Landscape phage probes for Salmonella typhimurium

Phage Display's Prospects for Early Diagnosis of Prostate Cancer

Prostate cancer (PC) is the second most diagnosed cancer among men. It was observed that early diagnosis of disease is highly beneficial for the survival of cancer patients. Therefore, the extension and increasing quality of life of PC patients can be achieved by broadening the cancer screening programs that are aimed at the identification of cancer manifestation in patients at earlier stages, before they demonstrate well-understood signs of the disease. Therefore, there is an urgent need for standard, sensitive, robust, and commonly available screening and diagnosis tools for the identification of early signs of cancer pathologies. In this respect, the "Holy Grail" of cancer researchers and bioengineers for decades has been molecular sensing probes that would allow for the diagnosis, prognosis, and monitoring of cancer diseases via their interaction with cell-secreted and cell-associated PC biomarkers, e.g., PSA and PSMA, respectively. At present, most PSA tests are performed at centralized laboratories using high-throughput total PSA immune analyzers, which are suitable for dedicated laboratories and are not readily available for broad health screenings. Therefore, the current trend in the detection of PC is the development of portable biosensors for mobile laboratories and individual use. Phage display, since its conception by George Smith in 1985, has emerged as a premier tool in molecular biology with widespread application. This review describes the role of the molecular evolution and phage display paradigm in revolutionizing the methods for the early diagnosis and monitoring of PC.

Recent Advances on Peptide-Based Biosensors and Electronic Noses for Foodborne Pathogen Detection

Foodborne pathogens present a serious issue around the world due to the remarkably high number of illnesses they cause every year. In an effort to narrow the gap between monitoring needs and currently implemented classical detection methodologies, the last decades have seen an increased development of highly accurate and reliable biosensors. Peptides as recognition biomolecules have been explored to develop biosensors that combine simple sample preparation and enhanced detection of bacterial pathogens in food. This review first focuses on the selection strategies for the design and screening of sensitive peptide bioreceptors, such as the isolation of natural antimicrobial peptides (AMPs) from living organisms, the screening of peptides by phage display and the use of in silico tools. Subsequently, an overview on the state-of-the-art techniques in the development of peptide-based biosensors for foodborne pathogen detection based on various transduction systems was given. Additionally, limitations in classical detection strategies have led to the development of innovative approaches for food monitoring, such as electronic noses, as promising alternatives. The use of peptide receptors in electronic noses is a growing field and the recent advances of such systems for foodborne pathogen detection are presented. All these biosensors and electronic noses are promising alternatives for the pathogen detection with high sensitivity, low cost and rapid response, and some of them are potential portable devices for on-site analyses.

Selection of Listeria monocytogenes InlA-Binding Peptides Using Phage Display—Novel Compounds for Diagnostic Applications?

Listeria monocytogenes is a pathogenic, gram-positive bacterium causing foodborne infections and listeriosis, an infection responsible for serious medical conditions, especially for pregnant women, newborns, or people with a weak immune system. Even after antibiotic treatment, 30% of clinical infections result in death. L. monocytogenes is able to enter and multiply in mammalian cells. Invasion into epithelial cells in the human intestine is mediated by the interaction of the bacterial surface protein internalin A (InlA) with the host cell receptor E-cadherin (E-cad). We have used phage display to select InlA-specific peptides consisting of 12 amino acids using a randomized, recombinant peptide library. We could demonstrate that the selected peptides bound to recombinant InlA protein as well as to L. monocytogenes cells. In vitro, some of the peptides inhibited the interaction between recombinant InlA and human E-cad. As far as we know, this is the first publication on the development of InlA-specific peptide ligands. In the future, our peptides might be used for the development of innovative diagnostic tools or even therapeutic approaches.

A Novel Peptide as a Specific and Selective Probe for Klebsiella pneumoniae Detection

Klebsiella pneumoniae is infamous for generating hospital-acquired infections, many of which are difficult to treat due to the bacterium’s multidrug resistance. A sensitive and robust detection method of K. pneumoniae can help prevent a disease outbreak. Herein, we used K. pneumoniae cells as bait to screen a commercially available phage-displayed random peptide library for peptides that could be used to detect K. pneumoniae. The biopanning-derived peptide TSATKFMMNLSP, named KP peptide, displayed a high selectivity for the K. pneumoniae with low cross-reactivity to related Gram-negative bacteria. The specific interaction between KP peptide and K. pneumoniae lipopolysaccharide resulted in the peptide’s selectivity against K. pneumoniae. Quantitative analysis of this interaction by enzyme-linked immunosorbent assay revealed that the KP peptide possessed higher specificity and sensitivity toward K. pneumoniae than commercially available anti-Klebsiella spp. antibodies and could detect K. pneumoniae at a detection limit of 10⁴ CFU/mL. These results suggest that KP peptide can be a promising alternative to antibodies in developing a biosensor system for K. pneumoniae detection.

