Inconsistencies in drug susceptibility testing of Mycobacterium tuberculosis: Current riddles and recommendations

Drug susceptibility testing (DST) of Mycobacterium tuberculosis is a crucial procedure to determine the effective drug regimen for patients' treatment. Reporting of erroneous DST results to the treating physician has adulterous effects on patients. As a first study of its type, the inconsistencies in reporting DST results of rifampicin and isoniazid from Saudi Arabia were assessed. An automated liquid culture-based DST and a molecular mutation detection technique were used. Performance of first-line drug susceptibility testing of 1904 clinical isolates showed 44 inconsistent results. The majority of the cases reported as MDR-TB from the referral laboratories could not reproduce the same results at a different site (Mycobacteriology Research Section). Of the 44 cases, 16 (36.3%) showed false resistance to isoniazid and rifampicin and on the other hand, 14 (31.8%) cases showed false susceptibility to the same drugs. The possible causes for the inconsistencies and recommendations to overcome the biases based on this experience are discussed.