Abstract
Assessment of the genetic stability of strains that have to be reproduced at industrial scale and then freeze dried or incorporated into a food matrix is extremely relevant, in order to guarantee consumers of the quality of probiotic products. Stability of plasmid complement of Lactobacillus paracasei subsp. paracasei isolate F19 ( Lactobacillus F19), a strain containing three extrachromosomal elements, was carefully checked in each step of the industrial reproduction process. Results did not detect any selection of cured derivatives. The plasmid profile was unaltered when compared with the plasmid content determined in the same strain by our laboratory 6 years earlier. Attention was then paid to the functional roles (if any) of the plasmid complement of Lactobacillus F19. Laboratory-induced cured derivatives of the strain were obtained and analyzed in detail as regards their probiotic and microbiological features, namely sugar fermentation pattern, drug and bile resistance and growth curves. Cured derivatives of L. paracasei F19 were obtained only after severe curing treatments. These mutants have been shown to retain all the properties of the wild-type strain.