Lysins breaking down the walls of Gram-negative bacteria, no longer a no-go

A comparative guide to expression systems for phage lysin production

Phage lysins, bacteriophage-encoded enzymes tasked with degrading their host's cell wall, are increasingly investigated and engineered as novel antibacterials across diverse applications. Their rapid action, tuneable specificity, and low likelihood of resistance development make them particularly interesting. Despite numerous application-focused lysin studies, the art of their recombinant production remains relatively undiscussed. Here, we provide an overview of the available expression systems for phage lysin production and discuss key considerations guiding the choice of a suitable recombinant host. We systematically surveyed recent literature to evaluate the hosts used in the lysin field and cover various recombinant systems, including the well-known bacterial host Escherichia coli or yeast Saccharomyces cerevisiae, as well as plant, mammalian, and cell-free systems. Careful analysis of the limited studies expressing lysins in various hosts suggests a host-dependent effect on activity. Nonetheless, the multitude of available expression systems should be further leveraged to accommodate the growing interest in phage lysins and their expanding range of applications.

Advances in the applications of Bacteriophages and phage products against food-contaminating bacteria

Food-contaminating bacteria pose a threat to food safety and the economy by causing foodborne illnesses and spoilage. Bacteriophages, a group of viruses that infect only bacteria, have the potential to control bacteria throughout the "farm-to-fork continuum". Phage application offers several advantages, including targeted action against specific bacterial strains and minimal impact on the natural microflora of food. This review covers multiple aspects of bacteriophages applications in the food industry, including their use as biocontrol and biopreservation agents to fight over 20 different genera of food-contaminating bacteria, reduce cross-contamination and the risk of foodborne diseases, and also to prolong shelf life and preserve freshness. The review also highlights the benefits of using bacteriophages in bioprocesses to selectively inhibit undesirable bacteria, such as substrate competitors and toxin producers, which is particularly valuable in complex microbial bioprocesses where physical or chemical methods become inadequate. Furthermore, the review briefly discusses other uses of bacteriophages in the food industry, such as sanitizing food processing environments and detecting specific bacteria in food products. The review also explores strategies to enhance the effectiveness of phages, such as employing multi-phage cocktails, encapsulated phages, phage products, and synergistic hurdle approaches by combining them with antimicrobials.

Characterization and Genome Analyses of the Novel Phages P2 and vB_AhydM-H1 Targeting Aeromonas hydrophila

Background

The emergence of antibiotic-resistant Aeromonas hydrophila strains presents a global health and aquaculture challenge. Bacteriophages offer promise as an alternative to antibiotics for treating drug-resistant Aeromonas infections.

Methods

Two new phages, P2 and vB_AhydM-H1, targeting pathogenic A. hydrophila were isolated from sewage water. Their morphology, growth characteristics, lytic activity, stability, and genomes were analyzed.

Results

Phage P2, a member of genus Ahphunavirus, and vB_AhydM-H1, a novel member of genus Pahsextavirus, exhibited narrow host ranges, extended latent periods, and typical burst sizes. Both phages remained stable at 40°C for 1 h and within a pH range of 4 to 10 for 3 h. The genomes of P2 and vB_AhydM-H1 spanned 42,660 bp with 49 open reading frames (ORFs) and 52,614 bp with 72 ORFs, respectively. Proteomic (ViPTree) and phylogenetic (VICTOR) analyses confirmed that both phages aligned with their respective families. DeepTMHMM predictions suggested that P2 and vB_AhydM-H1 encode three and four ORFs with transmembrane domains, respectively.

Conclusions

Safe for environmental and clinical use because of their lytic nature, and lack of virulence and resistance genes, these newly isolated phages expand the arsenal against antibiotic-resistant Aeromonas infections.

Development of novel antimicrobials with engineered endolysin LysECD7-SMAP to combat Gram-negative bacterial infections

BACKGROUND

Among the non-traditional antibacterial agents in development, only a few targets critical Gram-negative bacteria such as carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii or cephalosporin-resistant Enterobacteriaceae. Endolysins and their genetically modified versions meet the World Health Organization criteria for innovation, have a novel mode of antibacterial action, no known bacterial cross-resistance, and are being intensively studied for application against Gram-negative pathogens.

METHODS

The study presents a multidisciplinary approach, including genetic engineering of LysECD7-SMAP and production of recombinant endolysin, its analysis by crystal structure solution following molecular dynamics simulations and evaluation of antibacterial properties. Two types of antimicrobial dosage forms were formulated, resulting in lyophilized powder for injection and hydroxyethylcellulose gel for topical administration. Their efficacy was estimated in the treatment of sepsis, and pneumonia models in BALB/c mice, diabetes-associated wound infection in the leptin receptor-deficient db/db mice and infected burn wounds in rats.

RESULTS

In this work, we investigate the application strategies of the engineered endolysin LysECD7-SMAP and its dosage forms evaluated in preclinical studies. The catalytic domain of the enzyme shares the conserved structure of endopeptidases containing a putative antimicrobial peptide at the C-terminus of polypeptide chain. The activity of endolysins has been demonstrated against a range of pathogens, such as Klebsiella pneumoniae, A. baumannii, P. aeruginosa, Staphylococcus haemolyticus, Achromobacter spp, Burkholderia cepacia complex and Haemophylus influenzae, including those with multidrug resistance. The efficacy of candidate dosage forms has been confirmed in in vivo studies. Some aspects of the interaction of LysECD7-SMAP with cell wall molecular targets are also discussed.

CONCLUSIONS

Our studies demonstrate the potential of LysECD7-SMAP therapeutics for the systemic or topical treatment of infectious diseases caused by susceptible Gram-negative bacterial species and are critical to proceed LysECD7-SMAP-based antimicrobials trials to advanced stages.

Endolysins: a new antimicrobial agent against antimicrobial resistance. Strategies and opportunities in overcoming the challenges of endolysins against Gram-negative bacteria

Antibiotic-resistant bacteria are rapidly emerging, and the increasing prevalence of multidrug-resistant (MDR) Acinetobacter baumannii poses a severe threat to humans and healthcare organizations, due to the lack of innovative antibacterial drugs. Endolysins, which are peptidoglycan hydrolases encoded by a bacteriophage, are a promising new family of antimicrobials. Endolysins have been demonstrated as an effective therapeutic agent against bacterial infections of A. baumannii and many other Gram-positive and Gram-negative bacteria. Endolysin research has progressed from basic in vitro characterization to sophisticated protein engineering methodologies, including advanced preclinical and clinical testing. Endolysin are therapeutic agent that shows antimicrobial properties against bacterial infections caused by drug-resistant Gram-negative bacteria, there are still barriers to their implementation in clinical settings, such as safety concerns with outer membrane permeabilizers (OMP) use, low efficiency against stationary phase bacteria, and stability issues. The application of protein engineering and formulation techniques to improve enzyme stability, as well as combination therapy with other types of antibacterial drugs to optimize their medicinal value, have been reviewed as well. In this review, we summarize the clinical development of endolysin and its challenges and approaches for bringing endolysin therapies to the clinic. This review also discusses the different applications of endolysins.

