In vitro activity of antituberculous agents against Mycobacterium tuberculosis isolates from Bogota, DC (Colombia) evaluated by the Etest

Abstract

Tuberculosis tests for antimicrobial susceptibility takes weeks. However, delayed therapy, can compromise the patient, as well as lead to an increase in disease incidence. Among infectious diseases, tuberculosis continues to be a leading cause of death in the world. The E-test is a new concept for Minimal Inhibitory Concentrations (MIC) determinations for antimicrobial agents that is based on a predefined antibiotic gradient on a plastic strip calibrated with a continuous logarithmic MIC scale covering 15 two-fold dilutions. MICs of rifampin, isoniazid, and ethambutol were determined by using the E-test (AB BIODISK, Solna, Sweden) for 30 clinical strains of Mycobacterium tuberculosis isolated from four hospitals, and were compared with the Bactec method. To make the inoculum with a turbidity equivalent to a McFarland 3.0 standard, we obtained a sample from an agar surface and the Bactec 460, as described by the manufacturer. Excellent agreement (100% for rifampin, 96.8% for ethambutol, and 90% for isoniazid) was demonstrated between the E-test MIC distributions and the Bactec interpretive criteria for all clinical isolates of M. tuberculosis tested. The E-test appears to be a good alternative method for testing the susceptibility of M. tuberculosis isolates to the three, most-commonly-used therapeutic agents.