2.10

Skip to 0 minutes and 1 secondLab experiment.

Skip to 0 minutes and 5 secondsA spiking experiment is set up in the laboratory as follows. 25 grammes of a pork sample is weighed and homogenised to with 225 mils diluting buffer in a Stomacher instrument.

Skip to 0 minutes and 28 seconds10 of the 20 tubes are selected at random, and spiked with salmonella typhimurium culture.

Skip to 0 minutes and 37 secondsThe other 10 samples are not spiked.

Skip to 0 minutes and 44 secondsWell 1 contains magnetic beads plus 1 mil of homogenised spiked or non-spiked pork sample.

Skip to 0 minutes and 53 seconds1 mil of each of the 20 samples is then processed by Immunomagnetic Separation, or IMS, using the bead retriever instrument.

Skip to 1 minute and 3 secondsMixing takes place for 30 minutes, during which time any salmonella present bind to the peptide-coated magnetic beads. Then the magnet is switched on, and beads are captured from the sample for transfer to well two.

Skip to 1 minute and 20 secondsWell 2. Beads are released into one mil of wash buffer, and washed for one minute with mixing, to remove food components and other non-target bacteria from the magnetic beads.

Skip to 1 minute and 35 secondsThe magnet is then switched on, and beads are captured from the sample for transfer to well three.

Skip to 1 minute and 43 secondsWell 3 is a second wash. Same process as in well 2.

Skip to 1 minute and 51 secondsThe magnet is switched on. And beads are captured from the sample for transfer to well four.

Skip to 1 minute and 58 secondsWell 4. Beads are released into the final resuspension buffer, which for PCR is Tris-EDTA buffer.

Skip to 2 minutes and 10 secondsAt the end of IMS, magnetic beads are resuspended in 100 microliters of buffer.

Skip to 2 minutes and 30 secondsDNA is extracted from any captured salmonella cells by heating samples at 100 degrees C for 10 minutes in the heating block.

Skip to 2 minutes and 45 secondsSalmonella-specific PCR is carried out on all samples. And the presence or absence of the expected PCR product is recorded after agarose gel electrophoresis.

Lab experiment: IMS-PCR testing for salmonella in pork

Immunomagnetic separation (IMS) is a technique used in food testing laboratories to isolate foodborne pathogens such as Salmonella spp. from food samples.

It permits the capture and concentration of a target pathogen by means of microscopic magnetic beads coated in either target-specific antibody or peptide binders.

The video demonstrates the application of IMS to facilitate the extraction of Salmonella cells within meat samples and subsequent quantification of the level of contamination by polymerase chain reaction (PCR) analysis.

If you have any comments about the method, or if you have used this technique before please share your thoughts in the discussion area.

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This video is from the free online course:

Tackling Global Food Safety

Queen's University Belfast