LysGH15B, the SH3b domain of staphylococcal phage endolysin LysGH15, retains high affinity to staphylococci

New bacteriophage-derived lysins, LysJ and LysF, with the potential to control Bacillus anthracis

Bacillus anthracis is an etiological agent of anthrax, a severe zoonotic disease that can be transmitted to people and cause high mortalities. Bacteriophages and their lytic enzymes, endolysins, have potential therapeutic value in treating infections caused by this bacterium as alternatives or complements to antibiotic therapy. They can also be used to identify and detect B. anthracis. Endolysins of two B. anthracis Wbetavirus phages, J5a and F16Ba which were described by us recently, differ significantly from the best-known B. anthracis phage endolysin PlyG from Wbetavirus genus bacteriophage Gamma and a few other Wbetavirus genus phages. They are larger than PlyG (351 vs. 233 amino acid residues), contain a signal peptide at their N-termini, and, by prediction, have a different fold of cell binding domain suggesting different structural basis of cell epitope recognition. We purified in a soluble form the modified versions of these endolysins, designated by us LysJ and LysF, respectively, and depleted of signal peptides. Both modified endolysins could lyse the B. anthracis cell wall in zymogram assays. Their activity against the living cells of B. anthracis and other species of Bacillus genus was tested by spotting on the layers of bacteria in soft agar and by assessing the reduction of optical density of bacterial suspensions. Both methods proved the effectiveness of LysJ and LysF in killing the anthrax bacilli, although the results obtained by each method differed. Additionally, the lytic efficiency of both proteins was different, which apparently correlates with differences in their amino acid sequence. KEY POINTS: • LysJ and LysF are B. anthracis-targeting lysins differing from lysins studied so far • LysJ and LysF could be overproduced in E. coli in soluble and active forms • LysJ and LysF are active in killing cells of B. anthracis virulent strains.

Guiding antibiotics towards their target using bacteriophage proteins

Novel therapeutic strategies against difficult-to-treat bacterial infections are desperately needed, and the faster and cheaper way to get them might be by repurposing existing antibiotics. Nanodelivery systems enhance the efficacy of antibiotics by guiding them to their targets, increasing the local concentration at the site of infection. While recently described nanodelivery systems are promising, they are generally not easy to adapt to different targets, and lack biocompatibility or specificity. Here, nanodelivery systems are created that source their targeting proteins from bacteriophages. Bacteriophage receptor-binding proteins and cell-wall binding domains are conjugated to nanoparticles, for the targeted delivery of rifampicin, imipenem, and ampicillin against bacterial pathogens. They show excellent specificity against their targets, and accumulate at the site of infection to deliver their antibiotic payload. Moreover, the nanodelivery systems suppress pathogen infections more effectively than 16 to 32-fold higher doses of free antibiotics. This study demonstrates that bacteriophage sourced targeting proteins are promising candidates to guide nanodelivery systems. Their specificity, availability, and biocompatibility make them great options to guide the antibiotic nanodelivery systems that are desperately needed to combat difficult-to-treat infections.

Review on sterilization techniques, and the application potential of phage lyase and lyase immobilization in fighting drug-resistant bacteria

Many human health problems and property losses caused by pathogenic contamination cannot be underestimated. Bactericidal techniques have been extensively studied to address this issue of public health and economy. Bacterial resistance develops as a result of the extensive use of single or multiple but persistent usage of sterilizing drugs, and the emergence of super-resistant bacteria brings new challenges. Therefore, it is crucial to control pathogen contamination by applying innovative and effective sterilization techniques. As organisms that exist in nature and can specifically kill bacteria, phages have become the focus as an alternative to antibacterial agents. Furthermore, phage-encoded lyases are proteins that play important roles in phage sterilization. The in vitro sterilization of phage lyase has been developed as a novel biosterilization technique to reduce bacterial resistance and is more environmentally friendly than conventional sterilization treatments. For the shortcomings of enzyme applications, this review discusses the enzyme immobilization methods and the application potential of immobilized lyases for sterilization. Although some techniques provide effective solutions, immobilized lyase sterilization technology has been proven to be a more effective innovation for efficient pathogen killing and reducing bacterial resistance. We hope that this review can provide new insights for the development of sterilization techniques.

