Evaluation of PhageDX Salmonella Assay for Salmonella Detection in Hydroponic Curly Lettuce

Efficiency of Bacteriophage-Based Detection Methods for Non-Typhoidal Salmonella in Foods: A Systematic Review

Food contamination with non-typhoidal Salmonella (NTS) presents a significant public health risk, underscoring the critical need for rigorous food safety measures throughout the production, distribution, preparation, and consumption stages. Conventional diagnostic strategies are time-consuming and labor-intensive and are thus sub-optimal for throughput NTS detection. Bacteriophages (phages) are highly specialized bacterial viruses and exhibit extreme specificity for their hosts. This organic phage/bacterial interaction provides an invaluable tool that can potentially replace or complement existing S. enterica detection methods. Here, we explored work in this area and reviewed data from PubMed/MEDLINE, Embase, and ScienceDirect up to 4 November 2024. Thirty-five studies were selected from 607 retrieved articles using the JBI Critical Appraisal Checklist to ensure quality. Salmonella enrichment, rapid detection, and effective recovery in diverse food sources for various NTS serovars were targeted. Utilizing phages as bio-probes alongside lateral flow immunoassays, surface-enhanced Raman spectroscopy, fluorescence, and electrochemistry assays enabled rapid and highly sensitive detection of NTS, achieving limits as low as 7 to 8 CFU/mL within 30 min. Balancing detection sensitivity with rapid analysis time is essential. Further research and development will be pivotal to overcoming challenges and maximizing the efficiency of NTS phage-based detection to ensure optimal food safety.

Bacteriophage-based bioassays: an expected paradigm shift in microbial diagnostics

Bacteriophages, as abundant and specific agents, hold significant promise as a solution to combat the growing threat of antimicrobial resistance. Their unique ability to selectively lyse bacterial cells without harming humans makes them a compelling alternative to traditional antibiotics and point-of-care diagnostics. The article reviews the current landscape of diagnostic technologies, identify gaps and highlight emerging possibilities demonstrates a comprehensive approach to advancing clinical diagnosis of microbial pathogens and covers an overview of existing phage-based bioassays. Overall, the provided data in this review effectively communicates the potential of bacteriophages in transforming therapeutic and diagnostic paradigms, offering a holistic perspective on the benefits and opportunities they present in combating microbial infections and enhancing public health.

Development of a Replication-Deficient Bacteriophage Reporter Lacking an Essential Baseplate Wedge Subunit

Engineered bacteriophages (phages) can be effective diagnostic reporters for detecting a variety of bacterial pathogens. Although a promising biotechnology, the large-scale use of these reporters may result in the unintentional release of genetically modified viruses. In order to limit the potential environmental impact, the ability of these phages to propagate outside the laboratory was targeted. The phage SEA1 has been previously engineered to facilitate food safety as an accurate and sensitive reporter for Salmonella contamination. In this study, homologous recombination was used to replace the expression of an essential baseplate wedge subunit (gp141) in SEA1 with a luciferase, NanoLuc®. This reporter, referred to as SEA1Δgp141.NL, demonstrated a loss of plaque formation and a failure to increase in titer following infection of Salmonella. SEA1Δgp141.NL was thus incapable of producing infectious progeny in the absence of gp141. In contrast, production of high titer stocks was possible when gp141 was artificially supplied in trans during infection. As a reporter, SEA1Δgp141.NL facilitated rapid, sensitive, and robust detection of Salmonella despite an inability to replicate. These results suggest that replication-deficient reporter phages are an effective method to obtain improved containment without sacrificing significant performance or the ease of production associated with many phage-based diagnostic methods.

Characterization of a broad-spectrum endolysin rLysJNwz and its utility against Salmonella in foods

Salmonella is a common foodborne pathogen worldwide. The use of bacteriophage-encoded endolysins as antimicrobial agents is a promising approach for controlling pathogenic contamination. In this context, a recombinant endolysin named rLysJNwz, consisting of a single domain falling with the L-alanogyl-D-glutamate peptidase-like family, was cloned, expressed, and characterized. The yield of rLysJNwz was about 25 mg/L. Synergy between 7.5 μg/mL rLysJNwz and 0.5 mmol/L EDTA could decrease the viable counts of Salmonella NCTC 8271 by 93.28%. A synergistic effect between rLysJNwz and polymyxin B was demonstrated, exhibiting the MIC of polymyxin B decreased by twofold. Specifically, rlysJNwz had strong thermostability at temperatures (4-95 °C) and maintained high activity at pHs from 5.0 to 11.0. rlysJNwz was a metal ion-dependent peptidase, which activated by divalent metal ions such as Zn²⁺, Mn²⁺, or Ca²⁺. Moreover, it was also found that the synergism of rlysJNwz and EDTA had bactericidal activities against a broad range of Gram-negative bacteria, including several multidrug-resistant bacteria. The application of rLysJNwz combined with EDTA was evaluated on contaminated eggs and lettuce for 60 min, displaying more than 86.7% and 86.5% reduction of viable Salmonella, respectively. Hence, these results suggest that rLysJNwz is a potential antibacterial agent to control Salmonella, especially antibiotic-resistant pathogen contamination in the field of food safety. KEY POINTS: • rLysJNwz shows lytic activities against a broad range of Gram-negative bacteria. • Endolysin rLysJNwz is a stable metalloenzyme and has high thermostability. • rLysJNwz and 0.5 mmol/L EDTA synergistically inactivate Salmonella on eggs and lettuce.