Phage Amplification and Immunomagnetic Separation Combined with Targeted Mass Spectrometry for Sensitive Detection of Viable Bacteria in Complex Food Matrices

Progress in methods for the detection of viable Escherichia coli

Escherichia coli (E. coli) is a prevalent enteric bacterium and a necessary organism to monitor for food safety and environmental purposes. Developing efficient and specific methods is critical for detecting and monitoring viable E. coli due to its high prevalence. Conventional culture methods are often laborious and time-consuming, and they offer limited capability in detecting potentially harmful viable but non-culturable E. coli in the tested sample, which highlights the need for improved approaches. Hence, there is a growing demand for accurate and sensitive methods to determine the presence of viable E. coli. This paper scrutinizes various methods for detecting viable E. coli, including culture-based methods, molecular methods that target DNAs and RNAs, bacteriophage-based methods, biosensors, and other emerging technologies. The review serves as a guide for researchers seeking additional methodological options and aiding in the development of rapid and precise assays. Moving forward, it is anticipated that methods for detecting E. coli will become more stable and robust, ultimately contributing significantly to the improvement of food safety and public health.

Unlocking the potential of phages: Innovative approaches to harnessing bacteriophages as diagnostic tools for human diseases

Phages, viruses that infect bacteria, have been explored as promising tools for the detection of human disease. By leveraging the specificity of phages for their bacterial hosts, phage-based diagnostic tools can rapidly and accurately detect bacterial infections in clinical samples. In recent years, advances in genetic engineering and biotechnology have enabled the development of more sophisticated phage-based diagnostic tools, including those that express reporter genes or enzymes, or target specific virulence factors or antibiotic resistance genes. However, despite these advancements, there are still challenges and limitations to the use of phage-based diagnostic tools, including concerns over phage safety and efficacy. This review aims to provide a comprehensive overview of the current state of phage-based diagnostic tools, including their advantages, limitations, and potential for future development. By addressing these issues, we hope to contribute to the ongoing efforts to develop safe and effective phage-based diagnostic tools for the detection of human disease.

Bacteriophage-Based Biosensors: A Platform for Detection of Foodborne Bacterial Pathogens from Food and Environment

Foodborne microorganisms are an important cause of human illness worldwide. Two-thirds of human foodborne diseases are caused by bacterial pathogens throughout the globe, especially in developing nations. Despite enormous developments in conventional foodborne pathogen detection methods, progress is limited by the assay complexity and a prolonged time-to-result. The specificity and sensitivity of assays for live pathogen detection may also depend on the nature of the samples being analyzed and the immunological or molecular reagents used. Bacteriophage-based biosensors offer several benefits, including specificity to their host organism, the detection of only live pathogens, and resistance to extreme environmental factors such as organic solvents, high temperatures, and a wide pH range. Phage-based biosensors are receiving increasing attention owing to their high degree of accuracy, specificity, and reduced assay times. These characteristics, coupled with their abundant supply, make phages a novel bio-recognition molecule in assay development, including biosensors for the detection of foodborne bacterial pathogens to ensure food safety. This review provides comprehensive information about the different types of phage-based biosensor platforms, such as magnetoelastic sensors, quartz crystal microbalance, and electrochemical and surface plasmon resonance for the detection of several foodborne bacterial pathogens from various representative food matrices and environmental samples.

Measuring Single Bacterial Viability in Optical Traps with a Power Sweeping Technique

Assessing bacterial viability is crucial in public health, food safety, environmental microbiology, and other relevant fields. The classical agar plate counting method and the popular dye-based assays have shown their strengths, but they also have limitations including high time consumption, relatively complex sample preparations, and cytotoxicity. In this work, we present a new bacterial viability assay based on optical tweezers utilizing a power sweeping strategy. By monitoring and analyzing bacterial nanomotion in optical traps under different trapping laser powers, the slope of the proportionality between the quantified extent of motion and the trapping laser power was defined as the mobility restriction coefficient (MRC) to quantify bacterial viability. We first established a firm correlation between the viability and MRC by measuring alive and dead Escherichia coli and Photobacterium phosphoreum. Then the capability of real-time long-term characterization of the assay was validated by measuring the viability of individual P. phosphoreum while regulating the viability with an inactivation light. Notably, a 'spinning-induced stabilization' mechanism was proposed to explain the surprising increase of apparent bacterial mobility after inactivation. Overall, the assay was proved to be a reliable label-free bacterial viability assay at a single-cell level, which holds potential in antibiotic susceptibility testing, drug screening, and rapid diagnostics.

