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 mi lk, dairy products and salt water in one dairy were analyzed. Pulsed field gel electrophoresis (PFGE) and ribotyping were used to determine whether th ese strains isolated over a 8-month period are epidemiologically related. T he samples of raw milk were contaminated by different L. monocytogenes clon es. The clones isolated from dairy products (with the exception of one samp le) and salt water were identical. Comparative genetic analysis of the clon es isolated from raw milk, salt water and dairy products revealed the sourc e of contamination and identified the L. monocytogenes strain involved in t his process.