Antimicrobial bacteriophage-derived proteins and therapeutic applications

The Synergistic and Chimeric Mechanism of Bacteriophage Endolysins: Opportunities for Application in Biotherapeutics, Food, and Health Sectors

A major growing concern in the human and animal health sector is the emergence of antibiotic-resistant pathogenic bacteria due to the indiscriminate use of antibiotics. The exogenous application of bacteriophage endolysins causes abrupt lysis of the bacterial cell wall, which computes them as alternatives to antibiotics. Although naturally occurring endolysins may display limitations in solubility, lytic activity, and narrow lytic spectrum, novel strategies like developing chimeric endolysins and using endolysins in synergism with other antimicrobial agents are required to improve the lytic activity of natural endolysins. The modular structure of endolysins led to the development of novel chimeric endolysins via shuffling enzymatic and cell wall binding domains of different endolysins, using endolysins in a synergistic approach, and their applications in various in vitro and in vivo experiments and different applicable areas. This article aims to review the role of chimeric endolysins and their use in synergistic mode with other biofilm-reducing agents to control biofilm formation and deteriorating pre-formed biofilms in food, dairy, and medical industries. Promoting further development of phage technology and innovation in antibiotic therapy can achieve long-term sustainable development and economic returns.

From Dormancy to Eradication: Strategies for Controlling Bacterial Persisters in Food Settings

Bacterial persistence, a dormant state that enables microorganisms to survive harsh conditions, is a significant concern in food-industry settings, where traditional antimicrobial treatments often fail to eliminate these resilient cells. This article goes beyond conventional review by compiling critical information aimed at providing practical solutions to combat bacterial persisters in food production environments. This review explores the primary mechanisms behind persister cell formation, including toxin-antitoxin systems, the alarmone guanosine tetraphosphate (ppGpp), stochastic processes (in which persistence occurs as a random event), and the SOS response. Given the serious implications for food safety and quality, the authors also report a range of physical, chemical, and biological methods for targeting and eradicating persister cells. The strategies discussed, whether applied individually or in combination, offer varying levels of availability and applicability within the industry and can serve as a guide for implementing microbial contamination control plans. While significant progress has been achieved, further research is crucial to fully understand the complex mechanisms underlying bacterial persistence in food and to develop effective and targeted strategies for its eradication in food-industry settings. Overall, the translation of these insights into practical applications aims to support the food industry in overcoming this persistent challenge, ensuring safer, more sustainable food production.

Bacteria- and Phage-Derived Proteins in Phage Infection

Phages have exerted severe evolutionary pressure on prokaryotes over billions of years, resulting in major rearrangements. Without every enzyme involved in the phage-bacterium interaction being examined; bacteriophages cannot be used in practical applications. Numerous studies conducted in the past few years have uncovered a huge variety of bacterial antiphage defense systems; nevertheless, the mechanisms of most of these systems are not fully understood. Understanding the interactions between bacteriophage and bacterial proteins is important for efficient host cell infection. Phage proteins involved in these bacteriophage-host interactions often arise immediately after infection. Here, we review the main groups of phage enzymes involved in the first stage of viral infection and responsible for the degradation of the bacterial membrane. These include polysaccharide depolymerases (endosialidases, endorhamnosidases, alginate lyases, and hyaluronate lyases), and peptidoglycan hydrolases (ectolysins and endolysins). Host target proteins are inhibited, activated, or functionally redirected by the phage protein. These interactions determine the phage infection of bacteria. Proteins of interest are holins, endolysins, and spanins, which are responsible for the release of progeny during the phage lytic cycle. This review describes the main bacterial and phage enzymes involved in phage infection and analyzes the therapeutic potential of bacteriophage-derived proteins.

Combined antimicrobial activity of short peptide and phage-derived endolysin against antibiotic-resistant Salmonella Typhimurium

This study was designed to evaluate the combination effects of antimicrobial peptides (FK13 and FK16) and phage-encoded endolysin (LysPB32) on the inhibition of growth of polymyxin B-resistant Salmonella Typhimurium ATCC 19585 (STPMB). The inhibitory effects of FK13, FK16, and LysPB32 against STPMB were evaluated by using antimicrobial susceptibility, membrane permeability, biofilm reduction, cross-resistance, and mutant frequency assay. The minimum inhibitory concentrations (MICs) of FK13 and FK16 treated with LysPB32 (FK13+LysPB32 and FK16+LysPB32) against STPMB were decreased from more than 512 to 128 μg/ml and from 64 to 32 μg/ml, respectively. Compared to the control, the number of STPMB in the growing culture was reduced by 4.2 and 5.2 log CFU/ml, respectively, for FK13+LysPB32 and FK16+LysPB32 after 12-h incubation at 37 °C. All treatments (FK13, FK16, FK13+LysPB32, FK16+LysPB32) significantly increased the permeability of the outer membrane of STPMB. Biofilms were significantly decreased from OD600 of 0.6 to 0.16 for FK13+LysPB32 and from 0.6 to 0.13 for FK16+LysPB32. The ratios of MICs of erythromycin, ceftriaxone, polymyxin B, and ciprofloxacin to MIC of the control against STPMB were decreased to 0.50 for FK13+LysPB32 and FK16+LysPB32. The bactericidal activities of amikacin and gentamicin were enhanced for FK13+LysPB32 and FK16+LysPB32 (2-fold < MBC/MIC ratio). The mutant frequencies of STPMB to antibiotics were decreased when treated with FK13+LysPB32 and FK16+LysPB32. The results suggest that the combination of antimicrobial peptides and endolysins can be a promising strategy to control polymyxin B-resistant S. Typhimurium.

Engineering the bacteriophage 80 alpha endolysin as a fast and ultrasensitive detection toolbox against Staphylococcus aureus

The isolation and identification of pathogenic bacteria from a variety of samples are critical for controlling bacterial infection-related health problems. The conventional methods, such as plate counting and polymerase chain reaction-based approaches, tend to be time-consuming and reliant on specific instruments, severely limiting the effective identification of these pathogens. In this study, we employed the specificity of the cell wall-binding (CBD) domain of the Staphylococcus aureus bacteriophage 80 alpha (80α) endolysin towards the host bacteria for isolation. Amidase 3-CBD conjugated magnetic beads successfully isolated as few as 1 × 102 CFU/mL of S. aureus cells from milk, blood, and saliva. The cell wall hydrolyzing activity of 80α endolysin promoted the genomic DNA extraction efficiency by 12.7 folds on average, compared to the commercial bacterial genomic DNA extraction kit. Then, recombinase polymerase amplification (RPA) was exploited to amplify the nuc gene of S. aureus from the extracted DNA at 37 °C for 30 min. The RPA product activated Cas12a endonuclease activity to cleave fluorescently labeled ssDNA probes. We then converted the generated signal into a fluorescent readout, detectable by either the naked eye or a portable, self-assembled instrument with ultrasensitivity. The entire procedure, from isolation to identification, can be completed within 2 h. The simplicity and sensitivity of the method developed in this study make it of great application value in S. aureus detection, especially in areas with limited resource supply.

Characterization and application of LysSGF2 and HolSGF2 as potential biocontrol agents against planktonic and biofilm cells of common pathogenic bacteria

Antimicrobial resistance represents a global health emergency, necessitating the introduction of novel antimicrobial agents. In the present study, lysozyme and holin from Shigella flexneri 1.1868 phage SGF2, named LysSGF2 and HolSGF2, respectively, were cloned, expressed, and characterized. LysSGF2 and HolSGF2 showed lytic activities against S. flexneri 1.1868 cells at 4-55 °C and pH 3.1-10.3. LysSGF2 exhibited antimicrobial activity against five gram-negative and two gram-positive bacteria. HolSGF2 showed antimicrobial activity against four gram-negative and one gram-positive species. The antibacterial activities of LysSGF2 and HolSGF2 were determined in liquid beverages, including bottled water and milk. The relative lytic activity of LysSGF2 combined with HolSGF2 against the tested bacteria was approximately 46-77 % in water. Furthermore, the combination markedly decreased the viable counts of tested bacteria by approximately 3-5 log CFU/mL. LysSGF2 and HolSGF2 could efficiently remove biofilms on polystyrene, glass, and stainless-steel. The efficacy of the LysSGF2 and HolSGF2 combination against the tested bacteria on polystyrene was 58-71 %. Combination treatment effectively killed biofilm cells formed on stainless-steel and glass by 1-4 log CFU/mL. ese results indicate that LysSGF2 and HolSGF2 can successfully control both the planktonic and biofilm cells of common pathogenic bacteria, suggesting that the combined or single use of LysSGF2 and HolSGF2 may be of great value in food processing.