Current State of Development of Biosensors and Their Application in Foodborne Pathogen Detection

ABSTRACT

Foodborne disease outbreaks continue to be a major public health and food safety concern. Testing products promptly can protect consumers from foodborne diseases by ensuring the safety of food before retail distribution. Fast, sensitive, and accurate detection tools are in great demand. Therefore, various approaches have been explored recently to find a more effective way to incorporate antibodies, oligonucleotides, phages, and mammalian cells as signal transducers and analyte recognition probes on biosensor platforms. The ultimate goal is to achieve high specificity and low detection limits (1 to 100 bacterial cells or piconanogram concentrations of toxins). Advancements in mammalian cell-based and bacteriophage-based sensors have produced sensors that detect low levels of pathogens and differentiate live from dead cells. Combinations of biotechnology platforms have increased the practical utility and application of biosensors for detection of foodborne pathogens. However, further rigorous testing of biosensors with complex food matrices is needed to ensure the utility of these sensors for point-of-care needs and outbreak investigations.

HIGHLIGHTS

Antibody- and nucleic acid-based lateral flow immunoassay for Listeria monocytogenes detection

Listeria monocytogenes is an invasive opportunistic foodborne pathogen and its routine surveillance is critical for protecting the food supply and public health. The traditional detection methods are time-consuming and require trained personnel. Lateral flow immunoassay (LFIA), on the other hand, is an easy-to-perform, rapid point-of-care test and has been widely used as an inexpensive surveillance tool. In recent times, nucleic acid-based lateral flow immunoassays (NALFIA) are also developed to improve sensitivity and specificity. A significant improvement in lateral flow-based assays has been reported in recent years, especially the ligands (antibodies, nucleic acids, aptamers, bacteriophage), labeling molecules, and overall assay configurations to improve detection sensitivity, specificity, and automated interpretation of results. In most commercial applications, LFIA has been used with enriched food/environmental samples to ensure detection of live cells thus prolonging the assay time to 24-48 h; however, with the recent improvement in LFIA sensitivity, results can be obtained in less than 8 h with shortened and improved enrichment practices. Incorporation of surface-enhanced Raman spectroscopy and/or immunomagnetic separation could significantly improve LFIA sensitivity for near-real-time point-of-care detection of L. monocytogenes for food safety and public health applications.

Quantitative Assessment of SARS-CoV-2 Virus in Nasopharyngeal Swabs Stored in Transport Medium by a Straightforward LC-MS/MS Assay Targeting Nucleocapsid, Membrane, and Spike Proteins

Alternative methods to RT-PCR for SARS-CoV-2 detection are investigated to provide complementary data on viral proteins, increase the number of tests performed, or identify false positive/negative results. Here, we have developed a simple mass spectrometry assay for SARS-CoV-2 in nasopharyngeal swab samples using common laboratory reagents. The method employs high sensitivity and selectivity targeted mass spectrometry detection, monitoring nine constitutive peptides representative of the three main viral proteins and a straightforward pellet digestion protocol for convenient routine applications. Absolute quantification of N, M, and S proteins was achieved by addition of isotope-labeled versions of best peptides. Limit of detection, recovery, precision, and linearity were thoroughly evaluated in four representative viral transport media (VTM) containing distinct total protein content. The protocol was sensitive in all swab media with limit of detection determined at 2 × 10³ pfu/mL, corresponding to as low as 30 pfu injected into the LC-MS/MS system. When tested on VTM-stored nasopharyngeal swab samples from positive and control patients, sensitivity was similar to or better than rapid immunoassay dipsticks, revealing a corresponding RT-PCR detection threshold at Ct ∼ 24. The study represents the first thorough evaluation of sensitivity and robustness of targeted mass spectrometry in nasal swabs, constituting a promising SARS-CoV-2 antigen assay for the first-line diagnosis of COVID-19 and compatible with the constraints of clinical settings. The raw files generated in this study can be found on PASSEL (Peptide Atlas) under data set identifier PASS01646.