Lactococcus lactis secreting phage lysins as a potential antimicrobial against multi-drug resistant Staphylococcus aureus

BACKGROUND

Staphylococcus aureus is an opportunistic Gram-positive bacterium that can form biofilm and become resistant to many types of antibiotics. The treatment of multi-drug resistant Staphylococcus aureus (MDRSA) infection is difficult since it possesses multiple antibiotic-resistant mechanisms. Endolysin and virion-associated peptidoglycan hydrolases (VAPGH) enzymes from bacteriophage have been identified as potential alternative antimicrobial agents. This study aimed to assess the ability of Lactococcus lactis NZ9000 secreting endolysin and VAPGH from S. aureus bacteriophage 88 to inhibit the growth of S. aureus PS 88, a MDRSA.

METHOD

Endolysin and VAPGH genes were cloned and expressed in L. lactis NZ9000 after fusion with the SPK1 signal peptide for secretion. The recombinant proteins were expressed and purified, then analyzed for antimicrobial activity using plate assay and turbidity reduction assay. In addition, the spent media of the recombinant lactococcal culture was analyzed for its ability to inhibit the growth of the S. aureus PS 88.

RESULTS

Extracellular recombinant endolysin (Endo88) and VAPGH (VAH88) was successfully expressed and secreted from L. lactis which was able to inhibit S. aureus PS 88, as shown by halozone formation on plate assays as well as inhibition of growth in the turbidity reduction assay. Moreover, it was observed that the spent media from L. lactis NZ9000 expressing Endo88 and VAH88 reduced the viability of PS 88 by up to 3.5-log reduction with Endo88 being more efficacious than VAH88. In addition, Endo88 was able to lyse all MRSA strains tested and Staphylococcus epidermidis but not the other bacteria while VAH88 could only lyse S. aureus PS 88.

CONCLUSION

Recombinant L. lactisNZ9000 expressing phage 88 endolysin may be potentially developed into a new antimicrobial agent for the treatment of MDRSA infection.

Rapid and sensitive detection of Staphylococcus aureus using biolayer interferometry technology combined with phage lysin LysGH15

Staphylococcus aureus (S. aureus), considered as a common foodborne pathogenic microorganism, usually causes food poisoning and various infectious diseases. Therefore, development of rapid and accurate bacterial detection method is the key to preventing food poisoning and achieving early diagnosis and treatment of various infectious diseases caused by S. aureus. Biolayer interferometry (BLI) technology is a novel technique of label-free optical analysis for real-time monitoring of biomolecular interactions. The C54A mutation induced the lytic activity loss of phage lysin LysGH15 but retained the capacity for specific recognizing and binding S. aureus. In this study, a novel method for the detection of S. aureus was established using the C54A mutant LysGH15 as the receptor in combination with BLI. Using this BLI-based method, S. aureus whole cells could be directly assayed and the limit of detection was 13 CFU/mL with a binding time of 12 min. Because the C54A mutant LysGH15 recognizes S. aureus with very high specificity, the method can exclude potential interference from other bacterial species. In addition, this method could also distinguish between viable and dead S. aureus. Moreover, S. aureus was successfully detected in ice cubes and light soy sauce by using this method. Collectively, these results indicate that the LysGH15-based BLI method can be used as an efficient and reliable diagnostic tool in the field of food safety and other related fields for the rapid, sensitive, label-free, and real-time detection of S. aureus.

The Age of Phage: Friend or Foe in the New Dawn of Therapeutic and Biocontrol Applications?