Bacteriophage therapy as an innovative strategy for the treatment of Periprosthetic Joint Infection: a systematic review

BACKGROUND

Periprosthetic Joint Infection (PJI) following hip and knee arthroplasty is a catastrophic complication in orthopaedic surgery. It has long been a key focus for orthopaedic surgeons in terms of prevention and management. With the increasing incidence of antibiotic resistance in recent years, finding more targeted treatment methods has become an increasingly urgent issue. Bacteriophage Therapy (BT) has emerged as a promising adjunctive treatment for bone and joint infections in recent years. It not only effectively kills bacteria but also demonstrates significant anti-biofilm activity, garnering substantial clinical interest due to its demonstrated efficacy and relatively low incidence of adverse effects.

PURPOSE

This review aims to systematically evaluate the efficacy and safety of bacteriophage therapy in treating PJI following hip and knee arthroplasty, providing additional reference for its future clinical application.

METHODS

Following predefined inclusion and exclusion criteria, our team conducted a systematic literature search across seven databases (PubMed, Embase, Web of Science, Cochrane Library, ClinicalTrials.gov, CNKI, and WanFang Database). The search was conducted up to May 2024 and included multiple clinical studies on the use of bacteriophage therapy for treating PJI after hip and knee arthroplasty to assess its efficacy and safety.

RESULTS

This systematic review included 16 clinical studies after screening, consisting of 15 case reports and one prospective controlled clinical trial, involving a total of 42 patients with PJI treated with bacteriophage therapy. The average patient age was 62.86 years, and 43 joints were treated, with patients undergoing an average of 5.25 surgeries. The most common pathogen in these infections was Staphylococcus aureus, accounting for 18 cases. 33 patients received cocktail therapy, while nine were treated with a single bacteriophage preparation. Additionally, all patients underwent suppressive antibiotic therapy (SAT) postoperatively. All patients were followed up for an average of 13.55 months. There were two cases of recurrence, one of which resulted in amputation one year postoperatively. The remaining patients showed good recovery outcomes. Overall, the results from the included studies indicate that bacteriophage therapy effectively eradicates infectious strains in various cases of PJI, with minimal side effects, demonstrating promising clinical efficacy.

CONCLUSION

In the treatment of PJI following hip and knee arthroplasty, bacteriophages, whether used alone or in combination as cocktail therapy, have shown therapeutic potential. However, thorough preoperative evaluation is essential, and appropriate bacteriophage types and treatment regimens must be selected based on bacteriological evidence. Future large-scale, randomized controlled, and prospective trials are necessary to validate the efficacy and safety of this therapy.

A Critical Analysis of the Opportunities and Challenges of Phage Application in Seafood Quality Control

Seafood is an important source of food and protein for humans. However, it is highly susceptible to microbial contamination, which has become a major challenge for the seafood processing industry. Bacteriophages are widely distributed in the environment and have been successfully used as biocontrol agents against pathogenic microorganisms in certain food processing applications. However, due to the influence of environmental factors and seafood matrices, using bacteriophages for commercial-scale biocontrol strategies still faces some challenges. This article briefly introduces the current processes used for the production and purification of bacteriophages, lists the latest findings on the application of phage-based biocontrol in seafood, summarizes the challenges faced at the current stage, and provides corresponding strategies for solving these issues.

Bacteriophage as a potential biotherapeutics to combat present-day crisis of multi-drug resistant pathogens

The rise of Multi-Drug Resistant (MDR) bacterial pathogens to most, if not all, currently available antibacterial agents has become a global threat. As a consequence of the antibiotic resistance epidemic, phage therapy has emerged as a potential alternative to conventional antibiotics. Despite the high therapeutic advantages of phage therapy, they have not yet been successfully used in the clinic due to various limitations of narrow host specificity compared to antibiotics, poor adhesion on biofilm surface, and susceptibility to both human and bacterial defences. This review focuses on the antibacterial effect of bacteriophage and their recent clinical trials with a special emphasis on the underlying mechanism of lytic phage action with the help of endolysin and holin. Furthermore, recent clinical trials of natural and modified endolysins and some marketed products have also been emphasized with future prospective.

Agents Targeting the Bacterial Cell Wall as Tools to Combat Gram-Positive Pathogens

The cell wall is an indispensable element of bacterial cells and a long-known target of many antibiotics. Penicillin, the first discovered beta-lactam antibiotic inhibiting the synthesis of cell walls, was successfully used to cure many bacterial infections. Unfortunately, pathogens eventually developed resistance to it. This started an arms race, and while novel beta-lactams, either natural or (semi)synthetic, were discovered, soon upon their application, bacteria were developing resistance. Currently, we are facing the threat of losing the race since more and more multidrug-resistant (MDR) pathogens are emerging. Therefore, there is an urgent need for developing novel approaches to combat MDR bacteria. The cell wall is a reasonable candidate for a target as it differentiates not only bacterial and human cells but also has a specific composition unique to various groups of bacteria. This ensures the safety and specificity of novel antibacterial agents that target this structure. Due to the shortage of low-molecular-weight candidates for novel antibiotics, attention was focused on peptides and proteins that possess antibacterial activity. Here, we describe proteinaceous agents of various origins that target bacterial cell wall, including bacteriocins and phage and bacterial lysins, as alternatives to classic antibiotic candidates for antimicrobial drugs. Moreover, advancements in protein chemistry and engineering currently allow for the production of stable, specific, and effective drugs. Finally, we introduce the concept of selective targeting of dangerous pathogens, exemplified by staphylococci, by agents specifically disrupting their cell walls.

Antibacterial activity of bacteriophage-encoded endolysins against planktonic and biofilm cells of pathogenic Escherichia coli

This study was designed to assess the possibility of using bacteriophage-encoded endolysins for controlling planktonic and biofilm cells. The endolysins, LysEP114 and LysEP135, were obtained from plasmid vectors containing the endolysin genes derived from Escherichia coli phages. The high identity (>96 %) was observed between LysEP114 and LysEP135. LysEP114 and LysEP135 were characterized by pH, thermal, and lactic acid stability, lytic spectrum, antibacterial activity, and biofilm eradication. The molecular masses of LysEP114 and LysEP135 were 18.2 kDa, identified as muramidases. LysEP114 and LysEP135 showed high lytic activity against the outer membrane-permeabilized E. coli KCCM 40405 at below 37 °C, between pH 5 to 11, and below 70 mM of lactic acid. LysEP114 and LysEP135 showed the broad rang of lytic activity against E. coli KACC 10115, S. Typhimurium KCCM 40253, S. Typhimurium CCARM 8009, tetracycline-resistant S. Typhimurium, polymyxin B-resistant S. Typhimurium, chloramphenicol-resistant S. Typhimurium, K. pneumoniae ATCC 23357, K. pneumoniae CCARM 10237, and Shigella boydii KACC 10792. LysEP114 and LysEP135 effectively reduced the numbers of planktonic E. coli KCCM by 1.7 and 2.1 log, respectively, when treated with 50 mM lactic acid. The numbers of biofilm cells were reduced from 7.3 to 4.1 log CFU/ml and 2.2 log CFU/ml, respectively, when treated with LysEP114- and LysEP135 in the presence of 50 mM lactic acid. The results suggest that the endolysins in combination with lactic acid could be potential alternative therapeutic agents for controlling planktonic and biofilm cells.

