Significant differences between Lactobacillus casei subsp. casei ATCC 393T and a commonly used plasmid-cured derivative revealed by a polyphasic study.

Many studies on Lactobacillus casei subsp. casei (L. casei) have been carried out using strain ATCC 393 (pLZ15-). Four strains of L. casei ATCC 393T and three of ATCC 393 (pLZ15-) were compared using phenotypic methods and many of the available genotyping techniques. These tests showed that strains of ATCC 393T obtained from independent public type-culture collections were significantly different from the plasmid-free (pLZ15-) strains of ATCC 393T. These findings were confirmed by sequencing the first 580 nt (domain I) of the 16S and 23S rDNAs of the strains. Complete sequencing of the 16S rDNA of one representative strain from each group revealed that strain ATCC 393T from culture collections was 99% similar to Lactobacillus zeae ATCC 15820T and that the strain so far considered as L. casei ATCC 393 (pLZ15-) was, in turn, 100% similar to L. casei ATCC 334 and Lactobacillus paracasei subsp. paracasei ATCC 4022. All data obtained in this work indicate that the ancestral strain of ATCC 393 (pLZ15-) might never have been the strain that is now available from culture collections.