Abiotrophia elegans Strains Comprise 8% of the Nutritionally Variant Streptococci Isolated from the Human Mouth

Abstract

ABSTRACT Ninety-one isolates of nutritionally variant streptococci (NVS) that were previously isolated from the human mouth were regarded as consisting of 7 Streptococcus defectivus isolates, 78 Streptococcus adjacens isolates, and 6 Gemella morbillorum isolates. However, recent references to the taxonomic reclassification of NVS, from S. defectivus to Abiotrophia defectiva and from S. adjacens to Abiotrophia adiacens , and the newly introduced species Abiotrophia elegans as a third Abiotrophia species, emphasize the need for genetic analyses for identification of NVS. When PCR-restriction fragment length polymorphism (RFLP) and phylogenetic distances were examined based on 16S 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 previously identified as S. adjacens . Two isolates previously identified as G. morbillorum were related to A. adiacens . In biochemical tests, A. elegans and the seven isolates related to it possessed arginine dihydrolase (ADH) activity but the other Abiotrophia species did not. As a result, A. elegans strains comprised 8% of the 91 NVS isolates. Our findings suggest that A. elegans , A. adiacens , and A. defectiva exist in the human mouth in proportions of about 1:11:1 and that A. elegans can be genetically distinguished from the other two Abiotrophia species by PCR-RFLP analysis of 16S rRNA gene sequences and can be biochemically distinguished by ADH activity.