Characteristics of hen egg white lysozyme, strategies to break through antibacterial limitation, and its application in food preservation: A review

Hen egg white lysozyme (HEWL) is used as a food additive in China due to its outstanding antibacterial properties. It is listed as GRAS grade (generally recognized as safe) by the United States Food and Drug Administration (FDA, US) and has been extensively researched and used in food preservation. And the industrial production of HEWL already been realized. Given the complex food system that can affect the antibacterial activity of HEWL, and the limitations of HEWL itself on Gram-negative bacteria. Based on the structure and main biological characteristics of HEWL, this paper focuses on reviewing methods to enhance the stability and antibacterial properties of HEWL. Immobilization tactics such as chemically driven self-assembly, embedding and adsorption address the restriction of poor HEWL antibacterial activity effected by external factors. Both intermolecular and intramolecular modification strategies break the bactericidal deficiencies of HEWL itself. It also comprehensively analyzes the current application status and future prospects of HEWL in the food preservation. There was limited research on the biological methods in modifying HEWL. If the HEWL is genetically engineered, it can broaden its antimicrobial spectrum, improve its other biological activities, so as to further expand its application in the food industry. At present, research on HEWL mainly focused on its antibacterial properties, whereas its application in anti-inflammatory and antioxidant effects also presented great potential.

Gram-negative endolysins: overcoming the outer membrane obstacle

Our ability to control the growth of Gram-negative bacterial pathogens is challenged by rising antimicrobial resistance and requires new approaches. Endolysins are phage-derived enzymes that degrade peptidoglycan and therefore offer potential as antimicrobial agents. However, the outer membrane (OM) of Gram-negative bacteria impedes the access of externally applied endolysins to peptidoglycan. This review highlights recent advances in the discovery and characterization of natural endolysins that can breach the OM, as well as chemical and engineering approaches that increase antimicrobial efficacy of endolysins against Gram-negative pathogens.

Metal-Organic Framework Induced Stabilization of Proteins in Polymeric Nanoparticles

Developing protein confinement platforms is an attractive research area that not only promotes protein delivery but also can result in artificial environment mimicking of the cellular one, impacting both the controlled release of proteins and the fundamental protein biophysics. Polymeric nanoparticles (PNPs) are attractive platforms to confine proteins due to their superior biocompatibility, low cytotoxicity, and controllable release under external stimuli. However, loading proteins into PNPs can be challenging due to the potential protein structural perturbation upon contacting the interior of PNPs. In this work, we developed a novel approach to encapsulate proteins in PNPs with the assistance of the zeolitic imidazolate framework (ZIF). Here, ZIF offers an additional protection layer to the target protein by forming the protein@ZIF composite via aqueous-phase cocrystallization. We demonstrated our platform using a model protein, lysozyme, and a widely studied PNP composed of poly(ethylene glycol)-poly(lactic-co-glycolic acid) (PEG-PLGA). A comprehensive study via standard loading and release tests as well as various spectroscopic techniques was carried out on lysozyme loaded onto PEG-PLGA with and without ZIF protection. As compared with the direct protein encapsulation, an additional layer with ZIF prior to loading offered enhanced loading capacity, reduced leaching, especially in the initial stage, led to slower release kinetics, and reduced secondary structural perturbation. Meanwhile, the function, cytotoxicity, and cellular uptake of proteins encapsulated within the ZIF-bound systems are decent. Our results demonstrated the use of ZIF in assisting in protein encapsulation in PNPs and established the basis for developing more sophisticated protein encapsulation platforms using a combination of materials of diverse molecular architectures and disciplines. As such, we anticipate that the protein-encapsulated ZIF systems will serve as future polymer protein confinement and delivery platforms for both fundamental biophysics and biochemistry research and biomedical applications where protein delivery is needed to support therapeutics and/or nutrients.

Characterization of a Straboviridae phage vB_AbaM-SHI and its inhibition effect on biofilms of Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) is a popular clinical pathogen worldwide. Biofilm-associated antibiotic-resistant A. baumannii infection poses a great threat to human health. Bacteria in biofilms are highly resistant to antibiotics and disinfectants. Furthermore, inhibition or eradication of biofilms in husbandry, the food industry and clinics are almost impossible. Phages can move across the biofilm matrix and promote antibiotic penetration. In the present study, a lytic A. baumannii phage vB_AbaM-SHI, belonging to family Straboviridae, was isolated from sauce chop factory drain outlet in Wuxi, China. The DNA genome consists of 44,180 bp which contain 93 open reading frames, and genes encoding products morphogenesis are located at the end of the genome. The amino acid sequence of vB_AbaM-SHI endolysin is different from those of previously reported A. baumannii phages in NCBI. Phage vB_AbaM-SHI endolysin has two additional β strands due to the replacement of a lysine (K) (in KU510289.1, NC_041857.1, JX976549.1 and MH853786.1) with an arginine (R) (SHI) at position 21 of A. baumannii phage endolysin. Spot test showed that phage vB_AbaM-SHI is able to lyse some antibiotic-resistant bacteria, such as A. baumannii (SL, SL1, and SG strains) and E. coli BL21 strain. Additionally, phage vB_AbaM-SHI independently killed bacteria and inhibited bacterial biofilm formation, and synergistically exerted strong antibacterial effects with antibiotics. This study provided a new perspective into the potential application value of phage vB_AbaM-SHI as an antimicrobial agent.

Phage-inspired strategies to combat antibacterial resistance

Antimicrobial resistance (AMR) in clinically priority pathogensis now a major threat to public health worldwide. Phages are bacterial parasites that efficiently infect or kill specific strains and represent the most abundant biological entities on earth, showing great attraction as potential antibacterial therapeutics in combating AMR. This review provides a summary of phage-inspired strategies to combat AMR. We firstly cover the phage diversity, and then explain the biological principles of phage therapy that support the use of phages in the post-antimicrobial era. Furthermore, we state the versatility methods of phage therapy both from direct access as well as collateral access. Among the direct access approaches, we discuss the use of phage cocktail therapy, phage-encoded endolysins and the bioengineering for function improvement of used phages or endolysins. On the other hand, we introduce the collateral access, including the phages antimicrobial immunity combined therapy and phage-based novel antibacterial mimic molecules. Nowadays, more and more talented and enthusiastic scientist, doctors, pharmacists, media, authorities, and industry are promoting the progress of phage therapy, and proposed more phages-inspired strategy to make them more tractable to combat AMR and benefit more people, more animal and diverse environment in "one health" framework.

