'Artilysation' of endolysin λSa2lys strongly improves its enzymatic and antibacterial activity against streptococci

LysJEP8: A promising novel endolysin for combating multidrug-resistant Gram-negative bacteria

Antimicrobial resistance (AMR) is an escalating global health crisis, driven by the overuse and misuse of antibiotics. Multidrug-resistant Gram-negative bacteria, such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae, are particularly concerning due to their high morbidity and mortality rates. In this context, endolysins, derived from bacteriophages, offer a promising alternative to traditional antibiotics. This study introduces LysJEP8, a novel endolysin derived from Escherichia phage JEP8, which exhibits remarkable antimicrobial activity against key Gram-negative members of the ESKAPE group. Comparative assessments highlight LysJEP8's superior performance in reducing bacterial survival rates compared to previously described endolysins, with the most significant impact observed against P. aeruginosa, and notable effects on A. baumannii and K. pneumoniae. The study found that LysJEP8, as predicted by in silico analysis, worked best at lower pH values but lost its effectiveness at salt concentrations close to physiological levels. Importantly, LysJEP8 exhibited remarkable efficacy in the disruption of P. aeruginosa biofilms. This research underscores the potential of LysJEP8 as a valuable candidate for the development of innovative antibacterial agents, particularly against Gram-negative pathogens, and highlights opportunities for further engineering and optimization to address AMR effectively.

Bacteriophage-derived endolysins as innovative antimicrobials against bovine mastitis-causing streptococci and staphylococci: a state-of-the-art review

Bacteriophage-encoded endolysins, peptidoglycan hydrolases breaking down the Gram-positive bacterial cell wall, represent a groundbreaking class of novel antimicrobials to revolutionize the veterinary medicine field. Wild-type endolysins exhibit a modular structure, consisting of enzymatically active and cell wall-binding domains, that enable genetic engineering strategies for the creation of chimeric fusion proteins or so-called 'engineered endolysins'. This biotechnological approach has yielded variants with modified lytic spectrums, introducing new possibilities in antimicrobial development. However, the discovery of highly similar endolysins by different groups has occasionally resulted in the assignment of different names that complicate a straightforward comparison. The aim of this review was to perform a homology-based comparison of the wild-type and engineered endolysins that have been characterized in the context of bovine mastitis-causing streptococci and staphylococci, grouping homologous endolysins with ≥ 95.0% protein sequence similarity. Literature is explored by homologous groups for the wild-type endolysins, followed by a chronological examination of engineered endolysins according to their year of publication. This review concludes that the wild-type endolysins encountered persistent challenges in raw milk and in vivo settings, causing a notable shift in the field towards the engineering of endolysins. Lead candidates that display robust lytic activity are nowadays selected from screening assays that are performed under these challenging conditions, often utilizing advanced high-throughput protein engineering methods. Overall, these recent advancements suggest that endolysins will integrate into the antibiotic arsenal over the next decade, thereby innovating antimicrobial treatment against bovine mastitis-causing streptococci and staphylococci.

Antimicrobial peptide thanatin fused endolysin PA90 (Tha-PA90) for the control of Acinetobacter baumannii infection in mouse model

BACKGROUND

This study addresses the urgent need for infection control agents driven by the rise of drug-resistant pathogens such as Acinetobacter baumannii. Our primary aim was to develop and assess a novel endolysin, Tha-PA90, designed to combat these challenges.

METHODS

Tha-PA90 incorporates an antimicrobial peptide (AMP) called thanatin at its N-terminus, enhancing bacterial outer membrane permeability and reducing host immune responses. PA90 was selected as the endolysin component. The antibacterial activity of the purified Tha-PA90 was evaluated using an in vitro colony-forming unit (CFU) reduction assay and a membrane permeability test. A549 cells were utilized to measure the penetration into the cytosol and the cytotoxicity of Tha-PA90. Finally, infection control was monitored in A. baumannii infected mice following the intraperitoneal administration of Tha-PA90.

RESULTS

Tha-PA90 demonstrated remarkable in vitro efficacy, completely eradicating A. baumannii strains, even drug-resistant variants, at a low concentration of 0.5 μM. Notably, it outperformed thanatin, achieving only a < 3-log reduction at 4 μM. Tha-PA90 exhibited 2-3 times higher membrane permeability than a PA90 and thanatin mixture or PA90 alone. Tha-PA90 was found within A549 cells' cytosol with no discernible cytotoxic effects. Furthermore, Tha-PA90 administration extended the lifespan of A. baumannii-infected mice, reducing bacterial loads in major organs by up to 3 logs. Additionally, it decreased proinflammatory cytokine levels (TNF-α and IL-6), reducing the risk of sepsis from rapid bacterial lysis. Our findings indicate that Tha-PA90 is a promising solution for combating drug-resistant A. baumannii. Its enhanced efficacy, low cytotoxicity, and reduction of proinflammatory responses render it a potential candidate for infection control.

CONCLUSIONS

This study underscores the significance of engineered endolysins in addressing the pressing challenge of drug-resistant pathogens and offers insights into improved infection management strategies.

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.

The therapeutic effect of engineered phage, derived protein and enzymes against superbug bacteria

Defending against antibiotic-resistant infections is similar to fighting a war with limited ammunition. As the new century unfolded, antibiotic resistance became a significant concern. In spite of the fact that phage treatment has been used as an effective means of fighting infections for more than a century, researchers have had to overcome many challenges of superbug bacteria by manipulating phages and producing engineered enzymes. New enzymes and phages with enhanced properties have a significant impact on the ability to fight antibiotic-resistant infections, which is considered a window of hope for the future. This review, therefore, illustrates not only the challenges caused by antibiotic resistance and superbug bacteria but also the engineered enzymes and phages that are being developed to solve these issues. Our study found that engineered phages, phage proteins, and enzymes can be effective in treating superbug bacteria and destroying the biofilm caused by them. Combining these engineered compounds with other antimicrobial substances can increase their effectiveness against antibiotic-resistant bacteria. Therefore, engineered phages, proteins, and enzymes can be used as a substitute for antibiotics or in combination with antibiotics to treat patients with superbug infections in the future.

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.

