Detection of bacteria with bioluminescent reporter bacteriophage

Bacteriophage-Based Detection of Staphylococcus aureus in Human Serum

Bacteriophages have been investigated for clinical utility, both as diagnostic tools and as therapeutic interventions. In order to be applied successfully, a detailed understanding of the influence of the human matrix on the interaction between bacteriophage and the host bacterium is required. In this study, a cocktail of luciferase bacteriophage reporters was assessed for functionality in a matrix containing human serum and spiked with Staphylococcus aureus. The inhibition of signal and loss of sensitivity was evident with minimal amounts of serum. This phenotype was independent of bacterial growth and bacteriophage viability. Serum-mediated loss of signal was common, albeit not universal, among S. aureus strains. Immunoglobulin G was identified as an inhibitory component and partial inhibition was observed with both the f(ab’)₂ and Fc region. A modified bacteriophage cocktail containing recombinant protein A was developed, which substantially improved signal without the need for additional sample purification. This study highlights the importance of assessing bacteriophage activity in relevant host matrices. Furthermore, it identifies an effective solution, recombinant protein A, for promoting bacteriophage-based detection of S. aureus in matrices containing human serum.

The application and research progress of bacteriophages in food safety

The abuse of antibiotics and the emergence of drug-resistant bacteria aggravate the problem of food safety. Finding a safe and efficient antibiotic substitute is an inevitable demand for ensuring the safety of animal-derived food. Bacteriophages are a kind of virus that can infect bacteria, fungi or actinomycetes. They have the advantages of simple structure, strong specificity and non-toxic side effects to human body. Bacteriophages can not only differentiate live cells from dead ones, but also detect bacteria in a viable but nonculturable state. These characteristics make bacteriophages more and more widely used in food industry. This paper describes the concept and characteristics of bacteriophages, introduces the application of bacteriophages in pre-harvest production, food processing, storage and sales. Several methods of bacteriophage detection of foodborne pathogens are listed. Finally, the advantages and limitations of bacteriophages in food industry are summarized, and the application prospect of bacteriophages in food industry are prospected.

Engineered Reporter Phages for Rapid Bioluminescence-Based Detection and Differentiation of Viable Listeria Cells

The pathogen Listeria monocytogenes causes listeriosis, a severe foodborne disease associated with high mortality. Rapid and sensitive methods are required for specific detection of this pathogen during food production. Bioluminescence-based reporter bacteriophages are genetically engineered viruses that infect their host cells with high specificity and transduce a heterologous luciferase gene whose activity can be detected with high sensitivity to indicate the presence of viable target cells. Here, we use synthetic biology for de novo genome assembly and activation as well as CRISPR-Cas-assisted phage engineering to construct a set of reporter phages for the detection and differentiation of viable Listeria cells. Based on a single phage backbone, we compare the performance of four reporter phages that encode different crustacean, cnidarian, and bacterial luciferases. From this panel of reporter proteins, nanoluciferase (NLuc) was identified as a superior enzyme and was subsequently introduced into the genomes of a broad host range phage (A511) and two serovar 1/2- and serovar 4b/6a-specific Listeria phages (A006 and A500, respectively). The broad-range NLuc-based phage A511::nluc _CPS detects one CFU of L. monocytogenes in 25 g of artificially contaminated milk, cold cuts, and lettuce within less than 24 h. In addition, this reporter phage successfully detected Listeria spp. in potentially contaminated natural food samples without producing false-positive or false-negative results. Finally, A006::nluc and A500::nluc enable serovar-specific Listeria diagnostics. In conclusion, these NLuc-based reporter phages enable rapid, ultrasensitive detection and differentiation of viable Listeria cells using a simple protocol that is 72 h faster than culture-dependent approaches.IMPORTANCE Culture-dependent methods are the gold standard for sensitive and specific detection of pathogenic bacteria within the food production chain. In contrast to molecular approaches, these methods detect viable cells, which is a key advantage for foods generated from heat-inactivated source material. However, culture-based diagnostics are typically much slower than molecular or proteomic strategies. Reporter phage assays combine the best of both worlds and allow for near online assessment of microbial safety because phage replication is extremely fast, highly target specific, and restricted to metabolically active host cells. In addition, reporter phage assays are inexpensive and do not require highly trained personnel, facilitating their on-site implementation. The reporter phages presented in this study not only allow for rapid detection but also enable an early estimation of the potential virulence of Listeria isolates from food production and processing sites.

Rapid Colorimetric Detection of Bacterial Species through the Capture of Gold Nanoparticles by Chimeric Phages

Rapid, inexpensive, and sensitive detection of bacterial pathogens is an important goal for several aspects of human health and safety. We present a simple strategy for detecting a variety of bacterial species based on the interaction between bacterial cells and the viruses that infect them (phages). We engineer phage M13 to display the receptor-binding protein from a phage that naturally targets the desired bacteria. Thiolation of the engineered phages allows the binding of gold nanoparticles, which aggregate on the phages and act as a signal amplifier, resulting in a visible color change due to alteration of surface plasmon resonance properties. We demonstrate the detection of two strains of Escherichia coli, the human pathogens Pseudomonas aeruginosa and Vibrio cholerae, and two strains of the plant pathogen Xanthomonas campestris. The assay can detect ∼100 cells with no cross-reactivity found among the Gram-negative bacterial species tested here. The assay can be performed in less than an hour and is robust to different media, including seawater and human serum. This strategy combines highly evolved biological materials with the optical properties of gold nanoparticles to achieve the simple, sensitive, and specific detection of bacterial species.

