. IMPORTANCE One of the four most prevalent species of bovine mastitis-causing pathogens is S. uberis. Its ability to form biofilms confers on the bacteria greater resistance to antibiotics, requiring higher doses to be more effective. In a bid to limit antibiotic resistance development, the need for alternative antimicrobials is paramount. Bacteriocins such as nisin represent one such alternative that could alleviate the impact of mastitis caused by S. uberis. However, many strains of S. uberis have been shown to possess nisin resistance determinants, such as the nisin resistance protein (NSR). In this study, we demonstrate the ability of nisin and a nisin derivative termed PV that is insensitive to NSR to prevent and remove biofilms of NSR-producing S. uberis strains. These findings will add new information to the antimicrobial bacteriocins and control of S. uberis research fields specifically in relation to biofilms and nsr⁺ mastitis-associated strains.

Therapeutic Application of Lantibiotics and Other Lanthipeptides: Old and New Findings

Lanthipeptides are ribosomally synthesized and posttranslationally modified peptides, with modifications that are incorporated during biosynthesis by dedicated enzymes. Various modifications of the peptides are possible, resulting in a highly diverse group of bioactive peptides that offer a potential reservoir for use in the fight against a plethora of diseases. Their activities range from the antimicrobial properties of lantibiotics, especially against antibiotic-resistant strains, to antiviral activity, immunomodulatory properties, antiallodynic effects, and the potential to alleviate cystic fibrosis symptoms. Lanthipeptide biosynthetic genes are widespread within bacterial genomes, providing a substantial repository for novel bioactive peptides. Using genome mining tools, novel bioactive lanthipeptides can be identified, and coupled with rapid screening and heterologous expression technologies, the lanthipeptide drug discovery pipeline can be significantly sped up. Lanthipeptides represent a group of bioactive peptides that hold great potential as biotherapeutics, especially at a time when novel and more effective therapies are required. With this review, we provide insight into the latest developments made toward the therapeutic applications and production of lanthipeptides, specifically looking at heterologous expression systems.

Nisin variants from Streptococcus and Staphylococcus successfully express in NZ9800

AIMS

Increases in antimicrobial resistance have meant that the antimicrobial potential of lantibiotics is now being investigated irrespective of the nature of the producing organism. The aim of this study was to investigate whether natural nisin variants produced by non-Generally Recognized as Safe (GRAS) strains, such as nisin H, nisin J and nisin P, could be expressed in a well-characterized GRAS host.

METHODS AND RESULTS

This study involved cloning the nisin A promoter and leader sequence fused to nisin H, nisin J or nisin P structural gene sequences originally produced by Streptococcus hyointestinalis DPC 6484, Staphylococcus capitis APC 2923 and Streptococcus agalactiae DPC 7040, respectively. This resulted in their expression in Lactococcus lactis NZ9800, a genetically modified strain that does not produce nisin A.

CONCLUSIONS

Induction of the nisin controlled gene expression system demonstrates that these three nisin variants could be acted on by nisin A machinery provided by the host strain.

SIGNIFICANCE AND IMPACT OF THE STUDY

Describes the first successful heterologous production of three natural nisin variants by a GRAS strain, and demonstrates how such systems could be harnessed not only for lantibiotic production but also in the expansion of their structural diversity and development for use as future biotherapeutics.

Importance of the leader peptide sequence on the lanthipeptide secretion level

Lanthipeptides are ribosomally synthesized and posttranslationally modified peptides. Their precursor peptide comprises of an N-terminal leader peptide and a C-terminal core peptide. Here, the leader peptide is crucial for enzyme recognition especially for the modification enzymes and acts furthermore as a secretion signal for the lanthipeptide exporter. The core peptide is the target site for the posttranslational modifications and contains dehydrated amino acids and lanthionine rings. Nisin produced by the Gram-positive bacterium Lactococcus lactis is one of the best-studied lanthipeptides and used as a model system to study their modification and secretion processes. Nisin is secreted as a precursor peptide. Here, we present an in vivo secretion analysis of NisT in the absence of the modification machinery allowing the secretion of leader peptide mutants and their impact solely on the secretion activity of NisT. Additionally, we created leader peptide hybrids to provide new insights, how the secretion is effected by unnatural leader peptides. The focus on the secretion activity of the transporter alone enabled us to determine the recognition site of NisT within the leader peptide of nisin.

