Activity of rifampin against Mycobacterium tuberculosis in a reference center

Rifampin is a bactericidal antibiotic that acts both on extra- and intracellular bacilli. It inhibits RNA synthesis by binding to the beta-subunit in the RNA polymerase. A study was conducted on rifampin resistance from 1993 to 2002 with 1,794 Mycobacterium tuberculosis strains submitted to Mycobacteria Reference Center, Córdoba, Spain. A total of 1,460 of these strains came from pulmonary specimens and 235 from extrapulmonary specimens. All strains were identified by conventional morphological, bacteriological, biochemical, genetic, and chromatographic methods. For 99 strains, the source was not indicated. Initially, the BACTEC 460 TB system was used for antibiotic sensitivity testing. Since 1996, the ESP II system was also used. The strains ATCC27294 (sensitive to streptomycin, rifampin, ethambutol, and isoniazid) and ATCC38838 (resistant to rifampin) were used as controls. The resistance degree detected was 10.03%, of which 1.2% and 8.7% corresponded to primary and secondary resistances, respectively. A total of 137 strains showed multiresistance. The surveillance of resistance and of the potential factors that may lead to an increase in resistance is thus warranted.