Emerging roles of bacteriophage-based therapeutics in combating antibiotic resistance

Amid the growing challenge of antibiotic resistance on a global scale, there has been a notable resurgence in bacteriophage-based treatments, signaling a shift in our approach to managing infections. Bacteriophages (BPs), bacterial predators of nature, present a promising alternative for tackling infections caused by antibiotic-resistant pathogens. This review delves into the intricate relationship between bacteriophages and resistant bacteria, exploring various treatment strategies. Drawing upon both preclinical and clinical studies, the review highlights the effectiveness of bacteriophage therapy, particularly when integrated synergistically with conventional antibiotics. It discusses various treatment approaches for systemic and localized infections, demonstrating the adaptability of bacteriophage therapy across different clinical scenarios. Furthermore, the formulation and delivery of bacteriophages shed light on the various methods used to encapsulate and administer them effectively. It also acknowledges the challenge of bacterial resistance to bacteriophages and the ongoing efforts to overcome this hurdle. In addition, this review highlights the importance of the bacteriophage sensitivity profile (phagogram), which helps tailor treatment regimens to individual patients and specific pathogens. By surpassing the limitations of traditional antibiotics, bacteriophage-based therapies offer a personalized and potent solution against antibiotic resistance, promising to reshape the future of infectious disease management.

X-ray structure and mutagenesis analyses of Clostridioides difficile endolysin Ecd09610 glucosaminidase domain

Clostridioides difficile endolysin (Ecd09610) consists of an unknown domain at its N terminus, followed by two catalytic domains, a glucosaminidase domain and endopeptidase domain. X-ray structure and mutagenesis analyses of the Ecd09610 catalytic domain with glucosaminidase activity (Ecd09610CD53) were performed. Ecd09610CD53 was found to possess an α-bundle-like structure with nine helices, which is well conserved among GH73 family enzymes. The mutagenesis analysis based on X-ray structures showed that Glu405 and Asn470 were essential for enzymatic activity. Ecd09610CD53 may adopt a neighboring-group mechanism for a catalytic reaction in which Glu405 acted as an acid/base catalyst and Asn470 helped to stabilize the oxazolinium ion intermediate. Structural comparisons with the newly identified Clostridium perfringens autolysin catalytic domain (AcpCD) in the P1 form and a zymography analysis demonstrated that AcpCD was 15-fold more active than Ecd09610CD53. The strength of the glucosaminidase activity of the GH73 family appears to be dependent on the depth of the substrate-binding groove.

Yeast Expressing a Phage Endolysin Reduces Endogenous Clostridium perfringens Ex Vivo in 21-Day-Old Broiler Chicken Intestinal Fluids

The phage endolysin PlyCP41 when purified from Escherichia coli exhibits lytic activity against Clostridium perfringens (CP) in vitro. The anti-clostridial activity of PlyCP41 endolysin expressed in transgenic yeast (Saccharomyces cerevisiae) was verified in phosphate buffered saline via mixing experiments with cultured CP and transgenic yeast slurries followed by serial dilution plating and colony counts on tryptose sulfite cycloserine (CP indicator) plates. The transgenic yeast containing PlyCP41 resulted in a log10 4.5 reduction (99.997%; P < 0.01) of the cultured CP. In addition, this serial dilution plating assay was used to demonstrate that transgenic yeast slurries could reduce the endogenous CP content in fluids from three different gastrointestinal regions (proximal, medial, and distal) from 21-day-old broiler chickens. The transgenic yeast treatment of gut slurries resulted in a log 10 1.19, 4.53, and 1.28 reduction in proximal, medial, and distal gut slurries (90% to 99.99% of the endogenous CP; P < 0.01), respectively, compared to nontreatment controls. These results indicate that the phage endolysin PlyCP41 expressed in S. cerevisiae is effective at reducing the endogenous CP in gastrointestinal fluids of broiler chickens. Future studies will measure the anti-CP effect in vivo by administering transgenic yeast to broiler chickens in the feed.

Current Knowledge and Perspectives of Phage Therapy for Combating Refractory Wound Infections

Wound infection is one of the most important factors affecting wound healing, so its effective control is critical to promote the process of wound healing. However, with the increasing prevalence of multi-drug-resistant (MDR) bacterial strains, the prevention and treatment of wound infections are now more challenging, imposing heavy medical and financial burdens on patients. Furthermore, the diminishing effectiveness of conventional antimicrobials and the declining research on new antibiotics necessitate the urgent exploration of alternative treatments for wound infections. Recently, phage therapy has been revitalized as a promising strategy to address the challenges posed by bacterial infections in the era of antibiotic resistance. The use of phage therapy in treating infectious diseases has demonstrated positive results. This review provides an overview of the mechanisms, characteristics, and delivery methods of phage therapy for combating pathogenic bacteria. Then, we focus on the clinical application of various phage therapies in managing refractory wound infections, such as diabetic foot infections, as well as traumatic, surgical, and burn wound infections. Additionally, an analysis of the potential obstacles and challenges of phage therapy in clinical practice is presented, along with corresponding strategies for addressing these issues. This review serves to enhance our understanding of phage therapy and provides innovative avenues for addressing refractory infections in wound healing.

Synthetic mRNA delivered to human cells leads to expression of Cpl-1 bacteriophage-endolysin with activity against Streptococcus pneumoniae

Endolysins are bacteriophage-encoded hydrolases that show high antibacterial activity and a narrow substrate spectrum. We hypothesize that an mRNA-based approach to endolysin therapy can overcome some challenges of conventional endolysin therapy, namely organ targeting and bioavailability. We show that synthetic mRNA applied to three human cell lines (HEK293T, A549, HepG2 cells) leads to expression and cytosolic accumulation of the Cpl-1 endolysin with activity against Streptococcus pneumoniae. Addition of a human lysozyme signal peptide sequence translocates the Cpl-1 to the endoplasmic reticulum leading to secretion (hlySP-sCpl-1). The pneumococcal killing effect of hlySP-sCpl-1 was enhanced by introduction of a point mutation to avoid N-linked-glycosylation. hlySP-sCpl-1N215D, collected from the culture supernatant of A549 cells 6 h post-transfection showed a significant killing effect and was active against nine pneumococcal strains. mRNA-based cytosolic Cpl-1 and secretory hlySP-sCpl-1N215D show potential for innovative treatment strategies against pneumococcal disease and, to our best knowledge, represent the first approach to mRNA-based endolysin therapy. We assume that many other bacterial pathogens could be targeted with this novel approach.

Bacteriophages: Status quo and emerging trends toward one health approach

The alarming rise in antimicrobial resistance (AMR) among the drug-resistant pathogens has been attributed to the ESKAPEE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, Enterobacter sp., and Escherichia coli). Recently, these AMR microbes have become difficult to treat, as they have rendered the existing therapeutics ineffective. Thus, there is an urgent need for effective alternatives to lessen or eliminate the current infections and limit the spread of emerging diseases under the "One Health" framework. Bacteriophages (phages) are naturally occurring biological resources with extraordinary potential for biomedical, agriculture/food safety, environmental protection, and energy production. Specific unique properties of phages, such as their bactericidal activity, host specificity, potency, and biocompatibility, make them desirable candidates in therapeutics. The recent biotechnological advancement has broadened the repertoire of phage applications in nanoscience, material science, physical chemistry, and soft-matter research. Herein, we present a comprehensive review, coupling the substantial aspects of phages with their applicability status and emerging opportunities in several interdependent areas under one health concept. Consolidating the recent state-of-the-art studies that integrate human, animal, plant, and environment health, the following points have been highlighted: (i) The biomedical and pharmacological advantages of phages and their antimicrobial derivatives with particular emphasis on in-vivo and clinical studies. (ii) The remarkable potential of phages to be altered, improved, and applied for drug delivery, biosensors, biomedical imaging, tissue engineering, energy, and catalysis. (iii) Resurgence of phages in biocontrol of plant, food, and animal-borne pathogens. (iv) Commercialization of phage-based products, current challenges, and perspectives.