Extended overuse and misuse of antibiotics and other antibacterial agents has resulted in an antimicrobial resistance crisis. Bacteriophages, viruses that infect bacteria, have emerged as a legitimate alternative antibacterial agent with a wide scope of applications which continue to be discovered and refined. However, the potential of some bacteriophages to aid in the acquisition, maintenance, and dissemination of negatively associated bacterial genes, including resistance and virulence genes, through transduction is of concern and requires deeper understanding in order to be properly addressed. In particular, their ability to interact with mobile genetic elements such as plasmids, genomic islands, and integrative conjugative elements (ICEs) enables bacteriophages to contribute greatly to bacterial evolution. Nonetheless, bacteriophages have the potential to be used as therapeutic and biocontrol agents within medical, agricultural, and food processing settings, against bacteria in both planktonic and biofilm environments. Additionally, bacteriophages have been deployed in developing rapid, sensitive, and specific biosensors for various bacterial targets. Intriguingly, their bioengineering capabilities show great promise in improving their adaptability and effectiveness as biocontrol and detection tools. This review aims to provide a balanced perspective on bacteriophages by outlining advantages, challenges, and future steps needed in order to boost their therapeutic and biocontrol potential, while also providing insight on their potential role in contributing to bacterial evolution and survival.

Structural basis for recognition of bacterial cell wall teichoic acid by pseudo-symmetric SH3b-like repeats of a viral peptidoglycan hydrolase

Endolysins are bacteriophage-encoded peptidoglycan hydrolases targeting the cell wall of host bacteria via their cell wall-binding domains (CBDs). The molecular basis for selective recognition of surface carbohydrate ligands by CBDs remains elusive. Here, we describe, in atomic detail, the interaction between the Listeria phage endolysin domain CBD500 and its cell wall teichoic acid (WTA) ligands. We show that 3′O-acetylated GlcNAc residues integrated into the WTA polymer chain are the key epitope recognized by a CBD binding cavity located at the interface of tandem copies of beta-barrel, pseudo-symmetric SH3b-like repeats. This cavity consists of multiple aromatic residues making extensive interactions with two GlcNAc acetyl groups via hydrogen bonds and van der Waals contacts, while permitting the docking of the diastereomorphic ligands. Our multidisciplinary approach tackled an extremely challenging protein–glycopolymer complex and delineated a previously unknown recognition mechanism by which a phage endolysin specifically recognizes and targets WTA, suggesting an adaptable model for regulation of endolysin specificity.

Combining genetic, biochemical and computational approaches, we elucidated the molecular mechanisms underlying the recognition of Listeria wall teichoic acid by bacteriophage-encoded SH3b repeats.

Transient carriage and low-level colonization of orally administrated lytic and temperate phages in the gut of mice

Abstract

Many studies have shown the efficacy of phage therapy in reducing gastrointestinal pathogens. However, it is unclear whether phages can successfully colonize the gut when administered in an adequate amount for a long time. About 1 × 108 PFU/mL of purified lytic phage PA13076 or temperate phage BP96115 were fed daily to mice via drinking water over 31 days, to elucidate the distribution of phages in the gastrointestinal tract. At day 16 and 31, six different segments of the gastrointestinal tract with their contents, including stomach, duodenum, jejunum, ileum, cecum, colon, and fresh feces, were aseptically collected. The phage titers were determined using the double-layered plate method with S. Enteritidis ATCC 13076 or S. Pullorum SPu-109 used as host cells. The results indicated that a small portion of administered phages survived exposure to gastric acid and entered the intestinal tract. The prevalence of phages in the gastrointestinal tract was lower than 1% of the primary phage count. Highest phage titers were detected in the cecum with 104 ~ 105 PFU/g, and most of the phages were eliminated from the body via feces with 106 PFU/g. On day 16 and day 31, the same level of phage titers in different segments of the gastrointestinal tract indicated that the colonization of phages had reached saturation at day 16. These results demonstrate transient phage carriage and low-level colonization of orally administrated lytic and temperate gut phages in mice.

Graphical abstract

A novel flow cytometry assay based on bacteriophage-derived proteins for Staphylococcus detection in blood

