European Society of Mycobacteriology - Instituto Nacional de Saúde ...

DIRECT IDENTIFICATION OF Mycobacterium tuberculosis
COMPLEX, Mycobacterium avium COMPLEX
AND Mycobacterium kansasii IN SMEAR-POSITIVE CLINICAL SPECIMENS
PP-65
SUXING WANG, ZHI YU NEO, KE XIN MAK, MARIA DOLORES QUIENG, LI HWEI SNG
Central Tuberculosis Laboratory, Department of Pathology,
Singapore General Hospital
GenoType @ Mycobacteria Direct (GTMD) was used for direct identification Mycobacterium tuberculosis complex (MTBC),
M. avium, M. intracellulare, M. kansasii in 136 specimens from 122 patients. All 136 specimens were AFB smear positive with
ranges from 1+ to 4+. The GTMD correctly detected and identified 134 of 136 of the mycobacteria present. Compared
to results from culture, this indicates a sensitivity and specificity of GTMD assay of 98.5 and 100%, respectively. These
values increased to 100% when specimens with only MTBC isolation were considered. There were two discrepant results
during the study. The first was sputum from which M. avium complex was isolated which had been kept at –70 o C for
nearly 3 years. The test was negative for inhibitors and another sputum collected from same patient at same period was
detected as being positive for M. avium by GTMD. This may have been accounted for by degradation of the RNA or a
sampling issue. The second was a stool specimen from a HIV-positive patient who had M. avium complex isolated from
his stool. Both RNA isolation and amplification were repeated for the same specimen, and the presence of inhibitor was
confirmed. Two stool specimens from one HIV-positive patient were initially identified as containing M. avium complex
by AccuProbe. GTMD results showed bands matching M. intracellulae and M. kansasii, indicating possible co-infections in
this HIV-positive patient. This was confirmed when DNA probe was performed on growth from the LJ slant even though
there were no pigmented colonies and both specimens turned out to be positive for M. kansasii. It was most likely that
the mixed infection was not detected by routine methods as the M. intracellulare in this case, had outgrown M. kansasii as
the predominant organism in broth and solid cultures.
Direct identification by GTMD takes about 5 working hours compared to 3 to 5 weeks required for culture isolation
and species identification by conventional methods.
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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