The Next Generation of Drug Delivery: Harnessing the Power of Bacteriophages

The use of biomaterials, such as bacteriophages, as drug delivery vehicles (DDVs) has gained increasing interest in recent years due to their potential to address the limitations of conventional drug delivery systems. Bacteriophages offer several advantages as drug carriers, such as high specificity for targeting bacterial cells, low toxicity, and the ability to be engineered to express specific proteins or peptides for enhanced targeting and drug delivery. In addition, bacteriophages have been shown to reduce the development of antibiotic resistance, which is a major concern in the field of antimicrobial therapy. Many initiatives have been taken to take up various payloads selectively and precisely by surface functionalization of the outside or interior of self-assembling viral protein capsids. Bacteriophages have emerged as a promising platform for the targeted delivery of therapeutic agents, including drugs, genes, and imaging agents. They possess several properties that make them attractive as drug delivery vehicles, including their ability to specifically target bacterial cells, their structural diversity, their ease of genetic manipulation, and their biocompatibility. Despite the potential advantages of using bacteriophages as drug carriers, several challenges and limitations need to be addressed. One of the main challenges is the limited host range of bacteriophages, which restricts their use to specific bacterial strains. However, this can also be considered as an advantage, as it allows for precise and targeted drug delivery to the desired bacterial cells. The use of biomaterials, including bacteriophages, as drug delivery vehicles has shown promising potential to address the limitations of conventional drug delivery systems. Further research is needed to fully understand the potential of these biomaterials and address the challenges and limitations associated with their use.

Role of bacteriophages in shaping gut microbial community

Phages are the most diversified and dominant members of the gut virobiota. They play a crucial role in shaping the structure and function of the gut microbial community and consequently the health of humans and animals. Phages are found mainly in the mucus, from where they can translocate to the intestinal organs and act as a modulator of gut microbiota. Understanding the vital role of phages in regulating the composition of intestinal microbiota and influencing human and animal health is an emerging area of research. The relevance of phages in the gut ecosystem is supported by substantial evidence, but the importance of phages in shaping the gut microbiota remains unclear. Although information regarding general phage ecology and development has accumulated, detailed knowledge on phage-gut microbe and phage-human interactions is lacking, and the information on the effects of phage therapy in humans remains ambiguous. In this review, we systematically assess the existing data on the structure and ecology of phages in the human and animal gut environments, their development, possible interaction, and subsequent impact on the gut ecosystem dynamics. We discuss the potential mechanisms of prophage activation and the subsequent modulation of gut bacteria. We also review the link between phages and the immune system to collect evidence on the effect of phages on shaping the gut microbial composition. Our review will improve understanding on the influence of phages in regulating the gut microbiota and the immune system and facilitate the development of phage-based therapies for maintaining a healthy and balanced gut microbiota.

Molecular Machinery of the Triad Holin, Endolysin, and Spanin: Key Players Orchestrating Bacteriophage-Induced Cell Lysis and their Therapeutic Applications

Phage therapy, a promising alternative to combat multidrug-resistant bacterial infections, harnesses the lytic cycle of bacteriophages to target and eliminate bacteria. Key players in this process are the phage lysis proteins, including holin, endolysin, and spanin, which work synergistically to disrupt the bacterial cell wall and induce lysis. Understanding the structure and function of these proteins is crucial for the development of effective therapies. Recombinant versions of these proteins have been engineered to enhance their stability and efficacy. Recent progress in the field has led to the approval of bacteriophage-based therapeutics as drugs, paving the way for their clinical use. These proteins can be combined in phage cocktails or combined with antibiotics to enhance their activity against bacterial biofilms, a common cause of treatment failure. Animal studies and clinical trials are being conducted to evaluate the safety and efficacy of phage therapy in humans. Overall, phage therapy holds great potential as a valuable tool in the fight against multidrug- resistant bacteria, offering hope for the future of infectious disease treatment.

Multidisciplinary Methods for Screening Toxic Proteins from Phages and Their Potential Molecular Targets

This chapter presents a comprehensive methodology for the identification, characterization, and functional analyses of potentially toxic hypothetical proteins of unknown function (toxHPUFs) in phages. The methods begin with in vivo toxicity verification of toxHPUFs in bacterial hosts, utilizing conventional drop tests and following growth curves. Computational methods for structural and functional predictions of toxHPUFs are outlined, incorporating the use of tools such as Phyre2, HHpred, and AlphaFold2. To ascertain potential targets, a comparative genomic approach is described using bioinformatics toolkits for sequence alignment and functional annotation. Moreover, steps are provided to predict protein-protein interactions and visualizing these using PyMOL. The culmination of these methods equips researchers with an effective pipeline to identify and analyze toxHPUFs and their potential targets, laying the groundwork for future experimental confirmations.

Bacteriophage endolysin Ply113 as a potent antibacterial agent against polymicrobial biofilms formed by enterococci and Staphylococcus aureus

Antibiotic resistance in Enterococcus faecium, Enterococcus faecalis, and Staphylococcus aureus remains a major public health concern worldwide. Furthermore, these microbes frequently co-exist in biofilm-associated infections, largely nullifying antibiotic-based therapy. Therefore, it is imperative to develop an efficient therapeutic strategy for combating infections caused by polymicrobial biofilms. In this study, we investigated the antibacterial and antibiofilm activity of the bacteriophage endolysin Ply113 in vitro. Ply113 exhibited high and rapid lytic activity against E. faecium, E. faecalis, and S. aureus, including vancomycin-resistant Enterococcus and methicillin-resistant S. aureus isolates. Transmission electron microscopy revealed that Ply113 treatment led to the detachment of bacterial cell walls and considerable cell lysis. Ply113 maintained stable lytic activity over a temperature range of 4-45°C, over a pH range of 5.0-8.0, and in the presence of 0-400 mM NaCl. Ply113 treatment effectively eliminated the mono-species biofilms formed by E. faecium, E. faecalis, and S. aureus in a dose-dependent manner. Ply113 was also able to eliminate the dual-species biofilms of E. faecium-S. aureus and E. faecalis-S. aureus. Additionally, Ply113 exerted potent antibacterial efficacy in vivo, distinctly decreasing the bacterial loads in a murine peritoneal septicemia model. Our findings suggest that the bacteriophage endolysin Ply113 is a promising antimicrobial agent for the treatment of polymicrobial infections.

Cell wall polysaccharides of streptococci: A genetic and structural perspective

The Streptococcus genus comprises both commensal and pathogenic species. Additionally, Streptococcus thermophilus is exploited in fermented foods and in probiotic preparations. The ecological and metabolic diversity of members of this genus is matched by the complex range of cell wall polysaccharides that they present on their cell surfaces. These glycopolymers facilitate their interactions and environmental adaptation. Here, current knowledge on the genetic and compositional diversity of streptococcal cell wall polysaccharides including rhamnose-glucose polysaccharides, exopolysaccharides and teichoic acids is discussed. Furthermore, the species-specific cell wall polysaccharide combinations and specifically highlighting the presence of rhamnose-glucose polysaccharides in certain species, which are replaced by teichoic acids in other species. This review highlights model pathogenic and non-pathogenic species for which there is considerable information regarding cell wall polysaccharide composition, structure and genetic information. These serve as foundations to predict and focus research efforts in other streptococcal species for which such data currently does not exist.

Beyond faecal microbiota transplantation, the non-negligible role of faecal virome or bacteriophage transplantation

Intestinal microbiota, which contains bacteria, archaea, fungi, protists, and viruses including bacteriophages, is symbiotic and evolves together with humans. The balanced intestinal microbiota plays indispensable roles in maintaining and regulating host metabolism and health. Dysbiosis has been associated with not only intestinal diseases but other diseases such as neurology disorders and cancers. Faecal microbiota transplantation (FMT) or faecal virome or bacteriophage transplantation (FVT or FBT), transfers faecal bacteria or viruses, with a focus on bacteriophage, from one healthy individual to another individual (normally unhealthy condition), and aims to restore the balanced gut microbiota and assist in subduing diseases. In this review, we summarized the applications of FMT and FVT in clinical settings, discussed the advantages and challenges of FMT and FVT currently and proposed several considerations prospectively. We further provided our understanding of why FMT and FVT have their limitations and raised the possible future development strategy of FMT and FVT.

