Direct loop-mediated isothermal amplification assay for on-site detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a major human pathogen that may produce a variety of toxins and cause staphylococcal food poisoning. In the present study, a direct loop-mediated isothermal amplification (LAMP) assay was developed and validated to detect S. aureus in food samples. Without prior cultural enrichment and DNA extraction steps, bacterial DNA was released by heating at 100°C for 5 min and directly subjected to LAMP assay. Using a set of LAMP primers recognizing six distinct regions of nuc gene, the developed direct LAMP assay was highly specific, and the analytical sensitivity was determined to be 7.6 × 10² CFU/mL. Moreover, with the pre-mixed LAMP reagents stored at –20°C, the entire assay should be finished within 40 min. These features greatly simplified the operating procedure and made the direct LAMP a powerful tool for rapid and on-site detection of S. aureus in food samples.

Sensitive and rapid amperometric magnetoimmunosensor for the determination of Staphylococcus aureus

The preparation and characteristics of a disposable amperometric magnetoimmunosensor, based on the use of functionalized magnetic beads (MBs) and gold screen-printed electrodes (Au/SPEs), for the specific detection and quantification of Staphylococcal protein A (ProtA) and Staphylococcus aureus (S. aureus) is reported. An antiProtA antibody was immobilized onto ProtA-modified MBs, and a competitive immunoassay involving ProtA antigen labelled with HRP was performed. The resulting modified MBs were captured by a magnetic field on the surface of tetrathiafulvalene-modified Au/SPEs and the amperometric response obtained at -0.15 V vs the silver pseudo-reference electrode of the Au/SPEs after the addition of H2O2 was used as transduction signal. The developed methodology showed very low limits of detection (1 cfu S. aureus/mL of raw milk samples), and a good selectivity against the most commonly involved foodborne pathogens originating from milk. These features, together with a short analysis time (2 h), the simplicity, and easy automation and miniaturization of the required instrumentation make the developed methodology a promising alternative in the development of devices for on-site analysis.

Development and application of an electrochemical plate coupled with immunomagnetic beads (ELIME) array for Salmonella enterica detection in meat samples

Salmonella is one of the main organisms causing outbreaks of foodborne illness, and meat is one of the major vehicles of salmonellosis throughout the world. A novel analytical immunosensor array, based on a 96-well electrochemical plate coupled with immunomagnetic beads (ELIME array), is proposed for the detection of Salmonella in meat samples. After an optimization study, using Salmonella enterica serotype Enteritidis as reference antigen, the ability of the method to interact with a large number of Salmonella serovars commonly present in food was evaluated. The assay was then used to analyze samples of pork, chicken, beef, and turkey experimentally inoculated with Salmonella as well as real samples. The results were compared with those from the International Standard of Organization (ISO) culture method. The comparison showed that the ELIME array is able to detect a low number of Salmonella cells (1-10 CFU per 25 g) after only 6 h of incubation in a pre-enrichment broth. The investigation revealed a very good agreement between culture and ELIME array methods for meat samples, reducing the time for performing the analysis and obtaining the results quickly.