Evaluation of GenoType NTM-DR Assay for Identification of Mycobacterium chimaera

Abstract

Identification of species within the Mycobacterium avium complex (MAC) is difficult, and most current diagnostic laboratory tests cannot distinguish between species included in the complex. Differentiation of species within the MAC is important, as Mycobacterium chimaera has recently emerged as a major cause of invasive cardiovascular infections following open heart surgery. A new commercial diagnostic assay, GenoType NTM-DR ver. 1.0, is intended to differentiate between three species within the MAC, namely, Mycobacterium avium, Mycobacterium intracellulare, and Mycobacterium chimaera In this study, we investigated an archival collection of 173 MAC isolates using 16S rRNA and 16S-23S internal transcribed spacer (ITS) gene sequencing, and GenoType NTM-DR was evaluated for identifying M. chimaera and other species belonging to the MAC. Species identification of 157/173 (91%) isolates with the GenoType NTM-DR assay was in agreement with 16S rRNA and 16S-23S ITS gene sequencing results. Misidentification occurred with 16 isolates which belonged to four species included in the MAC that are rarely encountered in clinical specimens. Despite some limitations of this assay, GenoType NTM-DR had 100% specificity for identifying M. chimaera This novel assay will enable diagnostic laboratories to differentiate species belonging to the Mycobacterium avium complex and to accurately identify M. chimaera It can produce rapid results and is also more cost efficient than gene sequencing methods.

Keywords: GenoType NTM-DR; Mycobacterium avium complex; Mycobacterium chimaera; genotypic identification.

FIG 1

GenoType NTM-DR test strips of M. chimaera, M. intracellulare, and M. avium. All 79 M. chimaera, 49 M. intracellulare, and 29 M. avium isolates produced the correct species banding pattern. However, the universal control (UC) band were very faint in all the isolates tested and only bands with intensities stronger than those seen with the UC were considered. No antibiotic resistance mutation bands were present in the three test strips shown at the top of the figure.

FIG 2

Interpretation chart for the GenoType NTM-DR assay. The specificities of the bands are as follows: CC, conjugate control probe; UC, universal control probe; SP1 to SP10, species-specific probes [specific probes for macrolide resistance mediated by erm(41) which are not applicable to members of the Mycobacterium avium complex, specific probes for the rrl gene and rrs gene, and mutation probes for possible detection of resistance to macrolides and aminoglycosides]. Filled boxes indicate complete staining, striped boxes indicate facultative staining, and blank boxes indicate no staining. WT, wild type.