Expression of a recombinant endolysin from bacteriophage CAP 10-3 with lytic activity against Cutibacterium acnes

The bacteriophage CAP 10-3 forming plaques against Cutibacterium acnes which causes skin acne was previously isolated from human skin acne lesion. Incomplete whole genome sequence (WGS) of the bacteriophage CAP 10-3 was obtained and it had 29,643 bp long nucleotide with 53.86% GC content. The sequence was similar to C. acnes phage PAP 1-1 with a nucleotide sequence identity of 89.63% and the bacteriophage belonged to Pahexavirus. Bioinformatic analysis of the WGS predicted 147 ORFs and functions of 40 CDSs were identified. The predicted endolysin gene of bacteriophage CAP 10-3 was 858 bp long which was deduced as 285 amino acids (~ 31 kDa). The protein had the highest similarity with amino acid sequence of the endolysin from Propionibacterium phage PHL071N05 with 97.20% identity. The CAP 10-3 endolysin gene was amplified by PCR with primer pairs based on the gene sequence, cloned into an expression vector pET-15b and transformed into Escherichia coli BL21(DE3) strain. The predicted protein band (~ 33 kDa) for the recombinant endolysin was detected in an SDS-PAGE gel and western blot assay. The concentrated supernatant of cell lysate from E. coli BL21(DE3) (pET-15b_CAP10-3 end) and a partially purified recombinant CAP 10-3 endolysin showed antibacterial activity against C. acnes KCTC 3314 in a dose-dependent manner. In conclusion, the recombinant CAP 10-3 endolysin was successfully produced in E. coli strain and it can be considered as a therapeutic agent candidate for treatment of human skin acne.

Characterization of 29 newly isolated bacteriophages as a potential therapeutic agent against IMP-6-producing Klebsiella pneumoniae from clinical specimens

Carbapenemase-producing Enterobacteriaceae (CPE) are one of the most detrimental species of antibiotic-resistant bacteria globally. Phage therapy has emerged as an effective strategy for the treatment of CPE infections. In western Japan, the rise of Klebsiella pneumoniae strains harboring the pKPI-6 plasmid encoding bla IMP-6 is of increasing concern. To address this challenge, we isolated 29 phages from Japanese sewage, specifically targeting 31 K. pneumoniae strains and one Escherichia coli strain harboring the pKPI-6 plasmid. Electron microscopy analysis revealed that among the 29 isolated phages, 21 (72.4%), 5 (17.2%), and 3 (10.3%) phages belonged to myovirus, siphovirus, and podovirus morphotypes, respectively. Host range analysis showed that 18 Slopekvirus strains within the isolated phages infected 25-26 K. pneumoniae strains, indicating that most of the isolated phages have a broad host range. Notably, K. pneumoniae strain Kp21 was exclusively susceptible to phage øKp_21, whereas Kp22 exhibited susceptibility to over 20 phages. Upon administering a phage cocktail composed of 10 phages, we observed delayed emergence of phage-resistant bacteria in Kp21 but not in Kp22. Intriguingly, phage-resistant Kp21 exhibited heightened sensitivity to other bacteriophages, indicating a "trade-off" for resistance to phage øKp_21. Our proposed phage set has an adequate number of phages to combat the K. pneumoniae strain prevalent in Japan, underscoring the potential of a well-designed phage cocktail in mitigating the occurrence of phage-resistant bacteria. IMPORTANCE The emergence of Klebsiella pneumoniae harboring the bla IMP-6 plasmid poses an escalating threat in Japan. In this study, we found 29 newly isolated bacteriophages that infect K. pneumoniae strains carrying the pKPI-6 plasmid from clinical settings in western Japan. Our phages exhibited a broad host range. We applied a phage cocktail treatment composed of 10 phages against two host strains, Kp21 and Kp22, which displayed varying phage susceptibility patterns. Although the phage cocktail delayed the emergence of phage-resistant Kp21, it was unable to hinder the emergence of phage-resistant Kp22. Moreover, the phage-resistant Kp21 became sensitive to other phages that were originally non-infective to the wild-type Kp21 strains. Our study highlights the potential of a well-tailored phage cocktail in reducing the occurrence of phage-resistant bacteria.

LYZ2-SH3b as a novel and efficient enzybiotic against methicillin-resistant Staphylococcus aureus

BACKGROUND

Enzybiotics are promising alternatives to conventional antibiotics for drug-resistant infections. Exolysins, as a class of enzybiotics, show antibacterial effects against methicillin-resistant Staphylococcus aureus (MRSA). This study evaluated a novel exolysin containing an SH3b domain for its antibacterial activity against MRSA.

METHODS

This study designed a chimeric exolysin by fusing the Cell-binding domain (SH3b) from Lysostaphin with the lytic domain (LYZ2) from the gp61 enzyme. Subsequently, LYZ2-SH3b was cloned and expressed in Escherichia coli (E. coli). Finally, the antibacterial effects of LYZ2-SH3b compared with LYZ2 and vancomycin against reference and clinical isolates of MRSA were measured using the disc diffusion method, the minimal inhibitory concentration (MIC), and the minimal bactericidal concentration (MBC) assays.

RESULTS

Analysis of bioinformatics showed that LYZ2-SH3b was stable, soluble, and non-allergenic. Protein purification was performed with a 0.8 mg/ml yield for LYZ2-SH3b. The plate lysis assay results indicated that, at the same concentrations, LYZ2-SH3b has a more inhibitory effect than LYZ2. The MICs of LYZ2 were 4 µg/mL (ATCC 43,300) and 8 µg/mL (clinical isolate ST239), whereas, for LYZ2-SH3b, they were 2 µg/mL (ATCC 43,300) and 4 µg/mL (clinical isolate ST239). This suggests a higher efficiency of LYZ2-SH3b compared to LYZ2. Furthermore, the MBCs of LYZ2 were 4 µg/mL (ATCC 43,300) and 8 µg/mL (clinical isolate ST239), whereas, for LYZ2-SH3b, they were 2 µg/mL (ATCC 43,300) and 4 µg/mL (clinical isolate ST239), thus confirming the superior lytic activity of LYZ2-SH3b over LYZ2.

CONCLUSIONS

The study suggests that phage endolysins, such as LYZ2-SH3b, may represent a promising new approach to treating MRSA infections, particularly in cases where antibiotic resistance is a concern. But further studies are needed.

Combined antimicrobial effect of phage-derived endolysin and depolymerase against biofilm-forming Salmonella Typhimurium

This study was designed to evaluate the antimicrobial activity of phage-derived endolysin (LysPB32) and depolymerase (DpolP22) against planktonic and biofilm cells of Salmonella Typhimurium (STKCCM). Compared to the control, the numbers of STKCCM were reduced by 4.3 and 5.9 log, respectively, at LysPB32 and LysPB32 + DpolP22 in the presence of polymyxin B (PMB) after 48-h incubation at 37 °C. LysPB32 + DpolP22 decreased the relative fitness (0.8) and the cross-resistance of STKCCM to chloramphenicol (CHL), cephalothin (CEP), ciprofloxacin (CIP), and tetracycline (TET) in the presence of PMB. The MICtrt/MICcon ratios of CHL, CEP, CIP, PMB, and TET were between 0.25 and 0.50 for LysPB32 + DpolP22 in the presence of PMB. These results suggest that the application of phage-encoded enzymes with antibiotics can be a promising approach for controlling biofilm formation on medical and food-processing equipment. This is noteworthy in that the application of LysPB32 + DpolP22 could increase antibiotic susceptibility and decrease cross-resistance to other antibiotics.

Discovery of Bactericidal Proteins from Staphylococcus Phage Stab21 Using a High-Throughput Screening Method

In the escalating battle against antimicrobial resistance, there is an urgent need to discover and investigate new antibiotic strategies. Bacteriophages are untapped reservoirs of such potential antimicrobials. This study focused on Hypothetical Proteins of Unknown Function (HPUFs) from a Staphylococcus phage Stab21. We examined its HPUFs for bactericidal activity against E. coli using a Next Generation Sequencing (NGS)-based approach. Among the 96 HPUFs examined, 5 demonstrated cross-species toxicity towards E. coli, suggesting the presence of shared molecular targets between E. coli and S. aureus. One toxic antibacterial HPUF (toxHPUF) was found to share homology with a homing endonuclease. The implications of these findings are profound, particularly given the potential broad applicability of these bactericidal agents. This study confirms the efficacy of NGS in streamlining the screening process of toxHPUFs, contributes significantly to the ongoing exploration of phage biology, and offers promises in the search for potent antimicrobial agents.

