The range of genetically modified organism test kits is expanding and includes developments such as lateral flow or strip test devices. Eric Russell looks at some of the kits which are currently available.
Genetically modified organism (GMO) test kits have reduced both time and cost of GMO testing. They use the same principles as conventional plate and tube formats but the antibodies and other reagents are coated onto a membrane rather than on the inside of test wells or tubes.
The sample is added at one end of the device and travels by capillary action to the other end. In passing along the membrane the sample is exposed to zones of antibody reactive to the target analyte. The sample activates a control area at the far end of the strip to provide visual proof that it has passed through the system.
Rod Poland of Neogen Corporation says the company offers tests for three genetic traits: BT, Cry9C and CP4. These are available in microwell and easy-to-use strip test formats.
Agri-Screen for CP4 Strip Test is a lateral flow strip that can detect as little as 1 Roundup Ready soybean in 1000, or 1 Roundup Ready NK603 corn kernel in 800. CP4 is the protein added to crops to make them resistant to Roundup herbicides. The test can be read in five minutes.
Agri-Screen for Cry9C Strip Test offers 0.125 per cent sensitivity to Cry9C. The microwell version is in ELISA format, which allows batch runs, as well as providing sensitivity of 0.1 per cent. Cry9C is a protein produced by genes from the bacterium Bacillus thuringiensis and is added to corn to make it resistant to insect damage. Agri-Screen for Bt Microwell Test detects the Bt proteins Cry1AB, Cry1AC and Cry9C. It also uses an ELISA microwell format that allows batching, and offers a sensitivity of 0.1per cent. ELISA is an Enzyme-Linked ImmunoSorbent Assay.
Promega offers the Biosmart Allin 1.0 GMO Screening System which specifically screens for the cauliflower mosaic virus S35 promoter, used in many genes inserted into plants including cereals, oil producing plants and cocoa.
Cauliflower mosaic virus (CaMV) is a DNA virus affecting cauliflower and many other dicot species. Its importance is due to the promoter of its 35S ribosomal DNA, which is constitutively active in most plant tissues and has been widely used as a promoter for the expression of transgenes.
CaMV is a spherical, DNA-containing plant virus that is naturally transmitted by aphids to crops such as broccoli, cabbage and turnips. The virus is worldwide in its distribution and is found wherever susceptible crops are grown and is present in the food products derived from these crops.
Promega also offers a kit specifically for isolating DNA from food, called the Wizard Magnetic DNA Purification System for Food. This system is based on Promega's MagneSil magnetic bead technology for isolating DNA from foodstuffs including maize, cornmeal, corn seed, soy milk, soy flour and tofu.
DNA detection
Dr Angus Trowern, technical services scientist with Promega, says a generally accepted method for determining GMO content in foodstuffs is the detection of DNA sequences used in the genetic modification. As an example, the genetic modification of a commercially available soybean involves the introduction of a glyphosate-resistant 5-enol-pyruvyl-shikimate-3 phosphate synthase (EPSPS) gene and the elements used for EPSPS gene expression - which are 35S promoter and the nopaline synthase (NOS) transcription terminator sequence. 35S is radioactive sulphur, a radioactive isotope of 32S, an element found in proteins.
Detection of the 35S and the NOS sequences by polymerase chain reaction (PCR) methods is widely used for the identification of these GMO soybeans. PCR is a method for amplifying a DNA base sequence using a heat-stable polymerase - an enzyme that can synthesise new complementary DNA strands using a DNA template and primer. Amplification is the process of producing many DNA copies from one original DNA or RNA target region.
PCR has become the workhorse of genetic testing because of its simplicity and flexibility. Instead of having to construct a clone library from the DNA of each individual to be tested, PCR is used to amplify only the desired DNA sequences.
The Biosmart Allin 1.0 GMO Screening System is a nested multiplex PCR system for the detection of DNA from GMOs that contain the 35S promoter. In addition, the system contains soya (lectin) and maize (zein) specific primers, which are used to confirm the presence of these species in a sample. An internal control is provided to identify the presence of inhibitors in the reaction.
SCIL and its partner GeneScan Analytics provide both laboratory services for GMO testing, and a full range of PCR and ELISA test kits.
Its GMO Screen kit is a PCR system for 35S promoter and NOS terminator based on an agarose gel-electrophoresis detection. It contains all PCR reagents, positive GMO DNA, complete DNA extraction and a sophisticated protocol.
GMO Ident is similar to GMO Screen and offers eight PCR test kits for the specific identification of EU-approved or non-EU approved GMOs.
GMO Quant enables approved and non-approved GMOs to be quantified in plant parts. Tests are available for real-time PCR machines such as the ABIPRISM 7900, 7700 and 7000, GeneAmp5700 and LightCycler.
Rapid testing
SDI is a leader in rapid diagnostics for detecting GMOs in crops, grains and primary processed food and feed ingredients. Its Trait Check is a lateral flow format test system that detects specific GMOs in a wide range of crop and grain types. It reacts with the proteins produced by genetic modifications and is a very cost effective test with its time requirement of 5-10minutes.
GMO Check is a fully quantitive immunoassay-based test system using the ELISA concept where samples are measured against a set of standards of known GMO concentration. These test are highly sensitive with minimum detections down to 0.001per cent.
SDI says the advantage of GMO Check is its ability to test large batches of samples in parallel, which means a highly cost effective testing solution.
Richard Fielder, international marketing manager for Tepnel BioSystems, says the company provides test kits under the BioKits brand and a contract analytical service for both qualitative and quantitive analysis plus testing and training under the name BioGenetix.
The new BioKits DNA Extraction Kit is capable of producing the high yields of good quality DNA necessary for all forms of GM food and animal feed analysis. It uses magnetic particles to selectively purify DNA molecules from sample lysates. Fielder says it is more efficient and considerably simpler than other methods.
He points out that pure and clean DNA is a fundamental pre-requisite for performing most DNA based analysis; the capability of even the most optimised protocols will be limited by poor extraction. In DNA-based food testing, effective clean-up is vital due to the complex combination of constituents in the analytical sample; high salt or sugar contents of foods, for example, will invariably lead to inhibition of the PCR reaction.
The BioKits system uses Tepnel's proprietary magnetic bead technology to provide significant advantages over other methods of DNA extraction. The magnetic particles are specifically designed to bind DNA and not the unwanted matrix components of foods that could interfere with the PCR reaction.
The revolutionary combination of the quality and functional properties of the coating used on the particles means that the DNA is not precipitated, so co-precipitation of interfering components does not occur. Once the DNA has been immobilised on the surface of the particles they can be washed repeatedly.
