What is the meaning of repeated isolation of Mycobacterium africanum?

Mycobacterium africanum is a member of the tuberculosis complex, together with M. tuberculosis and M. bovis. Its morphological growth is quite different from that of M tuberculosis. It is a causative agent of the same tuberculosis disease, and its precise identification seems important only for epidemiological purposes. We report here the repetitive isolation of 17 M. africanum strains (among 321 TB complex strains) during a national primary resistance survey in C te d'Ivoire in 1995. All of the M. africanum strains were isolated in four regions located in the same geographical area. They showed biochemical heterogeneity yielding three patterns, none of which was specific to one region. Molecular analysis by RFLP for 14 strains showed identical patterns for four strains, two by two, and a clustering of 62-77% homology for eight of the 14 strains (57%). This report confirms that M. africanum is less frequent than M. tuberculosis. Its repeated isolation may reflect inter-human transmission. Biochemical similarities between strains may not always be associated with a common geographical origin.