Phage therapy for Acinetobacter baumannii infection

Acinetobacter is a gram-negative nosocomial pathogenic bacteria. The contributing factor for the pathogenicity of Acinetobacter is severe due to its property of antibacterial drug resistance. Often antibiotic treatment is used to treat bacterial infection, however due to the resistance of a broad range of antibiotics by Acinetobacter the treatment viability of this bacterial species seems to be reduced. To combat this diverse treatment options are being incorporated with phage therapy being an effective choice due to its intrinsic property to infect bacteria. In this chapter the various phage therapy used in recent times has been elaborated on. The phage therapy is considered to be in response to Carbapenem resistance. The various mode of phage propagation has been mentioned in this chapter along with the type of resistance conferred to the administered therapy. The chapter deals with the advances observed due to therapy of Acibel004, Acibel007, vB-GEC_Ab-M-G7, ZZ1 and Bacteriophage p54 containing Endolysin LysAB54 bacteriophages have been elucidated.

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.

Identification of three capsule depolymerases in a bacteriophage infecting Klebsiella pneumoniae capsular types K7, K20, and K27 and therapeutic application

BACKGROUND

Klebsiella pneumoniae capsular types K1, K2, K5, K20, K54, and K57 are prevalent hypervirulent types associated with community infections, and worrisomely, hypervirulent strains that acquired drug resistance have been found. In the search for alternative therapeutics, studies have been conducted on phages that infect K. pneumoniae K1, K2, K5, and K57-type strains and their phage-encoded depolymerases. However, phages targeting K. pneumoniae K20-type strains and capsule depolymerases capable of digesting K20-type capsules have rarely been reported. In this study, we characterized a phage that can infect K. pneumoniae K20-type strains, phage vB_KpnM-20.

METHODS

A phage was isolated from sewage water in Taipei, Taiwan, its genome was analyzed, and its predicted capsule depolymerases were expressed and purified. The host specificity and capsule-digesting activity of the capsule depolymerases were determined. The therapeutic effect of the depolymerase targeting K. pneumoniae K20-type strains was analyzed in a mouse infection model.

RESULTS

The isolated Klebsiella phage, vB_KpnM-20, infects K. pneumoniae K7, K20, and K27-type strains. Three capsule depolymerases, K7dep, K20dep, and K27dep, encoded by the phage were specific to K7, K20, and K27-type capsules, respectively. K20dep also recognized Escherichia coli K30-type capsule, which is highly similar to K. pneumoniae K20-type. The survival of K. pneumoniae K20-type-infected mice was increased following administration of K20dep.

CONCLUSIONS

The potential of capsule depolymerase K20dep for the treatment of K. pneumoniae infections was revealed using an in vivo infection model. In addition, K7dep, K20dep, and K27dep capsule depolymerases could be used for K. pneumoniae capsular typing.

Understanding the Molecular Basis for Homodimer Formation of the Pneumococcal Endolysin Cpl-1

The rise of multi-drug-resistant bacteria that cannot be treated with traditional antibiotics has prompted the search for alternatives to combat bacterial infections. Endolysins, which are bacteriophage-derived peptidoglycan hydrolases, are attractive tools in this fight. Several studies have already demonstrated the efficacy of endolysins in targeting bacterial infections. Endolysins encoded by bacteriophages that infect Gram-positive bacteria typically possess an N-terminal catalytic domain and a C-terminal cell-wall binding domain (CWBD). In this study, we have uncovered the molecular mechanisms that underlie formation of a homodimer of Cpl-1, an endolysin that targets Streptococcus pneumoniae. Here, we use site-directed mutagenesis, analytical size exclusion chromatography, and analytical ultracentrifugation to disprove a previous suggestion that three residues at the N-terminus of the CWBD are involved in the formation of a Cpl-1 dimer in the presence of choline in solution. We conclusively show that the C-terminal tail region of Cpl-1 is involved in formation of the dimer. Alanine scanning mutagenesis generated various tail mutant constructs that allowed identification of key residues that mediate Cpl-1 dimer formation. Finally, our results allowed identification of a consensus sequence (FxxEPDGLIT) required for choline-dependent dimer formation─a sequence that occurs frequently in pneumococcal autolysins and endolysins. These findings shed light on the mechanisms of Cpl-1 and related enzymes and can be used to inform future engineering efforts for their therapeutic development against S. pneumoniae.

The Post-Antibiotic Era: A New Dawn for Bacteriophages

Phages are the most biologically diverse entities in the biosphere, infecting specific bacteria. Lytic phages quickly kill bacteria, while lysogenic phages integrate their genomes into bacteria and reproduce within the bacteria, participating in the evolution of natural populations. Thus, lytic phages are used to treat bacterial infections. However, due to the huge virus invasion, bacteria have also evolved a special immune mechanism (CRISPR-Cas systems, discovered in 1987). Therefore, it is necessary to develop phage cocktails and synthetic biology methods to infect bacteria, especially against multidrug-resistant bacteria infections, which are a major global threat. This review outlines the discovery and classification of phages and the associated achievements in the past century. The main applications of phages, including synthetic biology and PT, are also discussed, in addition to the effects of PT on immunity, intestinal microbes, and potential safety concerns. In the future, combining bioinformatics, synthetic biology, and classic phage research will be the way to deepen our understanding of phages. Overall, whether phages are an important element of the ecosystem or a carrier that mediates synthetic biology, they will greatly promote the progress of human society.

Phages for treatment of Klebsiella pneumoniae infections

Klebsiella pneumoniae is an opportunistic pathogen involved in both hospital- and community-acquired infections. K. pneumoniae is associated with various infections, including pneumonia, septicemia, meningitis, urinary tract infection, and surgical wound infection. K. pneumoniae possesses serious virulence, biofilm formation ability, and severe resistance to many antibiotics especially hospital-acquired strains, due to excessive use in healthcare systems. This limits the available effective antibiotics that can be used for patients suffering from K. pneumoniae infections; therefore, alternative treatments are urgently needed. Bacteriophages (for short, phages) are prokaryotic viruses capable of infecting, replicating, and then lysing (lytic phages) the bacterial host. Phage therapy exhibited great potential for treating multidrug-resistant bacterial infections comprising K. pneumoniae. Hence, this chapter emphasizes and summarizes the research articles in the PubMed database from 1948 until the 15th of December 2022, addressing phage therapy against K. pneumoniae. The chapter provides an overview of K. pneumoniae phages covering different aspects, including phage isolation, different morphotypes of isolated phages, in vitro characterization, anti-biofilm activity, various therapeutic forms, in vivo research and clinical studies.

Endolysins of bacteriophages

Bacteriophage endolysins are a biologically active substances that play a specific role in the release of phage progeny by degrading the peptidoglycan of the host bacterium. In the light of antibiotic resistance, endolysins are considered as alternative therapeutic agents because of their exceptional ability to target bacterial cells. Aim summarization of the data on the biology, structure, mechanisms of action of bacteriophage endolysins, as well as on preparations based on them, which are at different stages of research. The results of studies of bacterial endolysins over the past 20 years were searched using the Internet resources PubMed, Web of Science, Scopus in English for the keywords: lysin, bacteriophages, holin, antibiotic resistance. The analysis of literature data showed that the structure of phage endolysins of Gram-positive and Gram-negative bacteria differs from each other and reflects differences in their architecture due to variation in the cell wall composition of these two major bacterial groups. Depending on the cleavable bond in peptidoglycan, endolysins can be divided into at least five different groups: glycosidases (two groups aminidases and muramidases), endopeptidases, specific amidogyrolases, and lytic transglycosylases. To date, endolysins effective against a number of pathogens have been studied, including Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Staphylococcus aureus, Mycobacterium spp., Pseudomonas aeruginosa, etc. A number of studies have shown the therapeutic potential of endolysins in combating antibiotic-resistant infections.