Immunomagnetic separation: An effective pretreatment technology for isolation and enrichment in food microorganisms detection

The high efficiency and accurate detection of foodborne pathogens and spoilage microorganisms in food are a task of great social, economic, and public health importance. However, the contamination levels of target bacteria in food samples are very low. Owing to the background interference of food ingredients and negative impact of nontarget flora, the establishment of efficient pretreatment techniques is very crucial for the detection of food microorganisms. With the significant advantages of high specificity and great separation efficiency, immunomagnetic separation (IMS) assay based on immunomagnetic particles (IMPs) has been considered as a powerful system for the separation and enrichment of target bacteria. This paper mainly focuses on the development of IMS as well as their application in food microorganisms detection. First, the basic principle of IMS in the concentration of food bacteria is presented. Second, the effect of different factors, including the sizes of magnetic particles (MPs), immobilization of antibody and operation parameters (the molar ratio of antibody to MPs, the amount of IMPs, incubation time, and bacteria concentration) on the immunocapture efficiency of IMPs are discussed. The performance of IMPs in different food samples is also evaluated. Finally, the combination of IMS and various kinds of detection methods (immunology-based methods, nucleic acid-based methods, fluorescence methods, and biosensors) to detect pathogenic and spoilage organisms is summarized. The challenges and future trends of IMS are also proposed. As an effective pretreatment technique, IMS can improve the detection sensitivity and shorten their testing time, thus exhibiting broad prospect in the field of food bacteria detection.

A magneto-fluorescence bacteria assay strategy based on dual colour sulfide fluorescent nanoparticles with high near-IR conversion efficiency

Anti-Stokes fluorescence induced by near-IR (NIR) radiation is particularly advantageous for the bioassay of complex samples, but most of the commonly used NIR-induced fluorescence nanomaterials such as up-conversion nanoparticles (UCNPs) do not exhibit satisfactory fluorescence intensity and work against achieving a highly sensitive bioassay. In this study, we a construct sensitive and specific bacteria biosensor based on the NIR-stimulated CaS: Eu, Sm, Mn and SrS: Ce, Sm, Mn nanoparticles. The fluorescent nanoparticles are conjugated with bacteria recognition fragments. In addition, the independent emission bands of these two types of fluorescent nanoparticles make it possible to detect and quantify Gram-positive strain and Gram-negative strain, simultaneously. Intense fluorescence and magnetic enrichment of magneto-fluorescence systems enable bacteria discrimination with the naked eye and improve sensitivity in trace bacteria detection (<20 CFU mL^-1). The linear relationship between the fluorescence intensity and bacterial concentration is established with a detection range of 25-10⁶ CFU mL^-1. Furthermore, this NIR-excited assay strategy demonstrates better anti-interference capability than UV/visible-excited assay methods, showing high potential and practical value for medical diagnostics and bacteria monitoring.

Colorimetric detection of Escherichia coli using engineered bacteriophage and an affinity reporter system

Reporter phage systems have emerged as a promising technology for the detection of bacteria in foods and water. However, the sensitivity of these assays is often limited by the concentration of the expressed reporter as well as matrix interferences associated with the sample. In this study, bacteriophage T7 was engineered to overexpress mutated alkaline phosphatase fused to a carbohydrate-binding module (ALP*-CBM) following infection of E. coli to enable colorimetric detection in a model system. Magnetic cellulose particles were employed to separate and concentrate the overexpressed ALP*-CBM in bacterial lysate. Infection of E. coli with the engineered phage resulted in a limit of quantitation of 1.2 × 10⁵ CFU, equating to 1.2 × 10³ CFU/mL in 3.5 h when using a colorimetric assay and 100 mL sample volume. When employing an enrichment step, < 10¹ CFU/mL could be visually detected from a 100 mL sample volume within 8 h. These results suggest that affinity tag modified enzymes coupled with a material support can provide a simple and effective means to improve signal sensitivity of phage-based assays. Graphical abstract.

