Contribution of the Rv2333c efflux pump (the Stp protein) from Mycobacterium tuberculosis to intrinsic antibiotic resistance in Mycobacterium bovis BCG

Objectives: To characterize the efflux pump encoded by the gene Rv2333c from Mycobacterium tuberculosis, and assess its contribution to intrinsic antibiotic resistance using Mycobacterium bovis BCG as a model organism. Methods: Firstly, the Rv2333c gene was expressed from a multicopy plasmid in M. bovis BCG. Secondly, the gene was inactivated in the chromosome of M. bovis BCG. Antibiotic susceptibility tests and tetracycline uptake/efflux experiments were carried out with the strains mentioned above. Results: When the Rv2333c gene was inactivated in the M. bovis BCG chromosome, there was a decrease in the MIC values of spectinomycin and tetracycline, and an increase in [H-3]tetracycline accumulation. When the Rv2333c gene was cloned into a multicopy plasmid, there was an increase in the MIC values of spectinomycin and tetracycline, and a decrease in [H-3]tetracycline accumulation. These results indicate that both antibiotics are substrates of the Rv2333c efflux pump, which has been named Stp, for Spectinomycin Tetracycline efflux Pump. Conclusions: The Rv2333c efflux pump (Stp protein) of M. tuberculosis contributes to intrinsic spectinomycin and tetracycline resistance.