Combinatorial biosynthesis for the generation of new-to-nature peptide antimicrobials

Natural peptide products are a valuable source of important therapeutic agents, including antibiotics, antivirals and crop protection agents. Aided by an increased understanding of structure-activity relationships of these complex molecules and the biosynthetic machineries that produce them, it has become possible to re-engineer complete machineries and biosynthetic pathways to create novel products with improved pharmacological properties or modified structures to combat antimicrobial resistance. In this review, we will address the progress that has been made using non-ribosomally produced peptides and ribosomally synthesized and post-translationally modified peptides as scaffolds for designed biosynthetic pathways or combinatorial synthesis for the creation of novel peptide antimicrobials.

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.

Insights in the Antimicrobial Potential of the Natural Nisin Variant Nisin H

Lantibiotics are a growing class of antimicrobial peptides, which possess antimicrobial activity against mainly Gram-positive bacteria including the highly resistant strains such as methicillin-resistant Staphylococcus aureus or vancomycin-resistant enterococci. In the last decades numerous lantibiotics were discovered in natural habitats or designed with bioengineering tools. In this study, we present an insight in the antimicrobial potential of the natural occurring lantibiotic nisin H from Streptococcus hyointestinalis as well as the variant nisin H F₁I. We determined the yield of the heterologously expressed peptide and quantified the cleavage efficiency employing the nisin protease NisP. Furthermore, we analyzed the effect on the modification via mass spectrometry analysis. With standardized growth inhibition assays we benchmarked the activity of pure nisin H and the variant nisin H F₁I, and their influence on the activity of the nisin immunity proteins NisI and NisFEG from Lactococcus lactis and the nisin resistance proteins SaNSR and SaNsrFP from Streptococcus agalactiae COH1. We further checked the antibacterial activity against clinical isolates of Staphylococcus aureus, Enterococcus faecium and Enterococcus faecalis via microdilution method. In summary, nisin H and the nisin H F₁I variant possessed better antimicrobial potency than the natural nisin A.

Combating Antimicrobial Resistance With New-To-Nature Lanthipeptides Created by Genetic Code Expansion

Due to the rapid emergence of multi-resistant bacterial strains in recent decades, the commercially available effective antibiotics are becoming increasingly limited. On the other hand, widespread antimicrobial peptides (AMPs) such as the lantibiotic nisin has been used worldwide for more than 40 years without the appearance of significant bacterial resistance. Lantibiotics are ribosomally synthesized antimicrobials generated by posttranslational modifications. Their biotechnological production is of particular interest to redesign natural scaffolds improving their pharmaceutical properties, which has great potential for therapeutic use in human medicine and other areas. However, conventional protein engineering methods are limited to 20 canonical amino acids prescribed by the genetic code. Therefore, the expansion of the genetic code as the most advanced approach in Synthetic Biology allows the addition of new amino acid building blocks (non-canonical amino acids, ncAAs) during protein translation. We now have solid proof-of-principle evidence that bioexpression with these novel building blocks enabled lantibiotics with chemical properties transcending those produced by natural evolution. The unique scaffolds with novel structural and functional properties are the result of this bioengineering. Here we will critically examine and evaluate the use of the expanded genetic code and its alternatives in lantibiotics research over the last 7 years. We anticipate that Synthetic Biology, using engineered lantibiotics and even more complex scaffolds will be a promising tool to address an urgent problem of antibiotic resistance, especially in a class of multi-drug resistant microbes known as superbugs.

Characterization of the nucleotide-binding domain NsrF from the BceAB-type ABC-transporter NsrFP from the human pathogen Streptococcus agalactiae

Treatment of bacterial infections is a great challenge of our era due to the various resistance mechanisms against antibiotics. Antimicrobial peptides are considered to be potential novel compound as antibiotic treatment. However, some bacteria, especially many human pathogens, are inherently resistant to these compounds, due to the expression of BceAB-type ABC transporters. This rather new transporter family is not very well studied. Here, we report the first full characterization of the nucleotide binding domain of a BceAB type transporter from Streptococcus agalactiae, namely SaNsrF of the transporter SaNsrFP, which confers resistance against nisin and gallidermin. We determined the NTP hydrolysis kinetics and used molecular modeling and simulations in combination with small angle X-ray scattering to obtain structural models of the SaNsrF monomer and dimer. The fact that the SaNsrF_H202A variant displayed no ATPase activity was rationalized in terms of changes of the structural dynamics of the dimeric interface. Kinetic data show a clear preference for ATP as a substrate, and the prediction of binding modes allowed us to explain this selectivity over other NTPs.