Development of engineered endolysins with in vitro intracellular activity against streptococcal bovine mastitis-causing pathogens

Bacteriophage-derived endolysins are a novel class of antimicrobials known to rapidly kill bacteria, including antibiotic-resistant strains. We here engineered endolysins against the bovine mastitis pathogens Streptococcus uberis, Streptococcus agalactiae and Streptococcus dysgalactiae, also targeting intracellular survival and biofilm formation. For this purpose, high-throughput DNA assembly was used to create a library with >80,000 theoretical endolysin variants for screening of their bacteriolytic activity against Gram-positive isolates from (sub)clinically affected cows. This lytic activity was evaluated by turbidity reduction and time-kill assays in phosphate-buffered saline and pasteurized whole cow's milk to allow a rank up of the most potent leading candidates. A top candidate was selected with a 4.0 log killing efficacy against S. uberis, also showing similar activity against S. agalactiae and S. dysgalactiae. This top candidate eradicated S. uberis biofilm and showed intracellular activity in two bovine mammary epithelial cell lines as was confirmed by confocal microscopy. A potentiating effect on cloxacillin, a beta-lactam penicillin used to intramammarily treat bovine Gram-positive mastitis, was observed for this top candidate endolysin in raw cow's milk from (sub)clinically infected udders. Our in vitro results indicate that engineered endolysins may have a future role as add-on in the treatment of bovine streptococcal mastitis.

Phage-induced bacterial morphological changes reveal a phage-derived antimicrobial affecting cell wall integrity

In a looming post-antibiotic era, antibiotic alternatives have become key players in the combat against pathogens. Although recent advances in genomic research allow scientists to fully explore an organism's genome in the search for novel antibacterial molecules, laborious work is still needed in order to dissect each individual gene product for its antibacterial activity. Here, we exploited phage-induced bacterial morphological changes as anchors to explore and discover a potential phage-derived antimicrobial embedded in the phage genome. We found that, upon vibriophage KVP40 infection, Vibrio parahaemolyticus exhibited morphological changes similar to those observed when treated with mecillinam, a cell wall synthesis inhibitor, suggesting the mechanism of pre-killing that KVP40 exerts inside the bacterial cell upon sieging the host. Genome analysis revealed that, of all the annotated gene products in the KVP40 genome that are involved in cell wall degradation, lytic transglycosylase (LT) is of particular interest for subsequent functional studies. A single-cell morphological analysis revealed that heterologous expression of wild-type KVP40-LT induced similar bacterial morphological changes to those treated with the whole phage or mecillinam, prior to cell burst. On the contrary, neither the morphology nor the viability of the bacteria expressing signal-peptide truncated- or catalytic mutant E80A- KVP40-LT was affected, suggesting the necessity of these domains for the antibacterial activities. Altogether, this research paves the way for the future development of the discovery of phage-derived antimicrobials that is guided through phage-induced morphological changes.

Novel endolysin LysMP for control of Limosilactobacillus fermentum contamination in small-scale corn mash fermentation

BACKGROUND

Traditional bioethanol fermentation industries are not operated under strict sterile conditions and are prone to microbial contamination. Lactic acid bacteria (LAB) are often pervasive in fermentation tanks, competing for nutrients and producing inhibitory acids that have a negative impact on ethanol-producing yeast, resulting in decreased yields and stuck fermentations. Antibiotics are frequently used to combat contamination, but antibiotic stewardship has resulted in a shift to alternative antimicrobials.

RESULTS

We demonstrate that endolysin LysMP, a bacteriophage-encoded peptidoglycan hydrolase, is an effective method for controlling growth of LAB. The LysMP gene was synthesized based on the prophage sequence in the genome of Limosilactobacillus fermentum KGL7. Analysis of the recombinant enzyme expressed in E. coli and purified by immobilized metal chelate affinity chromatography (IMAC) showed an optimal lysis activity against various LAB species at pH 6, with stability from pH 4 to 8 and from 20 to 40 °C up to 48 h. Moreover, it retains more than 80% of its activity at 10% ethanol (v/v) for up to 48 h. When LysMP was added at 250 µg/mL to yeast corn mash fermentations containing L. fermentum, it reduced bacterial load by at least 4-log fold compared to the untreated controls and prevented stuck fermentation. In comparison, untreated controls with contamination increased from an initial bacterial load of 1.50 × 107 CFU/mL to 2.25 × 109 CFU/mL and 1.89 × 109 CFU/mL after 24 h and 48 h, respectively. Glucose in the treated samples was fully utilized, while untreated controls with contamination had more than 4% (w/v) remaining at 48 h. Furthermore, there was at least a fivefold reduction in lactic acid (0.085 M untreated contamination controls compared to 0.016 M treated), and a fourfold reduction in acetic acid (0.027 M untreated contamination controls vs. 0.007 M treated), when LysMP was used to treat contaminated corn mash fermentations. Most importantly, final ethanol yields increased from 6.3% (w/v) in untreated contamination samples to 9.3% (w/v) in treated contamination samples, an approximate 50% increase to levels comparable to uncontaminated controls 9.3% (w/v).

CONCLUSION

LysMP could be a good alternative to replace antibiotics for mitigation of LAB contamination in biofuel refineries.

Characterization and Engineering Studies of a New Endolysin from the Propionibacterium acnes Bacteriophage PAC1 for the Development of a Broad-Spectrum Artilysin with Altered Specificity

The emergence of multidrug-resistant (MDR) bacteria has risen rapidly, leading to a great threat to global public health. A promising solution to this problem is the exploitation of phage endolysins. In the present study, a putative N-acetylmuramoyl-L-alanine type-2 amidase (NALAA-2, EC 3.5.1.28) from Propionibacterium bacteriophage PAC1 was characterized. The enzyme (PaAmi1) was cloned into a T7 expression vector and expressed in E. coli BL21 cells. Kinetics analysis using turbidity reduction assays allowed the determination of the optimal conditions for lytic activity against a range of Gram-positive and negative human pathogens. The peptidoglycan degradation activity of PaAmi1 was confirmed using isolated peptidoglycan from P. acnes. The antibacterial activity of PaAmi1 was investigated using live P. acnes cells growing on agar plates. Two engineered variants of PaAmi1 were designed by fusion to its N-terminus two short antimicrobial peptides (AMPs). One AMP was selected by searching the genomes of Propionibacterium bacteriophages using bioinformatics tools, whereas the other AMP sequence was selected from the antimicrobial peptide databases. Both engineered variants exhibited improved lytic activity towards P. acnes and the enterococci species Enterococcus faecalis and Enterococcus faecium. The results of the present study suggest that PaAmi1 is a new antimicrobial agent and provide proof of concept that bacteriophage genomes are a rich source of AMP sequences that can be further exploited for designing novel or improved endolysins.

