We propose to replace the species designation Mycobacterium tuberculosis subsp. caprae (Aranaz et al. 1999) by Mycobacterium bovis subsp. caprae comb. nov., since isolates of this subspecies share their main growth, biochemical and genetic characteristics with M. bovis and not with M. tuberculosis. These include negative biochemical test results for niacin accumulation and nitrate reduction as well as genetic features like the presence of an M. bovis-specific mutation in the oxyR locus, absence of the mtp40 sequence and a specific mutation in the gyrB gene, all of which have been described as characteristics for the differentiation of M. bovis. The only obvious biochemical character that differentiates the caprae subtype from other M. bovis isolates is susceptibility to pyrazinamide (PZA), which is due to the lack of a single point mutation in the pncA gene. However, susceptibility to PZA among clinical isolates of M. bovis isolates has been reported previously and, thus, may now been explained by a PZA-susceptible subspecies of M. bovis. We conclude that the species designation M. tuberculosis subsp. caprae is misleading and not correct in light of the biochemical and genetic characteristics and propose that the accurate designation of isolates of this subtype is M. bovis subsp. caprae.


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