Phage long tail fiber protein-immobilized magnetic nanoparticles for rapid and ultrasensitive detection of Salmonella

An electrochemical biosensor based on phage-encoded protein RBP 41 for rapid and sensitive detection of Salmonella

Salmonellosis caused by Salmonella contaminated food poses a serious threat to human health. The rapid and accurate detection of Salmonella is critical for preventing foodborne illness outbreaks. In this study, an electrochemical biosensor was developed using a newly identified biorecognition element, RBP 41, which is capable of specifically recognizing and binding to Salmonella. The biosensor was constructed through a layer-by-layer assembly of graphene oxide (GO), gold nanoparticles (GNPs), and RBP 41 on a glassy carbon electrode (GCE), with the GNPs amplifying the detection signal. The established biosensor was able to detect Salmonella in concentrations ranging from 3 to 106 CFU/mL within approximately 30 min by using differential pulse voltammetry (DPV) signal, and the estimated detection limit was to be 0.2984 Log10 CFU/mL. The biosensor demonstrated excellent specificity and was effective in detecting Salmonella in food matrices, such as skim milk and lettuce. Overall, this study highlights the potential of phage tail receptor binding proteins in biosensing and the proposed biosensor as a promising alternative for rapid and sensitive Salmonella detection in various samples.

A novel nanoparticle-based fluorescent sandwich immunoassay for specific detection of Salmonella Typhimurium

The diseases caused by foodborne pathogens have a serious impact on human health and social stability. Conventional detection methods can involve long assay times and complex pretreatment steps, making them unsuitable for rapid, large-scale analysis of food samples. We constructed a novel nano-fluorescence sandwich immunosorbent immunoassay (nano-FSIA) to rapidly detect Salmonella Typhimurium in food, based on strong covalent binding between streptavidin and biotin. We used antibodies coupled to large particle-size fluorescent microspheres as fluorescent probes for direct quantitative analysis of S. typhimurium in milk. The optimized parameters were determined, and specificity and sensitivity were validated in phosphate-buffered saline (PBS) and milk. The results demonstrated a wide dynamic detection range for S. typhimurium (103-108 colony forming units [CFU]/mL), with the limit of detection in PBS and milk at 234 and 346 CFU/mL, respectively. The results of nano-FSIA were consistent with those of plate counts and enzyme-linked immunosorbent assays, providing an effective and promising single-bacterium counting method for the rapid detection of Salmonella.

Sensitive detection of viable Cronobacter sakazakii by bioluminescent reporter phage emitting stable signals with truncated holin

As outbreaks of foodborne illness caused by the opportunistic pathogen Cronobacter sakazakii (Cs) continue to occur, particularly in infants consuming powdered infant formula (PIF), the need for sensitive, rapid, and easy-to-use detection of Cs from food and food processing environments is increasing. Here, we developed bioluminescent reporter bacteriophages for viable Cs-specific, substrate-free, rapid detection by introducing luciferase and its corresponding substrate-providing enzyme complex into the virulent phage ΦC01. Although the reporter phage ΦC01_lux, constructed by replacing non-essential genes for phage infectivity with a luxCDABE reporter operon, produced bioluminescence upon Cs infection, the emitted signal was quickly decayed due to the superior bacteriolytic activity of ΦC01. By truncating the membrane pore-forming protein holin and thus limiting its function, the bacterial lysis was delayed and the resultant engineered reporter phage ΦC01_lux_Δhol could produce a more stable and reliable bioluminescent signal. Accordingly, ΦC01_lux_Δhol was able to detect at least an average of 2 CFU/ml of Cs artificially contaminated PIF and Sunsik and food contact surface models within a total of 7 h of assays, including 5 h of pre-enrichment for Cs amplification. The sensitive, easy-to-use, and specific detection of live Cs with the developed reporter phage could be applied as a novel complementary tool for monitoring Cs in food and food-related environments for food safety and public health.

