Enhancement of Conventional Phenotypic Methods with Molecular-Based Methods for the More Definitive Identification of Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTM) have traditionally been identified by phenotypic characteristics, including morphology, growth rates, pigmentation, temperature preference, and biochemical testing profiles. Unfortunately, these methods are laborious, relatively slow, and often subjective, and they may cause delays or even errors in therapeutic strategies. Importantly, incorrect identification may occur, because more than one species can possess the same phenotypic traits. This phenotypic overlap is a special concern for newly described species, for which detailed phenotypic characteristics are often lacking. Recently, a major transformation from phenotypic to molecular methods was ignited by an increase in the number of publications recommending molecular techniques for more definitive identification of NTM. Molecular methods, including PCR restriction enzyme analysis and DNA gene sequence analysis, are currently advocated. The latter technique is now recognized as the “gold standard” for the identification of the NTM. Although declining in importance, phenotypic tests still play a role in the identification of the NTM, especially descriptions of new species.