Clinical Evaluation of Nontuberculous Mycobacteria (NTM) Elite Agar, a New Medium for the Isolation of NTM: a Multicenter Study

Abstract

Nontuberculous mycobacteria (NTM) are gaining interest with the increased number of infected patients. NTM Elite agar is designed specifically for the isolation of NTM without the decontamination step. We assessed the clinical performance of this medium combined with Vitek mass spectrometry (MS) matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) technology for the isolation and identification of NTM in a prospective multicenter study, including 15 laboratories (24 hospitals). A total of 2,567 samples from patients with suspected NTM infection were analyzed (1,782 sputa, 434 bronchial aspirates, 200 bronchoalveolar lavage samples, 34 bronchial lavage samples, and 117 other samples). A total of 220 samples (8.6%) were positive with existing laboratory methods against 330 with NTM Elite agar (12.8%). Using the combination of both methods, 437 isolates of NTM were detected in 400 positive samples (15.6% of samples). In total, 140 samples of the standard procedures (SP) and 98 of the NTM Elite agar were contaminated. NTM Elite agar showed a higher performance for rapidly growing mycobacteria (RGM) species than SP (7% versus 3%, P < 0.001). A trend has been noted for the Mycobacterium avium complex (4% with SP versus 3% with NTM Elite agar, P = 0.06). The time to positivity was similar (P = 0.13) between groups. However, the time to positivity was significantly shorter for the RGM in subgroup analysis (7 days with NTM and 6 days with SP, P = 0.01). NTM Elite agar has been shown to be useful for the recovery of NTM species, especially for the RGM. Using NTM Elite agar + Vitek MS system in combination with SP increases the number of NTM isolated from clinical samples.

Keywords: Mycobacterium; NTM Elite agar; culture; diagnosis; nontuberculous mycobacteria.