Mycobacterium africanum genotyping using novel spacer oligonucleotides in the direct repeat locus

This study involves a first evaluation of 25 novel spacer oligonucleotides in addition to the 43 routine spacers for molecular characterization of a panel of 65 isolates of tubercle bacilli from different geographic origins that were initially classified as Mycobacterium africanum based on phenotypic characters. The 68-spacer format defined four additional patterns, and three groups were identified. The relatively homogeneous groups A1 and A2 included strains from West Africa, and A3-1 included strains from East Africa. The presence of deletion region RD9 confirmed the reclassification of the M. africanum subtype II spoligopattern within group A3-1 as Mycobacterium tuberculosis. These isolates may represent a diverging branch of M. tuberculosis in Africa. The use of new spacers also suggested an undergoing evolution of M. africanum subtype I in West Africa. Our results showed that the strain differentiation within the M. tuberculosis complex is improved by using novel spacers, and extensive studies using new-generation spoligotyping may be helpful to better understand the evolution of M. africanum.