[Genetic analysis reveals misidentification of Mycobacterium lentiflavum as Mycobacterium intracellulare by the COBAS TaqMan MAI test].

Abstract

Objective: To evaluate COBAS TaqMan MAI test misidentification of Mycobacterium lentiflavum as Mycobacterium intracellulare.

Materials and methods: Preliminary comparative analysis identified 13 clinical isolates used in this study as COBAS Amplicor MAV and MIN-negative but COBAS TaqMan MAI-positive. The COBAS TaqMan MAI test limit of detection and reproducibility were evaluated by tenfold dilution series from 3 x 10(8) CFU/mL. Isolate 16S rDNA nucleotide sequences were compared with Mycobacterium avium and M. intracellulare.

Results: Discrepancies were observed between isolates identified as M. lentiflavum by 16S rDNA sequencing and as M. intracellulare by the COBAS TaqMan MAI test. The false-positive results were verified by sequence comparison of a randomly sampled clinical isolate and the M. intracellulare reference strain. Sequence analysis of M. lentiflavum and M. intracellulare 16S rDNA amplification products showed at least 3 mismatches between species. The high identity in the sequence was found for M. intracellulare by COBAS TaqMan MAI.

Conclusion: In Japan, commercially available nucleic acid probe- and amplification-based tests cannot identify M. lentiflavum. Correct identification, though challenging, is possible using standard cultivation procedures for colony growth. Misleading results using the COBAS TaqMan MAI kit may lead to erroneous diagnoses.