Metagenomic analysis of hot spring soil for mining a novel thermostable enzybiotic

The misuse and overuse of antibiotics have contributed to a rapid emergence of antibiotic-resistant bacterial pathogens. This global health threat underlines the urgent need for innovative and novel antimicrobials. Endolysins derived from bacteriophages or prophages constitute promising new antimicrobials (so-called enzybiotics), exhibiting the ability to break down bacterial peptidoglycan (PG). In the present work, metagenomic analysis of soil samples, collected from thermal springs, allowed the identification of a prophage-derived endolysin that belongs to the N-acetylmuramoyl-L-alanine amidase type 2 (NALAA-2) family and possesses a LysM (lysin motif) region as a cell wall binding domain (CWBD). The enzyme (Ami1) was cloned and expressed in Escherichia coli, and its bactericidal and lytic activity was characterized. The results indicate that Ami1 exhibits strong bactericidal and antimicrobial activity against a broad range of bacterial pathogens, as well as against isolated peptidoglycan (PG). Among the examined bacterial pathogens, Ami1 showed highest bactericidal activity against Staphylococcus aureus sand Staphylococcus epidermidis cells. Thermostability analysis revealed a melting temperature of 64.2 ± 0.6 °C. Overall, these findings support the potential that Ami1, as a broad spectrum antimicrobial agent, could be further assessed as enzybiotic for the effective treatment of bacterial infections. KEY POINTS: • Metagenomic analysis allowed the identification of a novel prophage endolysin • The endolysin belongs to type 2 amidase family with lysin motif region • The endolysin displays high thermostability and broad bactericidal spectrum.

Molecular characterization of the PhiKo endolysin from Thermus thermophilus HB27 bacteriophage phiKo and its cryptic lytic peptide RAP-29

Introduction

In the era of increasing bacterial resistance to antibiotics, new bactericidal substances are sought, and lysins derived from extremophilic organisms have the undoubted advantage of being stable under harsh environmental conditions. The PhiKo endolysin is derived from the phiKo bacteriophage infecting Gram-negative extremophilic bacterium Thermus thermophilus HB27. This enzyme shows similarity to two previously investigated thermostable type-2 amidases, the Ts2631 and Ph2119 from Thermus scotoductus bacteriophages, that revealed high lytic activity not only against thermophiles but also against Gram-negative mesophilic bacteria. Therefore, antibacterial potential of the PhiKo endolysin was investigated in the study presented here.

Methods

Enzyme activity was assessed using turbidity reduction assays (TRAs) and antibacterial tests. Differential scanning calorimetry was applied to evaluate protein stability. The Collection of Anti-Microbial Peptides (CAMP) and Antimicrobial Peptide Calculator and Predictor (APD3) were used to predict regions with antimicrobial potential in the PhiKo primary sequence. The minimum inhibitory concentration (MIC) of the RAP-29 synthetic peptide was determined against Gram-positive and Gram-negative selected strains, and mechanism of action was investigated with use of membrane potential sensitive fluorescent dye 3,3'-Dipropylthiacarbocyanine iodide (DiSC3(5)).

Results and discussion

The PhiKo endolysin is highly thermostable with melting temperature of 91.70°C. However, despite its lytic effect against such extremophiles as: T. thermophilus, Thermus flavus, Thermus parvatiensis, Thermus scotoductus, and Deinococcus radiodurans, PhiKo showed moderate antibacterial activity against mesophiles. Consequently, its protein sequence was searched for regions with potential antibacterial activity. A highly positively charged region was identified and synthetized (PhiKo105-133). The novel RAP-29 peptide lysed mesophilic strains of staphylococci and Gram-negative bacteria, reducing the number of cells by 3.7-7.1 log units and reaching the minimum inhibitory concentration values in the range of 2-31 μM. This peptide is unstructured in an aqueous solution but forms an α-helix in the presence of detergents. Moreover, it binds lipoteichoic acid and lipopolysaccharide, and causes depolarization of bacterial membranes. The RAP-29 peptide is a promising candidate for combating bacterial pathogens. The existence of this cryptic peptide testifies to a much wider panel of antimicrobial peptides than thought previously.

Design strategies for positively charged endolysins: Insights into Artilysin development

Endolysins are bacteriophage-encoded enzymes that can specifically degrade the peptidoglycan layer of bacterial cell wall, making them an attractive tool for the development of novel antibacterial agents. The use of genetic engineering techniques for the production and modification of endolysins offers the opportunity to customize their properties and activity against specific bacterial targets, paving the way for the development of personalized therapies for bacterial infections. Gram-negative bacteria possess an outer membrane that can hinder the action of recombinantly produced endolysins. However, certain endolysins are capable of crossing the outer membrane by virtue of segments that share properties resembling those of cationic peptides. These regions increase the affinity of the endolysin towards the bacterial surface and assist in the permeabilization of the membrane. In order to improve the bactericidal effectiveness of endolysins, approaches have been implemented to increase their net charge, including the development of Artilysins containing positively charged amino acids at one end. At present, there are no specific guidelines outlining the steps for implementing these modifications. There is an ongoing debate surrounding the optimal location of positive charge, the need for a linker region, and the specific amino acid composition of peptides for modifying endolysins. The aim of this study is to provide clarity on these topics by analyzing and comparing the most effective modifications found in previous literature.

A comprehensive review of the applications of bacteriophage-derived endolysins for foodborne bacterial pathogens and food safety: recent advances, challenges, and future perspective

Foodborne diseases are caused by food contaminated by pathogenic bacteria such as Escherichia coli, Salmonella, Staphylococcus aureus, Listeria monocytogenes, Campylobacter, and Clostridium, a critical threat to human health. As a novel antibacterial agent against foodborne pathogens, endolysins are peptidoglycan hydrolases encoded by bacteriophages that lyse bacterial cells by targeting their cell wall, notably in Gram-positive bacteria due to their naturally exposed peptidoglycan layer. These lytic enzymes have gained scientists' interest in recent years due to their selectivity, mode of action, engineering potential, and lack of resistance mechanisms. The use of endolysins for food safety has undergone significant improvements, which are summarized and discussed in this review. Endolysins can remove bacterial biofilms of foodborne pathogens and their cell wall-binding domain can be employed as a tool for quick detection of foodborne pathogens. We explained the applications of endolysin for eliminating pathogenic bacteria in livestock and various food matrices, as well as the limitations and challenges in use as a dietary supplement. We also highlight the novel techniques of the development of engineering endolysin for targeting Gram-negative bacterial pathogens. In conclusion, endolysin is safe and effective against foodborne pathogens and has no adverse effect on human cells and beneficial microbiota. As a result, endolysin could be employed as a functional bio-preservative agent to improve food stability and safety and maintain the natural taste of food quality.