Bloodstream infections (BSIs) are considered a major cause of death worldwide. Staphylococcus spp. are one of the most BSIs prevalent bacteria, classified as high priority due to the increasing multidrug resistant strains. Thus, a fast, specific and sensitive method for detection of these pathogens is of extreme importance. In this study, we have designed a novel assay for detection of Staphylococcus in blood culture samples, which combines the advantages of a phage endolysin cell wall binding domain (CBD) as a specific probe with the accuracy and high-throughput of flow cytometry techniques. In order to select the biorecognition molecule, three different truncations of the C-terminus of Staphylococcus phage endolysin E-LM12, namely the amidase (AMI), SH3 and amidase+SH3 (AMI_SH3) were cloned fused with a green fluorescent protein. From these, a higher binding efficiency to Staphylococcus cells was observed for AMI_SH3, indicating that the amidase domain possibly contributes to a more efficient binding of the SH3 domain. The novel phage endolysin-based flow cytometry assay provided highly reliable and specific detection of 1-5 CFU of Staphylococcus in 10 mL of spiked blood, after 16 hours of enrichment culture. Overall, the method developed herein presents advantages over the standard BSIs diagnostic methods, potentially contributing to an early and effective treatment of BSIs.

Biotherapeutic Approaches in Atopic Dermatitis

The skin microbiome plays a central role in inflammatory skin disorders such as atopic dermatitis (AD). In AD patients, an imbalance between pathogenic Staphylococcus aureus (S. aureus) and resident skin symbionts creates a state of dysbiosis which induces immune dysregulation and impairs skin barrier function. There are now exciting new prospects for microbiome-based interventions for AD prevention. In the hopes of achieving sustained control and management of disease in AD patients, current emerging biotherapeutic strategies aim to harness the skin microbiome associated with health by restoring a more diverse symbiotic skin microbiome, while selectively removing pathogenic S. aureus. Examples of such strategies are demonstrated in skin microbiome transplants, phage-derived anti-S. aureus endolysins, monoclonal antibodies, and quorum sensing (QS) inhibitors. However, further understanding of the skin microbiome and its role in AD pathogenesis is still needed to understand how these biotherapeutics alter the dynamics of the microbiome community; to optimize patient selection, drug delivery, and treatment duration; overcome rapid recolonization upon treatment cessation; and improve efficacy to allow these therapeutic options to eventually reach routine clinical practice.

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.

Development of a specific fluorescent phage endolysin for in situ detection of Clostridium species associated with cheese spoilage

Late blowing defect (LBD) is a major cause of spoilage in cheeses, caused by the growth of Clostridium spp. in the cheese matrix. We investigated the application of CTP1L, a bacteriophage endolysin active against Clostridium tyrobutyricum, and its enzymatically active and cell wall-binding domains (EAD and CBD) attached to green fluorescent protein (GFP) to detect dairy-related Clostridium species by fluorescence microscopy. GFP-CTP1L and GFP-CBD demonstrated specificity for Clostridium spp. by labelling 15 and 17 of 20 Clostridium strains, respectively, but neither bound to other members of the cheese microbiota. However, GFP-EAD did not label any Clostridium strain tested. Unexpectedly, GFP-CTP1L and GFP-CBD were also able to bind to clostridial spores. In addition, GFP-CBD allowed us to visualize the vegetative cells of C. tyrobutyricum directly in the matrix of a LBD cheese. Site-directed mutants of GFP-CTP1L and GFP-CBD were made to examine the amino acids involved in binding and oligomer formation. Oligomerization was not essential for binding, but specific mutations in the CBD which affected oligomer formation also affected binding and lytic activity. We conclude that GFP-CTP1L and GFP-CBD could be good biomarkers for rapid detection of Clostridium spores in milk, so measures can be taken for the prevention of LBD in cheese, and also provide effective tools to study the development of Clostridium populations during cheese ripening.

Recombinant Endolysins as Potential Therapeutics against Antibiotic-Resistant Staphylococcus aureus: Current Status of Research and Novel Delivery Strategies

Staphylococcus aureus is one of the most common pathogens of humans and animals, where it frequently colonizes skin and mucosal membranes. It is of major clinical importance as a nosocomial pathogen and causative agent of a wide array of diseases. Multidrug-resistant strains have become increasingly prevalent and represent a leading cause of morbidity and mortality. For this reason, novel strategies to combat multidrug-resistant pathogens are urgently needed. Bacteriophage-derived enzymes, so-called endolysins, and other peptidoglycan hydrolases with the ability to disrupt cell walls represent possible alternatives to conventional antibiotics. These lytic enzymes confer a high degree of host specificity and could potentially replace or be utilized in combination with antibiotics, with the aim to specifically treat infections caused by Gram-positive drug-resistant bacterial pathogens such as methicillin-resistant S. aureus. LysK is one of the best-characterized endolysins with activity against multiple staphylococcal species. Various approaches to further enhance the antibacterial efficacy and applicability of endolysins have been demonstrated. These approaches include the construction of recombinant endolysin derivatives and the development of novel delivery strategies for various applications, such as the production of endolysins in lactic acid bacteria and their conjugation to nanoparticles. These novel strategies are a major focus of this review.