Phage-Displayed Mimotopes of SARS-CoV-2 Spike Protein Targeted to Authentic and Alternative Cellular Receptors

The evolution of the SARS-CoV-2 virus during the COVID-19 pandemic was accompanied by the emergence of new heavily mutated viral variants with increased infectivity and/or resistance to detection by the human immune system. To respond to the urgent need for advanced methods and materials to empower a better understanding of the mechanisms of virus’s adaptation to human host cells and to the immuno-resistant human population, we suggested using recombinant filamentous bacteriophages, displaying on their surface foreign peptides termed “mimotopes”, which mimic the structure of viral receptor-binding sites on the viral spike protein and can serve as molecular probes in the evaluation of molecular mechanisms of virus infectivity. In opposition to spike-binding antibodies that are commonly used in studying the interaction of the ACE2 receptor with SARS-CoV-2 variants in vitro, phage spike mimotopes targeted to other cellular receptors would allow discovery of their role in viral infection in vivo using cell culture, tissue, organs, or the whole organism. Phage mimotopes of the SARS-CoV-2 Spike S1 protein have been developed using a combination of phage display and molecular mimicry concepts, termed here “phage mimicry”, supported by bioinformatics methods. The key elements of the phage mimicry concept include: (1) preparation of a collection of p8-type (landscape) phages, which interact with authentic active receptors of live human cells, presumably mimicking the binding interactions of human coronaviruses such as SARS-CoV-2 and its variants; (2) discovery of closely related amino acid clusters with similar 3D structural motifs on the surface of natural ligands (FGF1 and NRP1), of the model receptor of interest FGFR and the S1 spike protein; and (3) an ELISA analysis of the interaction between candidate phage mimotopes with FGFR3 (a potential alternative receptor) in comparison with ACE2 (the authentic receptor).

vB-ApyS-JF1, the First Trueperella pyogenes Phage, Shows Potential as an Alternative Treatment Strategy for Trueperella pyogenes Infections

Trueperella pyogenes (T. pyogenes) is an important opportunistic animal pathogen that causes huge economic losses to the animal husbandry industry. The emergence of bacterial resistance and the unsatisfactory effect of the vaccine have prompted investigators to explore alternative strategies for controlling T. pyogenes infection. Due to the ability of phages to kill multidrug-resistant bacteria, the use of phage therapy to combat multidrug-resistant bacterial infections has attracted attention. In this study, a T. pyogenes phage, vB-ApyS-JF1 (JF1), was isolated from sewage samples, and its whole genome and biological characteristics were elucidated. Moreover, the protective effect of phage JF1 on a mouse bacteremic model caused by T. pyogenes was studied. JF1 harbors a double-stranded DNA genome with a length of 90,130 bp (30.57% G + C). The genome of JF1 lacked bacterial virulence-, antibiotic resistance- and lysogenesis-related genes. Moreover, the genome sequence of JF1 exhibited low coverage (<6%) with all published phages in the NCBI database, and a phylogenetic analysis of the terminase large subunits and capsid indicated that JF1 was evolutionarily distinct from known phages. In addition, JF1 was stable over a wide range of pH values (3 to 11) and temperatures (4 to 50°C) and exhibited strong lytic activity against T. pyogenes in vitro. In murine experiments, a single intraperitoneal administration of JF1 30 min post-inoculation provided 100% protection for mice against T. pyogenes infection. Compared to the phosphate-buffered saline (PBS) treatment group, JF1 significantly (P < 0.01) reduced the bacterial load in the blood and tissues of infected mice. Meanwhile, treatment with phage JF1 relieved the pathological symptoms observed in each tissue. Furthermore, the levels of the inflammatory cytokines tumour necrosis factor-α (TNF-α), interferon-γ (IFN-γ), and interleukin-6 (IL-6) in the blood of infected mice were significantly (P < 0.01) decreased in the phage-treated group. Taken together, these results indicate that phage JF1 demonstrated great potential as an alternative therapeutic treatment against T. pyogenes infection.

Strategies for Surface Immobilization of Whole Bacteriophages: A Review

Bacteriophage immobilization is a key unit operation in emerging biotechnologies, enabling new possibilities for biodetection of pathogenic microbes at low concentration, production of materials with novel antimicrobial properties, and fundamental research on bacteriophages themselves. Wild type bacteriophages exhibit extreme binding specificity for a single species, and often for a particular subspecies, of bacteria. Since their specificity originates in epitope recognition by capsid proteins, which can be altered by chemical or genetic modification, their binding specificity may also be redirected toward arbitrary substrates and/or a variety of analytes in addition to bacteria. The immobilization of bacteriophages on planar and particulate substrates is thus an area of active and increasing scientific interest. This review assembles the knowledge gained so far in the immobilization of whole phage particles, summarizing the main chemistries, and presenting the current state-of-the-art both for an audience well-versed in bioconjugation methods as well as for those who are new to the field.

