Vancomycin-modified poly-l-lysine magnetic separation combined with multiplex polymerase chain reaction assay for efficient detection of Bacillus cereus in milk

Nucleic acid amplification-based strategy to detect foodborne pathogens in milk: a review

Milk contaminated with trace amounts of foodborne pathogens can considerably threaten food safety and public health. Therefore, rapid and accurate detection techniques for foodborne pathogens in milk are essential. Nucleic acid amplification (NAA)-based strategies are widely used to detect foodborne pathogens in milk. This review article covers the mechanisms of the NAA-based detection of foodborne pathogens in milk, including polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), rolling circle amplification (RCA), and enzyme-free amplification, among others. Key factors affecting detection efficiency and the advantages and disadvantages of the above techniques are analyzed. Potential on-site detection tools based on NAA are outlined. We found that NAA-based strategies were effective in detecting foodborne pathogens in milk. Among them, PCR was the most reliable. LAMP showed high specificity, whereas RPA and RCA were most suitable for on-site and in-situ detection, respectively, and enzyme-free amplification was more economical. However, factors such as sample separation, nucleic acid target conversion, and signal transduction affected efficiency of NAA-based strategies. The lack of simple and effective sample separation methods to reduce the effect of milk matrices on detection efficiency was noteworthy. Further research should focus on simplifying, integrating, and miniaturizing microfluidic on-site detection platforms.

Fluorescence detection of Staphylococcus aureus using vancomycin functionalized magnetic beads combined with rolling circle amplification in fruit juice

Staphylococcus aureus is a common foodborne pathogen that can cause a suppurative infection after eating contaminated food. Detection of S. aureus plays an important role in the food industry. In this study, a strategy for the detection of S. aureus using magnetic separation (MS) technology combined with rolling circle amplification (MS-RCA) was proposed. The strategy used antibiotics to capture bacteria and employed RCA products as signal output probes. Vancomycin (Van), as a commonly used antibiotic, can recognize peptidoglycan on the cell wall of Gram-positive bacteria and can effectively identify target bacteria. Therefore, we prepared BSAylated-Van functionalized magnetic beads (Van-MBs) for the pre-enrichment of S. aureus. To ensure the selectivity of this method, we used biotin-pig IgG to bind S. aureus. In addition, to amplify the output signal of the MS-RCA strategy, we introduced streptavidin (SA) and successfully obtained the Van-MBs@S. aureus@biotin-pig IgG@SA@biotin-RCA probe complex and used the biotin-avidin-system (BAS) by combining magnetic separation technology and RCA technology to realize the enrichment and specific detection of S. aureus. Furthermore, by optimizing the experimental conditions such as the magnetic separation time and the amount of Van-MBs, the detection performance of this method was improved. Under the optimal conditions, the detection limit of this method for S. aureus was 3.3 × 10² CFU/mL in fruit juice, and it was less affected by other bacteria.

Poly-l-lysine-functionalized magnetic beads combined with polymerase chain reaction for the detection of Staphylococcus aureus and Escherichia coli O157:H7 in milk

Rapid and credible detection of pathogens is essential to prevent and control outbreaks of foodborne diseases. In this study, a poly-l-lysine-functionalized magnetic beads (PLL-MB) strategy combined with a PCR assay was established to detect Staphylococcus aureus. We also detected Escherichia coli O157:H7 to further verify the strategy for gram-negative bacteria detection. Poly-l-lysine has strong positive charges because of its amino groups, which can conjugate with the carboxyl of carboxyl magnetic beads. Furthermore, it can be used to combine with bacteria through electrostatic adsorption. Under optimum conditions, the developed PLL-MB complexes showed 90% capture efficiency in phosphate-buffered saline and 85% capture efficiency in milk for S. aureus detection. The limit of detection of the PLL-MB-PCR assay was 10² cfu/mL (1.8 × 10² cfu/mL for S. aureus and 7 × 10² cfu/mL for E. coli O157:H7) in phosphate-buffered saline and milk samples. The whole assay can be performed within 4 h. The proposed strategy showed a lower limit of detection when compared with the conventional PCR assay without enrichment. In addition, this method exhibited the advantages of a high-efficient, cost-efficient, and simple operation, indicating its potential applications in foodborne pathogen detection.

Microfluidic Colorimetric Biosensors Based on MnO2 Nanozymes and Convergence-Divergence Spiral Micromixers for Rapid and Sensitive Detection of Salmonella

In-field screening of foodborne pathogens plays an important role in ensuring food safety. Thus, a microfluidic biosensor was developed for rapid and sensitive detection of Salmonella using manganese dioxide nanoflowers (MnO₂ NFs) for amplifying the biological signal, a microfluidic chip with a convergence-divergence spiral micromixer for performing automatic operations, and a smartphone app with a saturation calculation algorithm for processing the image. First, immune magnetic nanoparticles (MNPs), the sample, and immune MnO₂ NFs were fully mixed and sufficiently incubated in the spiral micromixer to form MNP-bacteria-MnO₂ sandwich complexes, which were magnetically captured in a separation chamber in the microfluidic chip. Then, a 3,3',5,5'-tetramethylbenzidine (TMB) substrate was injected and catalyzed by a MnO₂ NF nanomimetic enzyme on the complexes, resulting in the production of yellow catalysate. Finally, the catalysate was transferred into a detection chamber and its image was measured and processed using the smartphone app to determine the number of bacteria. This biosensor was able to detect Salmonella from 4.4 × 10¹ to 4.4 × 10⁶ CFU/mL in 45 min with a detection limit of 44 CFU/mL, and has the potential to provide a promising platform for on-site detection of foodborne bacteria.