A DNA probes is a fragment of DNA. Each probe can be used to reveal the presence of a specific ‘target’ DNA sequence within the rest of the organism’s DNA.
DNA probes have been highly successful in ‘fingerprinting’ people, in forensic medicine and in clinical medicine, and in isolating specific genes from DNA libraries.
These techniques should be adaptable to answering a number of questions related to food safety and quality.
Probe based methods have been developed for detection and enumeration of foodborne pathogens like Salmonella, Staphylococcus species, Listeria spp and hepatitis A virus.
In this method colonies that have grown up in selective agar are transferred to a membrane, which is then treated with reagents that lyse the cells. The denatured DNA is released and sticks to the membrane, which is then reacted with the DNA probe.
Lactic bacteria in wines and grape must have been detected by using DNA probes. L monocytogenes in artificially inoculated soft cheese and ground chicken have been detected using a hydrophobic grid membrane filter DNA probe.
Probes for typical plant pathogens like avocado sun blotch viroid, potato tuber spindle viroid and Erwinia amylovora can replace lengthy bioassays and give a clear-cut diagnosis of these plant diseases.
DNA probe technology has the potential to significantly shorten the sample analysis time in food borne pathogen detection. However, the continued requirement for a culture enrichment period will reduce the effectiveness of the technology, since it is the rate limiting step in the process.
The DNA probe must be highly selective for the organism to be determined. Selectivity is a function of the size of the DNA fragment used, the homogeneity of the DNA in terms of purity of strain, and the associating conditions.
Food analysis using DNA probes