Multiplexed detection of bacterial pathogens based on a cocktail of dual-modified phages

Rapid, quantitative, and sensitive assays for the multiplexed detection of bacterial pathogens are urgently needed for public health. Here, we report the generation of dual-modified phage sensors for the simultaneous detection of multiple pathogenic bacteria. The M13KE phage was dual modified to display the targeting peptide on the minor coat protein pIII (∼5 copies) and the streptavidin-binding (StrB) peptide on the major coat protein pVIII (∼2700 copies). The targeting peptide specifically recognizes the target bacteria, and the StrB peptide acts as the efficient signal amplification and transduction unit upon binding with fluorescently tagged streptavidin. The bright fluorescence emitted from individual target bacteria can be clearly distinguished from the background via both the flow cytometry and fluorescence microscopy. Three different dual-modified phages targeting E. coli O157:H7, Salmonella Typhimurium, and Pseudomonas aeruginosa were constructed, and high specificity was verified via a large excess of other non-target bacteria. Using a 40 mL sample volume, the target bacteria detection limit was approximately 10² cells/mL via flow cytometry measurement in the presence of other non-target bacteria. By combining these three dual-modified phages into a cocktail, simultaneous detection and quantification of three target bacterial pathogens was demonstrated with good linearity. The strategy of constructing dual-modified phage represents a promising tool in the detection of bacterial pathogens.

3D Phage-based biomolecular filter for effective high throughput capture of Salmonella Typhimurium in liquid streams

Foodborne illnesses caused by pathogens on fresh produce remain one of the most critical food safety problems the world faces. The recalls of pasta salad in 2018 and pre-cut melons in 2019 imply current methods in identifying the source of pathogens and outbreak prevention are inappropriate and time consuming. In this article, a new technology, called the 3D phage-based biomolecular filter, was developed to simultaneously capture and concentrate foodborne pathogens from large volumes of liquid streams (food liquid or wash water streams). The 3D phage-based filter consisted of phage-immobilized magnetoelastic (ME) filter elements, a filter pipe system, and a uniform magnetic field to fix and align the ME filter elements in the 3D filter column. The closely packed ME filter elements display a 3D layered structure which allows for enhanced surface interaction of the immobilized bacteriophage with specific pathogens in the passing liquid streams. As a result, a pathogen capture rate of more than 90% was achieved at a high flow rate of 3 mm/s with 20,000 ME filter elements. The capability of the 3D phage-based filter to capture pathogens in liquid streams at different filter element packing densities was further validated by experiments, finite element analysis and theoretical calculations. The capture rate increases significantly with larger numbers of ME filter elements placed in the testing pipe, and the turbulence flow induced by the 3D stacking of ME filter elements can further improve the capture efficiency. This technology enables rapid capture and analysis of large volume of water in processing fresh fruit and vegetables for the presence of small quantities of pathogens, which will ultimately benefit producers, the food industry, and society with improved food safety and production efficiency.

Efficient affinity-tagging of M13 phage capsid protein IX for immobilization of protein III-displayed oligopeptide probes on abiotic platforms

We developed a genetic approach to efficiently add an affinity tag to every copy of protein IX (pIX) of M13 filamentous bacteriophage in a population. Affinity-tagged phages can be immobilized on a surface in a uniform monolayer in order to position the pIII-displayed peptides or proteins for optimal interaction with ligands. The tagging consists of two major steps. First, gene IX (gIX) of M13 phage is mutated in Escherichia coli via genetic recombineering with the gIX::aacCI insertion allele. Second, a plasmid that co-produces the affinity-tagged pIX and native pVIII is transformed into the strain carrying the defective M13 gIX. This genetic complementation allows the formation of infective phage particles that carry a full complement (five copies per virion) of the affinity-tagged pIX. To demonstrate the efficacy of our method, we tagged a M13 derivative phage, M13KE, with Strep-tag II. In order to tag pIX with Strep-tag II, the phage genes for pIX and pVIII were cloned and expressed from pASG-IBA4 which contains the E. coli OmpA signal sequence and Strep-Tag II under control of the tetracycline promoter/operator system. We achieved the maximum phage production of 3 × 10¹¹ pfu/ml when Strep-Tag II-pIX-pVIII fusion was induced with 10 ng/ml of anhydrotetracycline. The complete process of affinity tagging a phage probe takes less than 5 days and can be utilized to tag any M13 or fd pIII-displayed oligopeptide probes to improve their performance.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Landscape Phage: Evolution from Phage Display to Nanobiotechnology