Endolysin LysEF-P10 shows potential as an alternative treatment strategy for multidrug-resistant Enterococcus faecalis infections

Phage-derived lysins can hydrolyse bacterial cell walls and show great potential for combating Gram-positive pathogens. In this study, the potential of LysEF-P10, a new lysin derived from a isolated Enterococcus faecalis phage EF-P10, as an alternative treatment for multidrug-resistant E. faecalis infections, was studied. LysEF-P10 shares only 61% amino acid identity with its closest homologues. Four proteins were expressed: LysEF-P10, the cysteine, histidine-dependent amidohydrolase/peptidase (CHAP) domain (LysEF-P10C), the putative binding domain (LysEF-P10B), and a fusion recombination protein (LysEF-P10B-green fluorescent protein). Only LysEF-P10 showed highly efficient, broad-spectrum bactericidal activity against E. faecalis. Several key functional residues, including the Cys-His-Asn triplet and the calcium-binding site, were confirmed using 3D structure prediction, BLAST and mutation analys. We also found that calcium can switch LysEF-P10 between its active and inactive states and that LysEF-P10B is responsible for binding E. faecalis cells. A single administration of LysEF-P10 (5 μg) was sufficient to protect mice against lethal vancomycin-resistant Enterococcus faecalis (VREF) infection, and LysEF-P10-specific antibody did not affect its bactericidal activity or treatment effect. Moreover, LysEF-P10 reduced the number of Enterococcus colonies and alleviated the gut microbiota imbalance caused by VREF. These results indicate that LysEF-P10 might be an alternative treatment for multidrug-resistant E. faecalis infections.

LysGH15 kills Staphylococcus aureus without being affected by the humoral immune response or inducing inflammation

The lysin LysGH15, derived from the staphylococcal phage GH15, exhibits a wide lytic spectrum and highly efficient lytic activity against methicillin-resistant Staphylococcus aureus (MRSA). Here, we found that LysGH15 did not induce resistance in MRSA or methicillin-sensitive S. aureus (MSSA) strains after repeated treatment. Although LysGH15 triggered the generation of LysGH15-specific antibodies in mice, these antibodies did not block lytic activity in vitro (nor the binding capacity of LysGH15). More importantly, when the antibody titre was highest in mice immunized with LysGH15, a single intravenous injection of LysGH15 was sufficient to protect mice against lethal infection with MRSA. These results indicated that LysGH15-specific antibodies did not affect the killing efficiency of LysGH15 against MRSA in vitro or in vivo. LysGH15 also reduced pro-inflammatory cytokines in mice with lethal infections. Furthermore, a high-dose LysGH15 injection did not cause significant adverse effects or pathological changes in the main organs of treated animals. These results provide further evidence for the administration of LysGH15 as an alternative strategy for the treatment of infections caused by MRSA.

Antimicrobial bacteriophage-derived proteins and therapeutic applications

Antibiotics have the remarkable power to control bacterial infections. Unfortunately, widespread use, whether regarded as prudent or not, has favored the emergence and persistence of antibiotic resistant strains of human pathogenic bacteria, resulting in a global health threat. Bacteriophages (phages) are parasites that invade the cells of virtually all known bacteria. Phages reproduce by utilizing the host cell's machinery to replicate viral proteins and genomic material, generally damaging and killing the cell in the process. Thus, phage can be exploited therapeutically as bacteriolytic agents against bacteria. Furthermore, understanding of the molecular processes involved in the viral life cycle, particularly the entry and cell lysis steps, has led to the development of viral proteins as antibacterial agents. Here we review the current preclinical state of using phage-derived endolysins, virion-associated peptidoglycan hydrolases, polysaccharide depolymerases, and holins for the treatment of bacterial infection. The scope of this review is a focus on the viral proteins that have been assessed for protective effects against human pathogenic bacteria in animal models of infection and disease.