Isolation and separation of Listeria monocytogenes using bacteriophage P100-modified magnetic particles

A bacteriophage-assisted magnetic separation method was developed for the isolation of Listeria monocytogenes from complex food matrices. The aim of this study is to understand the effect of phage immobilization methods and the magnetic particle sizes on the phage coupling and infectivity retention of the magnetic particles. In this study, bacteriophage P100-modified magnetic particles (PMMPs) were developed for the separation of L. monocytogenes from food matrices. Three sizes of magnetic particles (MP) (150 nm, 500 nm, and 1 μm) were used for phage immobilization via chemical and physical methods. The coupling ratio of phage was investigated, and the performance of each PMMP complex was evaluated by their L. monocytogenes capture efficiency. When compared to the chemical immobilization method, the physically immobilized PMMP complex achieved a higher capture efficiency initially, with excellent selectivity towards target bacteria. The PMMPs were further tested for selective isolation of L. monocytogenes using real food samples such as ground beef and whole milk.

Bacterial biosensing: Recent advances in phage-based bioassays and biosensors

In nature, different types of bacteria including pathogenic and beneficial ones exist in different habitats including environment, plants, animals, and humans. Among these, the pathogenic bacteria should be detected at earlier stages of infection; however, the conventional bacterial detection procedures are complex and time-consuming. In contrast, the advanced molecular approaches such as polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) have significantly reduced the detection time; nevertheless, such approaches are not acceptable to a large extent and are mostly laborious and expensive. Therefore, the development of fast, inexpensive, sensitive, and specific approaches for pathogen detection is essential for different applications in food industry, clinical diagnosis, biological defense and counter-terrorism. To this end, the novel sensing approaches involving bacteriophages as recognition elements are receiving immense consideration owing to their high degree of specificity, accuracy, and reduced assay times. Besides, the phages are easily produced and are tolerant to extreme pH, temperature, and organic solvents as compared to antibodies. To date, several phage-based assays and sensors have been developed involving different systems such as quartz crystal microbalance, magnetoelastic platform, surface plasmon resonance, and electrochemical methods. This review highlights different taxonomic species and genera of phages infecting eight common disease-causing bacterial genera. It further overviews the most recent advancements in phage-based sensing assays and sensors. Likewise, it elaborates various whole-phage and phage components-based assays. Overall, this review emphasizes the importance of electrochemical biosensors as simple, reliable, cost-effective, and accurate tools for bacterial detection.

Biotin-exposure-based immunomagnetic separation coupled with nucleic acid lateral flow biosensor for visibly detecting viable Listeria monocytogenes

Infectious diseases caused by Listeria monocytogenes pose a great threat to public health worldwide. Therefore, a rapid and efficient method for L. monocytogenes detection is needed. In this study, a biotin-exposure-based immunomagnetic separation (IMS) method was developed. That is, biotinylated antibody was first targeted to L. monocytogenes. Then, streptavidin-functionalized magnetic nanoparticles were added and anchored onto L. monocytogenes cells indirectly through the strong noncovalent interaction between streptavidin and biotin. Biotin-exposure-based IMS exhibited an excellent capability to enrich L. monocytogenes. Specifically, more than 90% of L. monocytogenes was captured when the bacterial concentration was lower than 10⁴ colony-forming units (CFU)/mL. Importantly, the antibody dosage was reduced by 10 times of that in our previous study, which used antibody direct-conjugated magnetic nanoparticles. Propidium monoazide (PMA) treatment prior to PCR amplification could eliminate the false-positive results from dead bacteria and detected viable L. monocytogenes sensitively and specifically. For viable L.monocytogenes detection, enriched L. monocytogenes was treated with PMA prior to asymmetric PCR amplification. The detection limits of the combined IMS with nucleic acid lateral flow (NALF) biosensor for viable L. monocytogenes detection were 3.5 × 10³ CFU/mL in phosphate buffer solution and 3.5 × 10⁴ CFU/g in lettuce samples. The whole assay process of recognizing viable L. monocytogenes was completed within 6 h. The proposed biotin-exposure-mediated IMS combined with a disposable NALF biosensor platform posed no health risk to the end user, and possessed potential applications in the rapid screening and identification of foodborne pathogens.