The development of phage engineering technology has led to the construction of a novel type of phage display library-a collection of nanofiber materials with diverse molecular landscapes accommodated on the surface of phage particles. These new nanomaterials, called the "landscape phage", serve as a huge resource of diagnostic/detection probes and versatile construction materials for the preparation of phage-functionalized biosensors and phage-targeted nanomedicines. Landscape-phage-derived probes interact with biological threat agents and generate detectable signals as a part of robust and inexpensive molecular recognition interfaces introduced in mobile detection devices. The use of landscape-phage-based interfaces may greatly improve the sensitivity, selectivity, robustness, and longevity of these devices. In another area of bioengineering, landscape-phage technology has facilitated the development and testing of targeted nanomedicines. The development of high-throughput phage selection methods resulted in the discovery of a variety of cancer cell-associated phages and phage proteins demonstrating natural proficiency to self-assemble into various drug- and gene-targeting nanovehicles. The application of this new "phage-programmed-nanomedicines" concept led to the development of a number of cancer cell-targeting nanomedicine platforms, which demonstrated anticancer efficacy in both in vitro and in vivo experiments. This review was prepared to attract the attention of chemical scientists and bioengineers seeking to develop functionalized nanomaterials and use them in different areas of bioscience, medicine, and engineering.

Sensitive colorimetric immunoassay of Vibrio parahaemolyticus based on specific nonapeptide probe screening from a phage display library conjugated with MnO2 nanosheets with peroxidase-like activity

Pathogen detection continues to receive significant attention due to the harmful effects of pathogens on public health. Herein, specific nonapeptide-fusion proteins pVIII (pVIII fusion) were isolated from phage VQTVQIGSD (designated by the sequence of a fused foreign peptide), which was specifically screened from the f8/9 landscape phage library against Vibrio parahaemolyticus (V. parahaemolyticus) in a high-throughput way. The as-prepared V. parahaemolyticus-specific recognition element is cheaper and more available than antibodies. Further, a highly sensitive colorimetric immunoassay for V. parahaemolyticus was established using pVIII fusion as capture probes coupled with protein-templated MnO₂ nanosheets (NSs) as signal probes. In the presence of a target bacterium, V. parahaemolyticus, a sandwich-type complex of pVIII fusion-V. parahaemolyticus-MnO₂ NS@pVIII fusion was formed through specific recognition of pVIII fusion and V. parahaemolyticus. The signal probes (MnO₂ NSs) could catalyze the reaction of 3,3',5,5'-tetramethylbenzidine and H₂O₂ to generate a colorimetric change. The proposed V. parahaemolyticus detection method demonstrated a wide detection range (20-10⁴ colony-forming units (CFU) mL^-1), low limit of detection (15 CFU mL^-1), excellent selectivity, and high reliability for real marine samples, showing potential application in marine microbiological detection and control.

Detection of Salmonella Typhimurium on Spinach Using Phage-Based Magnetoelastic Biosensors

Phage-based magnetoelastic (ME) biosensors have been studied as an in-situ, real-time, wireless, direct detection method of foodborne pathogens in recent years. This paper investigates an ME biosensor method for the detection of Salmonella Typhimurium on fresh spinach leaves. A procedure to obtain a concentrated suspension of Salmonella from contaminated spinach leaves is described that is based on methods outlined in the U.S. FDA Bacteriological Analytical Manual for the detection of Salmonella on leafy green vegetables. The effects of an alternative pre-enrichment broth (LB broth vs. lactose broth), incubation time on the detection performance and negative control were investigated. In addition, different blocking agents (BSA, Casein, and Superblock) were evaluated to minimize the effect of nonspecific binding. None of the blocking agents was found to be superior to the others, or even better than none. Unblocked ME biosensors were placed directly in a concentrated suspension and allowed to bind with Salmonella cells for 30 min before measuring the resonant frequency using a surface-scanning coil detector. It was found that 7 h incubation at 37 °C in LB broth was necessary to detect an initial spike of 100 cfu/25 g S. Typhimurium on spinach leaves with a confidence level of difference greater than 95% (p < 0.05). Thus, the ME biosensor method, on both partly and fully detection, was demonstrated to be a robust and competitive method for foodborne pathogens on fresh products.