Impact of the nisin modification machinery on the transport kinetics of NisT

Lanthipeptides are ribosomally synthesized and post-translationally modified peptides containing dehydrated amino acids and (methyl-)lanthionine rings. One of the best-studied examples is nisin produced by Lactococcus lactis. Nisin is synthesized as a precursor peptide comprising of an N-terminal leader peptide and a C-terminal core peptide. Amongst others, the leader peptide is crucial for enzyme recognition and acts as a secretion signal for the ABC transporter NisT that secretes nisin in a proposed channeling mechanism. Here, we present an in vivo secretion analysis of this process in the presence and absence of the nisin maturation machinery, consisting of the dehydratase NisB and the cyclase NisC. Our determined apparent secretion rates of NisT show how NisB and NisC modulate the transport kinetics of NisA. Additional in vitro studies of the detergent-solubilized NisT revealed how these enzymes and the substrates again influence the activity of transporter. In summary, this study highlights the pivotal role of NisB for NisT in the secretion process.

Evolution of Lantibiotic Salivaricins: New Weapons to Fight Infectious Diseases

Lantibiotic salivaricins are polycyclic peptides containing lanthionine and/or β-methyllanthionine residues produced by certain strains of Streptococcus salivarius, which almost exclusively reside in the human oral cavity. The importance of these molecules stems from their antimicrobial activity towards relevant oral pathogens which has so far been applied through the development of salivaricin-producing probiotic strains. However, salivaricins may also prove to be of great value in the development of new and novel antibacterial therapies in this era of emerging antibiotic resistance. In this review, we describe the biosynthesis, antimicrobial activity, structure, and mode of action of the lantibiotic salivaricins characterized to date. Moreover, we also provide an expert opinion and suggestions for future development of this important field of microbiology.

An overview of lantibiotic biosynthetic machinery promiscuity and its impact on antimicrobial discovery

Introduction: The continued emergence of drug resistant bacteria within the nosocomial and community environment recalcitrant to conventional antimicrobial therapies has enforced the requirement for novel therapeutics. This has led to a renewed interest in peptide antimicrobials, including ribosomally synthesized peptides termed lantibiotics. Lantibiotics represent a novel class of agents that many studies have highlighted as effective against a range of pathogenic bacteria.Areas covered: In this review, the modular nature of lantibiotic synthesis is discussed and how this can be exploited not only to improve known lantibiotics but also for the creation of new to nature lantibiotics exhibiting improved pharmacological properties, antimicrobial activity and ability to bypass bacterial resistance mechanisms.Expert opinion: The use of combinatorial biosynthetic systems to combine different modules or ring structures of known lantibiotics have also been utilized to create new to nature lantibiotics. To fully exploit the available information and its application to lantibiotic engineering, additional structure activity relationship (SAR) analysis is required to fully understand the impact of certain post-translational modifications and the impact they have upon the activity, stability and pharmacological properties.

Considerations and Caveats in Combating ESKAPE Pathogens against Nosocomial Infections

ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are among the most common opportunistic pathogens in nosocomial infections. ESKAPE pathogens distinguish themselves from normal ones by developing a high level of antibiotic resistance that involves multiple mechanisms. Contemporary therapeutic strategies which are potential options in combating ESKAPE bacteria need further investigation. Herein, a broad overview of the antimicrobial research on ESKAPE pathogens over the past five years is provided with prospective clinical applications.

Bypassing lantibiotic resistance by an effective nisin derivative

The need for new antibiotic compounds is rising and antimicrobial peptides are excellent candidates to fulfill this object. The bacteriocin subgroup lantibiotics, for example, are active in the nanomolar range and target the membranes of mainly Gram-positive bacteria. They bind to lipid II, inhibit cell growth and in some cases form pores within the bacterial membrane, inducing rapid cell death. Pharmaceutical usage of lantibiotics is however hampered by the presence of gene clusters in human pathogenic strains which, when expressed, confer resistance. The human pathogen Streptococcus agalactiae COH1, expresses several lantibiotic resistance proteins resulting in resistance against for example nisin. This study presents a highly potent, pore forming nisin variant as an alternative lantibiotic which bypasses the SaNSR protein. It is shown that this nisin derivate nisin_C28P keeps its nanomolar antibacterial activity against L. lactis NZ9000 cells but is not recognized by the nisin resistance protein SaNSR. Nisin_C28P is cleaved by SaNSR in vitro with a highly decreased efficiency, as shown by an cleavage assay. Furthermore, we show that nisin_C28P is still able to form pores in the membranes of L. lactis and is three times more efficient against SaNSR-expressing L. lactis cells than wildtype nisin.