Heterogeneity of the Species Lactobacillus acidophilus (Moro) Hansen and Moquot as Revealed by Biochemical Characteristics and DNA-DNA hybridisation

The “classical” and biochemical characters and the DNA-DNA homology of 37 strains of Lactobacillus acidophilus were determined. Two main homology groups, subdivided into 5 and 2 subgroups, respectively, were established. The subdivision into two main groups was found to correlate with the electrophoretic type of the L-lactic acid dehydrogenase and several features of the cell wall chemistry, whereas no phenotypical characters were found to distinguish the homology subgroups from each other. Therefore the subgroups were not named, although the homology among them was 50% or less, thus justifying their separation into distinct species. At present, only the two main homology groups are considered to constitute named species. The group which contains the type strain of L. acidophilus retains the epithet acidophilus, whereas the other group was recently described as the new species L. gasseri. The implications of the distinct heterogeneity of “L. acidophilus” for intestine bacteriology is discussed.