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.

The Broad-Spectrum Endolysin LySP2 Improves Chick Survival after Salmonella Pullorum Infection

Salmonella pullorum causes typical “Bacillary White Diarrhea” and loss of appetite in chicks, which leads to the death of chicks in severe cases; thus, it is still a critical issue in China. Antibiotics are conventional medicines used for Salmonella infections; however, due to the extensive long-term use and even abuse of antibiotics, drug resistance becomes increasingly severe, making treating pullorum disease more difficult. Most of the endolysins are hydrolytic enzymes produced by bacteriophages to cleave the host’s cell wall during the final stage of the lytic cycle. A virulent bacteriophage, YSP2, of Salmonella was isolated in a previous study. A Pichia pastoris expression strain that can express the Salmonella bacteriophage endolysin was constructed efficiently, and the Gram-negative bacteriophage endolysin, LySP2, was obtained in this study. Compared with the parental phage YSP2, which can only lyse Salmonella, LySP2 can lyse Salmonella and Escherichia. The survival rate of Salmonella-infected chicks treated with LySP2 can reach up to 70% and reduce Salmonella abundance in the liver and intestine. The treatment group showed that LySP2 significantly improved the health of infected chicks and alleviated organ damage caused by Salmonella infection. In this study, the Salmonella bacteriophage endolysin was expressed efficiently by Pichia pastoris, and the endolysin LySP2 showed good potential for the treatment of pullorum disease caused by Salmonella pullorum.

An endolysin Salmcide-p1 from bacteriophage fmb-p1 against gram-negative bacteria

AIMS

A novel endolysin Salmcide-p1 was developed as a promising candidate of new preservative and a supplement to effective enzyme preparations against gram-negative bacterial contaminations.

METHODS AND RESULTS

Salmcide-p1 was identified by complementing the genomic sequence of a virulent Salmonella phage fmb-p1. Salmcide-p1 of 112 μg ml^-1 could quickly kill Salmonella incubated with 100 mmol l^-1 EDTA, with no haemolytic activity. Meanwhile, Salmcide-p1 had a high activity of lysing Salmonella cell wall peptidoglycan. At different temperatures (4-75°C), pH (4-11) and NaCl concentration (10-200 mmol l^-1 ), the relative activity of Salmcide-p1 was above 60%. At 4°C, the combination of Salmcide-p1 and EDTA-2Na could inhibit the number of Salmonella Typhimurium CMCC 50115 in skim milk to less than 4 log CFU ml^-1 by 3 days, and the number of Shigella flexneri CMCC 51571 was lower than 4 log CFU ml^-1 by 9 days.

CONCLUSIONS

Salmcide-p1 had a wide bactericidal activity against gram-negative bacteria and showed a broader anti-Salmonella spectrum than the phage fmb-p1. The combination strategy of Salmcide-p1 and EDTA-2Na could significantly inhibit the growth of gram-negative bacteria inoculated in skim milk.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacteriophage endolysin as an antibacterial agent is considered to be a new strategy against bacterial contamination.

Bacteriophage-Mediated Control of Biofilm: A Promising New Dawn for the Future

Biofilms are complex microbial microcolonies consisting of planktonic and dormant bacteria bound to a surface. The bacterial cells within the biofilm are embedded within the extracellular polymeric substance (EPS) consisting mainly of exopolysaccharides, secreted proteins, lipids, and extracellular DNA. This structural matrix poses a major challenge against common treatment options due to its extensive antibiotic-resistant properties. Because biofilms are so recalcitrant to antibiotics, they pose a unique challenge to patients in a nosocomial setting, mainly linked to lower respiratory, urinary tract, and surgical wound infections as well as the medical devices used during treatment. Another unique property of biofilm is its ability to adhere to both biological and man-made surfaces, allowing growth on human tissues and organs, hospital tools, and medical devices, etc. Based on prior understanding of bacteriophage structure, mechanisms, and its effects on bacteria eradication, leading research has been conducted on the effects of phages and its individual proteins on biofilm and its role in overall biofilm removal while also revealing the obstacles this form of treatment currently have. The expansion in the phage host-species range is one that urges for improvement and is the focus for future studies. This review aims to demonstrate the advantages and challenges of bacteriophage and its components on biofilm removal, as well as potential usage of phage cocktail, combination therapy, and genetically modified phages in a clinical setting.

Synthetic antimicrobial peptides as enhancers of the bacteriolytic action of staphylococcal phage endolysins

Bacteriophage endolysins degrade the bacterial cell wall and are therefore considered promising antimicrobial alternatives to fight pathogens resistant to conventional antibiotics. Gram-positive bacteria are usually considered easy targets to exogenously added endolysins, since their cell walls are not shielded by an outer membrane. However, in nutrient rich environments these bacteria can also tolerate endolysin attack if they keep an energized cytoplasmic membrane. Hence, we have hypothesized that the membrane depolarizing action of antimicrobial peptides (AMPs), another attractive class of alternative antibacterials, could be explored to overcome bacterial tolerance to endolysins and consequently improve their antibacterial potential. Accordingly, we show that under conditions supporting bacterial growth, Staphylococcus aureus becomes much more susceptible to the bacteriolytic action of endolysins if an AMP is also present. The bactericidal gain resulting from the AMP/endolysin combined action ranged from 1 to 3 logs for different S. aureus strains, which included drug-resistant clinical isolates. In presence of an AMP, as with a reduced content of cell wall teichoic acids, higher endolysin binding to cells is observed. However, our results indicate that this higher endolysin binding alone does not fully explain the higher susceptibility of S. aureus to lysis in these conditions. Other factors possibly contributing to the increased endolysin susceptibility in presence of an AMP are discussed.

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.

