There were many types of microbiological technique used by the industries to isolate and identify foodborne pathogens in genetically modified food.

DNA Hybridization



The presence or absence of particular genes helps DNA probe hybridization to identify bacteria. DNA is made up two strands of nucleotide polymers that twist around each other, resulting in a double helix. These long nucleotide chains are held together by hydrogen bonds between specific pairs of nucleotides.


The hydrogen bonds can be broken by pH above 12 or the temperature above 95°C. When pH and temperature is raised, single-stranded molecules and DNA are denatured. On the other hand, when pH or temperature is lowered, the hydrogen bonds are re-attached between the AT and GC pairs, reforming double-stranded DNA. The origin of DNA strands taken from is of no importance however the strands must be complementary. If the strands of the double helix are from different sources, the molecules are called hybrids and the process is termed hybridization.

Gene probe (Gene Search) is made up of nucleic acid molecules, usually double-stranded DNA. It consists of either an entire gene or a fragment of a gene with a known function. Besides, nucleotide sequence of the known gene can also make short pieces of single-stranded DNA. These are commonly referred to as oligonucleotides.


To detect complementary DNA or RNA targets in samples (Golden rice), both natural and synthetic oligonucleotides are used. This is because double-stranded DNA probes must be denatured before the hybridization reaction. While on the other hand, oligonucleotide and RNA probes, which are single-stranded, do not need to be denatured.


High temperature and pH is used to denature target nucleic acids. After which, the labelled gene probe is added. If the target nucleic acid in the sample was found to contain the same type of nucleotide sequence of the gene, the probe will then form hydrogen bonds with the target. When this happens, the labelled probe will then becomes particularly associated with the target. The unreacted, labelled probe is removed by washing the solid support, and the presence of probe-target complexes is signalled by the bound label. (Food drug and administration,2009)


Some gene probes used to detect pathogenic bacteria in foods can be found in Table 1:


Food and Drug Administration (2009) BAM: Identification of Foodborne Bacterial Pathogens by Gene Probes. Retrieved on 30th June 2010 from http://www.fda.gov/Food/ScienceResearch/LaboratoryMethods/BacteriologicalAnalyticalManualBAM/UCM072659

Youtube(2008)DNA Test Methods - Hybridisation . Retrieved on 1st july from http://www.youtube.com/watch?v=76eKnmCtCTU&feature=player_embedded#!

Posted By: Alicia Chee