Engineering Bacteriophage-Based Biosensors

Bacteriophages have been used for diagnostic purposes in the past, but a lack of parallelizable engineering methods had limited their applicability to a narrow subset of diagnostic settings. More recently, however, advances in DNA sequencing and the introduction of more sensitive reporter systems have enabled novel engineering methods, which in turn have broadened the scope of modern phage diagnostics. Here we describe advanced methods to engineer the genomes of bacteriophages in a modular and rapid fashion.

MOF-Bacteriophage Biosensor for Highly Sensitive and Specific Detection of Staphylococcus aureus

To produce a sensitive and specific biosensor for Staphylococcus aureus, bacteriophages have been interfaced with a water-dispersible and environmentally stable metal-organic framework (MOF), NH₂-MIL-53(Fe). The conjugation of the MOF with bacteriophages has been achieved through the use of glutaraldehyde as cross-linker. Highly sensitive detection of S. aureus in both synthetic and real samples was realized by the proposed MOF-bacteriophage biosensor based on the photoluminescence quenching phenomena: limit of detection (31 CFU/mL) and range of detection (40 to 4 × 10⁸ CFU/mL). This is the first report exploiting the use of an MOF-bacteriophage complex for the biosensing of S. aureus. The results of our study highlight that the proposed biosensor is more sensitive than most of the previous methods while exhibiting some advanced features like specificity, regenerability, extended range of linear detection, and stability for long-term storage (even at room temperature).

Engineering of Bacteriophages Y2::dpoL1-C and Y2::luxAB for Efficient Control and Rapid Detection of the Fire Blight Pathogen, Erwinia amylovora

Erwinia amylovora is the causative agent of fire blight, a devastating plant disease affecting members of the Rosaceae Alternatives to antibiotics for control of fire blight symptoms and outbreaks are highly desirable, due to increasing drug resistance and tight regulatory restrictions. Moreover, the available diagnostic methods either lack sensitivity, lack speed, or are unable to discriminate between live and dead bacteria. Owing to their extreme biological specificity, bacteriophages are promising alternatives for both aims. In this study, the virulent broad-host-range E. amylovora virus Y2 was engineered to enhance its killing activity and for use as a luciferase reporter phage, respectively. Toward these aims, a depolymerase gene of E. amylovora virus L1 (dpoL1-C) or a bacterial luxAB fusion was introduced into the genome of Y2 by homologous recombination. The genes were placed downstream of the major capsid protein orf68, under the control of the native promoter. The modifications did not affect viability of infectivity of the recombinant viruses. Phage Y2::dpoL1-C demonstrated synergistic activity between the depolymerase degrading the exopolysaccharide capsule and phage infection, which greatly enhanced bacterial killing. It also significantly reduced the ability of E. amylovora to colonize the surface of detached flowers. The reporter phage Y2::luxAB transduced bacterial luciferase into host cells and induced synthesis of large amounts of a LuxAB luciferase fusion. After the addition of aldehyde substrate, bioluminescence could be readily monitored, and this enabled rapid and specific detection of low numbers of viable bacteria, without enrichment, both in vitro and in plant material.IMPORTANCE Fire blight, caused by Erwinia amylovora, is the major threat to global pome fruit production, with high economic losses every year. Bacteriophages represent promising alternatives to not only control the disease, but also for rapid diagnostics. To enhance biocontrol efficacy, we combined the desired properties of two phages, Y2 (broad host range) and L1 (depolymerase for capsule degradation) in a single recombinant phage. This phage showed enhanced biocontrol and could reduce E. amylovora on flowers. Phage Y2 was also genetically engineered into a luciferase reporter phage, which transduces bacterial bioluminescence into infected cells and allows detection of low numbers of viable target bacteria. The combination of speed, sensitivity, and specificity is superior to previously used diagnostic methods. In conclusion, genetic engineering could improve the properties of phage Y2 toward better killing efficacy and sensitive detection of E. amylovora cells.

Design and Elementary Evaluation of a Highly-Automated Fluorescence-Based Instrument System for On-Site Detection of Food-Borne Pathogens

A simple, highly-automated instrument system used for on-site detection of foodborne pathogens based on fluorescence was designed, fabricated, and preliminarily tested in this paper. A corresponding method has been proved effective in our previous studies. This system utilizes a light-emitting diode (LED) to excite fluorescent labels and a spectrometer to record the fluorescence signal from samples. A rotation stage for positioning and switching samples was innovatively designed for high-throughput detection, ten at most in one single run. We also developed software based on LabVIEW for data receiving, processing, and the control of the whole system. In the test of using a pure quantum dot (QD) solution as a standard sample, detection results from this home-made system were highly-relevant with that from a well-commercialized product and even slightly better reproducibility was found. And in the test of three typical kinds of food-borne pathogens, fluorescence signals recorded by this system are highly proportional to the variation of the sample concentration, with a satisfied limit of detection (LOD) (nearly 10²-10³ CFU·mL-1 in food samples). Additionally, this instrument system is low-cost and easy-to-use, showing a promising potential for on-site rapid detection of food-borne pathogens.