Dendritic systems for bacterial outer membrane disruption as a method of overcoming bacterial multidrug resistance

The alarming rise of multi-drug resistant microorganisms has increased the need for new approaches through the development of innovative agents that are capable of attaching to the outer layers of bacteria and causing permanent damage by penetrating the bacterial outer membrane. The permeability (disruption) of the outer membrane of Gram-negative bacteria is now considered to be one of the main ways to overcome multidrug resistance in bacteria. Natural and synthetic permeabilizers such as AMPs and dendritic systems seem promising. However, due to their advantages in terms of biocompatibility, antimicrobial capacity, and wide possibilities for modification and synthesis, highly branched polymers and dendritic systems have gained much more interest in recent years. Various forms of arrangement, and structure of the skeleton, give dendritic systems versatile applications, especially the possibility of attaching other ligands to their surface. This review will focus on the mechanisms used by different types of dendritic polymers, and their complexes with macromolecules to enhance their antimicrobial effect, and to permeabilize the bacterial outer membrane. In addition, future challenges and potential prospects are illustrated in the hope of accelerating the advancement of nanomedicine in the fight against resistant pathogens.

Beyond antibiotics: phage-encoded lysins against Gram-negative pathogens

Antibiotics remain the frontline agents for treating deadly bacterial pathogens. However, the indiscriminate use of these valuable agents has led to an alarming rise in AMR. The antibiotic pipeline is insufficient to tackle the AMR threat, especially with respect to the WHO critical category of priority Gram-negative pathogens, which have become a serious problem as nosocomial and community infections and pose a threat globally. The AMR pandemic requires solutions that provide novel antibacterial agents that are not only effective but against which bacteria are less likely to gain resistance. In this regard, natural or engineered phage-encoded lysins (enzybiotics) armed with numerous features represent an attractive alternative to the currently available antibiotics. Several lysins have exhibited promising efficacy and safety against Gram-positive pathogens, with some in late stages of clinical development and some commercially available. However, in the case of Gram-negative bacteria, the outer membrane acts as a formidable barrier; hence, lysins are often used in combination with OMPs or engineered to overcome the outer membrane barrier. In this review, we have briefly explained AMR and the initiatives taken by different organizations globally to tackle the AMR threat at different levels. We bring forth the promising potential and challenges of lysins, focusing on the WHO critical category of priority Gram-negative bacteria and lysins under investigation for these pathogens, along with the challenges associated with developing them as therapeutics within the existing regulatory framework.

New Strategies to Kill Metabolically-Dormant Cells Directly Bypassing the Need for Active Cellular Processes

Antibiotic therapy failure is often caused by the presence of persister cells, which are metabolically-dormant bacteria capable of surviving exposure to antimicrobials. Under favorable conditions, persisters can resume growth leading to recurrent infections. Moreover, several studies have indicated that persisters may promote the evolution of antimicrobial resistance and facilitate the selection of specific resistant mutants; therefore, in light of the increasing numbers of multidrug-resistant infections worldwide, developing efficient strategies against dormant cells is of paramount importance. In this review, we present and discuss the efficacy of various agents whose antimicrobial activity is independent of the metabolic status of the bacteria as they target cell envelope structures. Since the biofilm-environment is favorable for the formation of dormant subpopulations, anti-persister strategies should also include agents that destroy the biofilm matrix or inhibit biofilm development. This article reviews examples of selected cell wall hydrolases, polysaccharide depolymerases and antimicrobial peptides. Their combination with standard antibiotics seems to be the most promising approach in combating persistent infections.

LysGR1, a novel thermostable endolysin from Geobacillus stearothermophilus bacteriophage GR1

Geobacillus stearothermophilus is a highly thermophilic, spore-forming Gram-positive bacterium that causes flat sour spoilage in low-acid canned foods. To address this problem, we isolated G. stearothermophilus-infecting phage GR1 from the soil and characterized its endolysin LysGR1. Phage GR1 belongs to the Siphoviridae family and possesses a genome of 79,387 DNA bps with 108 putative open reading frames. GR1 demonstrated a very low degree of homology to previously reported phages, indicating that it is novel. The endolysin of GR1 (LysGR1) contains an N-terminal amidase domain as an enzymatically active domain (EAD) and two C-terminal LysM domains as a cell wall binding domain (CBD). Although GR1 is specific to certain strains of G. stearothermophilus, LysGR1 showed a much broader lytic range, killing all the tested strains of G. stearothermophilus and several foodborne pathogens, such as Clostridium perfringens, Listeria monocytogenes, and Escherichia coli O157:H7. LysGR1_EAD, alone, also exhibits lytic activity against a wide range of bacteria, including Bacillus cereus, which is not terminated by a full-length endolysin. Both LysGR1 and its EAD effectively remove the G. stearothermophilus biofilms and are highly thermostable, retaining about 70% of their lytic activity after a 15-min incubation at 70°C. Considering the high thermal stability, broad lytic activity, and biofilm reduction efficacy of LysGR1 and its EAD, we hypothesize that these enzymes could act as promising biocontrol agents against G. stearothermophilus and as foodborne pathogens.

An Ultrastable Self-Assembled Antibacterial Nanospears Made of Protein

Protein-based nanomaterials have broad applications in the biomedical and bionanotechnological sectors owing to their outstanding properties such as high biocompatibility and biodegradability, structural stability, sophisticated functional versatility, and being environmentally benign. They have gained considerable attention in drug delivery, cancer therapeutics, vaccines, immunotherapies, biosensing, and biocatalysis. However, so far, in the battle against the increasing reports of antibiotic resistance and emerging drug-resistant bacteria, unique nanostructures of this kind are lacking, hindering their potential next-generation antibacterial agents. Here, the discovery of a class of supramolecular nanostructures with well-defined shapes, geometries, or architectures (termed "protein nanospears") based on engineered proteins, exhibiting exceptional broad-spectrum antibacterial activities, is reported. The protein nanospears are engineered via spontaneous cleavage-dependent or precisely tunable self-assembly routes using mild metal salt-ions (Mg²⁺ , Ca²⁺ , Na⁺ ) as a molecular trigger. The nanospears' dimensions collectively range from entire nano- to micrometer scale. The protein nanospears display exceptional thermal and chemical stability yet rapidly disassemble upon exposure to high concentrations of chaotropes (>1 mm sodium dodecyl sulfate (SDS)). Using a combination of biological assays and electron microscopy imaging, it is revealed that the nanospears spontaneously induce rapid and irreparable damage to bacterial morphology via a unique action mechanism provided by their nanostructure and enzymatic action, a feat inaccessible to traditional antibiotics. These protein-based nanospears show promise as a potent tool to combat the growing threats of resistant bacteria, inspiring a new way to engineer other antibacterial protein nanomaterials with diverse structural and dimensional architectures and functional properties.