Genetically modified bacteriophages in applied microbiology

Bacteriophages represent a simple viral model of basic research with many possibilities for practical application. Due to their ability to infect and kill bacteria, their potential in the treatment of bacterial infection has been examined since their discovery. With advances in molecular biology and gene engineering, the phage application spectrum has been expanded to various medical and biotechnological fields. The construction of bacteriophages with an extended host range or longer viability in the mammalian bloodstream enhances their potential as an alternative to conventional antibiotic treatment. Insertion of active depolymerase genes to their genomes can enforce the biofilm disposal. They can also be engineered to transfer various compounds to the eukaryotic organisms and the bacterial culture, applicable for the vaccine, drug or gene delivery. Phage recombinant lytic enzymes can be applied as enzybiotics in medicine as well as in biotechnology for pathogen detection or programmed cell death in bacterial expression strains. Besides, modified bacteriophages with high specificity can be applied as bioprobes in detection tools to estimate the presence of pathogens in food industry, or utilized in the control of food-borne pathogens as part of the constructed phage-based biosorbents.

A Label-Free Electrochemical Impedance Cytosensor Based on Specific Peptide-Fused Phage Selected from Landscape Phage Library

One of the major challenges in the design of biosensors for cancer diagnosis is to introduce a low-cost and selective probe that can recognize cancer cells. In this paper, we combined the phage display technology and electrochemical impedance spectroscopy (EIS) to develop a label-free cytosensor for the detection of cancer cells, without complicated purification of recognition elements. Fabrication steps of the cytosensing interface were monitored by EIS. Due to the high specificity of the displayed octapeptides and avidity effect of their multicopy display on the phage scaffold, good biocompatibility of recombinant phage, the fibrous nanostructure of phage, and the inherent merits of EIS technology, the proposed cytosensor demonstrated a wide linear range (2.0 × 10(2) - 2.0 × 10(8) cells mL(-1)), a low limit of detection (79 cells mL(-1), S/N = 3), high specificity, good inter-and intra-assay reproducibility and satisfactory storage stability. This novel cytosensor designing strategy will open a new prospect for rapid and label-free electrochemical platform for tumor diagnosis.

Peptide microarray with ligands at high density based on symmetrical carrier landscape phage for detection of cellulase

Peptide microarrays evolved recently as a routine analytical implementation in various research areas due to their unique characteristics. However, the immobilization of peptides with high density in each spot during the fabricating process remains a problem, which will affect the performance of the resultant microarray greatly. To respond to this challenge, a novel peptide immobilization method using symmetrical phage carrier was developed in this work. The cellulytic enzyme endoglucanase I (EG I) was used as a model for selection of its specific peptide ligands from the f8/8 landscape library. Three phage monoclones were selected and identified by the specificity array, of which one phage monoclone displaying the fusion peptide EGSDPRMV (phage EGSDPRMV) could bind EG I specifically with highest affinity. Subsequently, the phage EGSDPRMV was used directly to construct peptide microarray. For comparison, major coat protein pVIII fused EG I specific peptide EGSDPRMV (pVIII-fused EGSDPRMV) which was isolated from phage EGSDPRMV was also immobilized by traditional method to fabricate peptide microarray. The fluorescent signal of the phage EGSDPRMV-mediated peptide microarray was more reproducible and about four times higher than the value for pVIII-fused EGSDPRMV-based microarray, suggesting the high efficiency of the proposed phage EGSDPRMV-mediated peptide immobilization method. Further, the phage EGSDPRMV based microarray not only simplified the procedure of microarray construction but also exhibited significantly enhanced sensitivity due to the symmetrical carrier landscape phage, which dramatically increased the density and sterical regularity of immobilized peptides in each spot. Thus, the proposed strategy has the advantages that the immobilizing peptide ligands were not disturbed by their composition and the immobilized peptides were highly regular with free amino-terminal.

Comparative study of thermal stability of magnetostrictive biosensor between two kinds of biorecognition elements

Magnetostrictive biosensors specific to Salmonella typhimurium were prepared by immobilizing antibody or phage as biorecognition elements onto the magnetostrictive sensor platform. The sensors were stored at temperatures of 25 °C (room temperature), 45 °C and 65 °C, respectively, and the ability to bind S. typhimurium was detected by testing the resonant frequency shift using a HP network analyzer after exposure to 1 mL of 1×10(9) cfu/mL of S. typhimurium at a predetermined schedule. The binding of S. typhimurium to biosensors was confirmed by Scanning Electron Microscopy (SEM). The results showed that there existed an initial sudden drop in the average density of S. typhimurium bound to the biosensor surface versus duration at different temperatures for the two kinds of recognition elements, and the binding ability to S. typhimurium of phage-immobilized biosensors was much better than that of antibody-immobilized biosensors, with longevity longer than 30 days at all tested temperatures, though decreasing gradually over the testing period. While the longevity of antibody-immobilized biosensors was only about 30, 8 and 5 days at room temperature (25 °C), 45 °C and 65 °C, respectively. Meanwhile, the activation energy of the two kinds of biosensors was investigated, and it was found that phage immobilized sensors showed much higher activation energy than antibody immobilized sensors, which resulted in less dependency on temperature and thus having much better thermal stability than antibody immobilized sensors.

