Analysis of Mutations in Streptomycin-Resistant Strains Reveals a Simple and Reliable Genetic Marker for Identification of the Mycobacterium tuberculosis Beijing Genotype

TheMycobacterium tuberculosis pandemic is a major health problem, further complicated by an increasing incidence of drug-resistant isolates and the existence of highly transmissible strains, such as those in the Beijing family. Streptomycin (STR)-resistantM. tuberculosis clinical isolates have been analyzed to look for mutations in therpsL ,rrs , andgidB genes. In addition, theRv1258c gene, which encodes Tap, an efflux pump that transports STR, has been sequenced. Mutations affecting codons 43 and 88 of therpsL gene were found in 44.4% of the strains, and 16.7% of the strains carried mutations in therrs gene, both of which probably contribute to STR resistance. Many strains presented with mutations in thegidB gene, but the implication of those mutations in STR resistance remains unclear. Interestingly, a cytosine nucleotide insertion between positions 580 and 581 (denominated Tap580 ) in theRv1258c gene has been found in all Beijing isolates included in this study, suggesting that it might be a novel polymorphism specific to the Beijing family ofM. tuberculosis . A simple and fast restriction fragment length polymorphism (RFLP)-PCR method for detecting the Tap580 insertion has been developed and used to screen a collection of 220 DNA samples obtained from cultures ofM. tuberculosis isolates and 30 respiratory specimens. In all cases, the Beijing and non-Beijing representative samples were identified correctly. Tap580 is a novel polymorphism specific to the highly transmissible Beijing family, which allows for fast detection of these strains even at the very early stages of infection.