Recent advances in bacteriophage-based methods for bacteria detection

Fast and reliable bacteria detection is crucial for lowering the socioeconomic burden related to bacterial infections (e.g., in healthcare, industry or security). Bacteriophages (i.e., viruses with bacterial hosts) pose advantages such as great specificity, robustness, toughness and cheap preparation, making them popular biorecognition elements in biosensors and other assays for bacteria detection. There are several possible designs of bacteriophage-based biosensors. Here, we focus on developments based on whole virions as recognition agents. We divide the review into sections dealing with phage lysis as an analytical signal, phages as capturing elements in assays and phage-based sensing layers, putting the main focus on development reported within the past three years but without omitting the fundamentals.

Beta-Hemolytic Bacteria Selectively Trigger Liposome Lysis, Enabling Rapid and Accurate Pathogen Detection

For more than a century, blood agar plates have been the only test for beta-hemolysis. Although blood agar cultures are highly predictive for bacterial pathogens, they are too slow to yield actionable information. Here, we show that beta-hemolytic pathogens are able to lyse and release fluorophores encapsulated in sterically stabilized liposomes whereas alpha and gamma-hemolytic bacteria have no effect. By analyzing fluorescence kinetics, beta-hemolytic colonies cultured on agar could be distinguished in real time with 100% accuracy within 6 h. Additionally, end point analysis based on fluorescence intensity and machine-extracted textural features could discriminate between beta-hemolytic and cocultured control colonies with 99% accuracy. In broth cultures, beta-hemolytic bacteria were detectable in under an hour while control bacteria remained negative even the next day. This strategy, called beta-hemolysis triggered-release assay (BETA) has the potential to enable the same-day detection of beta-hemolysis with single-cell sensitivity and high accuracy.

Decomposable quantum-dots/DNA nanosphere for rapid and ultrasensitive detection of extracellular respiring bacteria

Extracellular respiring bacteria (ERB) are a group of bacteria capable of transferring electrons to extracellular acceptors and have important application in environmental remediation. In this study, a decomposable quantum-dots (QDs)/DNA nanosphere probe was developed for rapid and ultrasensitive detection of ERB. The QDs/DNA nanosphere was self-assembled from QDs-streptavidin conjugate (QDs-SA) and Y-shaped DNA nanostructure that is constructed based on toehold-mediated strand displacement. It can release numerous fluorescent QDs-SA in immunomagnetic separation (IMS)-based immunoassay via simple biotin displacement, which remarkably amplifies the signal of antigen-antibody recognizing event. This QDs/DNA-nanosphere-based IMS-fluorescent immunoassay is ultrasensitive for model ERB Shewanella oneidensis, showing a wide detection range between 1.0 cfu/mL and 1.0 × 10⁸ cfu/mL with a low detection limit of 1.37 cfu/mL. Moreover, the proposed IMS-fluorescent immunoassay exhibits high specificity, acceptable reproducibility and stability. Furthermore, the proposed method shows acceptable recovery (92.4-101.4%) for detection of S. oneidensis spiked in river water samples. The proposed IMS-fluorescent immunoassay advances an intelligent strategy for rapid and ultrasensitive quantitation of low-abundance analyte and thus holds promising potential in food, medical and environmental applications.

