Monitoring of bacterial evolution and molecular identification of lactic acid bacteria in smoked salmon during storage

The microflora of cold smoked salmon (CSS) consists of Gram-negative bacteria Such as Photobacterium, Vibrio and Shewanella, and Grain-positive bacteria from the genera Carnobacterium, Lactobacillus and Brochothrix. In this work, 5 series of CSS samples from different Suppliers were stored for I week at 4degreesC and 4 weeks at 7degreesC. The enumeration of lactic acid bacteria (LAB) from each sample Was carried Out every week followed by isolation. Molecular identification was carried out on isolates obtained from 15 CSS samples stored at refrigeration temperature for 14 to 35 d. 158 Gram-positive bacteria were identified by PCR using specific primers and PCR-RFLP on the 16S-23S rDNA intergenic spacer region (ISR). 28 Carnobacterium piscicola strains, 15 Cb. divergens strains, 81 Lactobacillus curvatus strains and only 1 Lb. sakei strain were identified. In addition, 33 Gram-positive catalase-positive isolates were identified as Brochothrix thermosphacta. The modification of bacterial diversity in CSS during storage was also monitored by using the temporal temperature gradient gel electrophoresis (TTGE) technique. The migration allowed both Grain-positive bacteria (Cb. piscicola, Cb. divergens, Lb. curvatus, Lb. sakei and B. thermosphacta) and Grain-negative bacteria (P. phosphoreum and S. putrefaciens) to be differentiated. All the bacteria species (Cb. piscicola, Lb. curvatus and P. phosphoreum) identified after Culture could be specifically detected by TTGE.