Detection of Listeria monocytogenes from food samples by PCR after IMS-plating.

For rapid, accurate and sensitive detection of Listeria monocytogenes in food samples, colonies developed on the selective agar (Oxford agar) after immunomagnetic separation (IMS) were subjected to polymerase chain reaction (PCR) assay with the prf A1-2 primer pair. The proposed assay system was shown experimentally to be capable of specifically detecting the bacteria from food samples contaminated at more than 10(2) cfu/g. However, the enrichment culture after a short period of 16 h with the appropriate selective broth was needed before IMS-plating, because the bacterial contents in most actual food were as low as less than 10(2) cfu/g. However, even if the enrichment cultivation was employed before IMS, L. monocytogenes was detected within 3 days.