Primary identification of Aureobacterium spp. isolated from clinical specimens as "Corynebacterium aquaticum"

Over a 6-year period 11 yellow-pigmented gram-positive rods (GPRs) with an oxidative carbohydrate metabolism were isolated from clinical specimens or were received as reference cultures and tentatively identified as "Corynebacterium aquaticum" according to the guide of Hollis and Weaver for the differentiation of GPRs (D. G. Hollis and R. E. Weaver, Gram-Positive Organisms: a Guide to Identification, 1981). Because these isolates seemed to be rather heterogeneous, comparative analyses with the type strain of "C. aquaticum" as well as six type strains of species belonging to the genus Aureobacterium were performed by biochemical and chemotaxonomic methods. Only four clinical strains were found to be "C. aquaticum," whereas seven strains were found to belong to the genus Aureobacterium. Discriminative phenotypic reactions between "C. aquaticum" and Aureobacterium spp. included hydrolysis of gelatin and casein (both reactions negative for "C. aquaticum" strains but positive for most Aureobacterium strains). Moreover, peptidoglycan analysis provided a reliable means of differentiating yellow-pigmented GPRs at the genus level (diaminobutyric acid as the interpeptide bridge in "C. aquaticum" and glycine-ornithine as the interpeptide bridge in Aureobacterium spp.). Antimicrobial susceptibility testing revealed that vancomycin showed an intermediate MIC for three of the four clinical "C. aquaticum" isolates, whereas all Aureobacterium strains were susceptible to vancomycin. To our knowledge, this is the first report outlining the isolation of Aureobacterium spp. from clinical specimens. However, Aureobacterium isolates could not be identified to the species level by the tests used in the study.