Objective    To design a hair clamp DNA probe of rpsL 43 from streptomycin (SM)-resistant Mycobacterium tuberculosis and detect the liquid hybridization fluorescence signal between the amplified product of rpsL 43 and our hair clamp probe by fluorescence spectrophotometry in order to detect whether there is mutation at the site.     Methods    The software

Beacon designer

was used to design the hair clamp probe of rpsL 43. Fluorescence signal of hybridization between the amplified products of rpsL 43 from 20 strains isolated from Chongqing region and our probe was detected with fluorescence spectrophotometry. The sequences of the amplification products from different strains were compared.     Results    The difference in rpsL 43 PCR products between standard strain and SM-resistant one was very obvious when detecting the hybridization fluorescent signal by fluorescence spectrophotometer. We found fluorescent signal between our probe and the rpsL 43amplified products from the 20 SM-resistant strains and 10 H37RV standard strains. The mutation rate of SM-resistant strains was about 70% by our liquid hybridization assay

while the rate by sequencing was about 65%. Our assay found a false positive strain (504S).     Conclusion    Our liquid hybridization assay is easy and sensitive to detect rpsL 43 of SM-resistant Mycobacterium tuberculosis. The mutation site of RpsL 43 is one of the main reasons to cause SM-resistance in Mycobacterium tuberculosis in Chongqing region.