viernes, 10 de julio de 2009


Approval of new PCR based method to test Listeria in foods.
The BAX System Reverse-Transcriptase PCR Assay for Listeria species is a reliable method for detecting Listeria on stainless steel environmental surfaces in only 8 hours. Validation studies demonstrated that the BAX System Reverse-Transcriptase PCR Assay results were better than the U.S. Department of Agriculture/Food Safety and Inspection Service (USDA-FSIS) reference culture method.

A complementary technology is reverse-transcriptase PCR, which is used to detect RNA. Much like DNA, bacteria possess specific RNA sequences that are unique to the targeted organism. Each bacterial cell contains one DNA molecule and very large numbers of RNA molecules. Reverse-transcriptase PCR utilizes the multiple RNA copies to provide a “jump-start” to the DNA-based method and reduce overall time to result. In a typical BAX system application of reverse-transcriptase PCR, ribosomal RNA (r RNA) from the sample combines with the tableted PCR reagents, including primers, DNA polymerase, reverse transcriptase (an RNA- dependent DNA polymerase), nucleotides, and an RNA internal positive control that functions as a check for the activity of the reverse transcriptase and PCR steps of the assay.
When the mixture goes through a series of timed heating and cooling cycles, primers initially annel to the many copies of r RNA sequences. Increasing the temperature activates reverse-transcriptase, which synthesizes single strands of complementary DNA (c DNA). The temperature is then raised higher to inactivate the thermolabile reverse-transcriptase enzyme and activate the thermostable Taq polymerase.
Aporte: Ninoska Cordero Mattos
Fuente: Inside Laboratory Management. AOAC International

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