Optimized Silica-Binding Peptide-Mediated Delivery of Bactericidal Lysin Efficiently Prevents Staphylococcus aureus from Adhering to Device Surfaces

Staphylococcal-associated device-related infections (DRIs) represent a significant clinical challenge causing major medical and economic sequelae. Bacterial colonization, proliferation, and biofilm formation after adherence to surfaces of the indwelling device are probably the primary cause of DRIs. To address this issue, we incorporated constructs of silica-binding peptide (SiBP) with ClyF, an anti-staphylococcal lysin, into functionalized coatings to impart bactericidal activity against planktonic and sessile Staphylococcus aureus. An optimized construct, SiBP1-ClyF, exhibited improved thermostability and staphylolytic activity compared to its parental lysin ClyF. SiBP1-ClyF-functionalized coatings were efficient in killing MRSA strain N315 (>99.999% within 1 h) and preventing the growth of static and dynamic S. aureus biofilms on various surfaces, including siliconized glass, silicone-coated latex catheter, and silicone catheter. Additionally, SiBP1-ClyF-immobilized surfaces supported normal attachment and growth of mammalian cells. Although the recycling potential and long-term stability of lysin-immobilized surfaces are still affected by the fragility of biological protein molecules, the present study provides a generic strategy for efficient delivery of bactericidal lysin to solid surfaces, which serves as a new approach to prevent the growth of antibiotic-resistant microorganisms on surfaces in hospital settings and could be adapted for other target pathogens as well.

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.

Phage and phage lysins: New era of bio-preservatives and food safety agents

There has been an increase in the search and application of new antimicrobial agents as alternatives to use of chemical preservatives and antibiotic-like compounds by the food industry. The massive use of antibiotic has created a reservoir of antibiotic-resistant bacteria that find their way from farm to humans. Thus, there exists an imperative need to explore new antibacterial options and bacteriophages perfectly fit into the class of safe and potent antimicrobials. Phage bio-control has come a long way owing to advances with use of phage cocktails, recombinant phages, and phage lysins; however, there still exists unmet challenges that restrict the number of phage-based products reaching the market. Hence, further studies are required to explore for more efficient phage-based bio-control strategies that can become an integral part of food safety protocols. This review thus aims to highlight the recent developments made in the application of phages and phage enzymes covering pre-harvest as well as post-harvest usage. It further focuses on the major issues in both phage and phage lysin research hindering their optimum use while detailing out the advances made by researchers lately in this direction for full exploitation of phages and phage lysins in the food sector.

Bacteriophage Proteome: Insights and Potentials of an Alternate to Antibiotics

Introduction

The mounting incidence of multidrug-resistant bacterial strains and the dearth of novel antibiotics demand alternate therapies to manage the infections caused by resistant superbugs. Bacteriophages and phage=derived proteins are considered as potential alternates to treat such infections, and have several applications in health care systems. The aim of this review is to explore the hidden potential of bacteriophage proteins which may be a practical alternative approach to manage the threat of antibiotic resistance.

Results

Clinical trials are in progress for the use of phage therapy as a tool for routine medical use; however, the existing regulations may hamper their development of routine antimicrobial agents. The advancement of molecular techniques and the advent of sequencing have opened new potentials for the design of engineered bacteriophages as well as recombinant bacteriophage proteins. The phage enzymes and proteins encoded by the lysis cassette genes, especially endolysins, holins, and spanins, have shown plausible potentials as therapeutic candidates.

Conclusion

This review offers an integrated viewpoint that aims to decipher the insights and abilities of bacteriophages and their derived proteins as potential alternatives to antibiotics.

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.

Bacteriophage-encoded enzymes destroying bacterial cell membranes and walls, and their potential use as antimicrobial agents

Appearance of pathogenic bacteria resistant to most, if not all, known antibiotics is currently one of the most significant medical problems. Therefore, development of novel antibacterial therapies is crucial for efficient treatment of bacterial infections in the near future. One possible option is to employ enzymes, encoded by bacteriophages, which cause destruction of bacterial cell membranes and walls. Bacteriophages use such enzymes to destroy bacterial host cells at the final stage of their lytic development, in order to ensure effective liberation of progeny virions. Nevertheless, to use such bacteriophage-encoded proteins in medicine and/or biotechnology, it is crucial to understand details of their biological functions and biochemical properties. Therefore, in this review article, we will present and discuss our current knowledge on the processes of bacteriophage-mediated bacterial cell lysis, with special emphasis on enzymes involved in them. Regulation of timing of the lysis is also discussed. Finally, possibilities of the practical use of these enzymes as antibacterial agents will be underlined and perspectives of this aspect will be presented.

A Novel Acinetobacter baumannii Bacteriophage Endolysin LysAB54 With High Antibacterial Activity Against Multiple Gram-Negative Microbes

The rapid spread and emergence of multidrug-resistant Acinetobacter baumannii and other pathogenic Gram-negative bacteria spurred scientists and clinicians to look for alternative therapeutic agents to conventional antibiotics. In the present study, an A. baumannii bacteriophage p54 was isolated and characterized. Morphological and genome analysis revealed that bacteriophage p54 belongs to Myoviridae family with a genome size of 165,813 bps. A novel endolysin, namely LysAB54, showing low similarity with other well-known related endolysins, was cloned, expressed, and characterized from the bacteriophage p54. LysAB54 showed significant bactericidal activity against multidrug-resistant A. baumannii and other Gram-negative bacteria, including Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli, in the absence of outer membrane permeabilizers. Based on all those observations, LysAB54 could represent a potential agent for the treatment of multidrug-resistant Gram-negative superbugs.

Phage-Encoded Endolysins

Due to the global emergence of antibiotic resistance, there has been an increase in research surrounding endolysins as an alternative therapeutic. Endolysins are phage-encoded enzymes, utilized by mature phage virions to hydrolyze the cell wall from within. There is significant evidence that proves the ability of endolysins to degrade the peptidoglycan externally without the assistance of phage. Thus, their incorporation in therapeutic strategies has opened new options for therapeutic application against bacterial infections in the human and veterinary sectors, as well as within the agricultural and biotechnology sectors. While endolysins show promising results within the laboratory, it is important to document their resistance, safety, and immunogenicity for in-vivo application. This review aims to provide new insights into the synergy between endolysins and antibiotics, as well as the formulation of endolysins. Thus, it provides crucial information for clinical trials involving endolysins.

Antibiotic resistance and persistence-Implications for human health and treatment perspectives

Antimicrobial resistance (AMR) and persistence are associated with an elevated risk of treatment failure and relapsing infections. They are thus important drivers of increased morbidity and mortality rates resulting in growing healthcare costs. Antibiotic resistance is readily identifiable with standard microbiological assays, and the threat imposed by antibiotic resistance has been well recognized. Measures aiming to reduce resistance development and spreading of resistant bacteria are being enforced. However, the phenomenon of bacteria surviving antibiotic exposure despite being fully susceptible, so-called antibiotic persistence, is still largely underestimated. In contrast to antibiotic resistance, antibiotic persistence is difficult to measure and therefore often missed, potentially leading to treatment failures. In this review, we focus on bacterial mechanisms allowing evasion of antibiotic killing and discuss their implications on human health. We describe the relationship between antibiotic persistence and bacterial heterogeneity and discuss recent studies that link bacterial persistence and tolerance with the evolution of antibiotic resistance. Finally, we review persister detection methods, novel strategies aiming at eradicating bacterial persisters and the latest advances in the development of new antibiotics.