Antibiotic-affinity strategy for bioluminescent detection of viable Gram-positive bacteria using daptomycin as recognition agent

A bioluminescent method was proposed for rapid detection of viable Gram-positive bacteria based on a novel antibiotic-affinity strategy on a magnetic beads (MBs) platform. Daptomycin, a highly efficient lipopeptide antibiotic for Gram-positive bacteria, was used as a recognition agent to functionalize MBs. The daptomycin-functionalized MBs showed high capture and concentration efficiency for Gram-positive bacteria due to the strong binding between daptomycin and bacterial cell membrane in the presence of Ca²⁺ ion. The captured bacteria were lysed by hexadecyl trimethyl ammonium bromide solution, followed by a bioluminescent detection of the released intracellular adenosine triphosphate. Four Gram-positive bacteria, including Staphylococcus aureus, Streptococcus mutans, Bacillus subtilis and Staphylococcus epidermidis, were detected as model bacteria by this method. Under the optimal conditions, the bacteria could be detected within a linear range of 1.0 × 10²-3.0 × 10⁶ CFU mL^-1, with a detection limit of 33 CFU mL^-1. The whole detection procedure could be completed within 20 min. Gram-negative bacteria and dead Gram-positive bacteria showed negligible interference to the detection of viable Gram-positive bacteria. The proposed method was successfully applied to quantify the amount of viable Gram-positive bacteria in cheese, milk, lake water, human urine and physiological saline injection with acceptable recovery values ranging from 75.0% to 120.0%. The strategy possessed some advantages such as high sensitivity, short assay time and simple operation, thus showed great promise for food hygiene, environment monitoring, clinical diagnosis and drug safety.

Modified Bacteriophage S16 Long Tail Fiber Proteins for Rapid and Specific Immobilization and Detection of Salmonella Cells

Bacteriophage-based assays and biosensors rival traditional antibody-based immunoassays for detection of low-level Salmonella contaminations. In this study, we harnessed the binding specificity of the long tail fiber (LTF) from bacteriophage S16 as an affinity molecule for the immobilization, enrichment, and detection of Salmonella We demonstrate that paramagnetic beads (MBs) coated with recombinant gp37-gp38 LTF complexes (LTF-MBs) are highly effective tools for rapid affinity magnetic separation and enrichment of Salmonella Within 45 min, the LTF-MBs consistently captured over 95% of Salmonella enterica serovar Typhimurium cells from suspensions containing from 10 to 105 CFU · ml-1, and they yielded equivalent recovery rates (93% ± 5%, n = 10) for other Salmonella strains tested. LTF-MBs also captured Salmonella cells from various food sample preenrichments, allowing the detection of initial contaminations of 1 to 10 CFU per 25 g or ml. While plating of bead-captured cells allowed ultrasensitive but time-consuming detection, the integration of LTF-based enrichment into a sandwich assay with horseradish peroxidase-conjugated LTF (HRP-LTF) as a detection probe produced a rapid and easy-to-use Salmonella detection assay. The novel enzyme-linked LTF assay (ELLTA) uses HRP-LTF to label bead-captured Salmonella cells for subsequent identification by HRP-catalyzed conversion of chromogenic 3,3',5,5'-tetramethylbenzidine substrate. The color development was proportional for Salmonella concentrations between 102 and 107 CFU · ml-1 as determined by spectrophotometric quantification. The ELLTA assay took 2 h to complete and detected as few as 102 CFU · ml-1S Typhimurium cells. It positively identified 21 different Salmonella strains, with no cross-reactivity for other bacteria. In conclusion, the phage-based ELLTA represents a rapid, sensitive, and specific diagnostic assay that appears to be superior to other currently available tests.IMPORTANCE The incidence of foodborne diseases has increased over the years, resulting in major global public health issues. Conventional methods for pathogen detection can be laborious and expensive, and they require lengthy preenrichment steps. Rapid enrichment-based diagnostic assays, such as immunomagnetic separation, can reduce detection times while also remaining sensitive and specific. A critical component in these tests is implementing affinity molecules that retain the ability to specifically capture target pathogens over a wide range of in situ applications. The protein complex that forms the distal tip of the bacteriophage S16 long tail fiber is shown here to represent a highly sensitive affinity molecule for the specific enrichment and detection of Salmonella Phage-encoded long tail fibers have huge potential for development as novel affinity molecules for robust and specific diagnostics of a vast spectrum of bacteria.

