Phenotypic and Genotypic Characterization ofMycobacterium africanum Isolates from West Africa

摘要

The Mycobacterium tuberculosis complex includesM. tuberculosis, M. bovis, M. africanum, and M. microti. Most clinical isolates areM. tuberculosis or M. bovis. These species can be distinguished by phenotypes and genotypes. However, there is no simple definition of M. africanum, and some authors question the validity of this species. We analyzed 17 human isolates from Sierra Leone, identified as M. africanum by biochemical and growth characteristics. We sequenced polymorphic genes and intergenic regions. We amplified DNA from six loci with variable numbers of tandem repeats (VNTRs) and determined the exact number of repeats at each locus in each strain. All M. africanumisolates had the ancestral CTG Leu at katG codon 463. Drug-resistant M. africanum isolates had katGand rpoB mutations similar to those found in drug-resistantM. bovis and M. tuberculosis. Fourteen Sierra Leone M. africanum isolates (designated group A) hadkatG codon 203 ACC Thr, also found in M. africanum T (the T indicates type strain) from Senegal. Group A isolates clustered with M. africanum T by VNTR analysis. Three M. africanum isolates (group B) had katG codon 203 ACT Thr, found in M. tuberculosis T, and clustered with M. tuberculosis T by VNTR analysis. Phenotypic identification of M. africanumyielded a heterogeneous collection of strains. Genotypic analyses identified a cluster (M. africanum group A) which includedM. africanum T and was distinct from the rest of the M. tuberculosis complex. Future studies ofM. africanum should include both phenotypic and genotypic analyses.