Molecular Characterization of a Novel Lytic Enzyme LysC from Clostridium intestinale URNW and Its Antibacterial Activity Mediated by Positively Charged N-Terminal Extension

Peptidoglycan hydrolytic enzymes are considered to be a promising alternative to conventional antibiotics in combating bacterial infections. To identify novel hydrolytic enzymes, we performed a database search with the sequences of two thermostable endolysins with high bactericidal activity, studied earlier in our laboratory. Both these enzymes originate from Thermus scotoductus bacteriophages MAT2119 and vB_Tsc2631. A lytic enzyme LysC from Clostridium intestinale URNW was found to have the highest amino acid sequence similarity to the bacteriophage proteins and was chosen for further analysis. The recombinant enzyme showed strong activity against its host bacteria C. intestinale, as well as against C. sporogenes, Bacillus cereus, Micrococcus luteus, and Staphylococcus aureus, on average causing a 5.12 ± 0.14 log reduction of viable S. aureus ATCC 25923 cells in a bactericidal assay. Crystallographic studies of the protein showed that the catalytic site of LysC contained a zinc atom coordinated by amino acid residues His⁵⁰, His¹⁴⁷, and Cys¹⁵⁵, a feature characteristic for type 2 amidases. Surprisingly, neither of these residues, nor any other of the four conserved residues in the vicinity of the active site, His⁵¹, Thr⁵², Tyr⁷⁶, and Thr¹⁵³, were essential to maintain the antibacterial activity of LysC. Therefore, our attention was attracted to the intrinsically disordered and highly positively charged N-terminal region of the enzyme. Potential antibacterial activity of this part of the sequence, predicted by the Antimicrobial Sequence Scanning System, AMPA, was confirmed in our experimental studies; the truncated version of LysC (LysCΔ2–23) completely lacked antibacterial activity. Moreover, a synthetic peptide, which we termed Intestinalin, with a sequence identical to the first thirty amino acids of LysC, displayed substantial anti-staphylococcal activity with IC₅₀ of 6 μg/mL (1.5 μM). This peptide was shown to have α-helical conformation in solution in the presence of detergents which is a common feature of amphipathic α-helical antimicrobial peptides.

Bacteriophages and associated endolysins in therapy and prevention of mastitis and metritis in cows: Current knowledge

Bacteriophages and the associated endolysins have been proposed as an alternative to antibiotic treatment of mastitis and metritis in cows. Many bacteriophages have been isolated and characterized with a large amount of lytic potential against the bacteria causing mastitis and metritis in cows. Several endolysins with marked lytic activity against mastitis pathogens in vitro were also produced from staphylococcal and streptococcal bacteriophages. In the few clinical studies, however, there has been marginal efficacy of bacteriophages in the therapy of mastitis caused by Staphylococcus aureus. Similarly, lytic bacteriophages have marked antimicrobial activity in vitro against E. coli strains from the uteri of postpartum dairy cows. In clinical studies, however, neither administration of bacteriophages early postpartum nor prepartum was effective in the prevention of metritis in cows. More clinical studies on the effectiveness of bacteriophages and the associated endolysins in the prevention and therapy of mastitis and metritis in cows, therefore, are needed.

Approaches to optimize therapeutic bacteriophage and bacteriophage-derived products to combat bacterial infections

The emerging occurrence of antibiotic-resistant bacterial pathogens leads to a recollection of bacteriophage as antimicrobial therapeutics. This article presents a short overview of the clinical phage application including their use in military medicine and discusses the genotypic and phenotypic properties of a potential "ideal" therapeutic phage. We describe current efforts to engineer phage for their improved usability in pathogen treatment. In addition, phage can be applied for pathogen detection, selective drug delivery, vaccine development, or food and surface decontamination. Instead of viable phage, (engineered) phage-derived enzymes, such as polysaccharide depolymerases or peptidoglycan-degrading enzymes, are considered as promising therapeutic candidates. Finally, we briefly summarize the use of phage for the detection and treatment of "Category A priority pathogens".

Phage Lytic Protein LysRODI Prevents Staphylococcal Mastitis in Mice

Phage lytic proteins are promising antimicrobials that could complement conventional antibiotics and help to combat multi-drug resistant bacteria that cause important human and animal infections. Here, we report the characterization of endolysin LysRODI (encoded by staphylophage phiIPLA-RODI) and its application as a prophylactic mastitis treatment. The main properties of LysRODI were compared with those of endolysin LysA72 (encoded by staphylophage phiIPLA35) and the chimeric protein CHAPSH3b (derived from the virion-associated peptidoglycan hydrolase HydH5 and lysostaphin). Time-kill experiments performed with Staphylococcus aureus and Staphylococcus epidermidis demonstrated that the killing rate of LysRODI and CHAPSH3b is higher than that of LysA72 (0.1 μM protein removed 10⁷ CFU/ml of S. aureus in 30 min). Of note, all proteins failed to select resistant mutants as bacterial exposure to sub-lethal concentrations of the proteins did not alter the MIC values. Additionally, LysRODI and CHAPSH3b were non-toxic in a zebrafish embryo model at concentrations near the MIC (0.5 and 0.7 μM, respectively). Moreover, these two proteins significantly reduced mortality in a zebrafish model of systemic infection. In contrast to LysRODI, the efficacy of CHAPSH3b was dose-dependent in zebrafish, requiring higher-dose treatments to achieve the maximum survival rate. For this reason, LysRODI was selected for further analysis in mice, demonstrating great efficacy to prevent mammary infections by S. aureus and S. epidermidis. Our findings strongly support the use of phage lytic proteins as a new strategy to prevent staphylococcal mastitis.

