Use of the molecular typing methods to evaluate the control of Listeria monocytogenes contamination in a raw milk and dairy products.

Nineteen serogroup 1/2a Listeria monocytogenes strains isolated from raw milk, dairy products and salt water in one dairy were analyzed. Pulsed field gel electrophoresis (PFGE) and ribotyping were used to determine whether these strains isolated over a 8-month period are epidemiologically related. The samples of raw milk were contaminated by different L. monocytogenes clones. The clones isolated from dairy products (with the exception of one sample) and salt water were identical. Comparative genetic analysis of the clones isolated from raw milk, salt water and dairy products revealed the source of contamination and identified the L. monocytogenes strain involved in this process.