The preparation and therapeutic effects of β-glucan-specific nanobodies and nanobody-natamycin conjugates in fungal keratitis

Fungal keratitis (FK) is a severe infectious corneal disease. Since traditional eye drops exhibit poor dissolution and high corneal toxicity, the efficacy of current treatments for FK remains limited. It is needed to develop new approaches to control the cornea damage from FK. In this study, a nanobody (Nb) specific to β-glucan in the fungal cell wall was prepared. The conjugate of the Nb with natamycin (NAT), a traditional antifungal drug, was synthesized. Firstly, we found the Nb specific to β-glucan inhibited fungal growth by disrupting cell wall and biofilm formation.. In addition, the content of β-glucan in the fungal cell wall decreased after Nb treatment. The Nb also reduced the adhesion ability of fungal conidia to human corneal epithelial cells (HCECs). Further, we examined the difference between NAT and Nb-NAT in antifungal growth. Nb-NAT showed better antifungal effects than NAT which was caused by the interaction between Nb and β-glucan. Moreover, Nb concentration below 0.5 mg/mL did not affect the viability of HCECs. Nb-NAT had less cytotoxicity and ocular surface irritation than NAT. Nb specific to β-glucan attenuated Aspergillus fumigatus (A. fumigatus) virulence and relieved inflammatory responses in FK. Nb-NAT treatment of the cornea improved therapeutic effects compared with NAT. It decreased clinical scores and expression level of inflammatory factors. To our knowledge, this study is the first to report a Nb specific to β-glucan and Nb-NAT for the treatment of FK. These unique functions of the Nb specific to β-glucan and Nb-NAT would render it as an alternative molecule to control fungal infections including FK. STATEMENT OF SIGNIFICANCE: Fungal keratitis is a corneal disease with a high rate of blindness. Due to the poor dissolution and high corneal toxicity exhibited by traditional eye drops, the efficacy of current therapeutic treatments for fungal keratitis (FK) remains limited. To enhance the therapeutic effect of natamycin in treating fungal keratitis, this study developed an innovative approach by preparing a β-glucan-specific nanobody and loading it with the antifungal drug natamycin. The β-glucan-specific nanobody has the ability to control both fungal pathogen invasion and inflammation, which can cause damage to the cornea in FK. The conjugation with the β-glucan-specific nanobody significantly increased the antifungal capacity of natamycin and reduced its toxicity. The further application of natamycin conjugated with the β-glucan-specific nanobody could be expanded to other diseases caused by fungal pathogen infections.

A visual colorimetric assay based on phage T156 and gold nanoparticles for the sensitive detection of Salmonella in lettuce

In this study, a new technique was developed for visual and precise identification of Salmonella using phage T156-mediated aggregation of gold nanoparticles. The phage binds to gold nanoparticles in a dispersed and stable state under high NaCl concentrations. When Salmonella is introduced, the phage specifically recognizes and adsorbs the targeted bacteria, causing the AuNPs to undergo a discoloration reaction resulting in aggregation, which enables Salmonella visualization. The method has a detection range of 3.8 × 101-3.8 × 109 CFU/mL and a limit of detection of 38 CFU/mL and can produce results in approximately 80 min. The technique was also tested on field samples, including spiked lettuce, and was found to be accurate with a recovery rate of 81.0-119.2% and relative standard deviations ranging from 3.3% to 14.7%. Notably, this technique utilizes phages as recognition elements in colorimetric methods, offering simplicity, speed, and the ability to effectively distinguish between live and dead Salmonella. It demonstrates remarkable sensitivity, specificity, and accuracy. Furthermore, it presents a novel avenue for the rapid detection of other pathogenic bacteria.

Rapid separation and detection of Listeria monocytogenes with the combination of phage tail fiber protein and vancomycin-magnetic nanozyme

In this work, a lateral flow assay for Listeria monocytogenes was developed based on phage tail fiber protein (TFP) and triple-functional nanozyme probes with capture-separation-catalytic activity. Inspired by interaction between phage and bacteria, TFP of L. monocytogenes phage was immobilized on test line as capture molecule, which replaced traditional antibody and aptamer. After Gram-positive bacteria was captured and separated from samples by nanozyme probes modified with vancomycin (Van), TFP specifically recognized L. monocytogenes and overcame non-specific binding of Van. Special color reaction between Coomassie Brilliant Blue and bovine serum albumin which was an amplification carrier on probe was simply utilized as control zone to replace traditional control line. Relying on enzyme-like catalytic activity of nanozyme, this biosensor realized improved sensitivity and colorimetric quantitative detection with a detection limit of 10 CFU mL^-1. Analytic performance results suggested this TFP-based biosensor provided a portable, sensitive and specific strategy to detect pathogen.

