Molecular studies on the ecology of Listeria monocytogenes in the smoked fish processing industry

We have applied molecular approaches, including PCR-based detection strateg ies and DNA fingerprinting methods, to study the ecology of Listeria monocy togenes in food processing environments. A total of 531 samples, including raw fish, fish during the cold-smoking process, finished product, and envir onmental samples, were collected from three smoked fish processing faciliti es during five visits to each facility, a total of 95 (17.9%) of the sample s tested positive for L. monocytogenes using a commercial PCR system (BAX f or Screening/Listeria monocytogenes), including 57 (27.7%) environmental sa mples (n = 206), 8 (7.8%) raw material samples (n 102), 23 (18.1%) samples from fish in various stages of processing(n = 127), and 7 (7.3%) finished p roduct samples (n = 96). L. monocytogenes was isolated from 85 samples (16. 0%) using culture methods. Used in conjunction with a 48-h enrichment in Li steria Enrichment Broth, the PCR system had a sensitivity of 91.8% and a sp ecificity of 96.2%. To track the origin and spread of L. monocytogenes, iso lates were fingerprinted by automated ribotyping. Fifteen different ribotyp es were identified among 85 isolates tested. Ribotyping data established po ssible contamination patterns, implicating raw materials and the processing environment as potential sources of finished product contamination. Analys is of the distribution of ribotypes revealed that each processing facility had a unique contamination pattern and that specific ribotypes persisted in the environments of two facilities over time (P less than or equal to 0.00 06). We conclude that application of molecular approaches can provide criti cal information on the ecology of different L. monocytogenes strains in foo d processing environments. This information can be used to develop practica l recommendations for improved control of this important foodborne pathogen in the food industry.