Abiotrophia elegans strains comprise 8% of the nutritionally variant streptococci isolated from the human mouth

Ninety-one isolates of nutritionally variant streptococci (NVS) that were p reviously isolated from the human mouth were regarded as consisting of 7 St reptococcus defectivus isolates, 78 Streptococcus adjacens isolates, and 6 Gemella morbillorum isolates, However, recent references to the taxonomic r eclassification of NVS, from S. defectivus to Abiotrophia defectiva and fro m S, adjacens to Abiotrophia adiacens, and the newly introduced species Abi otrophia elegans as a third Abiotrophia species, emphasize the need for gen etic analyses for identification of NVS. When PCR-restriction fragment leng th polymorphism (RFLP) and phylogenetic distances were examined based on 16 S rRNA gene sequences, the results indicated that 7 of the 91 NVS isolates were closely related to A. elegans. These seven isolates consisted of four isolates previously identified as G. morbillorum and three isolates previou sly identified as S. adjacens. Two isolates previously identified as G. mor billorum were related to A. adiacens. In biochemical tests, A. elegans and the seven isolates related to it possessed arginine dihydrolase (ADH) activ ity but the other Abiotrophia species did not, As a result, A. elegans stra ins comprised 8% of the 91 NVS isolates. Our findings suggest that A. elega ns, A, adiacens, and A. defectiva exist in the human mouth in proportions o f about 1:11:1 and that A. elegans can be genetically distinguished from th e other two Abiotrophia species by PCR-RFLP analysis of 165 rRNA gene seque nces and can be biochemically distinguished by ADH activity.