CHEESE COMPONENTS REDUCE THE SENSITIVITY OF DETECTION OF LISTERIA-MONOCYTOGENES BY THE POLYMERASE CHAIN-REACTION

To test the sensitivity of the polymerase chain reaction (PCR) for det ecting Listeria monocytogenes, cheese samples were artificially contam inated after enrichment incubation. PCR was strongly inhibited by chee se components and not by the ingredients of the enrichment broth. Use of DNA-purification matrices (DNA Capture Reagent and Geneclean II) ma y increase the detection limit about 100-fold, as analysed for one che ese type. The detection limit ranged from 10 to 10(6) colony-forming u nits per millilitre, depending on the soft and semi-soft cheeses used. The effect was tested of using 1 muL of undiluted DNA preparation or 1 muL of the DNA preparation diluted 10-fold to the PCR experiments. T he results varied between cheeses and between experiments, so that opt imum sensitivity must be evaluated by both reactions.