ABSTRACT
Soon after the discovery of the bacterial agent of tuberculosis by Robert Koch in 1888, Lehmann and Neumann formally described Mycobacterium tuberculosis (1). By the early 1900s, culture techniques and bacteriological tests allowed the differentiation of M. tuberculosis from Mycobacterium bovis by growth rate, colonial morphology, biochemical characteristics, and behavior in experimental animals (2). According to the same criteria, Mycobacterium microti and Mycobacterium africanum were identified in the 1950s and in the 1970s, respectively. Moreover, serial passages of a M. bovis strain over 13 years on potato slices soaked in ox bile and glycerol led Calmette and Gue´rin to the selection of a strain that lost its virulence and was used for human vaccine purposes, beginning from 1921. DNA/DNA hybridization studies showed a high level of genomic relatedness among the above bacille, indicating that they all belong to a single species (3). Sequence analyses confirmed these data, showing that tubercle bacille share great genetic similarity, seen by homology at the DNA level of greater than 99% (4-6). However, some particular genetic and phenotypic characteristics based mainly on different host preferences have led researchers to maintain
the traditional species names, and to create additional ones. TheM. tuberculosis complex now encompassesM. tuberculosis, M. bovis, M. africanum (7), M. microti (8), Mycobacterium pinnipedii (9), and Mycobacterium caprae (10). In this chapter, the additional agent of tuberculosis, Mycobacterium canettii (11), is not included in the designation ‘‘M. tuberculosis complex’’ and will be discussed separately.