Bacteriophage lambda display systems: developments and applications

Bacteriophage (phage) Lambda (λ) has played a key historic role in driving our understanding of molecular genetics. The lytic nature of λ and the conformation of its major capsid protein gpD in capsid assembly offer several advantages as a phage display candidate. The unique formation of the λ capsid and the potential to exploit gpD in the design of controlled phage decoration will benefit future applications of λ display where steric hindrance and avidity are of great concern. Here, we review the recent developments in phage display technologies with phage λ and explore some key applications of this technology including vaccine delivery, gene transfer, bio-detection, and bio-control.

Phage protein-targeted cancer nanomedicines

Nanoencapsulation of anticancer drugs improves their therapeutic indices by virtue of the enhanced permeation and retention effect which achieves passive targeting of nanoparticles in tumors. This effect can be significantly enhanced by active targeting of nanovehicles to tumors. Numerous ligands have been proposed and used in various studies with peptides being considered attractive alternatives to antibodies. This is further reinforced by the availability of peptide phage display libraries which offer an unlimited reservoir of target-specific probes. In particular landscape phages with multivalent display of target-specific peptides which enable the phage particle itself to become a nanoplatform creates a paradigm for high throughput selection of nanoprobes setting the stage for personalized cancer management. Despite its promise, this conjugate of combinatorial chemistry and nanotechnology has not made a significant clinical impact in cancer management due to a lack of using robust processes that facilitate scale-up and manufacturing. To this end we proposed the use of phage fusion protein as the navigating modules of novel targeted nanomedicine platforms which are described in this review.

Production and evaluation of the utility of novel phage display-derived peptide ligands to Salmonella spp. for magnetic separation

AIMS

The objectives of this study were to produce Salmonella-specific peptide ligands by phage display biopanning and evaluate their use for magnetic separation (MS).

METHODS AND RESULTS

Four-phage display biopanning rounds were performed, and the peptides expressed by the two most Salmonella-specific (on the basis of phage-binding ELISA results) phage clones, MSal020401 and MSal020417, were chemically synthesized and coupled to MyOne™ tosylactivated Dynabeads(®). Peptide capture capability for whole Salmonella cells from nonenriched broth cultures was quantified by MS + plate counts and MS + Greenlight™ detection and compared to capture capability of anti-Salmonella (antibody-coated) Dynabeads(®). MS + Greenlight™ gave a more comprehensive picture of capture capability than MS + plate counts and showed that Peptide MSal020417-coated beads exhibited at least similar, if not better, capture capability to anti-Salmonella Dynabeads(®) (mean capture values of 36·0 ± 18·2 and 31·2 ± 20·1%, respectively, over Salmonella spp. concentration range 3 × 10(1) -3 × 10(6) CFU ml(-1)) with cross-reactivity of ≤1·9% to three other foodborne pathogens: Escherichia coli, Listeria monocytogenes and Campylobacter jejuni.

CONCLUSIONS

One of the phage display-derived peptide ligands was demonstrated by MS + Greenlight™ to be a viable antibody alternative for MS of Salmonella spp.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates an antibody-free approach to Salmonella detection and opens substantial possibilities for more rapid tests for this bacterium.

Bacteriophage-induced aggregation of oil sands tailings

Very large quantities of tailings are produced as a result of processing oil sands. After the sand particles settle out, a dense stable mixture of clay, silt, water with residual bitumen, salts, and organics called mature fine tailings (MFT) can remain in suspension for decades. Research into developing methods that would allow consolidation and sedimentation of the suspended particles is ongoing. We have studied the ability of a filamentous bacteriophage (called VP12 bearing the peptide DSQKTNPS at the N-terminus of the major coat protein pVIII) to aggregate MFT. To understand the biophysical basis of the aggregation, phage-induced aggregation of diluted MFT was measured at room temperature under varying conditions of pH, salt, detergent. Phage at concentrations of 5.0 × 10(11)/mL to 10(12)/mL induced rapid settling of the diluted MFT. The addition of sodium chloride (10 mM) lowered the concentration of phage required to induce aggregation. Since the non-ionic detergents Triton-X 100 and Tween-20, and the ionic detergent sodium deoxycholate had little effect, hydrophobic interactions do not appear to be a major contributor to the phage-induced aggregation of MFT. However, aggregation was prevented at pH values higher than 9.0 suggesting that positively charged amino acid residues are required for MFT aggregation by phage. Genetic engineering of the pVIII peptide sequence indicated that hydrogen bonding also contributes to phage-induced aggregation. In addition, replacing the basic residue lysine with an alanine in the recombinant peptide of VP12 completely prevented phage-induced aggregation. Three other phage displaying different amino acid sequences but all containing a lysine in the same position had variable aggregation efficiencies, ranging from no aggregation to rapid aggregation. We conclude that not only are the functional groups of the amino acids important, but the conformation that is adopted by the variable pVIII peptide is also important for phage-induced MFT aggregation.