Endolysins as emerging alternative therapeutic agents to counter drug-resistant infections

Endolysins are the lytic products of bacteriophages which 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 being considered as alternative therapeutic agents because of their exceptional ability to target bacterial cells when applied externally. Endolysins have been studied against a number of drug-resistant pathogens to assess their therapeutic ability. This review focuses on the structure of endolysins in terms of cell binding and catalytic domains, lytic ability, resistance, safety, immunogenicity and future applications. It primarily reviews recent advancements made in evaluation of the therapeutic potential of endolysins, including their origin, host range, applications, and synergy with conventional and non-conventional antimicrobial agents.

Contributions of Net Charge on the PlyC Endolysin CHAP Domain

Bacteriophage endolysins, enzymes that degrade the bacterial peptidoglycan (PG), have gained an increasing interest as alternative antimicrobial agents, due to their ability to kill antibiotic resistant pathogens efficiently when applied externally as purified proteins. Typical endolysins derived from bacteriophage that infect Gram-positive hosts consist of an N-terminal enzymatically-active domain (EAD) that cleaves covalent bonds in the PG, and a C-terminal cell-binding domain (CBD) that recognizes specific ligands on the surface of the PG. Although CBDs are usually essential for the EADs to access the PG substrate, some EADs possess activity in the absence of CBDs, and a few even display better activity profiles or an extended host spectrum than the full-length endolysin. A current hypothesis suggests a net positive charge on the EAD enables it to reach the negatively charged bacterial surface via ionic interactions in the absence of a CBD. Here, we used the PlyC CHAP domain as a model EAD to further test the hypothesis. We mutated negatively charged surface amino acids of the CHAP domain that are not involved in structured regions to neutral or positively charged amino acids in order to increase the net charge from -3 to a range from +1 to +7. The seven mutant candidates were successfully expressed and purified as soluble proteins. Contrary to the current hypothesis, none of the mutants were more active than wild-type CHAP. Analysis of electrostatic surface potential implies that the surface charge distribution may affect the activity of a positively charged EAD. Thus, we suggest that while charge should continue to be considered for future engineering efforts, it should not be the sole focus of such engineering efforts.

Recent perspectives on the virulent factors and treatment options for multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii (AB) is one of the most notorious and opportunistic pathogens, which caused high morbidity and mortality rate and World Health Organization (WHO) declared this bacterium as priority-1 pathogen in 2017. The current antibacterial agents, such as colistins, carbapenems, and tigecyclines have limited applications, which necessitate novel and alternative therapeutic remedies. Thus, the understanding of recent perspectives on the virulent factors and antibiotic resistance mechanism exhibited by the bacteria are extremely important. In addition to many combinatorial therapies of antibacterial, there is several natural compounds demonstrated significant antibacterial potential towards these bacteria. The computational systems biology and high throughput screening approaches provide crucial insights in identifying novel drug targets and lead molecules with therapeutics potential. Hence, this review provides profound insight on the recent aspects of the virulent factors associated with AB, role of biofilm formation in drug resistance and the mechanisms of multidrug resistance. This review further illustrates the status of current therapeutic agents, scope, and applications of natural therapeutics, such as herbal medicines and role of computational biology, immunoinformatics and virtual screening in novel lead developments. Thus, this review provides novel insight on latest developments in drug-resistance mechanism of multidrug-resistant A. baumannii (MDRAB) and discovery of probable therapeutic interventions.

The PlyB Endolysin of Bacteriophage vB_BanS_Bcp1 Exhibits Broad-Spectrum Bactericidal Activity against Bacillus cereus Sensu Lato Isolates

Lytic bacteriophages (or phages) drive bacterial mortality by elaborating exquisite abilities to bind, breach, and destroy bacterial cell membranes and subjugate critical bacterial cell functions. These antimicrobial activities make phages ideal candidates to serve as, or provide sources of, biological control measures for bacterial pathogens. In this study, we isolated the Myoviridae phage vB_BanS_Bcp1 (here referred to as Bcp1) from landfill soil, using a Bacillus anthracis host. The antimicrobial activities of both Bcp1 and its encoded endolysin, PlyB, were examined across different B. cereus sensu lato group species, including B. cereus sensu stricto, Bacillus thuringiensis, and Bacillus anthracis, with pathogenic potential in humans and multiple different uses in biotechnological applications. The Bcp1 phage infected only a subset (11 to 66%) of each B. cereus sensu lato species group tested. In contrast, functional analysis of purified PlyB revealed a potent bacteriolytic activity against all B. cereus sensu lato isolates tested (n = 79). PlyB was, furthermore, active across broad temperature, pH, and salt ranges, refractory to the development of resistance, bactericidal as a single agent, and synergistic with a second endolysin, PlyG. To confirm the potential for PlyB as an antimicrobial agent, we demonstrated the efficacy of a single intravenous treatment with PlyB alone or combination with PlyG in a murine model of lethal B. anthracis infection. Overall, our findings show exciting potential for the Bcp1 bacteriophage and the PlyB endolysin as potential new additions to the antimicrobial armamentarium.IMPORTANCE Organisms of the Bacillus cereus sensu lato lineage are ubiquitous in the environment and are responsible for toxin-mediated infections ranging from severe food poisoning (B. cereus sensu stricto) to anthrax (Bacillus anthracis). The increasing incidence of many of these infections, combined with the specter of antibiotic resistance, has created a need for novel antimicrobials with potent activity, including bacteriophages (or phages) and phage-encoded products (i.e., endolysins). In this study, we describe a broadly infective phage, Bcp1, and its encoded endolysin, PlyB, which exhibited a rapidly bacteriolytic effect against all B. cereus sensu lato isolates tested with no evidence of evolving resistance. Importantly, PlyB was highly efficacious in a mouse model of lethal bacteremia with B. anthracis Both the Bcp1 phage and the PlyB endolysin represent novel mechanisms of action compared to antibiotics, with potential applications to address the evolving problem of antimicrobial resistance.

The Preclinical and Clinical Progress of Bacteriophages and Their Lytic Enzymes: The Parts are Easier than the Whole

The therapeutic potential of phages has been considered since their first identification more than a century ago. The evident concept of using a natural predator to treat bacterial infections has, however, since then been challenged considerably. Initially, the vast success of antibiotics almost eliminated the study of phages for therapy. Upon the renaissance of phage therapy research, the most provocative and unique properties of phages such as high specificity, self-replication and co-evolution prohibited a rapid preclinical and clinical development. On the one hand, the typical trajectory followed by small molecule antibiotics could not be simply translated into the preclinical analysis of phages, exemplified by the need for complex broad spectrum or personalized phage cocktails of high purity and the more complex pharmacokinetics. On the other hand, there was no fitting regulatory framework to deal with flexible and sustainable phage therapy approaches, including the setup and approval of adequate clinical trials. While significant advances are incrementally made to eliminate these hurdles, phage-inspired antibacterials have progressed in the slipstream of phage therapy, benefiting from the lack of hurdles that are typically associated with phage therapy. Most advanced are phage lytic enzymes that kill bacteria through peptidoglycan degradation and osmotic lysis. Both phages and their lytic enzymes are now widely considered as safe and have now progressed to clinical phase II to show clinical efficacy as pharmaceutical. Yet, more initiatives are needed to fill the clinical pipeline to beat the typical attrition rates of clinical evaluation and to come to a true evaluation of phages and phage lytic enzymes in the clinic.

