Identification of listeria monocytogenes in food and environment by polymerase chain reaction

Abstract

Samples of mozzarella cheese, lettuce leaves (in suspension 1:10), tap water and wastewaters were artificially contaminated with L. monocytogenes in a ten‐fold decreasing number. DNA extracted directly from these samples was amplified by PCR technique utilizing two primers for target sequence. Amplified DNA fragment compared with one of known weight, was of 326 bp, characteristic of L. monocytogenes. Amplification was obtained up to a concentration of 3 cfu/ml in tap water, and in mozzarella cheese and lettuce leaves suspensions, corresponding to 30 cfu/g of this two products; up to 300 cfu/ml in wastewaters. In these last case probably some interference due to organic and inorganic compounds present inhibited PCR.

The present procedure does not require an enrichment culture step and is capable of identification of this microorganism within 3 h and a half.

Key words:

• Polymerase chain reaction (PCR)
• Listeria monocytogenes
• cheese
• lettuce
• tap water
• wastewaters