Direct identification of mycobacteria from MB/BacT Alert 3D bottles: Comparative evaluation of two commercial probe assays

The new INNO-LiPA Mycobacteria (Innogenetics, Ghent, Belgium), a reverse-hy bridization-based line probe assay, and the AccuProbe assay (Gen-Probe Inc. , San Diego, Calif.) were applied to MB/BacT Alert 3D (MB/BacT) system (Org anon Teknika, Boxtel, The Netherlands) culture bottles and evaluated for my cobacterial identification. From 2,532 respiratory and extrapulmonary speci mens submitted for culture, 168 were flagged positive by the MB/BacT system and promptly evaluated for identification (within 24 h). Each of 163 vials grew one mycobacterial isolate, including Mycobacterium tuberculosis compl ex (n = 73), M. avium complex (n = 3), M. avium (n = 8), M. intracellulare (n = 5), M. kansasii (n = 15), AL gordonae (n = 8), M. malmoense (n = 3), M . chelonae (n = 13), M. abscessus (n = 2), M. xenopi (n = 11), M. scrofulac eum (n = 2), Al. fortuitum (n = 7), M. terrae (n = 3), M. simiae (n = 2), M . celatum (n = 3), M. flavescens (n = 1), M. interjectum (n = 1), M. bohemi cum (n = 1), and M. pulveris (n = 2). Five cultures yielded mixed growth of two mycobacterial species: M. tuberculosis complex plus M. gordonae (n = 2 ), M. tuberculosis complex plus M. chelonae (n = 1), M. tuberculosis, compl ex plus M. xenopi (n = 1), and M. avium plus M. chelonae (n = 1). In testin g of one-isolate vials, both systems showed excellent sensitivity and speci ficity for all species and complexes for which they are licensed (nine for INNO-LiPA Mycobacteria versus six for AccuProbe). There were minor discrepa ncies in results for two isolates identified by INNO-LiPA Mycobacteria as M . avium - M. intracellulare - M. scrofulaceum (MAIS) complex and by AccuPro be as M. intracellulare. In testing of two-isolate vials, INNO-LiPA Mycobac teria correctly identified all isolates, while the AccuProbe assay failed t o identify three M. tuberculosis complex isolates and one M. avium isolate. The AccuProbe assay was completed within 2 h, while INNO-LiPA Mycobacteria required a 6-h period. In our opinion, INNO-LiPA Mycobacteria offers the f ollowing advantages: (i) it contains a genus-specific probe that, in additi on to being used in genus identification, may be used as an internal contro l for both the amplification and hybridization steps; (ii) it simultaneousl y identifies M. tuberculosis complex, MAIS complex, and seven other mycobac terial species, even from mixed cultures; (iii) its mycobacterial DNA ampli fication ensures reliable results independent from the concentration of via ble microorganisms; and (iv) it genotypically identifies M. kansasii and M. chelonae. In conclusion, even though INNO-LiPA Mycobacteria is considerabl y less easy to use than AccuProbe, requiring personnel skilled in molecular biology techniques, it represents an excellent approach for routine identi fication of frequently encountered mycobacteria.