Comparative analysis of the sensitivity of metagenomic sequencing and PCR to detect a biowarfare simulant (Bacillus atrophaeus) in soil samples

To evaluate the sensitivity of high-throughput DNA sequencing for monitoring biowarfare agents in the environment, we analysed soil samples inoculated with different amounts of Bacillus atrophaeus, a surrogate organism for Bacillus anthracis. The soil samples considered were a poorly carbonated soil of the silty sand class, and a highly carbonated soil of the silt class. Control soil samples and soil samples inoculated with 10, 10³, or 10⁵ cfu were processed for DNA extraction. About 1% of the DNA extracts was analysed through the sequencing of more than 10⁸ reads. Similar amounts of extracts were also studied for Bacillus atrophaeus DNA content by real-time PCR. We demonstrate that, for both soils, high-throughput sequencing is at least equally sensitive than real-time PCR to detect Bacillus atrophaeus DNA. We conclude that metagenomics allows the detection of less than 10 ppm of DNA from a biowarfare simulant in complex environmental samples.

Integrating recognition elements with nanomaterials for bacteria sensing

Pathogenic bacterial contamination is a major threat to human health and safety. In this review, we summarize recent strategies for the integration of recognition elements with nanomaterials for the detection and sensing of pathogenic bacteria. Nanoprobes can provide sensitive and specific detection of bacterial cells, which can be applied across multiple applications and industries.

Highly Specific Bacteriophage-Affinity Strategy for Rapid Separation and Sensitive Detection of Viable Pseudomonas aeruginosa

A virulent bacteriophage highly specific to Pseudomonas aeruginosa (P. aeruginosa) was isolated from hospital sewage using a lambda bacteriophage isolation protocol. The bacteriophage, named as PAP1, was used to functionalize tosyl-activated magnetic beads to establish a bacteriophage-affinity strategy for separation and detection of viable P. aeruginosa. Recognition of the target bacteria by tail fibers and baseplate of the bacteriophage led to capture of P. aeruginosa onto the magnetic beads. After a replication cycle of about 100 min, the progenies lysed the target bacteria and released the intracellular adenosine triphosphate. Subsequently, firefly luciferase-adenosine triphosphate bioluminescence system was used to quantitate the amount of P. aeruginosa. This bacteriophage-affinity strategy for viable P. aeruginosa detection showed a linear range of 6.0 × 10² to 3.0 × 10⁵ CFU mL^-1, with a detection limit of 2.0 × 10² CFU mL^-1. The whole process for separation and detection could be completed after bacteria capture, bacteriophage replication, and bacteria lysis within 2 h. Since the isolated bacteriophage recognized the target bacteria with very high specificity, the proposed strategy did not show any signal response to all of the tested interfering bacteria. Furthermore, it excluded the interference from inactivated P. aeruginosa because the bacteriophage could replicate only in viable cells. The proposed strategy had been applied for detection of P. aeruginosa in glucose injection, human urine, and rat plasma. In the further work, this facile bacteriophage-affinity strategy could be extended for detection of other pathogens by utilizing virulent bacteriophage specific to other targets.

Rapid screening of waterborne pathogens using phage-mediated separation coupled with real-time PCR detection

Escherichia coli O157:H7 is a ubiquitous pathogen which can be linked to foodborne outbreaks worldwide. In addition to the significant illnesses, hospitalizations, and deaths resulting from the outbreaks, there can be severe economic consequences to farmers, food manufacturers, and municipalities. A rapid detection assay which can validate sanitation and water quality would prove beneficial to these situations. Here, we report a novel bacteriophage-mediated detection of E. coli O157:H7 which utilizes the specific recognition between phages and their host cell as well as the natural lysis component of the infection cycle for DNA release. Carboxylic acid-functionalized magnetic beads were conjugated with bacteriophage and used to separate and concentrate E. coli O157:H7. The effects of bead incubation time, salinity, pH, and temperature on the bio-magnetic separation were investigated and compared to an antibody-based counterpart. The conditions of 0.01 M PBS, pH 7.0, and 20 min of reaction at 37 °C were found to be optimal. The capture efficiency of the coupled assay was approximately 20 % higher than that of antibody-based separation under extreme conditions. The resulting bead-phage-bacteria complexes were quantitatively detected by real-time PCR (qPCR). Our results demonstrated that the use of phage-based magnetic separation coupled with qPCR improved the sensitivity of detection by 2 orders of magnitude compared that without phage-based pre-concentration. Specificity and selectivity of the assay system was evaluated, and no cross-reactivity occurred when Salmonella typhimurium, Staphylococcus aureus, and Pseudomonas aeruginosa were tested. The total assay time was less than 2 h.

