Mycobacterium: Laboratory Characteristics of Slowly Growing Mycobacteria

Abstract

This chapter represents that detailed phenotypic methods of identification of mycobacteria. Although some phenotypic characterization remains important, it is now well recognized by experts in mycobacterial taxonomy that current accurate identification of organisms of both the Mycobacterium tuberculosis complex (MTBC) and the nontuberculous mycobacteria (NTM) requires molecular techniques for definitive identification to species level. The MTBC remains the most important group within the genus Mycobacterium from a global and clinical perspective. Mycobacterium species differ in the ability to grow at certain temperatures. For determination of the preferred growth temperature, solid culture media are inoculated with defined suspensions of mycobacteria and incubated at various temperatures. The chapter further highlights that some Mycobacterium species cannot use nicotinic acid, although they produce it in their biosynthetic pathways. Commercially available assays are intended for the detection of some of the most important Mycobacterium species and can be performed from both solid and liquid media. Two tests for the identification of several mycobacterial species are commercially available but are not yet FDA approved. The INNO-LiPA Mycobacteria v2 assay is based on the nucleotide differences in the 16S-23S rRNA gene spacer region. The GenoType Mycobacterium CM/AS test is based on the detection of species-specific sequences in the 23S rRNA gene. The major criterion for molecular strain typing is that the test isolates must all belong to the same species. Thus, definitive identification to the species level is an important prerequisite.