Identification and evaluation of a novel peptide binding to the cell surface of Staphylococcus aureus

Identification of short peptides that serve as specific ligands to biological materials such as microbial cell surfaces has major implications in better understanding the molecular recognition of cell surfaces. In this study we screened a commercially available random phage-display library against Staphylococcus aureus cells and identified peptides specifically binding to the bacteria. A synthetic peptide (SA5-1) representing the consensus sequence (VPHNPGLISLQG) of the bacteria-binding peptide was evaluated for its binding potential against S. aureus. Dot-blot, immunoblot assay and ELISA results revealed the SA5-1 peptide to be highly specific to S. aureus. The SA5-1 peptide binding was optimal between pH 6.0 and 8.0. Nanogold Transmission Electron Microscopy demonstrated that the SA5-1 binds to the outer membrane surface of S. aureus. Diagnostic potential of the SA5-1 peptide was evaluated in human platelet samples spiked with S. aureus and specific detection of the bacteria by biotinylated-SA5-1 and streptavidin-conjugated fluorescent quantum dots. Fluorometry results indicated that the peptide was able to detect ∼100 organisms per ml in a spiked biological sample providing a proof-of-concept towards potential of this peptide as a S. aureus diagnostic tool that can be of use in different detection platforms.

Development of anti-infectives using phage display: biological agents against bacteria, viruses, and parasites

The vast majority of anti-infective therapeutics on the market or in development are small molecules; however, there is now a nascent pipeline of biological agents in development. Until recently, phage display technologies were used mainly to produce monoclonal antibodies (MAbs) targeted against cancer or inflammatory disease targets. Patent disputes impeded broad use of these methods and contributed to the dearth of candidates in the clinic during the 1990s. Today, however, phage display is recognized as a powerful tool for selecting novel peptides and antibodies that can bind to a wide range of antigens, ranging from whole cells to proteins and lipid targets. In this review, we highlight research that exploits phage display technology as a means of discovering novel therapeutics against infectious diseases, with a focus on antimicrobial peptides and antibodies in clinical or preclinical development. We discuss the different strategies and methods used to derive, select, and develop anti-infectives from phage display libraries and then highlight case studies of drug candidates in the process of development and commercialization. Advances in screening, manufacturing, and humanization technologies now mean that phage display can make a significant contribution in the fight against clinically important pathogens.

Detection of Edwardsiella tarda by fluorometric or biosensor methods using a peptide ligand

In this study, we identified a peptide ligand for Edwardsiella tarda from a phage peptide library and tested two approaches for sensitive detection of the bacteria with the peptide labeled with fluorescein or biotin. At first, the fluorescent peptide was proved to be advantageous in the fluorescence polarization (FP) assay because sensitivity of the assay is maximized when a fluorophore is linked to a small molecule. The FP assay using the fluorescent peptide enabled detection of E. tarda in a range from 5.2×10(3) to 2.1×10(5) cells. Second, we devised a new assay method using a quartz crystal microbalance (QCM) biosensor connected to a filter module. When a mixture of E. tarda and the biotinylated peptide was injected into the filter module, the E. tarda-peptide complex was separated from the unbound peptide by a filter and detected with a streptavidin-coated QCM sensor chip. On injection of samples containing the biotinylated peptide and E. tarda, concentration-dependent frequency change was observed in a range from 8×10(2) to 8×10(6) cells. The two approaches are expected to facilitate development of assay methods using other bacteria-binding peptides.

The application of phage-displayed peptide libraries to ligand detection in eggs and larvae of Rhipicephalus (Boophilus) microplus

The cattle tick, Rhipicephalus (Boophilus) microplus is an ectoparasite of cattle and is one of the major limiting factors in the use of Bos taurus cattle in tropical and subtropical countries. Current control relies heavily on chemotherapy with synthetic acaricides, which is threatened by the development of resistant tick populations. Novel approaches to target discovery in cattle ticks may provide alternative strategies for the control of these parasites. The value of phage-display technology in target discovery was assessed using late-stage (20 d) R. microplus eggs. Eight, 15-mer phage peptides were isolated which preferentially bound to the eggs, or to the larvae visible within. Western blot analyses indicated that the phage clones all bound to the same 16 kDa tick antigen. The results indicate the potential utility of phage-display in detecting 'unknown' cell surface targets on R. microplus, or indeed a range of other parasite species, which may be suitable targets for chemotherapy or vaccination strategies.

