Polyphasic analysis indicates that Lactobacillus salivarius subsp. salivarius and Lactobacillus salivarius subsp. salicinius do not merit separate subspecies status

Lactobacillus salivarius Rogosa et al. 1953 was described as a homofermentative lactobacillus with two varieties: salivarius, typified inter alia by the ability to ferment rhamnose, and salicinius, characterized by the ability to ferment the glucoside salicin. These varieties have become accepted as subspecies divisions. We have examined the relatedness of 32 L. salivarius strains by a polyphasic approach. Carbohydrate fermentation profile analysis did not support clear distinction of the two subspecies. L. salivarius UCC118 was shown to be facultatively heterofermentative, confirming in silico genome analysis. 16S rRNA gene sequences and 16S-23S rRNA intergenic spacer region sequences provided no discrimination between any of the strains or subspecies. Broad subdivisions were distinguishable by pulsed-field gel genomic digest patterns, but they did not allow subspecific or phenotypic distinctions. A phylogeny based upon groEL gene sequences was discordant with rhamnose or salicin fermentation data for many taxa, and no reliable phenotypic correlations could be established. In the absence of meaningful taxonomic criteria, we therefore propose that Lactobacillus salivarius comprises a single species with no infraspecific taxa. Based on the present study and literature data, an emended description of the species Lactobacillus salivarius is provided.