Abstract
Rifampin resistance is a key prognostic marker for treatment success in tuberculosis patients. Recently, Wang et al. demonstrated that Rv2629 A191C mutations were present in 99.1% of rifampin-resistant and 0% of rifampin-susceptible clinical
Mycobacterium tuberculosis
isolates and that overexpression of the Rv2629 191C allele in
Mycobacterium smegmatis
produced an eightfold increase in rifampin resistance. These results suggested that Rv2629 could be a cause of rifampin resistance and a valuable target for rifampin resistance detection assays. We developed a molecular-beacon assay to study the association between Rv2629 191 alleles and rifampin resistance in 246 geographically and phylogenetically diverse clinical
M. tuberculosis
isolates. The 191C allele was present in 30/98 (30.6%) rifampin-resistant isolates and 25/148 (16.9%) rifampin-susceptible isolates and was more common in isolates from Asia. Phylogenetic analysis demonstrated complete overlap between the 191C allele and single nucleotide polymorphism cluster group 2 (SCG-2), a phylogenetic lineage that corresponds to the Beijing-W clade of
M. tuberculosis
. All 55 (100%) 191C isolates were SCG-2, while none of the 191 191A isolates were SCG-2 (
P
< 0.001). No association was found between the 191C allele and rifampin resistance in an analysis that included the SCG type (
P
= 1.0). Also, in contrast to the findings of Wang et al., we found that overexpression of either Rv2629 191 allele in
M. smegmatis
did not produce an increase in rifampin resistance. We conclude that the Rv2629 191C allele is not associated with rifampin resistance and that the allele cannot be used as a molecular target to detect rifampin resistance. The allele appears to be an excellent marker for the Beijing-W clade/SCG-2 phylogenetic group.