BACKGROUND
Mycobacterium tuberculosis
(MTB) is one of the most significant causes of mortality and morbidity. Early
diagnose is important especially in multiple drug resistant tuberculosis to avoid transmission. Traditional techniques requires at
least one to three weeks for diagnosis of tuberculosis. Diagnostic delays with multiple drug resistant tuberculosis are associated
with worse clinical outcomes and increased transmission The Xpert MTB/RIF assay is one of the new diagnostic device for the
diagnosis of tuberculosis and rapid detection of rifampicin resistance.
OBJECTIVE We assessed the performance of Xpert MTB/RIF assay for detecting rifampicin resistance using phenotypic drug
susceptibility tests as automated BD MGIT 960.
METHODS Total of 2136 specimens were included in the study. Xpert MTB/RIF testing was performed on samples, using
version 4 cartridges, according to the manufacturer’s recommendations. The MTBC culture and first-line phenotypic DST were
performed in automated BD MGIT 960 (Becton & Dickinson, USA) according to the recommendations of the manufacturer.
Agar proportion was used in the case of inconsistency for rifampicin resistance.
FINDINGS Thirty-four samples (19 respiratory and 15 nonrespiratory samples) were determined as positive for
M. tuberculosis
complex by Xpert MTB/RIF (Cepheid GeneXpert® System, USA). Xpert MTB/RIF assay detected 4/34 (11.7%) specimens as
rifampicin resistant. One of the rifampicin resistant isolates was determined susceptible in MGIT 960 automated system. This
isolate was also tested with agar proportion method and found susceptible to rifampicin.
MAIN CONCLUSION The Xpert MTB/RIF assay can be used as first-line assay for the detection of
M. tuberculosis. However,
microbiologists must be aware of the limitations of the assay.