Whole genome sequencing and annotation of a lysogenic phage vB_EcoP_DE5 isolated from donkey-derived Escherichia coli

A lysogenic phage vB_EcoP_DE5 (hereafter designated DE5) was isolated from donkey-derived Escherichia coli. The bacteriophage was examined by transmission electron microscopy, and the result showed that DE5 belonged to the genus Kuravirus. DE5 was sensitive to changes in temperature and pH, and it could maintain its activity at pH 7 and below 60 ℃. The whole genome sequencing revealed that DE5 had a double-stranded DNA genome of 77, 305 bp with 42.09% G+C content. A total of 126 open reading frames (ORFs) were identified, including functional genes related to phage integration, DNA replication and modification, transcriptional regulation, structural and packaging proteins, and host cell lysis. One phage integrase gene, one autotransporter adhesin gene, and one tRNA gene were predicted in the whole genome, and no genes associated with drug resistance were identified. The phage DE5 integrase contained 187 amino acids and belonged to the small serine recombinase family. BLASTn analysis revealed that phage DE5 had a high-sequence identity (96%) with E. coli phage SU10. Phylogenetic analysis showed that phage DE5 was a member of the genus Kuravirus. The whole genome sequencing of lysogenic phage DE5 enhanced our understanding of lysogenic phages and their therapeutic applications.

Bacteriophage-based techniques for elucidating the function of zebrafish gut microbiota

Bacteriophages (or phages) are unique viruses that can specifically infect bacteria. Since their discovery by Twort and d'Herelle, phages with bacterial specificity have played important roles in microbial regulation. The intestinal microbiota and host health are intimately linked with nutrient, metabolism, development, and immunity aspects. However, the mechanism of interactions between the composition of the microbiota and their functions in maintaining host health still needs to be further explored. To address the lack of methodology and functions of intestinal microbiota in the host, we first proposed that, with the regulations of special intestinal microbiota and applications of germ-free (GF) zebrafish model, phages would be used to infect and reduce/eliminate the defined gut bacteria in the conventionally raised (CR) zebrafish and compared with the GF zebrafish colonized with defined bacterial strains. Thus, this review highlighted the background and roles of phages and their functional characteristics, and we also summarized the phage-specific infection of target microorganisms, methods to improve the phage specificity, and their regulation within the zebrafish model and gut microbial functional study. Moreover, the primary protocol of phage therapy to control the intestinal microbiota in zebrafish models from larvae to adults was recommended including phage screening from natural sources, identification of host ranges, and experimental design in the animal. A well understanding of the interaction and mechanism between phages and gut bacteria in the host can potentially provide powerful strategies or techniques for preventing bacteria-related human diseases by precisely regulating in vitro and in vivo, which will provide novel insights for phages' application and combined research in the future. KEY POINTS: • Zebrafish models for clarifying the microbial and phages' functions were discussed • Phages infect host bacteria with exquisite specificity and efficacy • Phages can reduce/eliminate the defined gut bacteria to clarify their function.

Bacteriophage endolysin powders for inhaled delivery against pulmonary infections

Endolysins are bacteriophage-encoded enzymatic proteins that have great potential to treat multidrug-resistant bacterial infections. Bacteriophage endolysins Cpl-1 and ClyJ-3 have shown promising antimicrobial activity against Streptococcus pneumoniae, which causes pneumonia in humans. This is the first study to investigate the feasibility of spray-dried endolysins Cpl-1 and ClyJ-3 with excipients to produce inhalable powders. The two endolysins were individually tested with leucine and sugar (lactose or trehalose) for spray drying method followed by characterization of biological and physico-chemical properties. A complete loss of ClyJ-3 bioactivity was observed after atomization of the liquid feed solution（before the drying process）, while Cpl-1 maintained its bioactivity in the spray-dried powders. Cpl-1 formulations containing leucine with lactose or trehalose showed promising physico-chemical properties (particle size, crystallinity, hygroscopicity, etc.) and aerosol performances (fine particle fraction values above 65%). The results indicated that endolysin Cpl-1 can be formulated as spray dried powders suitable for inhaled delivery to the lungs for the potential treatment of pulmonary infections.

Characterization of a lytic Pseudomonas aeruginosa phage vB_PaeP_ASP23 and functional analysis of its lysin LysASP and holin HolASP

In this study, we isolated a lytic Pseudomonas aeruginosa phage (vB_PaeP_ASP23) from the sewage of a mink farm, characterized its complete genome and analyzed the function of its putative lysin and holin. Morphological characterization and genome annotation showed that phage ASP23 belonged to the Krylovirinae family genus Phikmvvirus, and it had a latent period of 10 min and a burst size of 140 pfu/infected cell. In minks challenged with P. aeruginosa, phage ASP23 significantly reduced bacterial counts in the liver, lung, and blood. The whole-genome sequencing showed that its genome was a 42,735-bp linear and double-stranded DNA (dsDNA), with a G + C content of 62.15%. Its genome contained 54 predicted open reading frames (ORFs), 25 of which had known functions. The lysin of phage ASP23 (LysASP), in combination with EDTA, showed high lytic activity against P. aeruginosa L64. The holin of phage ASP23 was synthesized by M13 phage display technology, to produce recombinant phages (HolASP). Though HolASP exhibited a narrow lytic spectrum, it was effective against Staphylococcus aureus and Bacillus subtilis. However, these two bacteria were insensitive to LysASP. The findings highlight the potential of phage ASP23 to be used in the development of new antibacterial agents.

Chemical-Biology and Metabolomics Studies in Phage-Host Interactions

For many years, several studies have explored the molecular mechanisms involved in the infection of bacteria by their specific phages to understand the main infection strategies and the host defense strategies. The modulation of the mechanisms involved in the infection, as well as the expression of key substances in the development of the different life cycles of phages, function as a natural source of strategies capable of promoting the control of different pathogens that are harmful to human and animal health. Therefore, this chapter aims to provide an overview of the mechanisms involved in virus-bacteria interaction to explore the main compounds produced or altered as a chemical survival strategy and the metabolism modulation when occurring a host-phage interaction. In this context, emphasis will be given to the chemistry of peptides/proteins and enzymes encoded by bacteriophages in the control of pathogenic bacteria and the use of secondary metabolites recently reported as active participants in the mechanisms of phage-bacteria interaction. Finally, metabolomics strategies developed to gain new insights into the metabolism involved in the phage-host interaction and the metabolomics workflow in host-phage interaction will be presented.

Bacteriophage therapy in infection after fracture fixation (IAFF) in orthopaedic surgery

Infection after fracture fixation (IAFF) in orthopaedic surgery is a significant complication that can lead to disability due to chronic infection and/or relapsing disease, non-union necessitating revision surgery. Management of IAFF is a major challenge facing orthopaedic surgeons across the world due to two key pathogenic mechanisms of Biofilm formation and antimicrobial resistance (AMR) against traditional antibiotics. Advanced prophylactic and treatment strategies to help eradicate established infections and prevent the development of such infections are necessary. Bacteriophage therapy represents an innovative modality to treat IAFF due to multi-drug resistant organisms. We assess the current role and potential therapeutic applications of the novel bacteriophage therapy in the management of these recalcitrant infections to achieve a successful outcome.