Advance in phage display technology for bioanalysis

Phage display technology has emerged as a powerful tool for target gene expression and target-specific ligand selection. It is widely used to screen peptides, proteins and antibodies with the advantages of simplicity, high efficiency and low cost. A variety of targets, including ions, small molecules, inorganic materials, natural and biological polymers, nanostructures, cells, bacteria, and even tissues, have been demonstrated to generate specific binding ligands by phage display. Phages and target-specific ligands screened by phage display have been widely used as affinity reagents in therapeutics, diagnostics and biosensors. In this review, comparisons of different types of phage display systems are first presented. Particularly, microfluidic-based phage display, which enables screening with high throughput, high efficiency and integration, is highlighted. More importantly, we emphasize the advances in biosensors based on phages or phage-derived probes, including nonlytic phages, lytic phages, peptides or proteins screened by phage display, phage assemblies and phage-nanomaterial complexes. However, more efficient and higher throughput phage display methods are still needed to meet an explosion in demand for bioanalysis. Furthermore, screening of cyclic peptides and functional peptides will be the hotspot in bioanalysis.

Mass spectrometry for the detection of bioterrorism agents: from environmental to clinical applications

In the current context of international conflicts and localized terrorist actions, there is unfortunately a permanent threat of attacks with unconventional warfare agents. Among these, biological agents such as toxins, microorganisms, and viruses deserve particular attention owing to their ease of production and dissemination. Mass spectrometry (MS)-based techniques for the detection and quantification of biological agents have a decisive role to play for countermeasures in a scenario of biological attacks. The application of MS to every field of both organic and macromolecular species has in recent years been revolutionized by the development of soft ionization techniques (MALDI and ESI), and by the continuous development of MS technologies (high resolution, accurate mass HR/AM instruments, novel analyzers, hybrid configurations). New possibilities have emerged for exquisite specific and sensitive detection of biological warfare agents. MS-based strategies for clinical application can now address a wide range of analytical questions mainly including issues related to the complexity of biological samples and their available volume. Multiplexed toxin detection, discovery of new markers through omics approaches, and identification of untargeted microbiological or of novel molecular targets are examples of applications. In this paper, we will present these technological advances along with the novel perspectives offered by omics approaches to clinical detection and follow-up.

Rapid Detection of Listeria by Bacteriophage Amplification and SERS-Lateral Flow Immunochromatography

A rapid Listeria detection method was developed utilizing A511 bacteriophage amplification combined with surface-enhanced Raman spectroscopy (SERS) and lateral flow immunochromatography (LFI). Anti-A511 antibodies were covalently linked to SERS nanoparticles and printed onto nitrocellulose membranes. Antibody-conjugated SERS nanoparticles were used as quantifiable reporters. In the presence of A511, phage-SERS nanoparticle complexes were arrested and concentrated as a visible test line, which was interrogated quantitatively by Raman spectroscopy. An increase in SERS intensity correlated to an increase in captured phage-reporter complexes. SERS limit of detection was 6 × 10(6) pfu·mL(-1), offering detection below that obtainable by the naked eye (LOD 6 × 10(7) pfu·mL(-1)). Phage amplification experiments were carried out at a multiplicity of infection (MOI) of 0.1 with 4 different starting phage concentrations monitored over time using SERS-LFI and validated by spot titer assay. Detection of L. monocytogenes concentrations of 1 × 10(7) colony forming units (cfu)·mL(-1), 5 × 10(6) cfu·mL(-1), 5 × 10(5) cfu·mL(-1) and 5 × 10(4) cfu·mL(-1) was achieved in 2, 2, 6, and 8 h, respectively. Similar experiments were conducted at a constant starting phage concentration (5 × 10(5) pfu·mL(-1)) with MOIs of 1, 2.5, and 5 and were detected in 2, 4, and 5 h, respectively.