The resurgence of phage-based therapy in the era of increasing antibiotic resistance: From research progress to challenges and prospects

Phage therapy was implemented almost a century ago but was subsequently abandoned when antibiotics emerged. However, the rapid emergence of drug-resistant, which has brought to the limelight situation reminiscent of the pre-antibiotic era, coupled with the unavailability of new drugs, has triggered the quest for an alternative therapeutic approach, and this has led to the rebirth of phage-derived therapy. Phages are viruses that infect and replicate in bacterial cells. Phage therapy, especially phage-derived proteins, is being given considerable attention among scientists as an antimicrobial agent. They are used alone or in combination with other biomaterials for improved biological activity. Over the years, much has been learned about the genetics and diversity of bacteriophages. Phage cocktails are currently being exploited for treating several infectious diseases as preliminary studies involving animal models and clinical trials show promising therapeutic efficacy. However, despite its numerous advantages, this approach has several challenges and unaddressed limitations. Addressing these issues requires lots of creativity and innovative ideas from interdisciplinary fields. However, with all available indications, phage therapy could hold the solution in this era of increasing antibiotic resistance. This review discussed the potential use of phages and phage-derived proteins in treating drug-resistant bacterial infections. Finally, we highlight the progress, challenges, and knowledge gaps and evaluate key questions requiring prompt attention for the full clinical application of phage therapy.

Improvement of the Antibacterial Activity of Phage Lysin-Derived Peptide P87 through Maximization of Physicochemical Properties and Assessment of Its Therapeutic Potential

Phage lysins are a promising alternative to common antibiotic chemotherapy. However, they have been regarded as less effective against Gram-negative pathogens unless engineered, e.g., by fusing them to antimicrobial peptides (AMPs). AMPs themselves pose an alternative to antibiotics. In this work, AMP P87, previously derived from a phage lysin (Pae87) with a presumed nonenzymatic mode-of-action, was investigated to improve its antibacterial activity. Five modifications were designed to maximize the hydrophobic moment and net charge, producing the modified peptide P88, which was evaluated in terms of bactericidal activity, cytotoxicity, MICs or synergy with antibiotics. P88 had a better bactericidal performance than P87 (an average of 6.0 vs. 1.5 log-killing activity on Pseudomonas aeruginosa strains treated with 10 µM). This did not correlate with a dramatic increase in cytotoxicity as assayed on A549 cell cultures. P88 was active against a range of P. aeruginosa isolates, with no intrinsic resistance factors identified. Synergy with some antibiotics was observed in vitro, in complex media, and in a respiratory infection mouse model. Therefore, P88 can be a new addition to the therapeutic toolbox of alternative antimicrobials against Gram-negative pathogens as a sole therapeutic, a complement to antibiotics, or a part to engineer proteinaceous antimicrobials.

Cecropin a Improves the Antibacterial Activity of Hen Egg White Lysozyme against Challenging Salmonella enterica Serovars

The prevalence of multidrug-resistant Salmonella enterica among animal- and plant-derived food products threatens global healthcare and economic sectors. Hen egg white lysozyme is widely exploited as a food preservative against Gram-positive pathogens. Nevertheless, its limited penetration of the outer membrane renders it ineffective against Gram-negative bacteria. Herein, we present a safe and effective approach to facilitate HEWL access to peptidoglycan layers using cecropin A. In silico analysis of cecropin A peptide revealed an amphipathic α-helical peptide with potential outer membrane permeabilizing activity through its interaction with both hydrophobic and ionic stabilizing forces. Evaluation of HEWL/cecropin A combination showed a cecropin A dose-dependent bacterial count reduction up to 4.16 and 3.18 ± 0.26 log units against Salmonella enterica ATCC 35664 at the logarithmic and stationary growth phases, respectively. Moreover, the combination displayed antibacterial activity of 2.1 ± 0.31 and ~1 log-unit reductions against Salmonella enterica serovars Kentucky, Typhimurium, and Enteritidis, respectively, whereas Hato and Shangani were found irresponsive. The cytotoxicity assay revealed compatibility of cecropin A with oral epithelial cells. These observations suggest HEWL/cecropin A combination as an effective and safe alternative to lysozyme against Salmonella enterica.

Characterization of Salmonella endolysin XFII produced by recombinant Escherichia coli and its application combined with chitosan in lysing Gram-negative bacteria

BACKGROUND

 Salmonella is a common foodborne pathogen, which can cause intestinal diseases. In the last decades, the overuse of antibiotics has led to a pandemic of drug-resistant bacterial infections. To tackle the burden of antimicrobial resistant pathogens, it is necessary to develop new antimicrobial drugs with novel modes of action. However, the research and development of antibiotics has encountered bottlenecks, scientific hurdles in the development process, as well as safety and cost challenges. Phages and phage endolysins are promising antibacterial agents that can be used as an alternative to antibiotics. In this context, the expression of endolysin derived from different phages through microbial cells as a chassis seems to be an attractive strategy.

RESULTS

 In this study, a new endolysin from the Salmonella phage XFII-1, named XFII, was screened and obtained. The endolysin yield exceeded 100 mg/mL by heterologous expression from E. coli BL21 and short induction. The endolysin XFII exhibited high bactericidal activity at a concentration of 0.5 μg/mL and reduced the OD600 nm of EDTA-pretreated E. coli JM109 from 0.8 to 0.2 within 5 min. XFII exhibited good thermo-resistance, as it was very stable at different temperatures from 20 to 80℃. Its bactericidal activity could keep constant at 4 °C for 175 days. In addition, the endolysin was able to exert lytic activity in eutrophic conditions, including LB medium and rabbit serum, and the lytic activity was even increased by 13.8% in 10% serum matrices. XFII also showed bactericidal activity against many Gram-negative bacteria, including Salmonella, E. coli, Acinetobacter baumannii, and Klebsiella pneumoniae. Surprisingly, the combination of endolysin XFII and chitosan showed a strong synergy in lysing E. coli and Salmonella without EDTA-pretreatment, and the OD600 nm of E. coli decreased from 0.88 to 0.58 within 10 min.

CONCLUSIONS

The novel globular endolysin XFII was screened and successfully expressed in E. coli BL21. Endolysin XFII exhibits a broad lysis spectrum, a rapid and strong bactericidal activity, good stability at high temperatures and under eutrophic conditions. Combined with chitosan, XFII could spontaneously lyse Gram-negative bacteria without pretreatment. This work presented the first characterization of combining endolysin and chitosan in spontaneously lysing Gram-negative bacteria in vitro.

