USE OF MOLECULAR TYPING METHODS TO TRACE THE DISSEMINATION OF LISTERIA-MONOCYTOGENES IN A SHRIMP PROCESSING PLANT

Molecular typing of bacteria has been widely used in epidemiological s tudies but not as extensively for tracing the transmission of pathogen ic bacteria in food plants. This study was conducted to examine the po tential use of two molecular typing methods, random amplified polymorp hic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE), t o trace Listeria monocytogenes contamination in a shrimp processing pl ant. Ribotyping and phage typing were also performed on a select numbe r of strains, One hundred fifteen strains of L. monocytogenes collecte d in different areas of a shrimp processing plant were first serotyped and then subtyped by molecular typing. RAPD and PFGE showed great pro mise for typing L. monocytogenes isolates since distinguishable and re producible DNA polymorphisms were obtained. When the composite profile from both (RAPD and PFGE) methods was generated, there was an increas e in the discriminatory power to discern differences between strains o f L. monocytogenes. The results indicated that environmental strains a ll fell into composite profile groupings unique to the environment, wh ile strains from both water and utensils shared another composite prof ile group. L. monocytogenes fresh shrimp isolates belonging to one pro file group were found in different areas of the processing line. This same profile group was also present in food handlers from the processi ng and packaging areas of the plant.