Enzybiotics: Enzyme-Based Antibacterials as Therapeutics

Antibiotics have saved millions of lives. However, the overuse and misuse of antibiotics have contributed to a rapid emergence of antibiotic resistance worldwide. In addition, there is an unprecedented void in the development of new antibiotic classes by the pharmaceutical industry since the first introduction of antibiotics. This antibiotic crisis underscores the urgent and increasing necessity of new, innovative antibiotics. Enzybiotics are such a promising class of antibiotics. They are derived from endolysins, bacteriophage-encoded enzymes that degrade the bacterial cell wall of the infected cell at the end of the lytic replication cycle. Enzybiotics are featured by a rapid and unique mode-of-action, a high specificity to kill pathogens, a low probability for bacterial resistance development and a proteinaceous nature. (Engineered) endolysins have been demonstrated to be effective in a variety of animal models to combat both Gram-positive and Gram-negative bacteria and have entered different phases of preclinical and clinical trials. In addition, mycobacteriophage-encoded endolysins have been successfully used to inhibit mycobacteria in vitro. In this chapter we focus on the (pre)clinical progress of enzybiotics as potent therapeutic agent against human pathogenic bacteria.

Phage Lysins for Fighting Bacterial Respiratory Infections: A New Generation of Antimicrobials

Lower respiratory tract infections and tuberculosis are responsible for the death of about 4.5 million people each year and are the main causes of mortality in children under 5 years of age. Streptococcus pneumoniae is the most common bacterial pathogen associated with severe pneumonia, although other Gram-positive and Gram-negative bacteria are involved in respiratory infections as well. The ability of these pathogens to persist and produce infection under the appropriate conditions is also associated with their capacity to form biofilms in the respiratory mucous membranes. Adding to the difficulty of treating biofilm-forming bacteria with antibiotics, many of these strains are becoming multidrug resistant, and thus the alternative therapeutics available for combating this kind of infections are rapidly depleting. Given these concerns, it is urgent to consider other unconventional strategies and, in this regard, phage lysins represent an attractive resource to circumvent some of the current issues in infection treatment. When added exogenously, lysins break specific bonds of the peptidoglycan and have potent bactericidal effects against susceptible bacteria. These enzymes possess interesting features, including that they do not trigger an adverse immune response and raise of resistance is very unlikely. Although Gram-negative bacteria had been considered refractory to these compounds, strategies to overcome this drawback have been developed recently. In this review we describe the most relevant in vitro and in vivo results obtained to date with lysins against bacterial respiratory pathogens.

Structure of an Acinetobacter Broad-Range Prophage Endolysin Reveals a C-Terminal α-Helix with the Proposed Role in Activity against Live Bacterial Cells

Proteins that include enzymatic domain degrading the bacterial cell wall and a domain providing transport through the bacterial outer membrane are considered as prospective compounds to combat pathogenic Gram-negative bacteria. This paper presents an isolation and study of an enzyme of this class naturally encoded in the prophage region of Acinetobacter baumannii AB 5075 genome. Recombinant protein expressed in E. coli exhibits an antimicrobial activity with respect to live cultures of Gram-negative bacteria reducing the population of viable bacteria by 1.5⁻2 log colony forming units (CFU)/mL. However the protein becomes rapidly inactivated and enables the bacteria to restore the population. AcLys structure determined by X-ray crystallography reveals a predominantly &alpha;&mdash;helical fold similar to bacteriophage P22 lysozyme. The С-terminal part of AcLys polypeptide chains forms an &alpha;&mdash;helix enriched by Lys and Arg residues exposed outside of the protein globule. Presumably this type of structure of the C-terminal &alpha;&mdash;helix has evolved evolutionally enabling the endolysin to pass the inner membrane during the host lysis or, potentially, to penetrate the outer membrane of the Gram-negative bacteria.

Characterization of a New Staphylococcus aureus Kayvirus Harboring a Lysin Active against Biofilms

Staphylococcus aureus is one of the most relevant opportunistic pathogens involved in many biofilm-associated diseases, and is a major cause of nosocomial infections, mainly due to the increasing prevalence of multidrug-resistant strains. Consequently, alternative methods to eradicate the pathogen are urgent. It has been previously shown that polyvalent staphylococcal kayviruses and their derived endolysins are excellent candidates for therapy. Here we present the characterization of a new bacteriophage: vB_SauM-LM12 (LM12). LM12 has a broad host range (>90%; 56 strains tested), and is active against several MRSA strains. The genome of LM12 is composed of a dsDNA molecule with 143,625 bp, with average GC content of 30.25% and codes for 227 Coding Sequences (CDSs). Bioinformatics analysis did not identify any gene encoding virulence factors, toxins, or antibiotic resistance determinants. Antibiofilm assays have shown that this phage significantly reduced the number of viable cells (less than one order of magnitude). Moreover, the encoded endolysin also showed activity against biofilms, with a consistent biomass reduction during prolonged periods of treatment (of about one order of magnitude). Interestingly, the endolysin was shown to be much more active against stationary-phase cells and suspended biofilm cells than against intact and scraped biofilms, suggesting that cellular aggregates protected by the biofilm matrix reduced protein activity. Both phage LM12 and its endolysin seem to have a strong antimicrobial effect and broad host range against S. aureus, suggesting their potential to treat S. aureus biofilm infections.