A Lysozyme Murein Hydrolase with Broad-Spectrum Antibacterial Activity from Enterobacter Phage myPSH1140

Bacteriophages and bacteriophage-derived peptidoglycan hydrolases (endolysins) present promising alternatives for the treatment of infections caused by multidrug resistant Gram-negative and Gram-positive pathogens. In this study, Gp105, a putative lysozyme murein hydrolase from Enterobacter phage myPSH1140 was characterized in silico, in vitro as well as in vivo using the purified protein. Gp105 contains a T4-type lysozyme-like domain (IPR001165) and belongs to Glycoside hydrolase family 24 (IPR002196). The putative endolysin indeed had strong antibacterial activity against Gram-negative pathogens, including E. cloacae, K. pneumoniae, P. aeruginosa, S. marcescens, Citrobacter sp., and A. baumannii. Also, an in vitro peptidoglycan hydrolysis assay showed strong activity against purified peptidoglycans. This study demonstrates the potential of Gp105 to be used as an antibacterial protein to combat Gram-negative pathogens.

Polymeric Coatings and Antimicrobial Peptides as Efficient Systems for Treating Implantable Medical Devices Associated-Infections

Many infections are associated with the use of implantable medical devices. The excessive utilization of antibiotic treatment has resulted in the development of antimicrobial resistance. Consequently, scientists have recently focused on conceiving new ways for treating infections with a longer duration of action and minimum environmental toxicity. One approach in infection control is based on the development of antimicrobial coatings based on polymers and antimicrobial peptides, also termed as “natural antibiotics”.

Essential Topics for the Regulatory Consideration of Phages as Clinically Valuable Therapeutic Agents: A Perspective from Spain

Antibiotic resistance is one of the major challenges that humankind shall face in the short term. (Bacterio)phage therapy is a valuable therapeutic alternative to antibiotics and, although the concept is almost as old as the discovery of phages, its wide application was hindered in the West by the discovery and development of antibiotics in the mid-twentieth century. However, research on phage therapy is currently experiencing a renaissance due to the antimicrobial resistance problem. Some countries are already adopting new ad hoc regulations to favor the short-term implantation of phage therapy in clinical practice. In this regard, the Phage Therapy Work Group from FAGOMA (Spanish Network of Bacteriophages and Transducing Elements) recently contacted the Spanish Drugs and Medical Devices Agency (AEMPS) to promote the regulation of phage therapy in Spain. As a result, FAGOMA was asked to provide a general view on key issues regarding phage therapy legislation. This review comes as the culmination of the FAGOMA initiative and aims at appropriately informing the regulatory debate on phage therapy.

An Overview of Antimicrobial Activity of Lysozyme and Its Functionality in Cheese

Due to the concern of consumers about the presence of synthetic preservatives, researchers and food manufacturers have recently conducted extensive research on the limited use of these preservatives and the introduction and use of natural preservatives, such as herbal extracts and essential oils, bacteriocins, and antimicrobial enzymes. Lysozyme is a natural enzyme with antimicrobial activity that has attracted considerable attention to be potentially utilized in various industries. Since lysozyme is an intrinsic component of the human immune system and has low toxicity; it could be considered as a natural antimicrobial agent for use in food and pharmaceutical industries. Lysozyme exerts antimicrobial activity against microorganisms, especially Gram-positive bacteria, by hydrolyzing 1,4-beta-linkages between N-acetylmuramic acid and N-acetylglucosamine in the cell wall. In addition, increased antimicrobial activity of lysozyme against Gram-negative bacteria could be achieved by the modification of lysozyme through physical or chemical interactions. Lysozyme is presented as a natural preservative in mammalian milk and can be utilized as a bio-preservative in dairy products, such as cheese. Both bacteria and fungi can contaminate and spoil the cheese; especially the one that is made traditionally by raw milk. Furthermore, uncontrolled and improper processes and post-pasteurization contamination can participate in the cheese contamination. Therefore, besides common preservative strategies applied in cheese production, lysozyme could be utilized alone or in combination with other preservative strategies to improve the safety of cheese. Hence, this study aimed to review the antimicrobial properties of lysozyme as natural antimicrobial enzyme and its functionality in cheese.

Bacteriophage Lytic Enzyme P9ly as an Alternative Antibacterial Agent Against Antibiotic-Resistant Shigella dysenteriae and Staphylococcus aureus

Developing new strategies to replace or supplement antibiotics to combat bacterial infection is a pressing task in the field of microbiological research. In this study, we report a lytic enzyme named P9ly deriving from the bacteriophage PSD9 that could infect multidrug-resistant Shigella. This enzyme was identified through whole-genome sequencing of PSD9. The results show that P9ly contains a conserved T4-like_lys domain and belongs to the phage lysozyme family. Recombinant P9ly obtained from protein purification presented biological activity and could digest bacterial cell walls (CW), resulting in the destruction of cell structure and leakage of intracellular components. Furthermore, P9ly exhibited bacteriolytic and bactericidal activity on different strains, especially multidrug-resistant Gram-negative Shigella dysenteriae and Gram-positive Staphylococcus aureus. Additionally, combined use of P9ly with ceftriaxone sodium (CRO) could decrease necessary dose of the antibiotic used and improve the antibacterial effect. In summary, under the current backdrop of extensive antibiotic usage and the continuous emergence of bacterial resistance, this study provides an insight into developing bacteriophage-based antibacterial agents against both Gram-negative and Gram-positive pathogens.

Application of Bacteriophages to Limit Campylobacter in Poultry Production

Campylobacter is a major foodborne pathogen with over a million United States cases a year and is typically acquired through the consumption of poultry products. The common occurrence of Campylobacter as a member of the poultry gastrointestinal tract microbial community remains a challenge for optimizing intervention strategies. Simultaneously, increasing demand for antibiotic-free products has led to the development of several alternative control measures both at the farm and in processing operations. Bacteriophages administered to reduce foodborne pathogens are one of the alternatives that have received renewed interest. Campylobacter phages have been isolated from both conventionally and organically raised poultry. Isolated and cultivated Campylobacter bacteriophages have been used as an intervention in live birds to target colonized Campylobacter in the gastrointestinal tract. Application of Campylobacter phages to poultry carcasses has also been explored as a strategy to reduce Campylobacter levels during poultry processing. This review will focus on the biology and ecology of Campylobacter bacteriophages in poultry production followed by discussion on current and potential applications as an intervention strategy to reduce Campylobacter occurrence in poultry production.

