Characterization of human clinical isolates of Dietzia species previously misidentified as Rhodococcus equi

Abstract

In this study, 16 human clinical isolates of Dietzia species previously misidentified as Rhodococcus equi were evaluated using phenotypic methods, including traditional and commercial (API Coryne) biochemical tests, antimicrobial susceptibility testing, and 16S rRNA gene and gyrB gene sequencing. Positive results for both the hydrolysis of adenine and Christie-Atkins-Munch-Petersen (CAMP) reaction allowed for differentiation between the Dietzia isolates and the type strain of Rhodococcus equi; however, traditional and commercial phenotypic profiles could not be used to reliably identify Dietzia species. The analysis of 16S rRNA gene and gyrB gene sequences could discriminate all Dietzia strains from the type strain of R. equi. Most Dietzia species had distinct 16S rRNA gene and gyrB gene sequences; however, the 16S rRNA gene sequences of the type strains of D. schimae and D. cercidiphylli were identical to D. maris and D. natronolimnaea, respectively. Based on comparative sequence analysis, five clinical isolates clustered with D. maris/D. schimae and nine with D. natronolimnaea/D. cercidiphylli. The two remaining isolates were found to be most closely related to the D. cinnamea/D. papillomatosis clade. Even though molecular analyses were not sufficiently discriminative to accurately identify all Dietzia species, the method was able to reliably identify isolates that were previously misidentified by phenotypic methods to the genus level.

First Isolation of Dietzia cinnamea from a Dog Bite Wound in an Adult Patient

“…This aerobic, catalase-positive, and oxidase-negative bacterium was found to grow at temperatures in the range of 22 to 45°C, forming smooth and yellow-pigmented colonies. In addition, Yassin and colleagues found that the type strain, DSM (11). Urea hydrolysis was also proven to be negative in commercial identification kits used in our study.…”

“…The colonial difference is best seen after 3 days of incubation, as all other Dietzia spp. have been shown to form at least slightly mucoid colonies in this time period (11). Furthermore, in clinical samples, Dietzia spp.…”

“…as Rhodococcus spp. This may explain why only a few cases of Dietzia species isolations from human sources have been reported, although members of this genus are widely distributed in diverse habitats, such as marine, soil, and even hospital environments (2,3,8,10,11,19). Recently, some additional phenotypic tests have been reported to help distinguish Dietzia spp.…”

“…Recently, some additional phenotypic tests have been reported to help distinguish Dietzia spp. from Rhodococcus spp., particularly from Rhodococcus equi (11). These tests included, e.g., Christie-Atkins-Munch-Petersen (CAMP) and adenine hydrolyze tests in which Dietzia spp.…”

Discovery of a cell wall porin in the mycolic‐acid‐containing actinomycete Dietzia marisDSM 43672

“…Dietzia sp. are only rarely reported as pathogens although they may often be misidentified, notably as rhodococci [2,8].…”