Evaluation of a fluorescence in situ hybridization assay for differentiation between tuberculous and nontuberculous Mycobacterium species in smears of Lowenstein-Jensen and mycobacteria growth indicator tube cultures using peptide nucleic acid probes

A new fluorescence in situ hybridization assay based on peptide nucleic aci d probes (MTB and NTM probes targeting tuberculous and nontuberculous speci es, respectively) for the identification of Mycobacterium tuberculosis comp lex and differentiation between tuberculous and nontuberculous mycobacteria (NTM) was evaluated using Lowenstein-Jensen (LJ) solid cultures from 100 c onsecutive sputum samples and 50 acid-fast bacillus (AFB)-positive sputum s amples as well as Mycobacteria Growth Indicator Tube (MGIT) liquid cultures from 80 AFB-positive sputum samples. Mycobacterium species could be identi fied from a total of 53 LJ cultures and 77 MGIT cultures. The diagnostic sp ecificities of the MTB and NTM probes were 100% for both cultures. The diag nostic sensitivities of the MTB probe for the LJ and MGIT cultures were 98 and 99%, respectively, whereas the sensitivities of the NTM probe were 57 a nd 100%, respectively. The relatively lo cv sensitivity of the NTM probe wa s due to a high proportion of M. fortuitum, which is not identified by the probe.