Heterologous surface display on lactic acid bacteria: non-GMO alternative?

Lactic acid bacteria (LAB) are food-grade hosts for surface display with potential applications in food and therapy. Alternative approaches to surface display on LAB would avoid the use of recombinant DNA technology and genetically-modified organism (GMO)-related regulatory requirements. Non-covalent surface display of proteins can be achieved by fusing them to various cell-wall binding domains, of which the Lysine motif domain (LysM) is particularly well studied. Fusion proteins have been isolated from recombinant bacteria or from their growth medium and displayed on unmodified bacteria, enabling heterologous surface display. This was demonstrated on non-viable cells devoid of protein content, termed bacteria-like particles, and on various species of genus Lactobacillus. Of the latter, Lactobacillus salivarius ATCC 11741 was recently shown to be particularly amenable for LysM-mediated display. Possible regulatory implications of heterologous surface display are discussed, particularly those relevant for the European Union.

Structural and biochemical characterization reveals LysGH15 as an unprecedented "EF-hand-like" calcium-binding phage lysin

The lysin LysGH15, which is derived from the staphylococcal phage GH15, demonstrates a wide lytic spectrum and strong lytic activity against methicillin-resistant Staphylococcus aureus (MRSA). Here, we find that the lytic activity of the full-length LysGH15 and its CHAP domain is dependent on calcium ions. To elucidate the molecular mechanism, the structures of three individual domains of LysGH15 were determined. Unexpectedly, the crystal structure of the LysGH15 CHAP domain reveals an "EF-hand-like" calcium-binding site near the Cys-His-Glu-Asn quartet active site groove. To date, the calcium-binding site in the LysGH15 CHAP domain is unique among homologous proteins, and it represents the first reported calcium-binding site in the CHAP family. More importantly, the calcium ion plays an important role as a switch that modulates the CHAP domain between the active and inactive states. Structure-guided mutagenesis of the amidase-2 domain reveals that both the zinc ion and E282 are required in catalysis and enable us to propose a catalytic mechanism. Nuclear magnetic resonance (NMR) spectroscopy and titration-guided mutagenesis identify residues (e.g., N404, Y406, G407, and T408) in the SH3b domain that are involved in the interactions with the substrate. To the best of our knowledge, our results constitute the first structural information on the biochemical features of a staphylococcal phage lysin and represent a pivotal step forward in understanding this type of lysin.

Bacteriophages and Their Derivatives as Biotherapeutic Agents in Disease Prevention and Treatment

The application of bacteriophages for the elimination of pathogenic bacteria has received significantly increased attention world-wide in the past decade. This is borne out by the increasing prevalence of bacteriophage-specific conferences highlighting significant and diverse advances in the exploitation of bacteriophages. While bacteriophage therapy has been associated with the Former Soviet Union historically, since the 1990s, it has been widely and enthusiastically adopted as a research topic in Western countries. This has been justified by the increasing prevalence of antibiotic resistance in many prominent human pathogenic bacteria. Discussion of the therapeutic aspects of bacteriophages in this review will include the uses of whole phages as antibacterials and will also describe studies on the applications of purified phage-derived peptidoglycan hydrolases, which do not have the constraint of limited bacterial host-range often observed with whole phages.

Application of bacteriophages for detection of foodborne pathogens

Bacterial contamination of food products presents a challenge for the food industry and poses a high risk for the consumer. Despite increasing awareness and improved hygiene measures, foodborne pathogens remain a threat for public health, and novel methods for detection of these organisms are needed. Bacteriophages represent ideal tools for diagnostic assays because of their high target cell specificity, inherent signal-amplifying properties, easy and inexpensive production, and robustness. Every stage of the phage lytic multiplication cycle, from the initial recognition of the host cell to the final lysis event, may be harnessed in several ways for the purpose of bacterial detection. Besides intact phage particles, phage-derived affinity molecules such as cell wall binding domains and receptor binding proteins can serve for this purpose. This review provides an overview of existing phage-based technologies for detection of foodborne pathogens, and highlights the most recent developments in this field, with particular emphasis on phage-based biosensors.

