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Background & objectives: The heterogeneity of group D streptococci led to the identification of various biotypes of Streptococcus equinus and Streptococcus bovis and to the description of new species. The objective of the present study was to improve the phenotypic delineation between species and to clarify their respective phylogenetic position.
Methods: Physiological and genomic analyses were carried out in 84 representative strains of the group D streptococci. Biotypes were determined with the API 20 strep and rapid ID 32 STREP systems of identification. Quantitative DNA-DNA hybridization under stringent conditions and values of the ATm allowed to delineate species and subspecies. The phylogenic position of the different genomic groups was determined by comparing the sequences of their 16S rDNA.
Results: Four DNA-clusters, including seven species or subspecies, were characterized. Differential associations of biochemical characters allowed their identification. S. equinus and the type strain of S. bovis belonged to a single species. S. gallolyticus, S. bovis biotype II.2, and S. macedonicus formed a single DNA-cluster including three different subspecies. These were designated as S. gallolyticus subsp. gallolyticus, S. gallolyticus subsp. pasteurianus, and S. gallolyticus subsp. macedonicus. The two other DNA-clusters corresponded to the two subspecies of 5. infantarius, and to S. alactolyticus.
Interpretation & conclusion; This study presented a new classification associated with an identification scheme of group D streptococci. The changes in this classification demonstrate the interest of a polyphagic approach of the bacterial identification.
Key words Group D streptococci * Streptococcus bovis * S. equinus * S. gallolyticus * S. infantarius * taxonomy
Group D streptococci, the common inhabitants of the intestinal flora of vertebrates, were first identified by their antigenic and biochemical characteristics1,2. Genomic studies confirmed the separation of enterococci from non enterococci3,4. The group D streptococcal strains were then commonly designated as S. equinus or S. bovis depending on their origin and on their biochemical characteristics. Identification of S. bovis strains was based on their phenotype. Biotypes I and II designated mannitol-positive and mannitol-negative strains, respectively. Biotype II included two different phenotypes according to the presence (biotype II.2) or absence (biotype II. 1) of [beta]-glucuronidase5.
In 1984, a genomic classification of the 'S. equinus/S. bovis' complex delineated six different DNA-groups6. The group 1 included both S. equinus and some biotype II....