Abiotrophia elegans sp. nov., a possible pathogen in patients with culture-negative endocarditis

Abstract

We isolated a hitherto undescribed microorganism from a patient with endocarditis. The microscopic appearance, a negative catalase reaction, and growth as satellite colonies next to Staphylococcus epidermidis suggested that this microorganism is a member of the genus Abiotrophia, formerly known as nutritionally variant streptococci. However, the clinical isolate described herein differed markedly from the known Abiotrophia spp., A. adiacens and A. defectiva, in terms of its (i) biochemical properties, (ii) restricted growth temperature range, (iii) whole-cell lysate polypeptide profile, and (iv) unique nutritional requirements. In contrast to the type strains of A. adiacens and A. defectiva, which used L-cysteine and pyridoxal hydrochloride as growth factors, the growth of the clinical isolate was only supported by L-cysteine hydrochloride and not by pyridoxal hydrochloride when the organism was tested in Todd-Hewitt or casein-soy peptone broth. Comparative 16S rRNA gene sequence analysis revealed that the microorganism was a member of the genus Abiotrophia and was most closely related to A. adiacens (96.9% homology). Phenotypic and phylogenetic data are consistent with the assumption of a new species within the genus Abiotrophia, for which we propose the name Abiotrophia elegans sp. nov. The unique nutritional requirements of this strain are of importance for diagnostic laboratories. The media of blood culture systems supplemented only with pyridoxal hydrochloride as a growth factor may fail to promote the growth of A. elegans sp. nov., and thus, these systems might not detect this microorganism as a possible cause of endocarditis.

FIG. 1

Coomassie-stained SDS-polyacrylamide gels. Microorganisms grown on Schaedler blood agar plates were washed twice in phosphate-buffered saline, resuspended in sample buffer, boiled, and separated by SDS–11% PAGE. The polypeptide profiles were visualized by Coomassie staining. Lane 1, low-molecular-mass markers (94, 67, 43, 30, 20, and 14 kDa); lane 2, A. adiacens; lane 3, A. defectiva; lane 4, strain B1333.

FIG. 2

Unrooted tree showing the phylogenetic relationships of strain B1333 to Abiotrophia spp. and related taxa. Distances were calculated by the neighbor-joining method. The evolutionary distance between any two taxa is the sum of the lengths of the horizontal lines between them. The bar indicates substitution rate per nucleotide.