Engineering of Phage-Derived Lytic Enzymes: Improving Their Potential as Antimicrobials

Lytic enzymes encoded by bacteriophages have been intensively explored as alternative agents for combating bacterial pathogens in different contexts. The antibacterial character of these enzymes (enzybiotics) results from their degrading activity towards peptidoglycan, an essential component of the bacterial cell wall. In fact, phage lytic products have the capacity to kill target bacteria when added exogenously in the form of recombinant proteins. However, there is also growing recognition that the natural bactericidal activity of these agents can, and sometimes needs to be, substantially improved through manipulation of their functional domains or by equipping them with new functions. In addition, often, native lytic proteins exhibit features that restrict their applicability as effective antibacterials, such as poor solubility or reduced stability. Here, I present an overview of the engineering approaches that can be followed not only to overcome these and other restrictions, but also to generate completely new antibacterial agents with significantly enhanced characteristics. As conventional antibiotics are running short, the remarkable progress in this field opens up the possibility of tailoring efficient enzybiotics to tackle the most menacing bacterial infections.

Characterization of the Lytic Capability of a LysK-Like Endolysin, Lys-phiSA012, Derived from a Polyvalent Staphylococcus aureus Bacteriophage

Antibiotic-resistant bacteria (ARB) have spread widely and rapidly, with their increased occurrence corresponding with the increased use of antibiotics. Infections caused by Staphylococcus aureus have a considerable negative impact on human and livestock health. Bacteriophages and their peptidoglycan hydrolytic enzymes (endolysins) have received significant attention as novel approaches against ARB, including S. aureus. In the present study, we purified an endolysin, Lys-phiSA012, which harbors a cysteine/histidine-dependent amidohydrolase/peptidase (CHAP) domain, an amidase domain, and a SH3b cell wall binding domain, derived from a polyvalent S. aureus bacteriophage which we reported previously. We demonstrate that Lys-phiSA012 exhibits high lytic activity towards staphylococcal strains, including methicillin-resistant S. aureus (MRSA). Analysis of deletion mutants showed that only mutants possessing the CHAP and SH3b domains could lyse S. aureus, indicating that lytic activity of the CHAP domain depended on the SH3b domain. The presence of at least 1 mM Ca²⁺ and 100 µM Zn²⁺ enhanced the lytic activity of Lys-phiSA012 in a turbidity reduction assay. Furthermore, a minimum inhibitory concentration (MIC) assay showed that the addition of Lys-phiSA012 decreased the MIC of oxacillin. Our results suggest that endolysins are a promising approach for replacing current antimicrobial agents and may contribute to the proper use of antibiotics, leading to the reduction of ARB.

Integration of Emerging Biomedical Technologies in Meat Processing to Improve Meat Safety and Quality

Modern-day processing of meat products involves a series of complex procedures designed to ensure the quality and safety of the meat for consumers. As the size of abattoirs increases, the logistical problems associated with large-capacity animal processing can affect the sanitation of the facility and the meat products, potentially increasing transmission of infectious diseases. Additionally, spoilage of food from improper processing and storage increases the global economic and ecological burden of meat production. Advances in biomedical and materials science have allowed for the development of innovative new antibacterial technologies that have broad applications in the medical industry. Additionally, new approaches in tissue engineering and nondestructive cooling of biological specimens could significantly improve organ transplantation and tissue grafting. These same strategies may be even more effective in the preservation and protection of meat as animal carcasses are easier to manipulate and do not have the same stringent requirements of care as living patients. This review presents potential applications of emerging biomedical technologies in the food industry to improve meat safety and quality. Future research directions investigating these new technologies and their usefulness in the meat processing chain along with regulatory, logistical, and consumer perception issues will also be discussed.

Csl2, a novel chimeric bacteriophage lysin to fight infections caused by Streptococcus suis, an emerging zoonotic pathogen

Streptococcus suis is a Gram-positive bacterium that infects humans and various animals, causing human mortality rates ranging from 5 to 20%, as well as important losses for the swine industry. In addition, there is no effective vaccine for S. suis and isolates with increasing antibiotic multiresistance are emerging worldwide. Facing this situation, wild type or engineered bacteriophage lysins constitute a promising alternative to conventional antibiotics. In this study, we have constructed a new chimeric lysin, Csl2, by fusing the catalytic domain of Cpl-7 lysozyme to the CW_7 repeats of LySMP lysin from an S. suis phage. Csl2 efficiently kills different S. suis strains and shows noticeable activity against a few streptococci of the mitis group. Specifically, 15 µg/ml Csl2 killed 4.3 logs of S. suis serotype 2 S735 strain in 60 min, in a buffer containing 150 mM NaCl and 10 mM CaCl₂, at pH 6.0. We have set up a protocol to form a good biofilm with the non-encapsulated S. suis mutant strain BD101, and the use of 30 µg/ml Csl2 was enough for dispersing such biofilms and reducing 1–2 logs the number of planktonic bacteria. In vitro results have been validated in an adult zebrafish model of infection.

Recent advances in therapeutic delivery systems of bacteriophage and bacteriophage-encoded endolysins

Antibiotics have been the cornerstone of clinical management of bacterial infection since their discovery in the early 20th century. However, their widespread and often indiscriminate use has now led to reports of multidrug resistance becoming globally commonplace. Bacteriophage therapy has undergone a recent revival in battle against pathogenic bacteria, as the self-replicating and co-evolutionary features of these predatory virions offer several advantages over conventional therapeutic agents. In particular, the use of targeted bacteriophage therapy from specialized delivery platforms has shown particular promise owing to the control of delivery location, administration conditions and dosage of the therapeutic cargo. This review presents an overview of the recent formulations and applications of such delivery vehicles as an innovative and elegant tool for bacterial control.

Biology of Acinetobacter baumannii: Pathogenesis, Antibiotic Resistance Mechanisms, and Prospective Treatment Options

Acinetobacter baumannii is undoubtedly one of the most successful pathogens responsible for hospital-acquired nosocomial infections in the modern healthcare system. Due to the prevalence of infections and outbreaks caused by multi-drug resistant A. baumannii, few antibiotics are effective for treating infections caused by this pathogen. To overcome this problem, knowledge of the pathogenesis and antibiotic resistance mechanisms of A. baumannii is important. In this review, we summarize current studies on the virulence factors that contribute to A. baumannii pathogenesis, including porins, capsular polysaccharides, lipopolysaccharides, phospholipases, outer membrane vesicles, metal acquisition systems, and protein secretion systems. Mechanisms of antibiotic resistance of this organism, including acquirement of β-lactamases, up-regulation of multidrug efflux pumps, modification of aminoglycosides, permeability defects, and alteration of target sites, are also discussed. Lastly, novel prospective treatment options for infections caused by multi-drug resistant A. baumannii are summarized.