Treating Bacterial Infections with Bacteriophage-Based Enzybiotics: In Vitro, In Vivo and Clinical Application

Over the past few decades, we have witnessed a surge around the world in the emergence of antibiotic-resistant bacteria. This global health threat arose mainly due to the overuse and misuse of antibiotics as well as a relative lack of new drug classes in development pipelines. Innovative antibacterial therapeutics and strategies are, therefore, in grave need. For the last twenty years, antimicrobial enzymes encoded by bacteriophages, viruses that can lyse and kill bacteria, have gained tremendous interest. There are two classes of these phage-derived enzymes, referred to also as enzybiotics: peptidoglycan hydrolases (lysins), which degrade the bacterial peptidoglycan layer, and polysaccharide depolymerases, which target extracellular or surface polysaccharides, i.e., bacterial capsules, slime layers, biofilm matrix, or lipopolysaccharides. Their features include distinctive modes of action, high efficiency, pathogen specificity, diversity in structure and activity, low possibility of bacterial resistance development, and no observed cross-resistance with currently used antibiotics. Additionally, and unlike antibiotics, enzybiotics can target metabolically inactive persister cells. These phage-derived enzymes have been tested in various animal models to combat both Gram-positive and Gram-negative bacteria, and in recent years peptidoglycan hydrolases have entered clinical trials. Here, we review the testing and clinical use of these enzymes.

Discovering the Potentials of Four Phage Endolysins to Combat Gram-Negative Infections

Endolysin-based therapeutics are promising antibacterial agents and can successfully supplement the existing antibacterial drugs array. It is specifically important in the case of Gram-negative pathogens, e.g., ESKAPE group bacteria, which includes Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species, and are highly inclined to gain multiple antibiotic resistance. Despite numerous works devoted to the screening of new lytic enzymes and investigations of their biochemical properties, there are significant breaches in some aspects of their operating characteristics, including safety issues of endolysin use. Here, we provide a comprehensive study of the antimicrobial efficacy aspects of four Gram-negative bacteria-targeting endolysins LysAm24, LysAp22, LysECD7, and LysSi3, their in vitro and in vivo activity, and their biological safety. These endolysins possess a wide spectrum of action, are active against planktonic bacteria and bacterial biofilms, and are effective in wound and burn skin infection animal models. In terms of safety, these enzymes do not contribute to the development of short-term resistance, are not cytotoxic, and do not significantly affect the normal intestinal microflora in vivo. Our results provide a confident base for the development of effective and safe candidate dosage forms for the treatment of local and systemic infections caused by Gram-negative bacterial species.

Engineering a lysin with intrinsic antibacterial activity (LysMK34) with cecropin A enhances its antibacterial properties against Acinetobacter baumannii

Bacteriophage-encoded lysins are increasingly reported as alternatives to combat Acinetobacter baumannii infections for which limited therapeutic options are available. Some lysins such as LysMK34 have a C-terminal amphipathic helix allowing them to penetrate the otherwise impermeable outer membrane barrier. Another approach to kill Gram-negative pathogens with lysins relies on fusion of a peptide with outer membrane permeabilizing properties to the lysin. In this work, we aimed to leverage the intrinsic antibacterial activity of LysMK34 by fusing the peptide cecropin A to its N-terminus via a linker of three Ala-Gly repeats, resulting in eLysMK34. The engineered lysin has an improved antibacterial activity compared to the parental lysin LysMK34 in terms of minimum inhibitory concentration (0.45 - 1.2 μM), killing rate and killing extent. eLysMK34 has an at least two-fold increased activity against stationary-phase cells and the bactericidal effect becomes less dependent on the intracellular osmotic pressure. Particularly colistin-resistant strains become highly susceptible to eLysMK34 and enhanced antibacterial activity is observed in complement-deactivated human serum. These observations demonstrate that fusion of a lysin with intrinsic antibacterial activity with a selected outer membrane permeabilizing peptide is a useful strategy to further improve the in vitro antibacterial properties of such lysins. Importance Phage lysins are a new class of enzyme-based antibiotics that increasingly gain interest. Lysins kill cells through rapid degradation of the peptidoglycan layer, resulting in sudden osmotic lysis. Whereas Gram-positive bacteria are readily susceptible to the action of lysins, Gram-negative bacteria are naturally resistant as the outer membrane protects their peptidoglycan layer. This work reveals that fusing an outer membrane permeabilizing peptide to a lysin with intrinsic antibacterial activity results in a superior lysin that shows improved robustness in its antibacterial activity, including against the most worrisome colistin-resistant strains A. baumannii.

Membrane-Permeable Antibacterial Enzyme against Multidrug-Resistant Acinetobacter baumannii

Bacteriophage endolysins (lysins, or murein hydrolases) are enzymes that bacteriophages utilize to degrade the cell wall peptidoglycans (PG) and subsequently disintegrate bacterial cells from within. Due to their muralytic activity, lysins are considered as potential candidates to battle against antibiotic resistance. However, most lysins in their native form lack the capability of trespassing the outer membrane (OM) of Gram-negative (G-ve) bacteria. To turn the bacteriophage enzymes into antibacterial weapons against G-ve bacteria, endowing these enzymes the capability of accessing the PG substrate underneath the OM is critical. Here we show that fusing a membrane-permeabilizing peptide CeA at the C-terminus of a muralytic enzyme LysAB2 renders a two-step mechanism of bacterial killing and increases the activity of LysAB2 against the multidrug resistant Acinetobacter baumannii by up to 100 000-folds. The engineered LysAB2, termed LysAB2-KWK here, also shows remarkable activity against A. baumannii at the stationary phase and a prominent capability to disrupt biofilm formation. In addition, the enzyme shows a broad antibacterial spectrum against G-ve bacteria, a decent tolerance to serum, and a prolonged storage life. LysAB2-KWK rescues the larva of the greater wax moth Galleria mellonella from A. baumannii infection through systemic administration. Altogether, our work equips a globular lysin with OM permeabilization activity to enable effective killing of G-ve bacteria, reveals the critical role of the C-terminus of a globular lysin in the antibacterial activity, and points toward a viable route to engineer globular lysins as antibacterial enzymes for potential clinical use against multidrug resistant G-ve bacteria.

Phage vB_PaeS-PAJD-1 Rescues Murine Mastitis Infected With Multidrug-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative pathogen that causes a variety of infections in humans and animals. Due to the inappropriate use of antibiotics, multi-drug resistant (MDR) P. aeruginosa strains have emerged and are prevailing. In recent years, cow mastitis caused by MDR P. aeruginosa has attracted attention. In this study, a microbial community analysis revealed that P. aeruginosa could be a cause of pathogen-induced cow mastitis. Five MDR P. aeruginosa strains were isolated from milk diagnosed as mastitis positive. To seek an alternative antibacterial agent against MDR, P. aeruginosa, a lytic phage, designated vB_PaeS_PAJD-1 (PAJD-1), was isolated from dairy farm sewage. PAJD-1 was morphologically classified as Siphoviridae and was estimated to be about 57.9 kb. Phage PAJD-1 showed broad host ranges and a strong lytic ability. A one-step growth curve analysis showed a relatively short latency period (20 min) and a relatively high burst size (223 PFU per infected cell). Phage PAJD-1 remained stable over wide temperature and pH ranges. Intramammary-administered PAJD-1 reduced bacterial concentrations and repaired mammary glands in mice with mastitis induced by MDR P. aeruginosa. Furthermore, the cell wall hydrolase (termed endolysin) from phage PAJD-1 exhibited a strong bacteriolytic and a wide antibacterial spectrum against MDR P. aeruginosa. These findings present phage PAJD-1 as a candidate for phagotherapy against MDR P. aeruginosa infection.