Novel chimeric lysin with high-level antimicrobial activity against methicillin-resistant Staphylococcus aureus in vitro and in vivo

The treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) is a challenge worldwide. In our search for novel antimicrobial agents against MRSA, we constructed a chimeric lysin (named as ClyH) by fusing the catalytic domain of Ply187 (Pc) with the non-SH3b-like cell wall binding domain of phiNM3 lysin. Herein, the antimicrobial activity of ClyH against MRSA strains in vitro and in vivo was studied. Our results showed that ClyH could kill all of the tested clinical isolates of MRSA with higher efficacy than lysostaphin as well as its parental enzyme. The MICs of ClyH against clinical S. aureus strains were found to be as low as 0.05 to 1.61 mg/liter. In a mouse model, a single intraperitoneal administration of ClyH protected mice from death caused by MRSA, without obvious harmful effects. The present data suggest that ClyH has the potential to be an alternative therapeutic agent for the treatment of infections caused by MRSA.

Bacteriophage endolysins as novel antimicrobials

Endolysins are enzymes used by bacteriophages at the end of their replication cycle to degrade the peptidoglycan of the bacterial host from within, resulting in cell lysis and release of progeny virions. Due to the absence of an outer membrane in the Gram-positive bacterial cell wall, endolysins can access the peptidoglycan and destroy these organisms when applied externally, making them interesting antimicrobial candidates, particularly in light of increasing bacterial drug resistance. This article reviews the modular structure of these enzymes, in which cell wall binding and catalytic functions are separated, as well as their mechanism of action, lytic activity and potential as antimicrobials. It particularly focuses on molecular engineering as a means of optimizing endolysins for specific applications, highlights new developments that may render these proteins active against Gram-negative and intracellular pathogens and summarizes the most recent applications of endolysins in the fields of medicine, food safety, agriculture and biotechnology.

Genomic characterization of lytic Staphylococcus aureus phage GH15: providing new clues to intron shift in phages

Phage GH15 is a polyvalent phage that shows activity against a wide range of Staphylcoccus aureus strains. This study analysed the genome of GH15. The genome size of GH15 (139 806 bp) was found to be larger than that of the known staphylococcal phages, and the G+C content (30.23 mol%) of GH15 was lower than that of any other staphylococcal myovirus phages. By mass spectrometry, ten structural proteins were identified. Analysis revealed that GH15 was closely related to phages G1, ISP, A5W, Sb-1 and K, and was moderately related to Twort. In light of the variability in identity, coverage, G+C content and genome size, coupled with the large number of mosaicisms, there certainly were close evolutionary relationships from K to Sb-1, A5W, ISP, G1 and finally GH15. Interestingly, all the introns and inteins present in the above phages were absent in GH15 and there appeared to be intron loss in GH15 compared with the intron gain seen in other phages. A comparison of the intron- and intein-related genes demonstrated a clear distinction in the location of the insertion site between intron-containing and intron-free alleles, and this might lead to the establishment of a consensus sequence associated with the presence of an intron or intein. The comparative analysis of the GH15 genome sequence with other phages not only provides compelling evidence for the diversity of staphylococcal myovirus phages but also offers new clues to intron shift in phages.

Complete genome sequence of Staphylococcus aureus bacteriophage GH15

GH15 is a polyvalent phage that shows activity against a wide range of Staphylococcus aureus strains. In this work, the complete genome sequence of GH15 was determined. With a genome size of 139,806 bp (double-stranded DNA), GH15 is the largest staphylococcal phage sequenced to date. The complete genome encodes 214 open reading frames (ORFs) and 4 tRNAs. The closest relatives are the class III staphylococcal myobacteriophages, including K, A5W, ISP, Sb-1, and G1. Interestingly, although corresponding gene sequences demonstrate very high similarity, all the introns and inteins present in the phages listed above are absent in GH15. As such, GH15 can be considered phylogenetically unique among the staphylococcal myobacteriophages, indicating the diversity of this family.