The development of methods for the detection of Salmonella in chickens by a combination of immunomagnetic separation and PCRs

Rapid and visual detection of Staphylococcus aureus in milk using a recombinase polymerase amplification-lateral flow assay combined with immunomagnetic separation

AIMS

The aim of this study was to develop a novel approach using lateral flow recombinase polymerase amplification (RPA-LF) combined with immunomagnetic separation (IMS) for the rapid detection of Staphylococcus aureus in milk.

METHODS AND RESULTS

Under optimum conditions, the average capture efficiency values (CEs) for S. aureus strains (10⁴ CFU ml^-1 ) was above 95.0% in PBST and ~80% in milk within 45 min with 0.7 mg immunomagnetic beads. The RPA-LF assay, which comprised DNA amplification via RPA at 39°C for 10 min and visualization of the amplicons through LF strips for 5 min, detected S. aureus within 15 min. The method only detected S. aureus and did not show cross-reaction with other bacteria, exhibiting a high level of specificity. Sensitivity experiments confirmed a detection limit of RPA-LF assay as low as 600 fg reaction^-1 for the S. aureus genome (corresponding to approximately 36 CFU of S. aureus), which was about 16.7-fold more sensitive than that of the conventional PCR method. When RPA-LF was used in combination with IMS to detect S. aureus inoculated into artificially contaminated milk, it exhibited a detection limit of approximately 40 CFU reaction^-1 .

CONCLUSIONS

The newly developed IMS-RPA-LF method enabled detection of S. aureus at levels as low as 40 CFU reaction^-1 in milk samples without culture enrichment for an overall testing time of only 70 min.

SIGNIFICANCE AND IMPACT OF THE STUDY

The newly developed IMS-RPA-LF assay effectively combines sample preparation, amplification, and detection into a single platform. Because of its high sensitivity, specificity, and speed, the IMS-RPA-LF assay will have important implications for the rapid detection of S. aureus in contaminated food.

Rapid detection of trace Salmonella in milk using an effective pretreatment combined with droplet digital polymerase chain reaction

Salmonella is one of the most dangerous food-borne pathogens around the world to cause a threat to humans and it is urgent to develop the rapid detection method of trace Salmonella in food. Although many advanced techniques have been widely applied to shorten the detection time, the pretreatment method usually used of traditional enrichment and plate culturing to separate Salmonella are complicated and time-consuming. Herein, we developed an effective pretreatment method based on in situ enrichment culture with an immunomagnetic separation step, combined with droplet digital polymerase chain reaction (ddPCR) technology to achieve rapid detection of trace Salmonella in milk, which allowed detecting as low as 10^-1 CFU/mL level of Salmonella. It took 8 h to perform the entire testing process from pretreatment to ddPCR detection and analysis. The pretreatment method could be a suitable platform integrating with many detection techniques for the rapid detection of trace Salmonella.