Engineered endolysin-based "artilysins" for controlling the gram-negative pathogen Helicobacter pylori

Helicobacter pylori infection can cause a variety of gastrointestinal diseases. In severe cases, there is a risk of gastric cancer. Antibiotics are often used for clinical treatment of H. pylori infections. However, because of antibiotic overuse in recent years and the emergence of multidrug-resistant bacteria, there is an urgent need to develop new treatment methods and drugs to achieve complete eradication of H. pylori. Endolysins and holins encoded by bacterial viruses (i.e., phages) represent a promising avenue of investigation. These lyase-based antibacterial drugs act on the bacterial cell wall to destroy the bacteria. Currently, a type of endolysin that has been studied more frequently acts on the amide bond between peptidoglycans, and holin is a transmembrane protein that can punch holes in the cell membrane. However, as a Gram-negative bacterium, H. pylori possesses a layer of impermeable lipopolysaccharides on the cell wall, which prevents endolysin interaction with the cell wall. Therefore, we designed a genetic linkage between an endolysin enzyme and a holin enzyme with a section of polypeptides (e.g., polycations and hydrophobic peptides) that enable penetration of the outer membrane. These complexes were designated "artilysins" and were efficiently expressed in Escherichia coli. In vitro bacteriostasis experiments showed that the purified artilysins had strong bacteriostatic effects on H. pylori. In addition, the surface of H. pylori was perforated and destroyed, as confirmed by electron microscopy, which was proved that artilysins had bacteriolytic effect on H. pylori.

Endolysin-Based Autolytic E. coli System for Facile Recovery of Recombinant Proteins

Recovery of recombinant proteins from the Escherichia coli cytoplasm depends on cell disruption by mechanical, chemical, and/or enzymatic methods, which usually cause incomplete cell breakage or protein denaturation. Controllable autolytic E. coli strains have been designed to facilitate the purification of recombinant proteins; however, these strains suffer from low recovery yield, slow cell lysis, or extensive strain engineering. Herein, we report an improved, highly efficient programmable autolytic E. coli platform, in which cell lysis is initiated upon the induced expression of T4 lysozyme with N-terminal fusion of a cell-penetrating peptide. Through the engineering of the peptide sequence and copy number, and by incorporating the fusion lytic gene into the E. coli genome, more than 99.97% of cells could be lysed within 30 min of induction regardless of cell age. We further tested the expression and release of a recombinant enzyme lysostaphin (Lst) and demonstrated that 4 h induction of the lytic gene after 3 h of Lst expression resulted in 98.97% cell lysis. Lst obtained from this system had the same yield, yet 1.63-fold higher activity, compared with that obtained from cells lysed by freeze-thawing and sonication. This autolytic platform shows potential for use in large-scale microbial production of proteins and other biopolymers.

Developing Innolysins Against Campylobacter jejuni Using a Novel Prophage Receptor-Binding Protein

Campylobacter contaminated poultry remains the major cause of foodborne gastroenteritis worldwide, calling for novel antibacterials. We previously developed the concept of Innolysin composed of an endolysin fused to a phage receptor binding protein (RBP) and provided the proof-of-concept that Innolysins exert bactericidal activity against Escherichia coli. Here, we have expanded the Innolysin concept to target Campylobacter jejuni. As no C. jejuni phage RBP had been identified so far, we first showed that the H-fiber originating from a CJIE1-like prophage of C. jejuni CAMSA2147 functions as a novel RBP. By fusing this H-fiber to phage T5 endolysin, we constructed Innolysins targeting C. jejuni (Innolysins Cj). Innolysin Cj1 exerts antibacterial activity against diverse C. jejuni strains after in vitro exposure for 45 min at 20°C, reaching up to 1.30 ± 0.21 log reduction in CAMSA2147 cell counts. Screening of a library of Innolysins Cj composed of distinct endolysins for growth inhibition, allowed us to select Innolysin Cj5 as an additional promising antibacterial candidate. Application of either Innolysin Cj1 or Innolysin Cj5 on chicken skin refrigerated to 5°C and contaminated with C. jejuni CAMSA2147 led to 1.63 ± 0.46 and 1.18 ± 0.10 log reduction of cells, respectively, confirming that Innolysins Cj can kill C. jejuni in situ. The receptor of Innolysins Cj remains to be identified, however, the RBP component (H-fiber) recognizes a novel receptor compared to lytic phages binding to capsular polysaccharide or flagella. Identification of other unexplored Campylobacter phage RBPs may further increase the repertoire of new Innolysins Cj targeting distinct receptors and working as antibacterials against Campylobacter.

Design, Overproduction and Purification of the Chimeric Phage Lysin MLTphg Fighting against Staphylococcus aureus

With the increasing spread of multidrug-resistant bacterial pathogens, it is of great importance to develop alternatives to conventional antibiotics. Here, we report the generation of a chimeric phage lysin, MLTphg, which was assembled by joining the lysins derived from Meiothermus bacteriophage MMP7 and Thermus bacteriophage TSP4 with a flexible linker via chimeolysin engineering. As a potential antimicrobial agent, MLTphg can be obtained by overproduction in Escherichia coli BL21(DE3) cells and the following Ni-affinity chromatography. Finally, we recovered about 40 ± 1.9 mg of MLTphg from 1 L of the host E. coli BL21(DE3) culture. The purified MLTphg showed peak activity against Staphylococcus aureus ATCC6538 between 35 and 40 °C, and maintained approximately 44.5 ± 2.1% activity at room temperature (25 °C). Moreover, as a produced chimera, it exhibited considerably improved bactericidal activity against Staphylococcus aureus (2.9 ± 0.1 log10 reduction was observed upon 40 nM MLTphg treatment at 37 °C for 30 min) and also a group of antibiotic-resistant bacteria compared to its parental lysins, TSPphg and MMPphg. In the current age of growing antibiotic resistance, our results provide an engineering basis for developing phage lysins as novel antimicrobial agents and shed light on bacteriophage-based strategies to tackle bacterial infections.