Rapid detection of Listeria monocytogenes by a PCR assay specific for an aminopeptidase

Specific and rapid detection of Listeria monocytogenes is very important wi th regard to food safety since all other species of Listeria appear to be n on-pathogenic to humans. Conventional microbiological detection methods are very time consuming. The polymerase chain reaction (PCR) is one of the mos t promising techniques for rapid detection of micro-organisms in food produ cts. We have developed a PCR assay, specific for L. monocytogenes,based on the gene encoding an aminopeptidase, which previously has not been describe d. for this species. The L. monocytogenes aminopeptidase shares strong sequence similarity with aminopeptidase C from Streptococcus thermophilous, Lactobacillus lactis, La ctobacillus helveticus, and with a cysteine proteinase from Saccharomyces c erevisiae. Polymerase chain reaction primers were synthesized based on the DNA sequence of the aminopeptidase gene. A 90 bp product was apparent with all L. monocytogenes strains tested but not with other species of Listeria or other bacterial genera. The PCR assay, which is performed directly from whole bacterial cells, does not involve DNA purification and can be conduct ed in 4 h. It provided positive identification of L. monocytogenes in mixed culture. (C) 1999 Academic Press.