Direct drug susceptibility testing of Mycobacterium tuberculosis using the proportional method: A multicenter study
Sirus Amini1, Sven Hoffner2, Mohammad Reza Allahyar Torkaman1
1Regional Tuberculosis Reference Laboratory, Tehran University of Medical Sciences, Tehran, Iran.
Introduction:
Conventional indirect drug susceptibility testing (DST) of Mycobacterium tuberculosis with solid media is inexpensive and reliable, but time-consuming. This study aimed to evaluate direct DST for testing sputum samples without culture to significantly reduce the time required to detect multidrug-resistant tuberculosis (MDR-TB).
Methods:
Direct and indirect DST of isoniazid (INH), rifampicin (RIF) and ethambutol (EMB) were performed on 334 sputum smear-positive specimens.
Results:
There was full agreement between the results obtained from direct testing and after isolation of the bacteria by culture. Thus, the sensitivity and specificity were observed to be 100% for all three tested drugs when compared with indirect DST. In comparison with indirect DST, none of the samples with the direct method took >25days to report the DST (between 15-25days with a mean detection time of 20 days).
Conclusions:
Direct DST on solid media was shown to give reliable results at a much earlier stage than conventional phenotypic DST. The direct method was found to be more rapid, more accurate and simpler. In addition, it reduced the handling of pathogenic bacteria and thus reduced the bio hazards related to conventional DST.
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