Separation and colorimetric detection of Escherichia coli by phage tail fiber protein combined with nano-magnetic beads

A colorimetric detection method for Escherichia coli (E. coli) in water was established based on a T7 phage tail fiber protein-magnetic separation. Firstly, the tail fiber protein (TFP) was expressed and purified to specifically recognize E. coli, which was verified by using fusion protein GFP-tagged TFP (GFP-TFP) and fluorescence microscopy. Then TFP conjugated with magnetic beads were applied to capture and separate E. coli. The TFP was covalently immobilized on the surface of magnetic beads and captured E. coli as verified by scanning electron microscopy (SEM). Finally, polymyxin B was used to lyse E. coli in solution and the released intracellular β-galactosidase (β-gal) could hydrolyze the colorimetric substrate chlorophenol red-β-D-galactopyranoside (CPRG), causing color change from yellow to purple. The high capture efficiencies of E. coli ranged from 88.70% to 95.65% and E. coli could be detected at a concentration of 10² CFU/mL by naked eyes. The specificity of the chromogenic substrate was evaluated using five different pathogen strains as competitors and tests with four kinds of real water samples showed recoveries of 86.00% to 92.25%. The colorimetric changes determined by visual inspection can be developed as an efficient platform for point-of-care detection of E. coli in resource-limited regions.

A perfect fit: Bacteriophage receptor-binding proteins for diagnostic and therapeutic applications

Bacteriophages are the most abundant biological entity on earth, acting as the predators and evolutionary drivers of bacteria. Owing to their inherent ability to specifically infect and kill bacteria, phages and their encoded endolysins and receptor-binding proteins (RBPs) have enormous potential for development into precision antimicrobials for treatment of bacterial infections and microbial disbalances; or as biocontrol agents to tackle bacterial contaminations during various biotechnological processes. The extraordinary binding specificity of phages and RBPs can be exploited in various areas of bacterial diagnostics and monitoring, from food production to health care. We review and describe the distinctive features of phage RBPs, explain why they are attractive candidates for use as therapeutics and in diagnostics, discuss recent applications using RBPs, and finally provide our perspective on how synthetic technology and artificial intelligence-driven approaches will revolutionize how we use these tools in the future.

Magnetic microbead enzyme-linked immunoassay based on phage encoded protein RBP 41-mediated for rapid and sensitive detection of Salmonella in food matrices

Rapid and sensitive quantitative detection methods are required to monitor and detect Salmonella throughout the food supply chain and early prevention of foodborne disease outbreaks. In this study, a magnetic microbead enzyme-linked immunoassay (MELISA) based on phage receptor binding protein was developed for rapid enrichment and detection of Salmonella in complex food matrices. RBP 41 from phage T102 acted as a species-specific recognition element for Salmonella by exploiting its strong binding capacity to Salmonella surface receptors. RBP 41-MBs were prepared by coupling recombinant RBP 41 with MBs and used to separate and enrich Salmonella cells from spiked food samples. The captured complexes were further integrated with ELISA procedures by HRP-labeled anti-Salmonella antibody for rapid and accurate detection of Salmonella. The whole method took <1.5 h and the detection limit was 10 CFU/mL. Therefore, MELISA was successfully developed for the detection of Salmonella in various spiked food samples (skim milk, lettuce, and chicken breast). The ELISA reaction process of this method was carried out on magnetic beads. It simplified the process of the traditional ELISA method and reduces the reaction time. This study expanded the use of phage-associated proteins and demonstrated the promising prospects for practical applications in the detection of foodborne pathogens.

Advances, applications, and limitations of portable and rapid detection technologies for routinely encountered foodborne pathogens

Traditional foodborne pathogen detection methods are highly dependent on pre-treatment of samples and selective microbiological plating to reliably screen target microorganisms. Inherent limitations of conventional methods include longer turnaround time and high costs, use of bulky equipment, and the need for trained staff in centralized laboratory settings. Researchers have developed stable, reliable, sensitive, and selective, rapid foodborne pathogens detection assays to work around these limitations. Recent advances in rapid diagnostic technologies have shifted to on-site testing, which offers flexibility and ease-of-use, a significant improvement from traditional methods' rigid and cumbersome steps. This comprehensive review aims to thoroughly discuss the recent advances, applications, and limitations of portable and rapid biosensors for routinely encountered foodborne pathogens. It discusses the major differences between biosensing systems based on the molecular interactions of target analytes and biorecognition agents. Though detection limits and costs still need further improvement, reviewed technologies have high potential to assist the food industry in the on-site detection of biological hazards such as foodborne pathogens and toxins to maintain safe and healthy foods. Finally, this review offers targeted recommendations for future development and commercialization of diagnostic technologies specifically for emerging and re-emerging foodborne pathogens.