Architectonics of phage-liposome nanowebs as optimized photosensitizer vehicles for photodynamic cancer therapy

Filamentous M13 phage can be engineered to display cancer cell-targeting or tumor-homing peptides through phage display. It would be highly desirable if the tumor-targeting phage can also carry anticancer drugs to deliver them to the cancer cells. We studied the evolution of structures of the complexes between anionic filamentous M13 phage and cationic serum-stable liposomes that encapsulate the monomeric photosensitizer zinc naphthalocyanine. At specific phage-liposome ratios, multiple phage nanofibers and liposomes are interwoven into a "nanoweb." The chemical and biological properties of the phage-liposome nanoweb were evaluated for possible application in drug delivery. This study highlights the ability of phage-liposome nanowebs to serve as efficient carriers in the transport of photosensitizers to cancer cells.

Phage-displayed peptides selected for binding to Campylobacter jejuni are antimicrobial

In developed countries, Campylobacter jejuni is a leading cause of zoonotic bacterial gastroenteritis in humans with chicken meat implicated as a source of infection. Campylobacter jejuni colonises the lower gastrointestinal tract of poultry and during processing is spread from the gastrointestinal tract onto the surface of dressed carcasses. Controlling or eliminating C.jejuni on-farm is considered to be one of the best strategies for reducing human infection. Molecules on the cell surface of C.jejuni interact with the host to facilitate its colonisation and persistence in the gastrointestinal tract of poultry. We used a subtractive phage-display protocol to affinity select for peptides binding to the cell surface of a poultry isolate of C.jejuni with the aim of finding peptides that could be used to control this microorganism in chickens. In total, 27 phage peptides, representing 11 unique clones, were found to inhibit the growth of C.jejuni by up to 99.9% in vitro. One clone was bactericidal, reducing the viability of C.jejuni by 87% in vitro. The phage peptides were highly specific. They completely inhibited the growth of two of the four poultry isolates of C.jejuni tested with no activity detected towards other Gram-negative and Gram-positive bacteria.

Peptides panned from a phage-displayed random peptide library are useful for the detection of Bacillus anthracis surrogates B. cereus 4342 and B. anthracis Sterne

Recent use of Bacillus anthracis as a bioweapon has highlighted the need for a sensitive monitoring system. Current bacterial detection tests use antibodies as bio-molecular recognition elements which have limitations with regard to time, specificity and sensitivity, creating the need for new and improved cost-effective high-affinity detection probes. In this study, we screened a commercially available bacteriophage-displayed random peptide library using Bacillus cereus 4342 cells as bait to identify peptides that could be used for detection of Bacillus. The method enabled us to identify two 12-amino acid consensus peptide sequences that specifically bind to B. cereus 4342 and B. anthracis Sterne, the nonpathogenic surrogates of B. anthracis strain. The two Bacillus-binding peptides (named BBP-1 and BBP-2) were synthesized with biotin tag to confirm their binding by four independent detection assays. Dot-blot analysis revealed that the peptides bind specifically to B. cereus 4342 and B. anthracis Sterne. Quantitative analysis of this interaction by ELISA and fluorometry demonstrated a detection sensitivity of 10(2) colony forming U/ml (CFU/ml) by both assays. When the peptides were used in combination with Qdots, the sensitivity was enhanced further by enabling detection of even a single bacterium by fluorescence microscopy. Immunoblot analysis and protein sequencing showed that BBP-1 and BBP-2 bound to the S-layer protein of B. anthracis Sterne. Overall, our findings validate the usefulness of synthetic versions of phage-derived peptides in combination with Qdot-liquid nanocrystals as high sensitivity bioprobes for various microbial detection platforms.

Landscape phage ligands for PC3 prostate carcinoma cells

Tumor-specific cytotoxicity of drugs can be enhanced by targeting them to tumor receptors using tumor-specific ligands. Phage display technology with its high throughput capacity for the analysis of targeting ligands possessing specific binding properties represents a very attractive tool in the quest for molecular ligands. Also, current phage nanobiotechnology concepts allow the use of intact phage particles and isolated phage coat proteins per se as components of nanomedicines. Herein, we describe the use of two landscape phage libraries to obtain phage ligands against PC3 prostate carcinoma cells. Following a very stringent selection scheme, we were able to identify three phage ligands, bearing the fusion peptides, DTDSHVNL, DTPYDLTG and DVVYALSDD that demonstrated specificity and selectivity to PC3 cells based on target-association assays, microscopy and flow cytometry. The phage ligands and their fusion coat proteins can be used as navigating modules in both therapeutic and diagnostic approaches to prostate carcinoma.