Identification of Atypical Rhodococcus -Like Clinical Isolates as Dietzia spp. by 16S rRNA Gene Sequencing

Abstract

Rhodococcus equi and Dietzia spp. are closely related actinomycetes that show similar phenotypic properties. In humans, R. equi is an opportunistic pathogen associated with severe immunodeficiency. Dietzia spp. are environmental bacteria that have been isolated recently from clinical material and are presumptively associated with human infections. During the last 5 years, 15 bacterial isolates from human clinical samples collected at the Hospital Marqués de Valdecilla, Santander, Spain, were identified as R. equi by the API Coryne test. 16S rRNA gene sequencing confirmed seven isolates to be true R. equi strains, whereas the other eight were identified as members of the genus Dietzia, including Dietzia maris (four isolates), Dietzia natronolimnaea (two isolates), and Dietzia timorensis and Dietzia sp. (one isolate each). The eight Dietzia isolates were highly sensitive to 12 antimicrobial compounds.

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

“…Furthermore, in clinical samples, Dietzia spp. can be reliably differentiated from members of other mycolic acid-containing genera by using 16S rRNA gene sequencing analysis (8,11,13). Although the potential of D. cinnamea to cause an infection was not able to be shown in our study, as an effective antimicrobial treatment was introduced without delay, previous reports by other authors suggest that Dietzia species have the potential to act as opportunistic pathogens (1,7,12,13,19).…”

Sputum Smear Concentration May Misidentify Acid-Fast Bacilli As Mycobacterium Tuberculosis in HIV-Infected Patients

“…In a multivariate analysis controlling for ‡Dietzia is closely related to Rhodococcus, many clinical isolates were previously misclassified as Rhodococcus through microbiological tests. 35 concentrated sputum smears, reports of fatigue and abnormal respiratory auscultation were found to be significant predictors of Mtb. To examine what bacilli other than Mtb could be responsible for AFB+ smears, we examined the 16S rDNA sequences in the samples.…”

Conjugal Transfer of a Virulence Plasmid in the Opportunistic Intracellular Actinomycete Rhodococcus equi

“…This finding is important in light of the fact that R. equi is primarily found in the soil, where it has ample access to other organisms to which it may pass virulence genes through conjugation. Perhaps such transfers could explain the occasional presence of typically nonpathogenic bacteria in human infections (35,42). This finding also warrants caution in reporting an infection to be caused by R. equi only on the basis of the presence of plasmid markers, as other related organisms might acquire this plasmid via conjugation.…”