Genome Analysis and Antibiofilm Activity of Phage 590B against Multidrug-Resistant and Extensively Drug-Resistant Uropathogenic Escherichia coli Isolates, India

Urinary tract infections (UTIs) are among the most common bacterial infections in humans. Uropathogenic Escherichia coli (UPEC), which are the most frequent agents causing community as well as hospital-acquired UTIs, have become highly drug-resistant, thus making the treatment of these infections challenging. Recently, the use of bacteriophages (or 'phages') against multidrug-resistant (MDR) and extensively drug-resistant (XDR) microorganisms has garnered significant global attention. Bacterial biofilms play a vital role in the pathogenesis of UTIs caused by UPEC. Phages have the potential to disrupt bacterial biofilms using lytic enzymes such as EPS depolymerases and endolysins. We isolated a lytic phage (590B) from community sewage in Chandigarh, which was active against multiple MDR and XDR biofilm-forming UPEC strains. During whole-genome sequencing, the 44.3 kb long genome of phage 590B encoded 75 ORFs, of which 40 were functionally annotated based on homology with similar phage proteins in the database. Comparative analysis of associated phage genomes indicated that phage 590B evolved independently and had a distinct taxonomic position within the genus Kagunavirus in the subfamily Guernseyvirinae of Siphoviridae. The phage disrupted biofilm mass effectively when applied to 24 h old biofilms formed on the Foley silicon catheter and coverslip biofilm models. To study the effect of intact biofilm architecture on phage predation, the biofilms were disrupted. The phage reduced the viable cells by 0.6-1.0 order of magnitude after 24 h of incubation. Regrowth and intact bacterial cells were observed in the phage-treated planktonic culture and biofilms, respectively, which indicated the emergence of phage-resistant bacterial variants. The phage genome encoded an endolysin which might have a role in the disruption and inhibition of bacterial biofilms. Moreover, the genome lacked genes encoding toxins, virulence factors, antibiotic resistance, or lysogeny. Therefore, lytic phage 590B may be a good alternative to antibiotics and can be included in phage cocktails for the treatment of UTIs caused by biofilm-forming MDR and XDR UPEC strains.

Tracking the phage trends: A comprehensive review of applications in therapy and food production

In the present scenario, the challenge of emerging antimicrobial resistance is affecting human health globally. The increasing incidences of multidrug-resistant infections have become harder to treat, causing high morbidity, and mortality, and are posing extensive financial loss. Limited discovery of new antibiotic molecules has further complicated the situation and has forced researchers to think and explore alternatives to antibiotics. This has led to the resurgence of the bacteriophages as an effective alternative as they have a proven history in the Eastern world where lytic bacteriophages have been used since their first implementation over a century ago. To help researchers and clinicians towards strengthening bacteriophages as a more effective, safe, and economical therapeutic alternative, the present review provides an elaborate narrative about the important aspects of bacteriophages. It abridges the prerequisite essential requirements of phage therapy, the role of phage biobank, and the details of immune responses reported while using bacteriophages in the clinical trials/compassionate grounds by examining the up-to-date case reports and their effects on the human gut microbiome. This review also discusses the potential of bacteriophages as a biocontrol agent against food-borne diseases in the food industry and aquaculture, in addition to clinical therapy. It finishes with a discussion of the major challenges, as well as phage therapy and phage-mediated biocontrols future prospects.

Phage derived lytic peptides, a secret weapon against Acinetobacter baumannii-An in silico approach

Acinetobacter baumannii is a bacterial pathogen that is commonly associated with hospital-acquired illnesses. Antimicrobial drug resistance in A. baumannii includes several penicillin classes, first and second-generation cephalosporins, cephamycins, most aminoglycosides, chloramphenicol, and tetracyclines. The recent rise in multidrug-resistant A. baumannii strains has resulted in an increase in pneumoniae associated with ventilators, urinary tract infections associated with the catheter, and bloodstream infections, all of which have increased complications in treatment, cost of treatment, and death. Small compounds known as antimicrobial peptides (AMPs) are known to have damaging effects on pathogenic bacteria. To determine their antimicrobial activity, AMPs are created from proteins acquired from various sources and evaluated in vitro. In the last phase of lytic cycle, bacteriophages release hydrolytic enzymes called endolysins that cleave the host's cell wall. Due to their superior potency and specificity compared to antibiotics, lysins are used as antibacterial agents. In the present study, different types of endolysin from phages of A. baumannii were selected based on an extensive literature survey. From the PhaLP database, the sequences of the selected lysins were retrieved in FASTA format and antimicrobial peptides were found among them. With the help of available bioinformatic tools, the anti-biofilm property, anti-fungal property, cell-penetrating property, and cellular toxicity of the antimicrobial peptides were determined. Out of the fourteen antimicrobial peptides found from the eight selected endolysins of A. baumannii specific phage, eight of them has anti-biofilm property, nine of them has anti-fungal property, five of them has cell-penetrating property and all of them are non-toxic.

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.

Phage Therapy: A Different Approach to Fight Bacterial Infections

Phage therapy is one of the alternatives to treat infections caused by both antibiotic-sensitive and antibiotic-resistant bacteria, with no or low toxicity to patients. It was started a century ago, although rapidly growing bacterial antimicrobial resistance, resulting in high levels of morbidity, mortality, and financial cost, has initiated the revival of phage therapy. It involves the use of live lytic, bioengineered, phage-encoded biological products, in combination with chemical antibiotics to treat bacterial infections. Importantly, phages will be removed from the body within seven days of clearing an infection. They target specific bacterial strains and cause minimal disruption to the microbial balance in humans. Phages for medication must be screened for the absence of resistant genes, virulent genes, cytotoxicity, and their interaction with the host tissue and organs. Since they are immunogenic, applying a high phage titer for therapy exposes them and activates the host immune system. To date, no serious side effects have been reported with human phage therapy. In this review, we describe phage–phagocyte interaction, bacterial resistance to phages, how phages conquer bacterial resistance, the role of genetic engineering and other technologies in phage therapy, and the therapeutic application of modified phages and phage-encoded products. We also highlight the comparison of antibiotics and lytic phage therapy, the pros and cons of phage therapy, determinants of human phage therapy trials, phage quality and safety requirements, phage storage and handling, and current challenges in phage therapy.

Safety Evaluation of a Novel Algal Feed Additive for Poultry Production

Feed additives are critical components for poultry health and the economic viability of antibiotic-free poultry production. The aim of the present study is to evaluate the safety of a novel algal-derived feed additive, a dried biomass powder produced from Chlamydomonas reinhardtii strain crAL082, modified to express an N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28) and a lysozyme-type enzyme (EC 3.2.1.17). A 42-day oral toxicity study showed that the crAL082 dried biomass powder was fully tolerated by broiler chicken based on the lack of detrimental effects found in performance, mortality, hematology, blood clinical chemistry, and histopathologic results compared with those of a nontreated control group, resulting in a "No Observed Adverse Effect Level" of 5000 ppm, the highest dose tested. The study demonstrates the first-ever safety result of a C. reinhardtii microalgae dried biomass powder used as a feed additive in broiler chickens. Furthermore, safety is shown for the two additional enzymes expressed within the C. reinhardtii crAL082 strain and ingested by the birds.

Genomic characterization of a new phage BUCT541 against Klebsiella pneumoniae K1-ST23 and efficacy assessment in mouse and Galleria mellonella larvae

Over the past decades, the spread of multi-drug-resistant Klebsiella pneumoniae (MDR-KP) is becoming a new threat and new effective therapies against this pathogen are needed. Bacteriophage (phage) therapy is considered to be a promising alternative treatment for MDR-KP infections compared with antibacterial drug usage. Here, we reported a new phage BUCT541 which can lyse MDR-KP ST23. The genome of BUCT541 is a double-stranded linear 46,100-bp long DNA molecule with 48% GC content through the Next generation sequencing (NGS) data. A total of 81 open reading frames and no virulence or antimicrobial resistance genes are annotated in the BUCT541 genome. BUCT541 was able to lyse 7 of the 30 tested MDR-KP according to the host range analysis. And the seven sensitive strains belonged to the K. pneumoniae K1-ST23. BUCT541 exhibited high thermal stability (4–70°C) and broad pH tolerance (pH 3-11) in the stability test. The in vivo results showed that BUCT541 (4 × 10⁵ plaque-forming units (PFU)/each) significantly increased the survival rate of K. pneumoniae infected Galleria mellonella from 5.3% to 83.3% within 48 h. Moreover, in the mouse lung infection model, high doses of BUCT541 (2 × 10⁷ PFU/each) cured 100% of BALB/c mice that were infected with K. pneumoniae. After 30 h of treatment with phage BUCT541 of the multiplicity of infection (MOI) = 10, the K. pneumoniae in the lungs of mice was lower than 10⁴ CFU/mL, compared to the control group 10⁹ CFU/mL. Together, these findings indicate that phage BUCT541 holds great promise as an alternative therapy with excellent stability and a wide lysis range for the treatment of MDR-KP ST23 infection.